Ionic Bonding
Ionic Bonding
Lesduur is: 90 minOnderdelen in deze les
Ionic Bonding
Open the lesson by linking the visible crystal structure of ionic substances to particle-level ideas: ions, electron transfer, and attraction.
Learning goal
I can explain how ions form, identify positive and negative ions, and use dot-and-cross diagrams to show ionic bonding.
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What comes to mind when you hear ionic bonding?
Use this to surface prior ideas such as electrons, charge, metals, non-metals, transfer, salt, or attraction. Pick out misconceptions too, especially if students say sharing instead of transfer.
Formation of ions
Atoms become ions when they gain or lose electrons.
losing electrons makes the particle positive
gaining electrons makes the particle negative
the number of protons does not change
Stress that ion formation changes charge, not the element itself. Students often confuse changing electron number with changing proton number.
Why atoms form ions
Many atoms form ions because a full outer shell is more stable than an incomplete one. Metals usually lose electrons from their outer shell, while non-metals usually gain electrons to fill theirs.
Keep the explanation at the school level: full outer shell as the driver. No need to introduce advanced ideas such as energy levels beyond this framing unless appropriate for the class.
Modelling electron transfer
Counters can represent electrons moving from one atom to another.
one counter moved away = electron lost
one counter received = electron gained
the total number of electrons stays the same
Use the teacher's specified resource here: counters. Emphasise transfer, not sharing. This helps separate ionic bonding from covalent bonding.
A simple example
Sodium has 1 electron in its outer shell. Chlorine has 7.
Sodium transfers 1 electron to chlorine.
Sodium atom → sodium ion, Na⁺
Chlorine atom → chloride ion, Cl⁻
If useful, connect this to the common ion cards resource: Na loses one, Cl gains one. Avoid overloading this slide with full shell notation if students are just meeting the idea.
Positive and negative ions
Positive ions are called cations
Negative ions are called anions
a cation has more protons than electrons
an anion has more electrons than protons
the charge shows the imbalance
Students do not need to memorise the words cation and anion immediately, but using them accurately supports later chemistry vocabulary.
How to identify an ion
To identify the ion, compare protons and electrons.
11 protons, 10 electrons = 1+
17 protons, 18 electrons = 1−
equal numbers = no overall charge
This is a key particle-level reasoning step. Make explicit that charge depends on the difference between proton number and electron number.
Common examples of ions
Group 1 metals usually form 1+ ions
Group 2 metals usually form 2+ ions
Group 7 non-metals usually form 1− ions
oxygen often forms 2− ions
ion names for non-metals usually end in -ide
Keep examples tightly linked to likely prior learning about groups in the periodic table. You can mention magnesium and oxide if students need another example before bonding slides.
What happens when an atom loses an electron?
It becomes positive
It becomes negative
It stays neutral
It gains protons
Tests the core idea from slides 2 to 6. The key misconception is that losing an electron changes proton number; it does not.
Complete the summary
Atoms form ions by gaining or losing electrons. When an atom loses electrons, it becomes positive. To identify charge, compare protons with electrons. Group 7 non-metals usually form 1− ions.
Echoes the phrasing from the ion formation and identification slides. Each blank is load-bearing vocabulary or charge knowledge.
How do you work out an ion's charge?
Expected elements: students should say that charge depends on the difference between protons and electrons, and that more protons gives a positive ion while more electrons gives a negative ion.
What is ionic bonding?
Ionic bonding is the strong electrostatic attraction between oppositely charged ions. The bond forms after electrons have been transferred from a metal atom to a non-metal atom.
Use the phrase 'strong electrostatic attraction' consistently. Students often incorrectly say the bond is the electron transfer itself; clarify that transfer creates ions, and attraction is the bond.
Ionic bonding in sodium chloride
In sodium chloride:
sodium forms Na⁺
chlorine forms Cl⁻
the opposite charges attract
many ions join in a giant ionic lattice
Do not present ionic compounds as separate paired molecules only. Introduce the idea of a repeating lattice now so later properties make sense.
Drawing dot-and-cross diagrams
Dot-and-cross diagrams show:
which electrons came from which atom
electron transfer between atoms
the charges on the ions after transfer
square brackets around each ion
Remind students that dots and crosses are just a tracking system; they do not mean different kinds of electrons.
Dot-and-cross example
For sodium chloride, draw:
sodium losing 1 outer electron
chlorine gaining that electron
[Na]⁺ with no outer-shell electron shown
[Cl]⁻ with a full outer shell
brackets and charges on both ions
Model the diagram carefully step by step. Students often forget brackets, charges, or which atom supplied the transferred electron.
More than one electron transferred
Some ionic compounds need more than one electron to be transferred.
Example: magnesium loses 2 electrons and oxygen gains 2 electrons, forming Mg²⁺ and O²⁻.
This extends the idea beyond 1:1 transfer without becoming a full naming lesson. It also prepares students to read charges correctly in diagrams.
What is the ionic bond in sodium chloride?
A shared pair of electrons
A transferred electron
Attraction of opposite ions
A neutral atom pair
Targets the common confusion from slide 9: electron transfer forms the ions, but the bond is the electrostatic attraction between them.
Complete the bonding description
In ionic bonding, electrons are transferred from a metal atom to a non-metal atom. This forms oppositely charged ions that attract each other. In a dot-and-cross diagram, each ion is shown in brackets with its charge written outside.
Checks both the bonding definition and the key conventions for dot-and-cross diagrams from slides 11 to 13.
Properties of ionic compounds
Ionic compounds usually:
have high melting and boiling points
form hard, brittle crystals
do not conduct electricity when solid
conduct electricity when molten or dissolved
Keep the list concise first; the next slide explains these properties using particles and movement of charge.
Why ionic compounds behave this way
Their properties come from the ionic lattice.
strong attractions need a lot of energy to overcome
in a solid, ions cannot move, so charge cannot flow
when molten or dissolved, ions can move and carry charge
Link each property directly to particle behaviour. This is the chemistry lens: explain observations using ions, forces, and movement.
Why ionic crystals are brittle
If layers in the lattice shift, ions with the same charge can line up next to each other.
Like charges repel, so the crystal can crack rather than bend.
Students often assume 'hard' means 'not breakable'. Distinguish hardness from brittleness clearly.
Why do ionic compounds conduct when molten?
Electrons are shared
Ions can move
The lattice is harder
Atoms become neutral
Links conductivity to particle movement, not to free electrons. This is the main explanatory idea in slides 14 to 16.
Complete the properties explanation
Ionic compounds have high melting points because the attractions in the lattice are strong. When solid, they do not conduct because the ions cannot move. If layers shift, like charges repel, so the crystal is brittle rather than bend.
Brings together the property explanations from slides 14 to 16, including the distinction between hard and brittle.
What is one thing you'll remember from this lesson?
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Which part of ionic bonding felt hardest today?
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Glossary
ion - a charged particle formed when an atom gains or loses electrons
cation - a positive ion
anion - a negative ion
ionic bonding - the strong electrostatic attraction between oppositely charged ions
electron transfer - movement of electrons from one atom to another
ionic lattice - a giant regular arrangement of oppositely charged ions
dot-and-cross diagram - a diagram showing outer-shell electrons and where they came from
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