Diatomic and Polyatomic Elements

1A 2A 3A 4A 5A 6A 7A 8A
(1) (2) (13) (14) (15) (16) (17) (18)
3B 4B 5B 6B 7B — 8B — 1B 2B
(3) (4) (5) (6) (7) (8) (9) (10) (11) (12)
1 H He
2 Li Be B C N O F Ne
3 Na Mg Al Si P S Cl Ar
4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
6 Cs Ba La   Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
7 Fr Ra Ac   Rf Db Sg Bh Hs Mt Ds Rg Uub — Uuq — — — —
6   Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
7   Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
Key:   diatomic element   polyatomic element

 

A number of elements are found in their elemental form as diatomic molecules.  In these molecules, two atoms are joined by one or more covalent bonds, forming a molecule with the general formula X2.

The elements found as diatomic molecules are hydrogen (H, element 1), nitrogen (N, element 7), oxygen (O, element 8), fluorine (F, element 9), chlorine (Cl, element 17), bromine (Br, element 35), and iodine (I, element 53).  (Their molecular formulas would be written as H2, N2, O2, F2, Cl2, Br2, and I2.)

  • Hydrogen atoms in the H2 molecule are joined by a single bond.
  • Halogen atoms in the X2 molecules (F2, Cl2, Br2, and I2), are also joined by single bonds.
  • Oxygen atoms in the O2 molecule are joined by a double bond.  (Actually, molecular orbital picture of O2 molecules is a great deal more complicated, but we'll get into that in another section.)
  • Nitrogen atoms in the N2 molecule are joined by a triple bond.

Some elements may be found in molecules of more than two atoms. 

  • At room temperature, sulfur consists of a ring of 8 sulfur atoms joined by single bonds.
  • Selenium also forms rings of 8 atoms.
  • White phosphorus consists of 4 atoms of phosphorus, with each of the atoms sitting at the corner of a tetrahedron.  In the more stable red phosphorus, the P4 tetrahedrons are linked together, resulting in a more stable, less reactive allotrope of phosphorus.