Ion Examples in Chemistry

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

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

Concept Recap

An atom or group of atoms that has gained or lost one or more electrons, resulting in a net positive charge (cation) or net negative.

An atom that's not neutral—it has more or fewer electrons than protons.

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: Ion starts by naming the element, charge, and relevant protons, neutrons, or electrons.

Common stuck point: Students often know a formula related to ion but skip the recognition step: Am I using particle counts, nuclear charge, mass number, electron arrangement, or isotope notation to describe an atom or ion? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I using particle counts, nuclear charge, mass number, electron arrangement, or isotope notation to describe an atom or ion?

Worked Examples

Example 1

easy
Sodium (Z=11Z = 11) loses one electron. Write the ion formed and its electron configuration.

Answer

Na+:  1s2 2s2 2p6\text{Na}^+:\; 1s^2\,2s^2\,2p^6

First step

1
Neutral Na: 1s2 2s2 2p6 3s11s^2\,2s^2\,2p^6\,3s^1 (11 electrons).

Full solution

  1. 2
    Losing 1 electron: Na+\text{Na}^+ with configuration 1s2 2s2 2p61s^2\,2s^2\,2p^6 (10 electrons).
  2. 3
    This is the same electron configuration as neon (isoelectronic with Ne).
Metals tend to lose electrons to form cations. Sodium loses its single valence electron to achieve the stable noble gas configuration of neon.

Example 2

medium
An unknown ion has 10 electrons, 8 protons, and 8 neutrons. Identify the element, write the ion symbol, and calculate its charge.

Practice Problems

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

Example 1

easy
Predict the ion formed by each: (a) calcium, (b) fluorine, (c) aluminum.

Example 2

medium
Aluminum loses 3 electrons. What ion forms, and why is its charge positive?

Example 3

easy
A sodium atom loses one electron. What ion forms and what is its charge?

Example 4

easy
A chlorine atom gains one electron. What ion forms and what is its charge?

Example 5

easy
Is a cation positive or negative?

Example 6

easy
Is an anion positive or negative?

Example 7

easy
When an atom becomes an ion, what stays the same: protons or electrons?

Example 8

easy
Magnesium loses 2 electrons. Write its ion.

Example 9

easy
Is SO42−\text{SO}_4^{2-} a single-atom ion or a polyatomic ion?

Example 10

easy
An oxygen atom gains 2 electrons. Write its ion and charge.

Example 11

medium
An ion has 13 protons and 10 electrons. Identify the element and the ion charge.

Example 12

medium
A neutral atom has 16 electrons. To reach an octet, does it gain or lose, and what ion results?

Example 13

medium
Why does calcium form a Ca2+Ca^{2+} ion rather than Ca2−Ca^{2-}?

Example 14

medium
Potassium and chlorine react. Write both ions and show the resulting compound's neutrality.

Example 15

medium
Aluminum and oxygen form ions Al3+Al^{3+} and O2−O^{2-}. What is the neutral compound formula?

Example 16

medium
A particle has 17 protons and 18 electrons. Cation or anion, and what charge?

Example 17

medium
Why is the ammonium ion NH4+\text{NH}_4^+ called polyatomic, and what is its charge?

Example 18

medium
Lithium and fluorine react. Write each ion and the resulting neutral compound.

Example 19

medium
A particle has 8 protons and 10 electrons. Cation or anion, what charge, and what ion?

Example 20

challenge
An ion is isoelectronic with neon (10 electrons), has a +2 charge, and is a metal. Identify it.

Example 21

challenge
Iron can form Fe2+Fe^{2+} or Fe3+Fe^{3+}. Each starts from neutral iron (26 electrons). Give the electron count of each ion and explain why two charges exist.

Example 22

challenge
Calcium phosphate uses Ca2+Ca^{2+} and the polyatomic phosphate PO43−\text{PO}_4^{3-}. Derive the neutral formula.

Example 23

easy
Calcium loses 2 electrons. Write the ion.

Example 24

easy
Fluorine gains 1 electron. Write the ion.

Example 25

medium
Predict the ion formed by sulfur (Z = 16).

Example 26

medium
Predict the ion formed by potassium (Z = 19).

Example 27

medium
An ion has 16 protons and 18 electrons. Write the ion symbol.

Example 28

medium
An ion has 13 protons and 10 electrons. Write the ion symbol.

Example 29

medium
Write the ionic formula for the compound between Mg and Cl.

Example 30

medium
Write the formula for the ionic compound between Al and O.

Example 31

medium
Write the formula for the ionic compound formed from NH4+\text{NH}_4^+ and SO42−\text{SO}_4^{2-}.

Example 32

medium
Which ion has the same electron configuration as neon: Na+\text{Na}^+ or Cl−\text{Cl}^-?

Example 33

medium
An ion has charge +1, 11 protons, and a noble-gas electron configuration. Which ion is it?

Example 34

medium
Which is larger: a Na atom or a Na+\text{Na}^+ ion? Why?

Example 35

medium
Which is larger: a Cl atom or a Cl−\text{Cl}^- ion? Why?

Example 36

hard
List the ions produced when 1 mol of Al2(SO4)3\text{Al}_2(\text{SO}_4)_3 dissociates in water.

Example 37

medium
Write the formula for iron(III) chloride.

Example 38

medium
Predict the ion of nitrogen (Z = 7) when it gains 3 electrons.
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Background Knowledge

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

electronatom