Free Chemistry NEET Video Lectures for Classification of Elements and Periodicity in Properties

00:00:02 [Music] My name is Maravanji Shivaramaya Balak Krishna that is MS Balak Krishna. I'm a professor of chemistry at the Indian Institute of Technology, Bombay, Mumbai. I have been there since 1996 teaching inorganic chemistry all aspects of inorganic chemistry and also doing research in the broad field of inorganic chemistry. My research interests include the chemistry of main group elements and trans elements and also we design new phosphins and phosphorus based compounds to explore their coordination chemistry,

00:00:54 organometry chemistry and also their possible utility in organic transformations as homogeneous catalysts. We also study anti-cancer properties of copper one complexes of phosphines and containing some pod liants. When it comes to the course that I'm going to offer, it has about 12 to 13 lectures and I have classified the main group chemistry into four categories. One is chemistry of main group elements forming hydrates that is main group element hydrates and main group element oxides and main group

00:01:36 element halides. I have also included the interaction of main group elements with carbon and organic mates to form organometallic compounds or organo element compounds. In this course, uh after giving some introduction to the periodic table, classification of elements, periodic trends and periodic properties, I have also spoken about the bonding concept that is used in main group chemistry. However, I could not do justification for molecular orbital theory that I will be doing at later stage. And so because of time

00:02:14 constraints I could not include several other aspects concerned with main group elements in this course. For example, solving problems and application of some of these elements in various uses and also the chemistry we come across in day-to-day life. So all these things I have planned in my next course that is going to be coming in January 2018. That's a full-fledged course that has all aspects of main group chemistry that includes the spectroscopic aspects, all bonding aspects and also several

00:02:48 problems and how compounds can be characterized using various NMR techniques and other things and also in between I'm trying to include some fascinating stories of elements and their discovery besides talking about some chemistry that we see in day-to-day life. For example, you take onion. No matter what the price of onion is, whether it's 20 rupees or 200 rupees, whether who is cutting it, where it is cut, for what purpose it is cut, and how it is cut, everyone who cuts it cries or it brings

00:03:26 tears in the eyes of the person who cuts it. On a lighter note, it's an exemplary and universal secular vegetable. Jokes apart. Then what is the chemistry behind onion making people cry? In fact, when you are cutting onion, a chemical called propaneol oxide, sulfur oxide is released that interacts with another enzyme present in onion to generate sulfur triioxide. Sulfur triioxid is a gas. When it starts moving, it interacts with moisture present in the ice to form sulfuric acid that starts irritating our eyes and more

00:04:11 and more tear comes to dilute it and wash it away. And for example, SO3 plus H2O gives H2SO4. Like that many interesting things are there that I would like to share with you in my next series of lectures on chemistry of main group elements. And this before my lecture my email address will be displayed and you are most welcome to give suggestions and also if you have any queries you can always write to me and all those things I will try to include in my next lecture series. With your kind permission I would like to

00:04:47 begin my lecture series. I hope you will enjoy and you will learn some chemistry through my lectures. [Music] Welcome to my first lecture on the chemistry of main group elements. Uh in this lecture I will be discussing about the important aspects of the arrangement of elements and periodic properties. That means the classification of elements and periodic properties. Before I get into this one, I would like to speak about some of the important people or individuals who have contributed significantly to arrange some of the

00:05:32 known elements then in some order to understand their physical and chemical properties. So in this regard several people have worked. However, when the modern periodic table came into picture, the major architect was Russian chemist Dimitri Mandel. Several other contributed significantly uh to Mandel's periodic table. So let us discuss some of those things and today in the classification of elements and periodic properties aspect what we are going to understand is the position of elements. That means in what way elements are kept

00:06:14 in a particular group and how they are related to the remaining elements in the group and also in that particular row. That means how group wise classification was made. What are the parameters that were looked into before classifying these elements group wise and period wise and then we shall look into periodic trends. That means the relative atomic size, electro negativity, electron affinity, ionation, enthalpy, all those aspects, how they are related to atoms in each period or in a group. And then naming the elements. Of course,

00:06:51 uh now 118 elements are known. All of them have been named. However, in future if some elements are discovered, say for example having atomic number 120, 133 or 140, how to name them. For this up has given some norms and how to follow that one we shall look into it later. And also the classification of elements into S, P, D and F block elements. That means basically how they were classified. That means if they have electrons in the the veence electrons if they have valence electrons in s orbital they are

00:07:30 essentially called as s block elements and if they have veence electrons in the p block p orbitals they are called p block elements. Similarly, if they have valence electrons in D and F, they are called as D and F block elements. And then we shall look into the significant periodic trends in physical and chemical properties. And then we can also look into the comparison of reactivity of elements. That means what are the important compounds we come across with respect to main group elements and how

00:08:01 we can compare with other compounds of same type with other groups. That means essentially we can also draw a relationship between ionization enthalpy and metallic properties. So let us look into the basis for classification of elements. It's a known fact that elements are the basic units of all types of matter including both living as well as non-living things. And you'll be surprised to know if you look into the number of elements known in the past until 1800 only 31 elements were known.

