Exercise 1 | Structure and Bonding in Organic Molecules

Chlorine (Z=17) exists in two naturally occuring isotopes.
The most abundant (75.77%) has 18 neutrons and the other 20

  1. Use the XZA formalism to describe both isotopes.
  2. What is the electronic configuration of chlorine?

Magnesium has an electronic configuration of 1s2 2s2 2p6 3s2

  1. What is the most stable ion of magnesium?
  2. What is the simplest neutral compound which can be formed from magnesium and chlorine?



  1. Cl1735 and Cl1737
  2. Z = 11 ⇒ 17 electrons ⇒ 1s22s23s23p5
  3. Nearest noble gas is Ne (1s22s22p6)
    Mg needs to lose 2 electrons to get Ne’s configuration
    The most stable ion of magnesium is Mg2+
  4. Mg’s most stable ion is Mg2+ and Cl’s most stable ion is Cl-
    For electroneutrality we need two Cl- for one Mg2+ ⇒ MgCI2