Electronic Configuration Of Elements To Verify Place In Periodic Table - Session 3

Effect of oxidation on Electro negativity. Electro negativity rises with the rise in oxidation state of an element. The higher the electro negativity, the more an element attracts electrons. Atoms with high electro negativity oxidation number is typically nonmetallic. They have negative oxidation numbers. The others that have low electro negativity are metallic in nature. They have positive oxidation numbers. The oxidation state does not change within a group of the periodic table. This is because all the elements within the group have the same valency. What happens when moving from left-to-right across the periodic table? The oxidation increases from one to four and then reduces from four to one.

Effect of charge on electro negativity. Positively charged protons in nucleus attract the negative charge electrons. Therefore, if there are more protons, there will be more attraction of electrons. This results in higher electro negativity. Therefore, electro negativity increases from left-to-right in the periodic table.

Electron Affinity.It is a change in energy when a neutral atom in gaseous phase gains an electron. It releases energy in this process. It is the likely hood of a neutral atom to gain an electron. An atom carries neutral charge and converts to a negative ion by gaining an electron.As the change in energy is an exothermic process, the ΔE is negative for Electron Affinity. Therefore Electron Affinity is positive. The higher the Electron Affinity of an atom is, the more it is capable of accepting electrons. Atoms with low Electron Affinity do not accept electrons easily.

Electron affinity can be measure by change in energy occurs while gaining electrons as EA = -ΔE. There are two types of affinities we must know. First Electron Affinity. It is energy released when an electron added to a neutral atom. Second Electron Affinity.It is energy released when an electron is added to negative ion.Second Second Electron is positive. This is because more energy is required to add electron to negative ion, as compared to neutral atom.

Let see example of oxygen; for first and second electron affinities. The First electron affinity of oxygen is as follows. It is the negative change in energy when adding one electron to a neutral oxygen atom. The second electron affinity is in positive. That’s because it is difficult to add electron to already negative ion. That’s because of repulsion of negative charges. As we know, ionization energies are always concerned with the formation of positive ions.

Electron affinities are related to negative ions. They are equivalent to ionization energies. Their use is mostly confined to elements in group 16 and 17 of periodic table. Do you know the trend of electron affinity in the periodic table?.Electron Affinity depends on the size of atom. In other words, atomic radius. As radius of atoms increase, attraction for electrons decreases. Therefore, their electron affinity decreases.

Stability of Valance Shell.As valance shell increases, attraction for electrons decreases. Therefore, electron affinity decreases. Electron Affinity is higher for smaller atoms.Electronic Configuration.For stable electronic configurations, such as p³, p⁶, d⁵, d¹⁰, f⁷, f ¹⁴ half filled and fully filled, Electron Affinity is higher. For other electronic configurations which are less stable, electron affinity is low.

Extent of Nuclear Charge.Nuclear charge is also known as atomic number. It increases across a period. It also increases down the group of the periodic table. If there is increase in nuclear charge, it means there is an increase in positive charge due to protons. This results in greater applied force and higher Electron Affinity.Electron Affinity increases across a period in relation to nuclear charge. However, it decrease in group from top to bottom. This is because each atom is significantly larger than the atom above it. Thus, an added electron is further away from nucleus.

Ability to form ions across period.As electron affinity increases across period from left-to-right, its ability to form ions by adding electrons to neutral atoms becomes difficult. The ability to form ions decreases across period due to decrease in atomic radius and electrons are more attached to nucleus. This makes it difficult to add or remove electrons to form ions.Trends for period 2 and 3 of periodic table.The second period has lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, and neon. Meanwhile, the third period has sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, and argon.

Since Ne,Neon, N and Be have fully-filled, half-filled and full-filled sub shells respectively, they exhibit high electron affinity than others.There are some exceptions for C and N , F and Cl.Carbon has greater affinity for electron than nitrogen because nitrogen has more stable half-filled valance shell. Thus is has less affinity for electrons.Fluorine, due to its smaller size, has high electron density. Therefore it has lesser electron affinity than chlorine.The first electron affinity for second and third period is are negative. Meanwhile second electron affinity is a positive value. This is because it is more difficult to add electron to already negative ion.Trends are as shown.

Atomic radius.It is distance between nucleus and electrons in outermost or valance shell. It is measured in picometers.Can you guess radius of any element?.In hydrogen there is only one electron is around the nucleus. The distance between this valance electron and nucleus is atomic radius of hydrogen.In the same way there are three electrons are in Lithium and only one of them is in outermost shell. Therefore, the distance between this outermost shell and nucleus is atomic radius of Lithium.

Atomic radius trends across period.From left-to-right of a period, the atomic number increases while numbers of shells remains constant. Therefore, high attraction between protons and electrons results in reduction in atomic size, due to attraction of electron towards nucleus. So, atomic radius decreases from left-to-right in period.From top to bottom in a group, the atomic number increases and the number of shells increases. This results in an increase in shielding effect. Therefore, the atomic radius increases down the group because of less attraction between electrons and the nucleus.

Uncertainty in atomic radius. When we talk about atomic radius, the position of electron in valance shell is uncertain. Therefore, we use the principle of uncertainty to find the position of valance electron. According to this principle, the momentum and position of an electron cannot describe at the same time. If we know the position, then the momentum is unknown and vice versa.

There are several types of atomic radius. Atomic radius is determined in bonded atoms because single atoms do not exist in free state. Covalent Radius. Covalent Radius is a type of radius determined from atoms bonded as covalent bonds. This bond can be between two similar or different atoms. This example shows the covalent radius of Chlorine.

Metallic Radius. Metallic Radius is between atoms bonded through metallic bonds. This example shows the metalic radius of Sodium.

Vander Waal’s Radius. Vander Waal’s Radius is the radius between molecules bonded with Vander Waal’s forces. This example shows the Vander Wall’s radius of Helium. It is noteworthy that Vander waal’s radius is greater than metallic radius. Metallic radius is greater than covalent radius.

Ionic Radius. Ionic radius is measured using the distance between anions and cations having ionic bonds. The placement of anions and anions inside ionic compounds can been seen as packing of spheres. Cations occupy the smaller spaces between the anions. Small cations occupy tetrahedral holes between anions. Larger cations occupy octahedral holes between anions. But larger cations can occupy cubic holes in a simple cubic array of anions.

Here is an example of ionic radius of NaCl. The distance between two ions inside an ionic crystal is determined by X-ray crystallography. X-ray crystallography gives the lengths of the sides of the unit cell of a crystal. The length of each edge of the unit cell of sodium chloride is found to be 564.02 picometers. Each edge of the unit cell of sodium chloride can be considered to have the atoms arranged as Na⁺, Cl⁻, Na⁺ and so forth.

Therefore, the edge is twice the separation between Sodium and Chlorine. So the distance between the Na⁺ and Cl⁻ ions is half of 564.02, which is 282.01. However, X-ray crystallography only gives the distance between ions. It does not indicate where the boundary is between those ions. So it does not directly give ionic radii.

The nature of ion also contribute to the increase and decrease of radius. A cation is always smaller than its parent atoms. This is because it has a greater nuclear charge than its parent atoms. Therefore, with increase in positive oxidation state, radius decreases.

An anion is always larger than its parent atom. This is because it has a lower nuclear charge than its parent atom. Therefore, with increase in negative oxidation state, radius increases.