00:08:41 In the next 65 years the number rose to 63 and by 1984 that's after almost 120 years 107 elements were known and another five elements were added in 1997 and in 2004 113 and 114 uh elements were discovered and in 2016 we have now 118 elements and out Of these 118 elements, 90 elements plus neptunium, plutonium, octinium, proactinium which exist in uranium war such as pitch blend are stable elements and the rest are radioactive. Uh let us look into the contribution of some people before Dimitri Manderle proposed

00:09:34 his periodic table. In 1800, German chemist John Doer then available elements he made into several groups of three elements and he called them as triads. For example, I have listed some of them. You can look into it. Uh lithium, sodium and potassium were kept in one group. Calcium, stranchium and berium were kept in another group and similarly chlorine, bromine, iodine were kept in another group. and he made an important observation. The observation was the atomic weight of the middle one was almost the average of the first and the

00:10:14 third element that you can see clearly. Sodium has atomic weight of 23 and if you take the sum of the atomic weights of lithium and sodium that comes around 46. So that means sodium has 23 half of that one. And similarly calcium atomic weight is 40 and berium atomic weight is 137. Together it comes around 177. And the stranchium atomic weight is almost half of that one. It's 88. Same trend was seen in case of halogen series given here. Bromine atomic weight is 80. It is half of the or average of the atomic

00:10:55 weights of chlorine as well as iodine. He made this observation. However, it didn't this observation did not give much information about the arrangement or their periodic trends or properties. And later French geologist Aebdon Chan Cottoy in 1862 arranged then known elements in the order of increasing atomic weight and and he made a cylindrical table of elements to display the properties of those elements known and during the same time another English chemist called John Nuland in 1865 he arranged the element

00:11:38 elements in increasing order of their atomic weight. And he noted very important point that every eighth element having the properties similar to the first element and this was called the law of octaves. In fact, those who are familiar with music notes, they can recall every eighth note being similar to the first octave of music. And this whatever the octave method John proposed was good up to calcium and not fully accepted. However, for his painstaking work, Royal Society London awarded Davy Medal in 1887.

00:12:20 And later in 1860s, two chemists, one from Russia, Dimitri Mandalu and Lther Mayor from Germany worked independently to arrange these elements in a proper order. In 1869, both succeeded in arranging the elements in the increasing order of their atomic weights and showed the similarities appearing in physical and chemical properties at regular intervals. Lother mayor plotted physical properties such as atomic weight, melting point, boiling point against atomic weight and showed periodically repeating pattern in

00:13:00 contrast to octave format suggested by John. Mayor identified the change in the length of the repeating pattern and in in 1868 he was ready with almost the modern periodic table. However, he did not publish his results. Meanwhile, Russian chemist Dimitri Mander published his periodic table in 1869 with an important statement. I quote, "The properties of the elements are a periodic function of their atomic weight." I repeat again the properties of the elements are a periodic function of their atomic weight. Mandal arranged

00:13:41 then known elements in horizontal row and vertical columns in a table with increasing order of their atomic weight in such a way that elements with similar properties occupy the same vertical group. The interesting intelligent aspect is he gave importance to similarities in the empirical formula and properties and atomic weight was not strictly followed wherever there was controversy. For example, despite lower atomic weight of iodine. If you have periodic table very handy, you can have a look at it. In fact, the atomic weight

00:14:16 of iodine is much lower compared to tourum. However, while sorting out these, Dimitry placed torium in group 16 along with oxygen, sulfur and selenium and placed iodine in group 17 along with florine, chlorine, bromine and iodine. And what he did was actually correct. So also he predicted the properties of some unknown elements and he left gap in the table at appropriate places. For example, he left gap below aluminum and also below silicon and called the elements to be discovered as ea aluminum

00:15:00 and ea silicon. So he predicted the existence of gallium and germanmanium. they were discovered later and described their general properties before they were being discovered and you can see some of his early work and his handwritten things are given in this slide. Of course, this was taken directly from Wikipedia. The web details are given below this one. If you are interested, you can read that article and get more information. Manderly's uh 1871 proposed periodic table was published in 1905. You can see here uh

