A) Electronegativity
Electronegativity – measure how easy it is for an atom to gain electrons and how much an atom will pull electrons away from other atoms it has bonded to / covalent bond (similar to electron affinity but the difference is electron affinity deals with isolated atoms in the gas phase).
Across the periodic table (left to right)
Electronegativity increases.
Left side: prefer to lose electrons.
Right side: prefer to gain electrons.
Noble gases: no electron affinity.
Down the periodic table
Electronegativity decreases.
It is because the shielding effect (nuclear charge increases but screening effect increase and the atomic size increases and as a result, the effective charge decrease).
B) Electron Affinity
Electron affinity – the energy change that occurs when a gaseous atom picks up an extra electron.
First electron affinity is exothermic:
Example: O (g) + e –> O- (g)
First electron is pulled/attracted by the positively charged oxygen atom nucleus.
Second electron affinity is endothermic:
Example: O- (g) + e –> O2- (g)
Second electron is repelled by the existing negative charge on the oxygen ion.
Across the periodic table (left to right)
Left: elements want to lose electrons to be the nearest noble gas. As result, not much energy is released when these elements gain an extra electron. Electron affinity to be slightly negative.
Right: elements want to gain electrons to be the nearest noble gas. As result, a very high energy to be released. Electron affinity to be more negative.
Down the periodic table
Elements want to gain electron less (shielding effect)
Bottom: elements have less negative electron affinities.
C) Variation of the Period of d-block Element
Across the periodic table – First series (left to right)
Atomic size is approximately the same (except Sc and Ti).
Effective nuclear charge remains almost.
High melting points and boiling points (except Zn).
Density increases (but decreases for zinc).
1st and 2nd ionisation energies of the elements increase slightly (as the proton numbers increase)
3rd and 4th ionisation energies of the elements increase drastically.