4.2 Covalent bonding

When elements have difference in electronegativity less than 1.8. Usually between non-metal elements

Electrostatic attraction between positively charged nuclei and shared pair of bonding electrons

To achieve full outer shell of electrons

Amount of energy needed to break bonds between atoms

Distance between nuclei of bonded atoms

Bond length increases down a group as atomic radius increases which means less effective nuclear charge. Number of energy levels also increases

As bond length decreases, bond strength increases and vice versa. More distance means less attraction

They are shorter and stronger as attraction is greater with more bonds

As bond strength increases, reactivity decreases. eg. N2 has triple bond which means it’s unreactive as it requires too much energy to overcome attraction. It is less reactive than O2

A bond where both bonding electrons come from one atom

AlCl3 has a polar covalent bond and it needs 2 more electrons for an octet. At high temp, it exists as a normal molecule but at lower temp it combines with another AlCl3 to form a DIMER

Non-polar covalent bond

Pure covalent as electrons are shared equally

There is unequal sharing of electrons which forms a bond dipole (one element is more attractive)

H-F bond

Even though it has difference of more than 1.8, it’s two non-metals so it’s covalent

Polarity of H-X bond decreases as you go down a group

It points towards the element with higher electronegativity as electrons are pulled in that direction