00:15:39 his first periodic table was in this form. And when Manderly proposed his periodic table, the structure of atom and electrons were unknown. In fact, electrons were discovered by JJ Thomson only in 1897 and modern atomic theory was proposed by Neils Boore in 1913. Work of English physicist Henry Mosley on X-ray spectra of elements and atomic theory showed that the atomic number zed is a more fundamental property of an element not actually its atomic weight. So Mandel's periodic law thus modified

00:16:17 as I quote the physical and chemical properties of the elements or periodic functions of their atomic numbers. I repeat again the physical and chemical properties of the elements or periodic functions of their atomic numbers not atomic weight as it was suggested earlier atomic number of an element is equal to its nuclear charge that is in a neutral atom. If you consider the number of electrons are essentially equal to the number of protons in the nucleus. Thus, by simply knowing the electronic configuration, it is possible to

00:16:53 recognize the periodic variations and trends across a period or in a group. Since periodic law is governed by the electronic configuration, the variation in electronic configuration determine the physical and chemical properties of elements and their compounds. You can see the the skeleton of periodic table is shown here and uh it is classified into four uh groups or four blocks. One is S block having alkaly metals and alkaline earth metals that is 10 10 elements plus hydrogen sitting in the alkaly metal group that is s1 block and

00:17:34 s2 block. Then we have uh six p block elements starting from s_ub_2 p1 electronic configuration to s2 p6 of noble gases or inert gases. Then we have uh three d10 blocks. You can see here s1 block s2 block and we have p block having 30 elements plus one helium 31. And then we have three uh d block elements that is 3d, 4d and 5d each one having anywhere between 1 to 10 electrons in their d orbital. Then we have 30 fb block elements belongs to 4f and 5f group. So this is how all the elements are classified in the periodic

00:18:19 table and and earlier notation if you see the numbers given were different. For example, alkaline metal and alkaline and earth metal that is S block elements were called 1 A and 2 A and then D block elements were called as 3B, 4 B, 5 B, 6 B, 7B in the same sequence and the three next groups were called as eight and without giving any uh alphabet and then uh 1 B and 2 B were given to copper and zinc group and then boron group was considered as 3A. A and carbon was 4 A. O nitrogen group was 5 A and oxygen

00:19:00 group was 6 A and H hallogen group was 7 A and inert gas were 8A. Now the entire periodic table is classified into 18 groups starting from 1 to 18 and most of the textbooks are also following the numbering as 1 to 18 not following A or B type. It is convenient to follow the group one, group two like that. That means group one, group two and group 13, 14, 15, 16 and 17 are uh main group elements. Whereas 3 to 12 are essentially called uh D block elements. And this is the the present periodic table. You can see all 118 elements have

00:19:44 been named properly. And let us say uh we have some unknown elements as I mentioned earlier. And if unknown elements are there for example having atomic number greater than 118 how to name them name them for that one UPSC has made some formula and we can see that one here. For example uh we have to use the corresponding name and abbreviation for numerals zero should be called nil and n. And if it is one that is un and then abbreviation will be u. It continues like that. And similarly if you have digit 9 that name should be n e

00:20:25 n and abbreviation is n. For example if you want to name an element having atomic number 11 9. So in 119 we have 1 1 and 9. We can use un nom. That means the first letter should be capital and then the second one you consider only first letter and the the last number also consider one letter so that it becomes u u e that is unium. Similarly, if you want to name an element with atomic number 134, that should be unriodium and the abbreviation is UTQ. Symbol is UTQ. And similarly for 146, one can name

00:21:10 it as UN quad hexium and UQH. Similarly for 158 one can conveniently name it unpent octium that is U PO. So this is how unknown elements can be named. And for example, if element 119 is discovered, what is its electronic configuration? So as I had mentioned earlier, so we have 118 elements known and they have been numbered. For example, for Z= 118, the name is Nessen. O G A N E S N. And one can also write its electronic configuration as starting from redon the previous inert gas element. In fact belongs to inert gas

00:21:58 element group. And the electronic configuration of sunen is radon 54 6d10 7s2 and 7p6. Now we can consider this as an inert gas and simply we can write the atomic number of Z 119 electronic configuration of Z 119 as WG in the bracket and simply 8 S1 that means if an element with atomic number 119 is discovered that belongs to alkalimetal group having one electron in s orbital in its valent shell and it will be placed below the alkalytal franchial ium. So electronic configuration is nothing but the

