Chemical bonds, ionic, covalent and metallic

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Chemical Bonds

Atoms combine with other atoms by moving electrons, which can be thought of as the 'language of chemistry'.
Atoms bond to achieve a full outer shell of electrons, which gives a more stable arrangement.
There are three types of strong chemical bond studied at GCSE: ionic, covalent and metallic.
Ionic bonding occurs when metals and non-metals react by transferring electrons, forming oppositely charged ions that attract via electrostatic forces.
Covalent bonding occurs when non-metal atoms share pairs of electrons.
Metallic bonding occurs in metals and alloys, where atoms share delocalised electrons.
Intermolecular forces are not chemical bonds; they are much weaker (about one-tenth the strength of a chemical bond) and do not involve electron transfer or sharing.

O₂ dot-and-cross diagram: a double covalent bond formed by two shared pairs of electrons.

Ionic Bonding

Ionic bonding is the strong electrostatic force of attraction between oppositely charged ions.
It forms when a metal atom transfers one or more electrons to a non-metal atom.
Metal atoms lose electrons to become positive ions (cations); non-metal atoms gain electrons to become negative ions (anions).
Ions form to obtain a full outer shell, giving them the electronic structure of a noble gas.
The charge on an ion relates to its group number: Group 1 metals form 1+ ions, Group 2 metals form 2+ ions, Group 6 non-metals form 2− ions, and Group 7 non-metals form 1− ions.
In dot and cross diagrams for ionic compounds, each ion is enclosed in square brackets with its charge written as a superscript at the top right.
For example, sodium (Group 1) loses one electron to form Na⁺, and chlorine (Group 7) gains one electron to form Cl⁻, giving the formula NaCl.
Magnesium (Group 2) loses two electrons to form Mg²⁺, and oxygen (Group 6) gains two electrons to form O²⁻, giving the formula MgO.

Ionic bonding in sodium chloride.

Ionic Compounds

Ionic compounds form giant ionic lattices – regular arrangements of alternating positive and negative ions tightly packed together.
Strong electrostatic forces of attraction act in all directions between oppositely charged ions, holding the lattice together.
Because many strong electrostatic forces must be overcome, ionic compounds have high melting and boiling points.
Solid ionic compounds do not conduct electricity because the ions are fixed in position; when molten or aqueous, the ions are free to move and carry charge, so they conduct.
3D ball and stick models show the arrangement of ions in space but represent ionic bonds as sticks; in reality, ionic bonds are electrostatic forces acting in all directions.
The 3D space-filling model is more accurate because it shows that there is little space between ions.
All models have limitations: they may not correctly represent relative ion sizes or the true nature of the electrostatic forces.

Electrical conductivity of ionic compounds

Covalent Bonding

Covalent bonding occurs when non-metal atoms share pairs of electrons to obtain a full outer shell.
Covalent bonds are very strong and form due to the electrostatic attraction between the shared pair of electrons and the positive nuclei of both atoms.
When two or more atoms are covalently bonded, they form a molecule.
Shared electrons are called bonding electrons; outer-shell electrons not involved in bonding are called non-bonding electrons.
Weak intermolecular forces exist between individual molecules; these are much weaker than covalent bonds.
Simple covalent molecules do not conduct electricity because they do not contain free electrons.
Covalent substances may consist of small molecules (e.g. H₂, H₂O, CO₂) or giant covalent structures (e.g. diamond, graphite, silicon dioxide).

H₂ dot-and-cross diagram: single covalent bond formed by one shared pair of electrons.

Dot and Cross Diagrams for Covalent Molecules

Dot and cross diagrams show how electrons are shared in covalent molecules.
You need to be able to draw dot and cross diagrams for: hydrogen (H₂), chlorine (Cl₂), oxygen (O₂), nitrogen (N₂), hydrogen chloride (HCl), water (H₂O), ammonia (NH₃) and methane (CH₄).
Only outer-shell electrons are shown; for example, chlorine has 7 outer electrons, not all 17.
The shared pair of electrons must be drawn in the overlapping region between the two atoms.
In water (H₂O), oxygen has 6 outer electrons; it shares 2 with hydrogen atoms, leaving 4 non-bonding electrons (2 lone pairs).
In methane (CH₄), carbon has 4 outer electrons, all of which are shared with four hydrogen atoms.
A double bond contains two pairs of electrons (4 electrons in total).

Cl₂ dot-and-cross diagram: single covalent bond formed by one shared pair of electrons.

