Ionic and Covalent Bonds: Transfer or Share?

0:00When atoms bond, do they transfer or share electrons? What decides?

0:06Bonds use valence electrons, the outer shell electrons. Sodium has one, chlorine has seven.

0:16Electronegativity is how strongly an atom pulls on bonding electrons.

0:21Sodium's value is 0.93 and chlorine's is 3.16, a difference of 2.23.

0:30Chlorine pulls much harder, so sodium's electron moves to chlorine.

0:36Sodium lost an electron, so it is a positive ion: a particle with a charge.

0:42Chlorine gained one, so it is a negative chloride ion, with eight valence electrons.

0:49The opposite charges attract. This attraction is an ionic bond.

0:55In solid sodium chloride, the ions stack in a repeating pattern called a crystal lattice.

1:03Each ion is surrounded by opposite charges, so there is no single sodium chloride molecule.

1:10The formula NaCl gives the ratio: one sodium ion for every chloride ion.

1:18Now two chlorine atoms: both are 3.16, so the difference is zero.

1:25Neither atom can take an electron, so each shares one.

1:30This shared pair holds the atoms together: a covalent bond.

1:36Counting the shared pair, each has eight valence electrons. This is a chlorine molecule.

1:43So the big difference meant transfer, and zero difference meant sharing.

1:49Transferring electrons makes ionic bonds; sharing them makes covalent bonds.