00:22:43 distribution of electrons into the orbitals. All alkaly metals have one electron in their veence shell that is having s1 electronic configuration whereas alkaly earth metals have s2 electronic configuration that is two electrons in their veence shell. Similarly, P block elements have S2 P1 to S2 P6 electronic configuration. That's where that means they have 3 to 8 electrons in their veence shell. Similarly, D block elements have S2 D1 to S2D10 electronic configuration having anywhere 3 to 12 electrons in their

00:23:19 veence shell. That means essentially 3D block starts with atomic number 21 with scandium ends with zinc that is atomic number 30 and the 4D series starts with atomic number 39 for atrium to 48 for cadmium and 5d group starts with halfmium with atomic number 72 and ends with mercury that is 80 and 4f starts with lanthanum 57 to luteium 71 one and similarly five block starts with 89 octinium to 1 or3 laurenium. So both are inner transition elements that is 4F and 5F block are called inner transit

00:24:00 elements and I have listed here the electronic configuration for first group elements. It is very easy to write you can follow this sequence and of course this obeys of BO principle and all whatever that is proposed to arrange the electrons in the increasing order of their energy. So you can see sodium atomic number 11, potassium atomic number 19, rubidium 37, cescium 55 and franchium 87. Either you can expand it and write fully or you can take the previous inert gas configuration and just add the valence electron present in

00:24:34 it. So for example when you are writing franchium its atomic number is 87. The previous inert gas is redon with 86. So you can write red on 7 S1. Same sequence is followed in case of all elements whether they are from group one, group two or group three. So now let's look into some of the periodic properties. And when we talk about periodic properties, we should know what are the terms we should be familiar with. One is ionization energy or ionization enthalpy and electron negativity or electron

00:25:07 attachment enthalpy and electron affinity or electron attachment affinity and electro negativity. So these three terms we should make familiar so that understanding of the properties would be very easy. So what we are going to learn is the concept of ionation energy or ionation enthalpy and electro negativity in surveying the periodic table in the properties of the oxides, chlorides and hydrates of main group elements. And of course after making some of these compounds in order to understand their geometry and shape

00:25:44 we have to have a proper bonding concept. So here the most appropriate bonding concept is VCPR theory that is valential electron pair repulsion theory and the use of VCPR in predicting the basic molecular shapes and basic molecular orbital theory for describing the bonding in atomic molecule can be conveniently used here and ion energy and electron affinity should be referred as ionation enthalpies and electron attachment enthalpies though energies are commonly used. In latest textbooks, instead of using ionation energy, they

00:26:22 refer it as ionation enthalpy. And similarly for electron affinity, they call it electron attachment enthalpy. So one can follow conveniently the new convention. And now let us look into uh the formation of compounds. So what would happen when an element forms a chemical bond? It's basically the atoms can lose an electron or atoms can gain an electron or atoms can share a pair of electrons. So that leads to the formation of chemical bond. If the chemical bonds are formed, what are the types of chemical bonds we have and how

00:27:02 to decide the nature of the chemical bond? For example, we have ionic bond is there and also coalent bond is there. Again coalent bonds can be classified into two categories. Polar coalent bond and non-polar coalent bond. Apart from that one we have some weak forces that holds some of these atoms or molecules together. They are called vanderos interactions. Landon forces and also hydrogen bonding. Let us all learn all these things in a systematic way. For example, when a atom in its plus say n plus oxen state

00:27:44 loses one electron to go to next higher oxygen state that is called the ionization. So that means so this information as I said while making a chemical bond either electrons are lost either electrons are gained or electrons are shared with other atoms and how to analyze this one means it essentially about knowing the nature of a particular atom whether it's ready to give an electron ready to gain an electron or ready to share an electron that information comes from some of these periodic properties called

00:28:27 ionation enthalpy, electro negativity and electron attachment enthalpy. I have given some first ionation energy. In this table here you can see that for lithium it is plus 526 kiloj per mole and for sodium it is 502 kj per mole. Whereas for potassium it is plus 425 koj per mole and for rubidium it is plus 409 and for cium it is plus 382 kj per mole. You can see some trends that is followed here. If you see carefully, these values are decreasing as you progress from lithium to cesium. Why this ionation energy is decreasing.

00:29:07 So essentially when you go down a group, the electrons are added to the next higher shell. As a result, what happens? Atomic size increases. As the atomic size increases, the veence electrons move farther away from the nucleus. As a result they are held less firmly compared to the same in lighter elements. As a result what happens when they move little farther from the nucleus removal of those electrons would be easy. As a result what happens in a group the heavier elements show the lower value for ionation energy.