Metallic Bonding

Metals consist of giant structures of atoms arranged in a regular pattern, sometimes called metallic lattices.
The outer-shell electrons of metal atoms are delocalised – free to move throughout the whole structure.
When electrons leave the outer shell, the remaining atoms become positively charged metal ions.
The delocalised electrons form a 'sea of electrons' that moves freely between the positive metal ions.
Metallic bonding is the strong electrostatic attraction between the positive metal ions and the sea of delocalised electrons.
This type of bonding occurs in pure metals and in alloys (mixtures of metals).
Delocalised electrons are not transferred as in ionic bonding; they move freely throughout the entire metallic lattice.

Metallic bonding and malleability

Representing Molecules and Structures

Dot and cross diagrams are useful for showing the sharing or transfer of electrons and indicating which atom the electrons come from, but they do not show 3D arrangement or relative sizes.
Ball and stick models show the arrangement of atoms in 3D space and are useful for visualising molecular shape, but they do not show electron movement and exaggerate the space between atoms.
2D displayed formulae are simple representations that show which atoms are present and how they are connected, but they do not show shape or relative sizes.
Empirical formula gives the simplest whole-number ratio of atoms of each element in a compound.
To find empirical formula from a diagram: count the atoms of each element, write the ratio, and simplify to the smallest whole numbers.
For example, ethene (C₂H₄) has an empirical formula of CH₂; methane (CH₄) has an empirical formula of CH₄ (already simplest).
Polymers are very large molecules made from many smaller repeating units joined by covalent bonds (e.g. polyethene, PVC).

Sizes of Atoms and Molecules

An atom is typically about 0.1 nanometres (nm) in size, which is 0.0000000001 m or 10⁻¹⁰ m.
Simple molecules contain only a few atoms, so their sizes are similar to those of atoms.
The smallest molecule is hydrogen (H₂), which is about 0.074 nm long (7.4 × 10⁻¹¹ m).
Electron microscopy can produce images of individual atoms and simple molecules.
For example, pentacene (C₂₂H₁₄) was first imaged in 2009 using atomic force microscopy.

Key Terminology and Common Misconceptions

Ionic bond: strong electrostatic attraction between oppositely charged ions.
Covalent bond: strong bond formed when atoms share pairs of electrons.
Metallic bond: strong electrostatic attraction between positive metal ions and delocalised electrons.
Cation: positive ion formed when an atom loses electrons. Anion: negative ion formed when an atom gains electrons.
Lattice: regular repeating arrangement of particles (ions in ionic compounds, atoms in metals).
Avoid saying atoms 'want' or 'need' a full outer shell; instead, say they achieve a full outer shell to become more stable.
Do not describe ionic bonding as sharing electrons – it involves transfer of electrons.
Do not confuse intermolecular forces with covalent bonds; intermolecular forces are weak and between molecules, while covalent bonds are strong and within molecules.

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1.Which type of bonding is found in methane?
Easy
- AIonic
- BCovalent
- CMetallic
- DHydrogen
2.Which of the following statements about a chlorine molecule are correct? (select all that apply)
Easy
- AA chlorine molecule has the formula Cl₂
- BChlorine is bonded metallically
- CAtoms are typically 0.1 nanometres in size
- DChlorine is a solid at room temperature
- EChlorine atoms share a pair of electrons
3.Hydrogen gas has the same type of bonding as chlorine. Why is hydrogen a gas at room temperature?
Easy
- AThe intermolecular forces are strong
- BThe bonding in hydrogen is weak
- CThe intermolecular forces are weak
- DThe covalent bonds are broken
4.What is the correct electronic configuration of a chlorine atom?
Easy
- A2.7
- B2.8.7
- C2.8.8.7
- D2.7.8
5.Which of these oxides contains covalent bonds?
Medium
- AAluminium oxide
- BCarbon dioxide
- CSodium oxide
- DLead oxide
6.When water boils, the covalent bond between the atoms is broken.
Medium
True or false?
7.What is formed when a hydrogen atom and a chlorine atom join together?
Easy
- AA hydrogen chloride atom
- BA hydrogen chlorine molecule
- CA hydrogen chloride molecule
- DA hydrogen chlorine ion
8.What is the size of a typical atom?
Easy
- A0.1 nm
- B0.1 μm
- C0.1 mm
- D0.1 cm

