Higher Elements and Oxidation States
Now as my friend just discussed various historical developments that led to the formulation of the periodic table, but one very important historical development was observed by Moseley in 1913. His observation changed the entire understanding of the periodic table. Because what he observed was, he observed that there is relationship between the x-ray spectra and the atomic number. Now what happened was, he took high energy electrons and focused them on the target which was made up of the elements and on the bombarding of the electrons with the target, the x-rays were produced. So what he did was he tried to find out a relationship between the x-ray frequencies which were emitted and the atomic number. And with that he came to the conclusion that the square root of the frequency is equal to a(Z – b). So this was the relationship that he could find out. Now what is a and b over here? These two are a constant values, where Moseley said that these two values would be exactly the same for any element. The only thing that would change is Z. So what he did was, he started plotting the graph between the square root of the frequencies and the atomic number and what he observed was it was a straight line. Now when he put forward his theory and his observations to the entire world, everyone was surprised. Why? Because till now we have been studying that the Periodic Table was because of the atomic masses, or the mass number. But Moseley changed the entire thing by saying that the periodic table is actually based upon the atomic numbers. Now what happened was, when this observation came, as a conclusion then this was the periodic table that we got. Right? Now in this periodic table, if you see we have groups and periods. Now if you look very carefully, there will be 18 groups and 7 periods. So this is how this actual periodic table was classified. Now over here if you take a look, there are few of the elements which are yet not discovered. But still we have the space for them, so we know that there might be a possibility that these elements would be there. Now, actually only 114 elements till now have been discovered. So what happened was there was this problem that occurred between the United States of America and the Soviet Union, which is Russia. What happened was they discovered an element with the atomic number 104. Now Americans said that since they have found that element they would name it as Rutherfordium and the Soviet Union people, the Russians, said that no we have discovered it so we will name it as Kirchatovium. Now this was for 104 only. Now this led to a major, major problem in the world of chemistry because there were two nations now fighting for the name. So what IUPAC did was, they came up with a very fine idea of the nomenclature of finding out or assigning the names to the elements which have the atomic number more than 100. So what they did was they gave us the nomenclature rules where they said that number 1 denoted by ‘un’, zero would be denoted by ‘nil’, and similarly you will have ‘bi’, ‘tri’ and all. Now this is the list you would be using. Now, using this list how do you find out the name. Let’s see. Now 104, is 1, 0 and 4. So there are three numbers in it. So 1 would be ‘un’. Zero would be ‘nil’ and 4 over would be ‘quad’. Right, so you will just merge all of them and add the word ‘ium’ after that. Now why ‘ium’? Whenever ‘ium’ is added or whichever element has the word ‘ium’ in the end that are supposed to be metals. So in the initial phases we consider the element that we are going to find out as a metal. But then when we start observing the different physical and chemical properties, that is the time we start saying that, okay it might be a non-metal, it might be a metalloid. But in the initial phases we always assume it to be a metal. So not only with 100 atomic numbers or above that, any element in the periodic table that you have which ends with ‘ium’ would always be a metal. Similarly, if I have say another atomic number, say, 117. Now how do I name that again? So for 1 it would be ‘un’, for another 1 it would be ‘un’ again, and for 7 it would be ‘sept’. And ‘ium’. So it would become ununseptium. So this is how you can do the nomenclature part. Let’s bring back the periodic table again, which was called as the modern periodic table. Now, over here there was a certain problem that happened where hydrogen, we assumed, that we cannot assign a place to hydrogen because of its anomalous behavior every time depending on what conditions or what neighbor elements is it having. Now, if you look at the periodic table, the modern periodic table, there are certain groups and periods that we discuss. Now there are blocks also. Now similar to what we have in our societies where we are living there are particular blocks. So similarly in the periodic table also we have blocks. The first two groups are classified as s block. From group 13 to group 18 it is classified as p block. All the elements in the center from 3 to 12 are considered as the d block elements and the ones which are written over here are called as the f block elements. Now how is this block determined? So over here when you write the electronic configuration of a particular element the last electron, whichever subshell it enters that is the block. Now similarly if you take the example of sodium. Now sodium has the electronic configuration of 1s2, 2s2, 3p6 and 3s1. Right? Now the last electron has entered the s subshell. So that means this particular element that is sodium, would lie in the s block. So similar to this you can find out which block a particular element would be there by just finding out the electronic configuration.