00:29:42 And similarly ionation energy is given for potassium and aluminium here for comparison because in case of potassium we have first ionation energy that is very low and in case of aluminium we have s2 p1 electronic configuration. You can anticipate the removal of three electrons to generate aluminium 3+. The first ionation energy for potassium and aluminium are 425 and 584. And second ionation energy is 3058 and 1823. And third ionation energy is 4418 and 2751. That means you can always look into

00:30:20 those values and you can analyze and judge why the values are. So in case of potassium it is very easy to remove the electron from its valent shell. Whereas in case of aluminum there is an increment in the nuclear charge. As a result it is a bit difficult to remove the p electron. And of course once of removing the p electron then you have to remove the two electrons that becomes much easier. And in case of potassium now we have to remove the electron from the inner core that is very difficult.

00:30:50 As a result second and third ion energy increases remarkably. So potassium for the same reason does not show other higher octates and its oxate is + one whereas aluminium can show conveniently plus three octates. After analyzing the first ionation energies of group one elements and also looking into first, second and third ion energies of potassium as well as aluminium. Uh we have got some information about these things. That means this whatever the this information we get about ionation energy it will tell us about the nature

00:31:26 of the bond types whether they are going to be ionic or coalent and by knowing this chemical and physical properties of substance can be predicted very easily. Ionation energy essentially refers to the loss of an electron from the gaseous atom or ion. This ionation energy decreases down a group, increases along a period. Compare the charge to size ratio. That would tell you more information about that one. I would show you the relative sizes of all elements in the periodic table in a couple of minutes. Let us look into the plot of

00:32:02 the first energy for the elements starting from lithium to calcium. You can see clearly here uh the values corresponding to lithium here. Of course uh here helium and hydrogen is given and the lithium shows uh relatively low ion energy compared to these two that is anticipated here because of the increase in the size of lithium. Whereas when we move from lithium to berillium the first ion energy increases here and again in case of boron it drops and then it continues until we have nitrogen and again drops in case of oxygen here the

00:32:42 question is nitrogen and oxygen if you compare the electro negativity oxygen is being more electrogative than nitrogen however the first ion energy of oxygen is much lower than nitrogen it is simply Because nitrogen has s2p3 electronic configuration. S2P3 because of half filled p orbital. It is relatively stable compared to s2 p4 electronic configuration shown by oxygen. That means oxygen has a tendency to lose one of the electron readily to attain s2p3 electronic configuration. As a result the first ion energy of oxygen is little

00:33:19 lower compared to first ion energy of nitrogen. And same analogy can be explained again in case of phosphorus and sulfur. Whereas in case of magnesium it goes up from sodium because here effective nuclear charge increases. That means by looking into the position of the elements and their electronic configuration and effective nuclear charge. We should be able to analyze the first ion energy of the elements. And you can see here electronic configuration I have shown here. Berillium we have to remove essentially

00:33:53 the two electrons and in case of boron you have to remove three electrons. The first electron comes from 2p. In case of nonen we have n2 s2 p3 electronic configuration. In case of oxygen we have s2 p4 electronic configuration. So this electronic configuration added with the electro negativity and also the effective nuclear charge and the atomic size can tell you the trends and also how to guess the relative uh values without much difficult. That means the kinks in the ion energy we see in this plot for boron and wo can be

00:34:30 explained simply by looking into the electronic configuration. Now look into the second ionation energy and first ion energy comparison is made in this plot. And again the trends whatever we follow in the first ion energy is very similar to what we observe in the second ion energy of some of these elements shown here. And I have also given the electro negativity value on ping scale here for some important elements. As I said florine is the most electrogative element having the value 4.0. 0 whereas

00:35:05 the next most electrogative element is oxygen having 3.5 and the electro negativity values of chlorine as well as nitrogen are more or less comparable little fractional differences there however both of them show very close to 3.0 value whereas carbon has 2.5 as well as sulfur has 2.5 hydrogen electro negative is 2.1 and boron has 2.0 zero value and alkaly metals are least electro negative and sodium shows about 0.9 and similarly if you look into first electron affinities uh florine shows - 322 kiloj per mole and whereas chlorine

00:35:46 shows little higher than florine that is - 349 kiloj per mole whereas bromine value is - 325 and for iodine it is -295 kilo j per mole that means here the first electron Affinity for florine it is little less compared to chlorine simply because the size of florine is much smaller when you are putting additional electron to make it f minus uh you are essentially putting eight electrons very close to the smaller atom and because of intereleron repulsion its electron affinity value is much lower compared to chlorine whereas in chlorine

00:36:25 because of little larger size it can accommodate comfortably the electron taken to make it as chloride annion. That means the electro negativity refers to the tendency of an atom in a molecule to attract electron to itself. The most widely used scale is devised by Linus polling. As I had mentioned, this is based on bond energies. The most electronegative elements are in the top right of the periodic table with florine being the most electrogative with a maximum value of 40 on polling scale and least electrogative atoms are in the S