Plus de questions

9.What is the formula of ammonia?
Easy
- ANH
- BNH₂
- CNH₃
- DN₂H₃
10.Which statement about a double bond is correct?
Medium
- AA double bond contains two electrons
- BA double bond contains two pairs of electrons
- CA double bond contains four pairs of electrons
- DA double bond contains one pair of electrons
11.Methane is a simple molecule and does not conduct electricity. Which statement is the correct reason for this?
Medium
- AElectrons are fixed in position
- BThe ions are free to move and carry a charge
- CThere are no free electrons to carry the charge
- DThe bonds contain no electrons
12.How many non-bonding electrons does each oxygen atom have in a carbon dioxide molecule?
Easy
- A2
- B4
- C5
- D6
13.What is the molecule H₂S called?
Easy
- AHydrogen sulfide
- BHydrogen sulfur
- CSulfur hydride
- DSulfur hydrogen
14.Which statements are true about a molecule of hydrogen sulfide (H₂S)? (select all that apply)
Medium
- AAll atoms in the molecule are non-metals
- BThe molecule contains double covalent bonds
- CAll the electrons in the atoms are shown
- DThere are 4 non-bonding electrons
- EThe molecule is held together by ionic bonds
15.Which of the following is a property of ionic compounds?
Easy
- AThey conduct electricity when solid
- BThey have low melting points
- CThey conduct electricity when molten or aqueous
- DThey are made of molecules
16.Which statement best describes metallic bonding?
Medium
- AThe electrostatic attraction between positive metal ions and a sea of delocalised electrons
- BThe sharing of pairs of electrons between metal atoms
- CThe transfer of electrons from metal atoms to non-metal atoms
- DThe attraction between oppositely charged ions in a lattice
17.Put these structures in order of size, starting with the smallest.
Easy
- oxygen atom
- oxygen nucleus
- oxygen molecule
- proton
18.Draw one straight line from each object to its correct size.
Medium
- atom
- small molecule
- nucleus
- about 0.1 nm
- about 0.074 nm
- about 10⁻¹⁴ m
19.Which instrument allows scientists to see individual atoms?
Easy
- AElectron microscope
- BLight microscope
- COscilloscope
- DTelescope
20.Which statements about a metallic lattice are correct? (select all that apply)
Medium
- AThe metal ions are positively charged
- BThe delocalised electrons are shared between the positive ions
- CThe delocalised electrons are transferred to non-metal atoms
- DThe metal ions are held in a regular repeating pattern
- EThe bonding is the strong electrostatic attraction between positive ions and delocalised electrons
21.Which statements about the limitations of models of bonding are correct? (select all that apply)
Medium
- ADot and cross diagrams do not show the 3D arrangement of atoms
- BBall and stick models show the movement of electrons
- CBall and stick models place atoms further apart than they really are
- DDot and cross diagrams show the relative sizes of atoms accurately
- E2D displayed formulae cannot show the shape of a molecule in 3D space
22.In a giant ionic lattice, the positive and negative ions are arranged in a regular alternating pattern.
Easy
True or false?
23.Which statement explains why solid sodium chloride does not conduct electricity, but molten sodium chloride does?
Medium
- AIn the solid, ions are fixed in the lattice; when molten, the ions are free to move
- BIn the solid, electrons are fixed in position; when molten, the electrons are free to move
- CIn the solid, the ions are neutral; when molten, the ions become charged
- DIn the solid, the covalent bonds break; when molten, the ions are free to move
24.Which row correctly shows the ions formed in magnesium oxide?
Medium
- AMg²⁺ and O²⁻
- BMg⁺ and O⁻
- CMg²⁻ and O²⁺
- DMg⁻ and O⁺
25.Sodium oxide has the formula Na₂O. Which statements about the ions in sodium oxide are correct? (select all that apply)
Medium
- AEach sodium atom loses one electron to form Na⁺
- BEach oxygen atom gains two electrons to form O²⁻
- CThe formula needs two sodium ions for every oxide ion to balance the charges
- DEach oxygen atom loses two electrons to form O²⁺
- EThe formula needs one sodium ion for every oxide ion to balance the charges
26.A dot and cross diagram shows one carbon atom and four hydrogen atoms bonded together. What is the molecular formula of this substance?
Medium
- ACH₄
- BC₄H
- CCH
- DC₄H₄
27.A dot and cross diagram shows a molecule containing two carbon atoms and four hydrogen atoms. What is the empirical formula of this molecule?
Medium
- ACH₂
- BC₂H₄
- CCH₄
- DC₄H₂
28.An ionic compound is formed from element X in Group 2 and element Y in Group 7. What is the formula of the compound?
Medium
- AXY
- BXY₂
- CX₂Y
- DX₂Y₃
29.A dot and cross diagram shows a molecule containing one nitrogen atom and three hydrogen atoms. What is the molecular formula of this substance?
Medium
- ANH₃
- BN₃H
- CNH
- DN₂H₆
30.A diagram of a solid shows a regular, repeating arrangement of positive and negative ions held together in all directions. Which statements about this solid are correct? (select all that apply)
Medium
- AThe solid has a giant ionic lattice structure
- BThe solid will conduct electricity when solid
- CThe solid has a high melting point
- DThe ions are held together by weak intermolecular forces
- EThe solid contains delocalised electrons
31.In metallic bonding, the delocalised electrons are transferred from the metal atoms to non-metal atoms.
Easy
True or false?
32.Why can metals be bent and shaped without breaking?
Medium
- AThe layers of positive ions can slide over each other
- BThe covalent bonds between the atoms break and reform
- CThe delocalised electrons are fixed in position
