 | H 2.2 |  | He | |||||
| Li 1.0 | Be 1.6 | B 2.0 | C 2.6 | N 3.0 | O 3.4 | F 4.0 | Ne | |
| Na 0.93 | Mg 1.3 | Al 1.6 | Si 1.9 | P 2.2 | S 2.6 | Cl 3.2 | Ar | |
| K 0.82 | Ca 1.0 | Ga 1.6 | Ge 1.8 | As 2.2 | Se 2.6 | Br 3.0 | Kr | |
| Rb 0.82 | Sr 0.95 | In 1.8 | Sn 2.0 | Sb 2.1 | Te 2.1 | I 2.7 | Xe | |
| Cs 0.79 | Ba 0.89 | Tl 1.6 | Pb 2.3 | Bi 2.0 | Po 2.0 | At | ||
The only truly non-polar bonds are those between atoms of the same element.
When considering binary compounds (those containing only two different elements), the type of bonding between the elements can be correlated with the difference in electronegativity of those elements.
NaCl and NH3 are binary compounds.
If the difference in the electronegativity of the two different elements in the compound is greater than 2.0the bond between the atoms is predominantly ionic
the substance exists as an infinite lattice where cations surround anions and vice versa.
Ionic binary compounds generally have a metal bonded to a non-metal.
the substance exists as an infinite lattice where cations surround anions and vice versa.
Ionic binary compounds generally have a metal bonded to a non-metal.
The difference in electronegativity of the elements in NaCl is 2.2.
NaCl exists as an infinite lattice, a portion of which is shown at the left.
NaCl exists as an infinite lattice, a portion of which is shown at the left.
If the difference in electronegativity between two bonded atoms less than 2.0,
the bond is pure covalent (equal sharing of electrons - if there is no difference in electronegativity)
or polar covalent (unequal sharing of electrons - if there is any difference in electronegativity)
the substance exists as molecules (discrete small groups of atoms).
Molecular binary compounds generally have two non-metallic elements bonded to one another. 
or polar covalent (unequal sharing of electrons - if there is any difference in electronegativity)
the substance exists as molecules (discrete small groups of atoms).
Molecular binary compounds generally have two non-metallic elements bonded to one another. The electronegativity difference for the two elements in ammonia (NH3) is 0.8.
A representation of a molecule of ammonia is shown at the left.
A representation of a molecule of ammonia is shown at the left.
It should be emphasised that the 2.0 number above is somewhat arbitrary because the bonding between atoms in binary compounds is in fact a continuum from purely covalent (as in F2) to ionic (as in LiF).
The diagram (van Arkel triangle) shows this along its left-hand side using elements and compounds from the second row of the periodic table.
The van Arkel triangle also illustrates a similar continuum from both covalent bonding and ionic bonding to metallic bonding.