00:37:01 block that is S1 and S2 block that is alkaline metals and alkaline earth metals. So electro negativity is a very useful general parameter for predicting the general chemical behavior of an element and gives good indication of bond types. Two elements with large electro negativity difference will tend to form ionic compounds. For example, halides when they interact with group one or group two elements. For example, if you consider sodium chloride, it's the bond is ionic in nature. Small electronity differences are enough when

00:37:36 one of the element is highly electropositive metal. Two elements with very similar or intermediate electro negativity values will tend to form coalent bonds. For example, if you consider CH bond in methane, it is coalent in nature. The electroy difference between the carbon and hydrogen is minimum. That means carbon has 2.5 whereas hydrogen has 2.1. As a result, you can anticipate it to be a coalent bond. And I have shown here the relative atomic sizes of all elements in the periodic table. You can see

00:38:11 carefully and each group atomic size increases and in each row atomic size decreases. The reason is very simple. And if you consider elements given in a group, steadily the size is increasing as more and more electrons are added to the next higher shell. and and as a result what happens atomic size increases and the group one lost element is largest atomic size it has whereas helium has the smallest atomic size and if you see for example period two where we have lithium berillium boron carbon nitrogen oxygen florine and neon here

00:38:52 basically the added electrons are going to the same shell as a result effective nuclear charge is increasing ing. As a result, the added electrons are coming very close to the nucleus and you can see the shrinkage of atomic size. So these trends are followed in all the groups. For example, you take any group the heavier elements are larger in size and atomic size steadily increases down the group and the atomic size steadily decreases across a period. So that means now let us look into the main group

00:39:28 elements and their compounds and based on the bonding types. Okay, we can classify the compounds of main group elements into ionic, coalent or polymeric to molecular. The general features of the chemistry of the main group elements and their selected compounds can be understood simply by analyzing and rationalizing the variation in electrogivity of the elements as a very very useful qualitative tool. The most important compounds of main group elements are hydrides, oxides and halides. And of course we can also consider another

00:40:06 group of compounds such as orgonometric compounds or interaction of main group elements with uh carbon or organic matees. That means overall although it appear like enormous all available compounds of main group elements can be simply brought simply classified into four categories. The interaction of all elements with hydrogen to form hydrides. all elements of main group elements to interact with oxygen to form oxides and also that can be extended to other oxygen group elements such as sulfur, selenium and tourium and also the

00:40:46 interaction of all main group elements with hogen series including florine, tomine, chlorine, bromine iodine and and if you understand the trends of these four class of compounds understanding the chemistry of main group elements will be much easier. So the classification is very simple. Let us look into uh the some of the features of P block elements uh and the properties how they change. Pock elements are essentially contain non-metallic elements and of course metals are good conductors of heat and electricity and

00:41:26 in solid metals the electrons are extensively deoized over the whole material. That means the valence electrons whatever you come across in a typical metal they are not confined to the valence shell of that particular atom in the latis they can freely move to the next atom. That means you can assume as a a stream of electrons moving over the autumn surface uh making them good conductors of heat and electricity and this property increases as we have more and more electrons in their veent shell and non-metallic elements in this

00:42:01 context are essentially insulators and have no deoizing bonding instead being formed from localized coalent bonds. In the center of the P block, there are so-called metal elements such as boron and silicon which show intermediate electro negativities. They also show relatively low electrical conductivity compared to metals. But this metallic property increases with the temperature. That means uh simply we can say in the periodic table if you look into the elements the non-metallic property increases across a period and the

00:42:40 metallic properties increases down the group. Main group elements can be roughly classified as metals with an electro negativity less than two as non-metals with electro negativity greater than 2.2 as nonmetals. That means main group elements can be simply classified as metals if the electro negativity value is less than two and as non-metals if they have electro negativity greater than 2.2. So with this scale we should be able to classify the elements as metals and non-metals and in some case as metales

00:43:19 or semiconductors. Let us consider the first long period. The change in properties can be nicely understood just by looking at the first long period starting from sodium and ends with argon and sodium and magnesium are both electropositive metals. The next element aluminium is a metal but shows several characteristics of non-metals in form many coalent compounds. In group 14, carbon is a non-metal whereas silicon is a metaloid and being a semiconductor and has compounds which show characteristics

00:43:53 of both metal and non-metal compounds. In group 15, of course, nitrogen is a true non-metal and phosphorus is also a non-metal. However, phosphorus onwards the remaining elements are truly non-metals but with some metallic properties. And if you look into the antimony and bismouth metallic properties increases and bismouth is a main group metal. And in case of group 16 and 17 sulfur and chlorine are the true non-metals. Sulfur exists mainly coalent S8 rings and also in other forms or even also in higher r form and

00:44:33 chlorine forms diatomic coalently bonded molecules. Argon exists as a monatomic gas under ambient conditions and does not participate in chemical bonding owing to its filled valance shell and very high ion energy associated with it because of having S2P6 electronic configuration. But when we go down in any of the main group, elements become more metallic in character parallel by a decrease in electro negativity. That means electro negativity can be directly correlated to the metallic properties.