- DThe ions are held together by weak intermolecular forces
33.Match each substance to the type of bonding it contains.
Medium
- Sodium chloride
- Chlorine
- Copper
- Ionic bonding
- Covalent bonding
- Metallic bonding
34.Put these particles in order of size, starting with the smallest.
Medium
- Electron
- Proton
- Oxygen atom
- Oxygen molecule
35.A diagram of a molecule shows one carbon atom and two oxygen atoms. What is the empirical formula of this molecule?
Medium
- ACO₂
- BCO
- CC₂O₄
- DC₂O
36.A student is given a 3D model of a solid in which positive and negative ions are shown as spheres connected by sticks. Which limitation of this ball-and-stick model is correct?
Medium
- AIt shows the ions too close together, with no space between them.
- BIt represents the ionic bond as a stick, but the bond is actually an electrostatic force acting in all directions.
- CIt does not show the charges on the ions.
- DIt shows the ions arranged randomly rather than in a regular pattern.
37.In a dot-and-cross diagram of an ionic compound, square brackets are used around each ion and the charge is written outside the brackets at the top right.
Easy
True or false?
38.Which of the following statements about the structure and bonding of a metal are correct? (select all that apply)
Medium
- AThe metal consists of a giant lattice of positive ions.
- BThe delocalised electrons are transferred permanently to non-metal atoms.
- CThe delocalised electrons are free to move throughout the whole structure.
- DMetallic bonding is the strong electrostatic attraction between positive ions and delocalised electrons.
- EThe positive ions are held in fixed positions by strong covalent bonds.
39.Match each particle to its correct description.
Medium
- Cation
- Anion
- Delocalised electron
- A negatively charged ion formed when an atom gains electrons
- An electron that is free to move throughout a metal structure
- A positively charged ion formed when an atom loses electrons
40.Put these steps in the correct order to describe how a sodium atom and a chlorine atom form sodium chloride.
Medium
- A chlorine atom gains one electron to form a chloride ion (Cl⁻).
- A sodium atom loses one electron to form a sodium ion (Na⁺).
- The oppositely charged ions are held together by strong electrostatic forces.
41.Complete the sentence about bonding in ammonia.
Easy
When a nitrogen atom and a hydrogen atom bond to produce ammonia, electrons are ____.
42.How many bonding electrons are in the outer shell of the oxygen atom in a water molecule?
Medium
43.A magnesium atom loses two electrons to form an Mg²⁺ ion. How many electrons does the Mg²⁺ ion have?
Medium
44.Complete the table showing the charges on ions formed from these groups.
Medium
Group 1 metals form ____ ions, Group 2 metals form ____ ions, Group 6 non-metals form ____ ions, and Group 7 non-metals form ____ ions.
45.What is a positive ion called?
Easy
46.Complete the sentence about the electrons in a covalent bond.
Medium
In a covalent bond, a pair of electrons is ____ between the two atoms, and these electrons are called ____ electrons.
47.An oxygen atom (atomic number 8) forms an oxide ion with a charge of 2−. How many electrons are in this ion?
Medium
48.Complete the sentence about the particles in a covalent bond.
Easy
A covalent bond is formed when two atoms share a ____ of electrons.
49.What is the name of the strong electrostatic force of attraction that holds oppositely charged ions together in a giant lattice?
Medium
50.A typical atom is about 0.1 nanometres in size. Give this size in metres, in scientific notation, as the value of the power of ten. For example, if the answer were 10⁻⁵ m you would enter -5.
Easy
51.A fluorine ion, F⁻, has an atomic number of 9 and a mass number of 19. How many electrons does the F⁻ ion contain?
Medium
52.A magnesium ion, Mg²⁺, has an atomic number of 12 and a mass number of 24. How many neutrons does the Mg²⁺ ion contain?
Medium
53.Describe what happens when a covalent bond is formed between a hydrogen atom and a chlorine atom.
Hard
54.Explain how a magnesium atom and an oxygen atom form an ionic bond in magnesium oxide. Include the electron transfer and the charges on the ions.
Hard
55.Describe what a covalent bond is. Include the particles involved and how they interact.
Hard
56.Explain why a ball and stick model is not a perfect representation of a molecule's structure.
Hard
57.Explain why solid sodium chloride does not conduct electricity, but molten sodium chloride does. Include the particles responsible for carrying charge.
Medium
58.How many bonding electrons are in the outer shell of the oxygen atom in a water molecule?
Medium
- A6 electrons
- B5 electrons
- C4 electrons
- D3 electrons
59.A magnesium atom loses two electrons to form an Mg²⁺ ion. How many electrons does the Mg²⁺ ion have?
Medium
- A9
- B10
- C12
- D11
60.An oxygen atom (atomic number 8) forms an oxide ion with a charge of 2−. How many electrons are in this ion?
Medium
- A9 electrons
- B12 electrons
- C11 electrons
- D10 electrons
61.A typical atom is about 0.1 nanometres in size. Give this size in metres, in scientific notation, as the value of the power of ten. For example, if the answer were 10⁻⁵ m you would enter -5.
Easy
- A-9 m (as power of ten)
- B-10 m (as power of ten)
- C-8 m (as power of ten)
- D-11 m (as power of ten)
62.A fluorine ion, F⁻, has an atomic number of 9 and a mass number of 19. How many electrons does the F⁻ ion contain?
Medium
- A10
- B12
- C11
- D9
63.A magnesium ion, Mg²⁺, has an atomic number of 12 and a mass number of 24. How many neutrons does the Mg²⁺ ion contain?
Medium
- A13
- B11
- C12
- D14