Now I will tell you how to tackle the most difficult problem that a student faces, i.e. to memorize the periodic table. Now what I will do is I will help you memorize the periodic table with the exact positions of the element. Ready? HeLiNa Ka Ruby Cse Fraud Bena Mango Ca Strawberry Bana Rakha BAl Gayab In Taliban College Situdents Gets Snome Problem Nati-Pota Asha Sab Bimar OS Se Teri Pooja False Cl Br I Act Hero Ne Aruna Kumari Ka Xedon-Radon kar diya Sceshi Thi Violet Car Mein FeCo Nita Cuda Zahan Cuda daan Hgo. How was that? Now there are many, many methods available on the net. You can google it up or find it on YouTube and how you can memorize the periodic table. This is my favorite method. So I will just go slow and make you observe it. So the first one is HeLiNa Ka Ruby Cse Fraud. The second one is – Bena Mango Ca Strawberry Ba na Rakha. Group 13 is – BAl Gayab In Taliban. Then it is – College Situdents Gets Snome Problem. Then it is Nati-Pota Asha Sab Bimar. OS Se Teri Pooja. False Cl Br I Act. Hero Ne Aruna Kumari Ka Xedon-Redon kar diya. Sceshi Thi Violet Car Mein FeCo Nita Cuda Zahan Cuda daan Hgo. These are the elements that you should know. So this is, if you know it, it’s perfect.
Now you must be wondering why exactly do we need to memorize the periodic table. Because there are many, many physical properties that we will be dealing with and I would be telling you what are the periodic trends in that. So you don’t have to memorize the properties of each and every element. You can just check the trend in that particular group. And this is what is termed as the periodicity. So if I define periodicity, it is the basic reoccurrence of the similar properties of an element after certain regular intervals when the elements are arranged in the increasing order of atomic number. That is what is called as periodic properties. Now there are numerous physical properties which show periodic variations such as melting point, boiling point, density, enthalpy of vaporization, enthalpy of fusion, but all these are indirectly related to the electronic configurations or what we will be dealing with is the physical properties which are directly dependent on the electronic configuration such as the atomic radius, the valency, the ionization enthalpy, the electron gain enthalpy and the electronegativity. So these are the 5 or 6 properties that we will be taking up in this chapter. Now if I summarize the oxidation states and their correlation with the metals and the non-metals you just have to memorize 8 numbers. That is if I have a number line from 1 to 8 and suppose this number line indicates the number of Valence electrons. Now just by looking at the number of Valence electrons you can easily predict what will be the oxidation number or whether it will be a metal or a non-metal or a metalloid. Now how would you do that? If the Valence electrons are 1, 2 or 3, the oxidation states would be +1, +2 or +3 because they would want to lose the electron to gain the stability by having the noble gas configuration. Similarly, the ones which have 5, 6 and 7, would have the oxidation states as -3, -2 and -1. Now, the ones which have the plus oxidation states would always act as metals and the ones which have the negative oxidation states would always act as the non-metals. Now there is something left with the Valence electrons as 4. Now the ones which have 4, they are probably the metalloids or the semi-metals, because they can have the oxidation states as +4 or -4 depending on the neighboring atoms. So that is why they are the metalloids which behave as metals and non-metals. And the last one that we have is the Valence electron as 8 and we all know that it would be a noble gas. So this is how you can correlate the number of Valence electrons, the oxidation states and the metal and non-metal characteristic.