00:45:05 As electro negativity decreases, metallic property increases. As electro negativity increases across a period non-metallic properties increases. The properties of main group element compounds such as hydrates range from ionic in case of S block metals. That means whether you make hydrates of alkaline metals or alkaline earth metals, they're essentially ionic hydrides. Exception with the berilium which has coalent character because of the smaller size of berilium and whereas in case of aluminium it is polymeric and

00:45:38 rest of the hydrates of p block elements are essentially equivalent hydrates. The group one and group two elements are less electro negative than hydrogen that is nitrogen shows.9 whereas hydrogen electronity is 2.1. So the bonding are essentially ionic and they form compounds having composition MH because here alkal exists in plus one state and hydrogen will be in minus1 state. These hydrates react very violently with water generating hydrogen gas. And for berilium and boron the electro negativity difference with hydrogen is

00:46:14 very small and berillium hydrate is coalent and boron hydrates are also coalent clusters. And of course here the formation of cluster is essentially because of the electron deficiency due to the configuration we have s2p1 where uh in order to form minimum bonds we are in charge of two electrons. As a result, boron hydrates form numerous neutral as well as ionic hydrates that we shall see in more detail when we look into the group 13 chemistry. In group 14, the hydrates are all coalent molecular species typical of CH4 that is

00:46:54 methane. Similarly, the group 15, 16 and 17 element hydrates are all coalent molecular species. And the acidity of these hydrates in aquous solution increases on moving to the right as electro negativity difference between H and the element increases and the HX bond in case of H hallogens becomes more polarized and it will be a polar coalent bond having a delta plus charge on hydrogen and delta minus on halides. This has influence on the physical properties such as boiling point and other things.

00:47:37 Those things we shall study in more detail in their respective group chemistry. Let us consider this uh problem here. So predict the properties of the hydrates formed by elements with electro negativities 0.9 and 3.5. That means we have two elements of the main group elements having electro negativity value.9 and 3.5 and we know the electro negativity of hydrogen that is 2.1. If hydrogen interacts with an element with electro negativity.9 it has to be ionic in nature and similarly when the element having

00:48:16 electro negativity 3.5 interacts with hydrogen and if hydride is formed that has to be coalent in nature. So you can see here the answer I have given and you have seen that the sodium has.9 electro negativity that means it readily forms a hydride of the type NH whereas in case of 3.5 it is chlorine it is essentially hydrogen chloride or HCl so the first one is ionic hydride the second one is coalent hydride this is how these values will help you in understanding the nature of the bonding and also to the

00:48:53 properties of the corresponding compounds of main group elements like hydrates. The properties of the chlorides follow a broadly similar pattern with chlorates of metals being ionic and of non-metals being coalent molecules. For the group one and group two metals again except berilium the chlorates are ionic solids which form neutral solutions in water. The chlorates of small highly polarizing metal ions such as berilium, aluminium, gallium and some other elements are polymer in the solid state. The majority

00:49:28 of the chlorides of group 14 and 15 elements and bcl3 or molecular coalent species. The chlorides of the p block elements and berilium generally give acid solutions in water because they readily react with it rather than simply dissolving in it. And carbon tetrachloride unlike silicon tetrachloride does not react with water to give an acidic solution and this is purely kinetic effect. I would tell you why CL4 doesn't react with water whereas S4 readily reacts with water under go hydrarolysis to form SiO2 through the

00:50:08 formation of hydrogen chloride. Those things we shall discuss in group 14 chemistry. Let us consider the main group element oxides. For main group oxides, there is a similar trend from ionic oxides for the bottom left elements through polymeric oxides in the center, many of which are amphoteric in nature. Two molecular coalent oxides for the elements of higher electro negativity on the outmost right side of the P block. Oxygen is the second most electrogative element forms ionic oxides with group one and group two elements.

