What are the key learning points about bonding?
An ionic bond is the attraction between oppositely charged ions. happens when Subatomic particle, with a negative charge and a very small mass relative to protons and neutrons. transfer from a metal The smallest particle of an element. We often think of atoms as tiny spheres, but in fact they are made from smaller particles called protons, neutrons and electrons. to a non‑metal atom, creating oppositely charged Electrically charged particle, formed when an atom gains or loses electrons. that attract strongly.
A covalent bond is formed by a shared pair of electrons. occurs between non‑metals when atoms share pairs of electrons to achieve stable outer An energy level around the nucleus where electrons can be found orbiting., forming molecules.
Dot‑and‑cross diagrams show electron transfer in ionic bonding and electron sharing in covalent bonding.
What are ions?
Atoms tend to lose or gain A subatomic particle with relative mass of ¹⁄₁₈₄₀. The relative charge of an electron is -1. to form a full outer An energy level around the nucleus where electrons can be found orbiting..
An ion is a charged particle.
They are formed when atoms gain or lose electrons to form a full outer shell.
Ions are charged because the number of protons is different from the number of electrons.
A molecular ion is a particle made of more than one atom that has an overall positive or negative charge.
A negative ion is called an anion.
A position ion is called a cation.
Simple ions have full outer shells, and the stable electronic configuration of the noble gases.
Key fact
Ions are formed by the transfer of electrons.
Positive ions are usually formed from metal atoms and negative ions are usually formed from non-metal atoms.
A chemical bond can form between oppositely charged ions – this is called an ionic bond.
How do negative and positive ions form?
Atoms gain electrons in their outer shell when they form negative ions, called anions.
These ions are negative because they contain more electrons than protons.
Atoms lose electrons from their outer shell when they form positive ions, called cations.
These ions are positive because they contain more protons than electrons.
What are some examples of ion charges and groups?
| Group | Element symbol | Ion charge | Ion symbol |
|---|---|---|---|
| 1 | Na | + | Na+ |
| 2 | Mg | 2+ | Mg2+ |
| 6 | O | 2- | O2- |
| 7 | Cl | - | Cl - |
Key facts
When writing the charge on the ion, remember to put the number before the positive or negative symbol (2+).
Just write + or – if the charge is 1+ or 1-.
When a non-metal atom turns into an ion, the element’s name changes to end in ‘-ide.’
For example, a fluorine atom turns into a fluoride ion.
Question
A magnesium atom and a fluorine atom are shown below.
Show how both atoms can form a full outer shell by gaining or losing electrons.
Work out the charge on the ions formed.
Answer
| The magnesium atom loses two electrons to get a full outer shell. | The fluorine atom gains one electron to get a full outer shell. |
| The magnesium ion has lost two negative electrons, so it now has a 2+ charge. It is a cation. | The fluoride ion has gained one negative electron, so it now has a - charge. It is an anion. |
What types of bonding are studied for Single Award science?
There are two types of bonding studied at GCSE Single Award:
Ionic bonding
Covalent bonding
What is ionic bonding?
Ionic bonding occurs in A substance formed when two or more elements are chemically combined. that contain a metal (usually a Group 1 or 2 element) and a non-metal (usually a Group 6 or 7 element).
They bond to form metal compounds.
When forming an ionic compound:
- A subatomic particle with relative mass of ¹⁄₁₈₄₀. The relative charge of an electron is -1. are transferred from the metal atom to the non-metal atom.
- This forms oppositely-charged ions.
- The metal ion has a positive charge.
- The non-metal ion has a negative charge.
- An ionic bond is the attraction between these oppositely-charged ions.
- Ionic bonding is strong and requires substantial amounts of energy to break.
Ionic bonding takes place between a metal and a non-metal.
For example, sodium (metal) and chlorine (non-metal) can form an ionic bond.
How to draw dot and cross diagrams (Higher tier only)
Dot and cross diagrams help us to model when ions are formed from atoms.
Here’s an example using sodium and chlorine.
They form ions which bond to form sodium chloride.
Image caption, 1. Draw the electronic configuration of each atom – one element with dots and the other with crosses.
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Here are some other examples of dot and cross diagrams for the formation of ions in ionic compounds.
These are for magnesium oxide and calcium chloride.
Image caption, 1. Ionic bonding in magnesium oxide (MgO) starts with a magnesium and oxygen atom.
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Question
Draw a dot and cross diagram to show the bonding in lithium fluoride.
Summary of ionic bonding
Ionic bonding
NARRATOR:
Ionic bonding — it's all about opposites attracting!
Not that kind of "opposites attracting"!
We're talking about charged particles, known as ions… Ions are formed when atoms lose or gain electrons.
And that makes them either positively or negatively charged.
Oppositely charged ions are attracted to each other by really strong electrostatic forces… forming what are known as ionic bonds.A good example of a substance containing ionic bonds is sodium chloride, or as we call it, table salt.
It's a compound of a metal and a non-metal, and it's made from positive sodium ions and negative chloride ions.
Ions form when electrons transfer from metal atoms to non-metal atoms.
The atoms of sodium, and other metals, have incomplete outer shells.
When they react with a non-metal, they lose all their outer electrons, so the shell below becomes the new outer shell — and it's complete.
It has no space for any other electrons.
