IB chemistry HL: 2.2.5 and 6- Bond polarity and molecule polarity

electronegativity

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

factors which affect electronegativity

• nuclear charge

• atomic radius ( the more right on the period, the smaller the atomic radius )

• amount of shielding done by inner electrons

(same as first ionisation energy)

what is the trend of electronegativity across a period

It increases, except for noble gases which have an electronegativity of 0. while shielding stays the same, nuclear charge, and thus atomic radius, increased and respectively decreased

What happens to electronegativity as you go down a group?

it decreases; shielding and nuclear charge, cancel each other out, but the atomic radius increases going down a group

pure covalent bond

both atoms have equal ability to attract bonding electrons

how does the electronegativity of atoms have to be for an ionic bond to occur

If the electronegativity between two atoms is high then the bonding will be

polar covalent bonds

A covalent bond in which the sharing of the bonding electrons is unequal. the electrons will be closer to the more electronegative atom

Polar Ionic

Distorted Ions

how to predict bond types

• bonds between atoms are rarely urely ionic or purely covalent

• there is a gradual transition from Ionic to covalent

• if the difference in electronegativity is 0.4 or less, the bond will be non polar covalent/ pure covalent

• if the difference in electronegativity is 0.4 (more around 1) to 2, the bond will be polar covalent/

• over 2, mainly ionic

what is a dipole

charge difference inside a molecule

how to predict nonpolar molecules

Molecules that have no lone pairs/ are symmetrically arragned have a resulting force of 0, thus even if theur have dipoles, the molecule ends up nonpolar

how to predict polar molecules

molecules with lone pair have dipoles which do not cancel out (because they aren’t symmetrically arranged or if they are, they don’t have the same magnitudes), and thus are polar ( eg water )