Atoms to molecules

A molecule is a group of atoms held by chemical bonds. In the simple covalent picture, each atom wants a certain number of bonds — its valence.

• H · 1 bond

  Hydrogen is done with a duet of 2 electrons.

• O · 2 bonds

  Oxygen wants 8 in its outer shell — two more than it has.

• N · 3 bonds

  Ammonia is NH₃.

• C · 4 bonds

  Methane is CH₄. Carbon is the builder.

• Cl / F · 1 bond

  Halogens want one more electron.

Ionic pairs such as NaCl are a transfer, not a share. The lab still lets you place them as a pair and will say so.