Formation of Ions

• Atoms are neutral if the number of protons is equal to the number of electrons.
• The formation of an ion happens when the atom donates or receives electron(s).
• There are two types of ions;
  • Positive ion
    • Also known as a cation.
    • Formed when an electron is being donated from a neutral atom.
    • The number of protons is more than the number of electrons.
    • \(X \rightarrow X^{n+} + ne^-\)
  • Negative ion
    • Also known as an anion.
    • Formed when an electron is being received to a neutral atom.
    • The number of protons is less than the number of electrons.
    • \(Y + me^- \rightarrow Y^{m-}\)

• If X and Y react to each other:
  • \(X^{n+} + Y^{m-} \rightarrow X_mY_n\)
• In general, metals are mostly positive ions, and non-metals are negative ions.
• The positive ions are usually from group 1, 2 and 13.
• The positive ion will donate electron(s) from the valence shell in order to achieve the stable duplet or octet arrangement.

Formation of Ionic Bond

• Sodium chloride is an example of an ionic compound.
  • Sodium has an electron arrangement of \(2.8.1\).
  • In order for the atom to gain a stable octet arrangement, the atom has to donate the valence electron.
  • Chloride has an electron arrangement of  \(2.8.7\).
  • In order for the atom to gain a stable octet arrangement, the atom has to receive one electron. 
  •  When the sodium atom donates the electron to the chloride, then the ionic bond is formed because of the electrostatic forces between the two ions.
  • The substance is now is called sodium chloride.
  • The equation is:
    • \(Na^+ + Cl^- \rightarrow NaCl\)

Electron arrangement of sodium chloride