Cartes mémo

What are the three types of strong chemical bond studied at GCSE?

Ionic, covalent and metallic.

In ionic bonding, what happens to the particles?

Oppositely charged ions are held together by strong electrostatic forces of attraction.

In covalent bonding, what do the particles do?

Atoms share pairs of electrons.

In metallic bonding, what do the particles share?

Atoms share delocalised electrons.

Which type of bonding occurs in compounds formed from metals combined with non-metals?

Ionic bonding.

Which type of bonding occurs in most non-metallic elements and in compounds of non-metals?

Covalent bonding.

Which type of bonding occurs in metallic elements and alloys?

Metallic bonding.

When a metal atom reacts with a non-metal atom, what happens to the electrons in the outer shell of the metal atom?

They are transferred to the non-metal atom.

What type of ion do metal atoms form, and how?

Metal atoms lose electrons to become positively charged ions (cations).

What type of ion do non-metal atoms form, and how?

Non-metal atoms gain electrons to become negatively charged ions (anions).

What is the charge on ions formed by Group 1 metals?

1+.

What is the charge on ions formed by Group 2 metals?

2+.

What is the charge on ions formed by Group 6 non-metals?

2−.

What is the charge on ions formed by Group 7 non-metals?

1−.

What is an ionic compound?

A giant structure of ions held together by strong electrostatic forces of attraction between oppositely charged ions.

Why do ionic compounds have high melting and boiling points?

Because strong electrostatic forces act in all directions between the oppositely charged ions in the giant lattice, so a lot of energy is needed to overcome them.

What is a covalent bond?

A strong bond formed when two atoms share a pair of electrons; the shared pair is attracted to the positive nuclei of both atoms.

What are the electrons called that are shared in a covalent bond?

Bonding electrons.

What are non-bonding electrons?

Outer-shell electrons that are not involved in covalent bonding.

Why do simple covalent molecules not conduct electricity?

Because they do not contain free electrons.

What are the weak forces between individual simple molecules called?

Intermolecular forces.

In metallic bonding, what are delocalised electrons?

Electrons from the outer shell of metal atoms that are free to move throughout the whole structure.

What does metallic bonding consist of?

A lattice of positive metal ions in a 'sea' of delocalised electrons, held together by strong electrostatic attraction.

What is the charge on the metal ions in a metallic lattice?

Positive, because they have lost their outer-shell electrons.

What is the formula of sodium chloride?

NaCl.

What is the formula of magnesium oxide?

MgO.

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