Ionic vs Covalent (College Board AP Chemistry)

Ionic bonding

• An ionic bond is formed when a metal donates electrons to a non metal
  • The metal becomes a positive ion (cation) because it has lost electrons

Forming a Cation

Forming cations by the removal of electrons from metals

• The non metal becomes a negative ion (anion) because it has gained electrons

Forming an Anion

Forming anions by the addition of electrons to nonmetals

• The ionic bond is formed because metals and the non metals want to have a full outer shell of electrons
• The difference in electronegativity, using the Pauling’s scale, between the atoms that are part of an ionic bond is greater than 2.0
• A full outer shell implies more stability, that is why noble gasses do not form ions
• When the ionic bond is formed, their electron configurations are the same as their closest noble gas. Sodium chloride will be used as the main example below
  • Na has one valence electron. Na in sodium chloride (NaCl) loses one electron to form Na⁺ Therefore, Na⁺ has the electron configuration 1s² 2s² 2p⁶, which is the same as Ne
  • Cl has seven valence electrons. Cl in sodium chloride (NaCl) gains one electron to form Cl^- Therefore, Cl^- has the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶, which is the same as Ar
  • When ions are formed, an strong Coulombic force of attraction is formed between the oppositely charged ions

Forming an Ionic Bond

Cations and anions bond together using strong Coulombic forces of attraction, which require a lot of energy to overcome

Covalent bonding

• A covalent bond is formed when two nonmetals share a pair of electrons
• Atoms form covalent bonds to gain a full outer shell of electrons
• There are two types of covalent bonds: polar and nonpolar
  • This classification depends on the difference in electronegativities between the atoms in the bond

Ionic vs covalent compounds

• The best way to differentiate between ionic or covalent compounds is analyzing the physical and chemical properties

Table comparing the properties between ionic and covalent compounds