Classification Of Elements And Periodicity In Properties

- Confused? Not any more, understand most confusing terms of the chapter in a very easy method.
1
All s-block elements predominately form ionic compounds.
Ionic bonding is a type of chemical bond in which valence electrons are lost from one atom and gained by another. Ionic bonds involve a cation and an anion.
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So, elements that easily lose or gain electrons will readily form ionic compounds.
If we analyse s-block elements they can easily form cations because they have:
a. large size
b. low ionization enthalpy
c. low electron affinity
We can draw a conclusion that all s-block elements predominantly form ionic compounds.
But this statement is not completely true.
Li and Be do not readily form ionic compounds even though they are s-block elements. The reason being Li and Be have high ionisation enthalpy in the group, so the tendency to form cation is less.
As a result and the tendency to form ionic compounds is low and these elements are more prone to form covalent bonds.
2
Isoelectronic species always have the same ionization enthalpy. No.
Isoelectronic species are those that have the same number of electrons.
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For example, neon and Sodium ion are isoelectronic species as each have 10 electrons.
Ionization Enthalpy of elements is the amount of energy that an isolated gaseous atom requires to lose an electron in its ground state. As both Neon and Sodium have same number of electrons in their orbitals, does it mean that the ionization enthalpy of these elements would be the same? No.
Though Neon and Sodium have the same number of electron, they do not have the same atomic number (or number of protons).
Given the same number of electrons, 10, as in this case, the one with the higher number of protons will have higher effective nuclear charge and thus, a smaller size. And the smaller the size of the ion, the harder it will be to kick an electron from it and therefore, higher will be its ionization enthalpy.
So, with 11 protons will have a higher ionisation enthalpy than Ne which has 10 protons in its nucleus.
3
Is electron gain enthalpy and electron affinity the same?
Electron affinity and electron gain enthalpy are very closely related terms.
So are they exactly the same?
Well, there is a subtle difference between the two.
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Electron gain enthalpy is the energy that releases when an isolated neutral atom gains one extra electron, whereas electron affinity refers to the tendency of an isolated atom to obtain an electron. Electron affinity is the negative of electron gain enthalpy.