Chemical Bonding Part 4: BOND POLARITY

polar bond

a covalent bond between two atoms where the electrons forming the bond are unequally distributed.

This causes the molecule to have a permanent dipole moment where one end is slightly positive(d⁺) and the other is slightly negative(d⁻).

non polar bond

a covalent bond between two atoms where the electrons forming the bond are equally distributed.

The molecule will have a temporary dipole moment where one end is slightly positive(d⁺) and the other is slightly negative(d⁻) when there is another molecule nearby.

Are diatomic gases polar or non polar/why?

Non-polar, since the atoms have equal electronegativity so the electrons are equally attracted to both nuclei

Why is C-H non polar?

They have similar electronegativities

Why is C-C non polar

They have the same electronegativity

What happens in polar bonds

The bonding electrons move towards the more electronegative atom in the pair

Common Non Polar Molecules

CCl₄, CO₂ (linear and dipole moment will cancel out ), noble gases, homonuclear diatomic elements and any molecules that contains only C-H bonds

permanent dipole

A small charge difference across a bond resulting from a difference in electronegativities of the bonded atoms.

What is a dipole? What is a dipole moment?

A dipole is a separation of opposite electrical charges. A dipole is quantified by its dipole moment (μ).

A dipole moment is the a product of the charge and the distance between the charges.

The larger the difference in the electronegativity between the two atoms, the greater the magnitude of the dipole moment the more polar the bond.

The direction of an electric dipole moment is represented by arrow and it points towards the more electronegative atom,

Bond Polarity

is determined by the difference in electronegativities of the bonding atoms.

The greater the difference in electronegativity, the more polar the covalent bond.

Polarising power of cation

refers to polarisation/distortion of the anion electron cloud.

depends on charge density (charge/size) i.e. the higher the charge and the smaller the cation, the stronger is its polarising power.

Polarisability of anion

refers to the ease of being polarised/distorted by the cation.

depends on charge and size, electron clouds of large anions are easier to distort than those of small anions.

C-H bond and P-H bond are

non-polar (small difference in electronegativity between two atoms)

Example of polarising power of Li⁺ vs Na⁺ in LiCl vs NaCl

Li⁺ is more polarising than Na⁺