Y1 · XII · #22Chemical bonds

Ionic bond

Introduction

When atoms have very different "appetites" for electrons, they don't share them fairly — instead, one atom gives up an electron completely and another takes it. This full transfer of electrons creates oppositely charged particles that attract each other strongly. This is the ionic bond, one of the three main types of chemical bonding you'll meet this month, alongside covalent and metallic bonds.

What causes an ionic bond?

An ionic bond forms between a metal and a non-metal. Metals have low electronegativity (they don't hold onto electrons tightly), so they lose electrons easily to form positive ions (cations). Non-metals have high electronegativity and gain electrons to form negative ions (anions). The oppositely charged ions are then held together by strong electrostatic attraction.

You can actually predict whether a bond will be ionic using electronegativity values:

If the electronegativity difference (Δχ) is greater than 1.7, the bond is likely ionic
If Δχ is less than 0.5, the bond is essentially non-polar covalent
If Δχ is between 0.5 and 1.7, the bond is polar covalent (Talbot, p.134)

It's worth remembering that ionic and covalent bonding are two extremes on a spectrum — real bonds often sit somewhere in between, showing partial ionic or partial covalent character.

Worked Example 1: Predicting bond type

Question: Using electronegativity values, predict the bonding type in sodium chloride (NaCl). (χ Na = 0.9, χ Cl = 3.2)

Answer:

Δχ =

Ask ChemBuddy about this →

Source excerpts

From Chemistry for the IB Diploma 3e · Talbot

p.134relevance 10.6

Electronegativity values (Pauling scale) There are some simple rules for predicting the type of chemical bond based upon the electronegativity differences: ■ If the difference in electronegativity values is greater than 1.7, then the bond is likely to b e i onic. For example, francium fluoride (FrF) would be highly ionic. ■ If the difference in electronegativity values is less …

p.135relevance 10.2

S2.1 The ionic model 123 ■Charge-shift bonds Israeli chemist Sason Shaik and French chemist Philippe Hiberty collaborated to study molecules using computer simulations based on Linus Pauling’s valence bond theory. One of the molecules they studied was the fluorine molecule, F2, which they found was best described by including an ionic form, F+ F−, with the familiar covalent for…

p.143relevance 8.9

to the same pair of shared electrons. This holds the nuclei together. – – + + smaller attraction larger attraction ■Figure S2.14 A simple electrostatic model of the covalent bond in the hydrogen molecule, H2 ■Figure S2.15 The unequal sharing of the electron pair in a polar covalent bond such as that in I–Cl In some cases, a stable electronic arrangement may only be achieved if …

p.343relevance 8.8

or break the attractive forces between a shared pair or pairs of electrons and the two nuclei. If enough energy is expended, two well separated atoms with no bonding attraction between them can be formed. This c oncept is illustrated in Figure R1.16 using the hydrogen m olecule. Similarly, overcoming the electrostatic forces of attraction between the oppositely charged ions in …