00:50:45 For example, if you consider sodium oxide that is Na2O and calcium oxide CaO which are basic oxides. Why we call it as basic oxide is when you treat the sodium oxide or calcium oxide with water they readily form highly alkaline solutions of the corresponding metal. For example, in case of sodium oxide we get sodium hydroxide. In case of calcium oxide we get calcium hydroxide and hence the oxides of alkali and alkaline earth metals are called basic oxides. So that means sodium oxide when it reacts with water it gives

00:51:38 sodium hydroxide. Similarly calcium oxide when it reacts with water it readily forms very strong alkaly solutions such as calcium hydroxide. One can also write as Ca twice or here 2 Na O. Group 13 oxides such as boron triioxide and aluminium triioxide are polymeric and aluminium triioxide is amphoteric in nature. Any amphoteric oxide dissolves in both acidic as well as basic solution. In group 14, the oxides of the lightest element that is carbon such as carbon monoxide, carbon dioxide, there is one more carbon oxide that's called

00:52:34 carbon sub oxide that is C3O2 or molecular oxides. In contrast, silica that is silicon dioxide is a polymeric oxide. CO2 is an acidic oxide since it dissolves in water giving an acidic solution. That means electropositive metal oxides are basic in nature whereas P block element oxides are acidic in nature as they give acid solution when they interact with water. In group 15 and 16 oxides of nitrogen are all molecular coalent species many of which are acidic while those of sulfur that is sulfur dioxide and sulfur triioxide both

00:53:16 are acidic in nature or they are acidic oxides for example SO3 when it's reacted reacts with water it readily forms H2SO4 4. That means it can also be simply shown as plus SO4 2 minus. Similarly, group 17 and group 18 in case of group 18 in only xenon they form oxides which are molecular species in nature. Let us look into the bonding concepts that are used for understanding the geometry and shapes of the main group element compounds. Uh in this effort in this uh process of uh coming up with some structure and

00:54:12 bonding concepts to explain bonding in the main group elements. The contribution largest contribution to start with came from Gilbert Newton Louu in 1916. He proposed the theory of bonding at University of California at Berkeley and he added information about electrons in the periodic table and he also worked on purification of heavy water that is D2O and also he proposed acidbased theory and his contribution is immense in understanding the acid base interactions that's the reason his concept is also known as Louis acid base

00:54:52 concept and also he worked in the field of photochemistry and in fact he was nominated 41 times for Nobel Prize and he was found dead on March 23rd 1946 in his laboratory. At that time he was working with hydrogen cyanide and some people thought that he has committed suicide. However, uh his life ended on a very sad note and he will be remembered as long as main group chemistry is is practiced in several laboratories and his contribution is very immense in refining and coming with new concepts to

00:55:35 explain the geometry bonding and reactivity of all main group elements. So far we were discussing about the classification of elements and periodic properties. Under this title we learned several new terms that is electro negativity, electron affinity or electron attachment enthalpy and ionization energy and then electronic configuration. So P block elements and S block elements are essentially the main group elements. And we have two S block elements having one electron in their veence shell. They are called alkaline

00:56:15 metals having two electrons in their veence shell having alkaline earth metals. And we have s_ub_2 p1 starting from boron to s_ub_2 p8 p6 with neon that means having six groups of five each elements having s2 p1 to s2 that is 3 to 8 electrons in their veence shell and also we looked into the relative sizes those size increases down the group and also atomic size decreases across a period and also electro negativity increases es across a period and electro negativity decreases across down a group. And similarly

00:56:55 electropositivity increases down the group. And some of these things if you remember understanding their chemistry would be much easier and for convenience all compounds of main group elements can be simply classified into four categories. One is interaction of all main group elements with hydrogen. The compounds are called hydrates. These hydrates can be either ionic hydrates or coalent hydrates or having polar coalent property or non-polar coalent properties. And also they we will also come across metallic hydrates. And with

00:57:36 oxides again alkaline metals and alkaline earth metals form ionic oxides and which are basic in nature whereas p block element forms oxides which are essentially acidic in nature. And same thing is true in case of halates. All main group elements interact with H hallogens to form the corresponding halides. And these halates of alkaline metal and alkaline earth metals are ionic in nature and they readily dissociate in water. Whereas hydrates of p block elements are coalent in nature. So some of these things we have

00:58:12 understood and these aspects what we have understood will come very handy when we start discussing the chemistry of individual groups. And before I proceed to the chemistry of individual groups, I shall discuss on the structure and bonding concepts and how the structure and bonding concepts evolved starting from Louis dot structures to what we have today molecular orbital theory where we consider linear combination of atomic orbitals to arrive at very interesting molecular orbitals which can explain almost all properties

00:58:45 of main group elements. All these things I will be discussing in my next lecture. Uh, thank you very much. [Music]