Question

12. Give the general trend in the periodic table (period, group) for the main group elements (Groups I-VIII) for a) sizes of atoms, cations, anions (same charge) b) ionization energies c) electron affinities d) electronegativities

Answer 1

a) If we move from top to bottom along a group, size of atoms, anions and cations increases as energy levels increases with increasing number of electrons.

While across a period from left to right the atom and ions size decreases as number of electrons increasing in the same energy levels so nucleons attract more the electrons and decrease the size.

b) Ionization energy is the minimum energy required to remove an outermost electron from electronic shell. Along a group from top to bottom it decreases as size of elements increasing so attraction of outermost electrons towards nucleons is decreasing.

Whereas boundation of electrons towards nucleon across the period from left to right is increasing. So the energy required to remove an electron is going to be difficult from left to right.

c) Electron affinity is the energy released when we add an electron to the outermost shell of the atom. Electron affinity along a group decreases and across the period increases. Down the group electrons are farther away from the nucleus. So it will have very less tendency to accept any external electrons. Across a period the elements have tendency to gain the octet stability so after adding an electron it gets extra octet stability and it has more electron attraction power.

d) Electronegativity is the tendency to attract an electron towards an atom. Its trend is similar to ionisation energy trend. Along the period increases while across the group decreases. It is because across the period electron density increases. The number of energy sub shells are same but number of electrons are increasing so the electronegativity increases.

Along the group, the number of sub shell is increasing so the distance between the nucleons and electrons is increasing and attraction decreasing so the electronegativity decreases.