An atom that loses an electron becomes a positively charged ion.
So, sodium atoms are written as Na, while sodium ions are written as Na⁺.
But the electrons must go somewhere when they leave metal atoms…
And they do — they're gained by non-metal atoms that have incomplete outer shells, making those shells complete.
The extra electrons turn the atoms into negatively charged ions. So, chlorine atoms are simply written as Cl, while chloride ions are Cl⁻.
And look! Now the ions have opposite charges — opposites attract and electrostatic forces pull them together.
That's your ionic bond right there!
Hello, table salt!
So, ions can form amazing structures — not just table salt.
In ionic compounds, the oppositely charged ions attract each other from all directions, forming solid structures known as giant ionic lattices.
Ionic bonds are really strong — it takes a lot of energy to break them, meaning ionic compounds have high melting and boiling points and are solid at room temperature.
Another property of these structures is that they don’t conduct electricity when they’re solid.
Why’s that? Well, an electric current is a flow of charged particles.
Solid ionic compounds don’t conduct because their charged particles — their ions — can’t move about.
They’re locked in place in the lattice structure.
If we want them to conduct electricity, we have to break the lattice up by melting or dissolving the ionic compound.
So there you go — the strength of opposites attracting…
Really!?
What is covalent bonding?
A covalent bond is formed when two atoms share electrons to obtain a The elements in Group 0 of the Periodic Table, named for their lack of chemical reactivity. The order electrons are arranged in different shells..
Covalent bonding occurs between non-metal atoms.
Covalent bonds are strong and require substantial amounts of energy to break.
Key terms
Covalent bond: a shared pair of electrons.
Molecule: two or more atoms covalently bonded together.
Diatomic: two atoms covalently bonded together in a molecule. O2, N2 and Cl2 are examples of diatomic molecules.
A covalent bond can be represented as a single line.
These diagrams show a molecule of methane and water both of which share electrons forming single covalent bonds when a molecule is formed.
Some molecules like oxygen share two pairs of electrons to make a double covalent bond.
VIDEO: Summary of covalent bonds
Covalent bonding
NARRATOR
Luckily for us, atoms don't always just sit around.
They can stick to other atoms and create amazing things — like the salt and vinegar on your chips. So how do they do it?
Well, one of the main ways is through covalent bonding.
It occurs in most non-metal elements, and it's how atoms bond to form molecules — and these can be elements, or compounds (made up of two or more different elements).
So, what brings these atoms together?
Electrons.
Most atoms have outer shells of electrons that aren't completely filled up — they've still got room for some more…
If they share electrons, they can fill up their outer shell — and form molecules.
And when two atoms get all cosy with each other, and share a pair of electrons between them, that's a covalent bond.To draw covalent bonds, we use dot and cross diagrams.
For instance — carbon dioxide consists of one carbon atom bonded to two oxygen atoms.
Now, carbon is in group 4 of the periodic table, so it has four electrons in its outer shell.
And for that outer shell to be completed, it needs four more.
Oxygen is in group 6, so — you've guessed it — it has six electrons in its outer shell.
So, when forming carbon dioxide, each oxygen atom shares two electrons, forming a double covalent bond with a carbon atom.
When that happens, the outer shell of the carbon atom is completed — four of its own electrons and two from each of the oxygen atoms.Do note that both oxygen atoms still have four non-bonding electrons that are just left over.
Now — there's a difference between simple covalent structures, and something called giant covalent structures.
Methane, the gas that's used in your Bunsen burners, exists as simple covalent molecules.
That means the atoms in each individual methane molecule are held together by covalent bonds —but there's not much holding one molecule to another — only weak intermolecular forces.
And it doesn't take much energy to overcome them.
On the other hand, giant covalent structures are made up of a huge number of atoms, all joined by covalent bonds in continuous 3D networks.
For example, let's have a look at diamond.
That’s made of carbon atoms, and each carbon atom is bonded to four other carbon atoms to form a continuous regular lattice.
Covalent bonds are strong — and there are loads of them in diamond, making it the hardest natural substance in the world!
And giving it a ridiculously high melting point.
Graphite is another giant covalent substance.
And though it's made from the same stuff as diamond — it is nothing but carbon atoms — it's really quite different — it's all soft and slippery.
Why?
Well, in graphite, each atom is bonded to three, not four, other carbon atoms.
They end up forming layers with only weak intermolecular forces between them — making it all slippery and crumbly.
The carbon atoms in graphite don’t share all their outer electrons, so they have non-bonding outer electrons.
These electrons are free to move around the lattice, which means graphite can do something rather useful that diamond can't —it can conduct electricity.
So there can be a fair bit of difference in the way covalent structures are formed.
But they all contain those strong covalent bonds, which of course are just atoms, sharing electrons…
Well, sharing is caring.
How to draw dot and cross diagrams (Higher tier only)
We can use dot and cross diagrams to show how a pair of electrons forms a covalent bond.
Here is the dot and cross diagram for oxygen (O2), a Two atoms covalently bonded. molecule.
Notice the lone pairs of electrons and the two shared pairs of electrons.
Here are the dot and cross diagrams for some other common molecules.
Key fact
A covalent bond can be represented by a line (–) in structural formulae.
A single covalent bond is when two atoms share a single pair of electrons.