electronegativity and polarity

electronegativity definition

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

factors that affect electronegativity

nuclear charge

atomic radius

shielding

what is nuclear charge

number of protons of an atom

going across periodic table, nuclear charge increases

going down periodic table, nuclear charge increases

atomic radius

distance from the nucleus to the outer shell

going across the periodic table, radius decreases (proton number increases, so attraction for electrons increases, electrons pulled closer to nucleus)

going down periodic table, radius increases because there are more shells

shielding

repulsion between electrons in neighbouring shells

going across periodic table, shielding stays the same (number of shells stays the same)

going down the periodic table, shielding increases because there are more shells so more repulsion between each other

trend in electronegativity going down a group

decreases

atomic radius increases

nuclear charge increases

shielding increases

therefore nuclear attraction decreases

trend in electronegativity going across a period

atomic radius decreases

nuclear charge increases

shielding stays the same

nuclear attraction increases

polar covalent bonds

two atoms in the covalent bond have different electronegativity

the more electronegative atom has a greater share of the electrons and is delta negative

non-polar covalent bonds

two atoms in the covalent bond have the same electronegativity

pair of electrons shared equally

CH bonds are always non-polar

non polar molecules

can have polar bonds but all the dipole moments cancel out through symmetry

molecule is symmetrical if there are 0 lone pairs and all bonds are the same

polar molecules

have polar bonds and the molecule is unsymmetrical through lone pairs or different bonds