Electronegativity and bond polarity

Define electronegativity

The ability of an atom to attract the bonding electrons in a covalent bond

What happens to electronegativity down a group and why (1+4)

• Decreases

• Greater radius

• More shielding

• Less attraction

• Despite increasing nuclear charge

What happens to electronegativity across a period and why (1+3)

• increases

• More protons (increasing nuclear charge)

• Greater attractuib

Which is the most electronegative element

Flurine

Are non-metals or metals more electronegative

Non-metals

What is the ideal ionic compound

Completely separate, spherical ions and the electron densities are apart from each other

What is the ideal covalent compound

A compound with the electron density exactly in between the species

What is the electronegativity of CH4 (C=2.5, H=2.1)

0.4

2.5-2.1, only take find the difference once between the two species ie not 2.5 - 4(2.1)

When does covalent bonding occur (2)

• Small difference in electronegativity

• Species of high electronegativity

When does metallic bonding occur (2)

• small difference in electronegativity

• Species of low electronegativity

Explain the continuum of bonding

A continuum of bonding has 2 extremes, ionic and covalent. Large differences in EN make the bonds more ionic in character, small difference in EN make the bonding more covalent in character.

What is a polar covalent bond

A covalent bond with some ionic character

What does polarity refer to

A separation of electric charge leading to a molecule having an electric dipole because one element has a greater ability to attract the bonding pair of electrons.

Define polarisation

The distortion of a negatively charged ion’s electron cloud by a positively charged ion

Define polarisability

The ease at which the charge distribution of ion/atom is distorted

Which cations have the greatest polarising power

Small and highly charged

What affects the polarisability of an anion

The ionic radius - larger radii means it is more easily distorted

Why does BeCl2 show covalent bonding

Because Be2+ is small and highly charged so polarises the Cl- ion

There is a small difference in electronegativity so electrons are shared

What factors determine whether a molecule has a permanent dipole

• the shape of the molecule

• The polarity of individual bonds

Describe a non-polar molecule

A molecule which has a symmetrical arrangements of dipoles/polar bonds

• all the bonds need to be identical and no lone pairs on central ato,

Describe a polar molecule

A non-symmetrical molecule that has different bonds or identical bonds with a lone pair on the central atom