Ionic Bond Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Ionic Bond.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

A chemical bond formed by the electrostatic attraction between oppositely charged ions, created when one atom transfers one or more electrons to another atom.

One atom gives electrons away; another takes them. Opposites attract.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Ionic Bond starts by identifying valence electrons, likely charges or sharing, and the structure that follows.

Common stuck point: Students often know a formula related to ionic bond but skip the recognition step: Am I explaining a substance by electron behavior, bond type, molecular shape, polarity, or attractions between particles? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I explaining a substance by electron behavior, bond type, molecular shape, polarity, or attractions between particles?

Worked Examples

Example 1

easy
Show how magnesium and oxygen form an ionic bond in MgO\text{MgO}.

Answer

Mg→Mg2++2e−;O+2e−→O2−\text{Mg} \rightarrow \text{Mg}^{2+} + 2e^-;\quad \text{O} + 2e^- \rightarrow \text{O}^{2-}

First step

1
Mg (Group 2) has 2 valence electrons. It loses both to form Mg2+\text{Mg}^{2+}.

Full solution

  1. 2
    O (Group 16) has 6 valence electrons. It gains 2 electrons to form O2−\text{O}^{2-}.
  2. 3
    The electrostatic attraction between Mg2+\text{Mg}^{2+} and O2−\text{O}^{2-} forms the ionic bond in MgO.
Ionic bonds form when electrons are transferred from a metal to a nonmetal, creating oppositely charged ions that attract each other. The ratio of ions ensures overall electrical neutrality.

Example 2

medium
Predict the formula of the ionic compound formed between aluminum and oxygen.

Example 3

medium
Determine the formula of the ionic compound formed by magnesium and nitrogen.

Example 4

medium
Iron(III) and oxygen combine to form an ionic compound. Write its formula and name.

Example 5

medium
Explain why MgO\text{MgO} has a higher melting point than NaCl\text{NaCl}.

Example 6

medium
Explain why molten NaCl\text{NaCl} conducts electricity but solid NaCl\text{NaCl} does not.

Example 7

hard
Write the formula of the ionic compound formed by aluminum and sulfate (SO42−\text{SO}_4^{2-}).

Example 8

hard
Two ionic compounds, NaCl\text{NaCl} and NaF\text{NaF}, have similar charge magnitudes. Which has the larger lattice energy, and why?

Example 9

hard
Write the formula of the ionic compound formed by iron(II) and phosphate (PO43−\text{PO}_4^{3-}).

Example 10

hard
Predict which compound has a higher melting point: CaO\text{CaO} or KCl\text{KCl}. Justify with Coulomb's law.

Example 11

challenge
In the rock-salt structure of NaCl\text{NaCl}, how many nearest-neighbor Cl−\text{Cl}^- ions surround each Na+\text{Na}^+ ion, and what is this number called?

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
Write the formula for the ionic compound formed by lithium and fluorine.

Example 2

medium
Describe how magnesium and oxygen form an ionic bond in magnesium oxide (MgO\text{MgO}).

Example 3

easy
What kind of force holds an ionic bond together?

Example 4

easy
In an ionic bond, are electrons shared or transferred?

Example 5

easy
Which pair forms an ionic bond: Na\text{Na} and Cl\text{Cl}, or H\text{H} and H\text{H}?

Example 6

easy
Sodium gives one electron to chlorine. Write the two ions formed.

Example 7

easy
Do ionic compounds form discrete molecules or extended lattices?

Example 8

easy
Why are ionic compounds typically solids at room temperature?

Example 9

easy
What is the formula of the ionic compound from Ca2+Ca^{2+} and Cl−Cl^-?

Example 10

easy
Why does solid salt not conduct electricity, but molten salt does?

Example 11

medium
Write the ionic compound formula formed by aluminum and oxygen, showing charge balance.

Example 12

medium
Explain why ionic compounds are brittle and shatter when struck.

Example 13

medium
Sodium oxide forms from sodium and oxygen. Determine its formula via charge balance.

Example 14

medium
Why does an ionic bond not exist as a single isolated pair like Na+Cl−Na^+Cl^- floating alone in a crystal?

Example 15

medium
Magnesium chloride contains Mg2+Mg^{2+} and Cl−Cl^-. How many electrons did magnesium transfer, and to how many chlorines?

Example 16

medium
Why does sodium chloride dissolve in water even though its ionic bonds are strong?

Example 17

medium
Sodium sulfate uses Na+Na^+ and the polyatomic SO42−\text{SO}_4^{2-}. Write the formula and identify the bond types present.

Example 18

medium
Write the formula of the ionic compound formed by lithium and nitrogen, showing charge balance.

Example 19

medium
Why do molten ionic compounds conduct electricity while molten covalent molecular compounds usually do not?

Example 20

challenge
Predict and compare the formulas of potassium oxide and calcium oxide, then state which has the stronger ionic attraction and why.

Example 21

challenge
A compound conducts when dissolved in water, has a high melting point, and is brittle. A student says it must be covalent. Correct them with reasoning.

Example 22

challenge
Iron(III) oxide forms from Fe3+Fe^{3+} and O2−O^{2-}. Derive its formula and explain why iron needs a Roman numeral.

Example 23

easy
Predict the formula of the ionic compound formed between potassium (K+\text{K}^+) and bromine (Br−\text{Br}^-).

Example 24

easy
Write the charges that calcium and chlorine carry in an ionic compound.

Example 25

easy
Write the formula of the ionic compound formed by sodium and sulfur.

Example 26

easy
Which of these compounds is ionic: CO2\text{CO}_2, NaCl\text{NaCl}, or CH4\text{CH}_4?

Example 27

medium
Name the ionic compound KCl\text{KCl} using standard nomenclature.

Example 28

medium
Write the formula of the ionic compound formed by ammonium (NH4+\text{NH}_4^+) and sulfate (SO42−\text{SO}_4^{2-}).

Example 29

medium
How many electrons does a barium atom lose to form Ba2+\text{Ba}^{2+}?

Example 30

medium
Predict whether Rb\text{Rb} and I\text{I} form an ionic bond, and write the formula.

Example 31

medium
What ion does sulfur typically form?

Example 32

hard
Why are ionic crystals typically hard but brittle?

Example 33

hard
A compound has formula X2O3\text{X}_2\text{O}_3 where O is oxide (O2−\text{O}^{2-}). What is the charge on X\text{X}?

Example 34

hard
Approximate electronegativity difference for an ionic bond is roughly above what threshold (Pauling scale)?
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Background Knowledge

These ideas may be useful before you work through the harder examples.

ionchemical bond