Which types of atoms usually form covalent bonds?

Non-metal atoms bonded to other non-metal atoms.

How many shared pairs are in a CO₂ molecule?

Four, in two double bonds, O=C=O.

How many covalent bonds are in a CH₄ molecule?

Four single bonds, one from carbon to each hydrogen.

What is special about the nitrogen atom in NH₃?

It has three bonding pairs and one non-bonding pair of electrons.

Why do simple molecular substances have low boiling points?

The forces between molecules are weak and need little energy to overcome.

Do the covalent bonds break when a simple molecular substance boils?

No, only the weak forces between molecules are overcome.

Why do simple molecular substances not conduct electricity?

They have no ions and no free electrons.

What is a giant covalent structure?

A huge network of atoms joined by strong covalent bonds.

Why does diamond have a very high melting point?

A lot of energy is needed to break the many strong covalent bonds.

Why does graphite conduct electricity?

Each carbon uses only three outer electrons in bonds, so one electron per atom is delocalised and can move.

Why is graphite soft and slippery?

Its layers can slide over each other.

Name two uses of silica.

Making glass, and as sand in building.

Covalent bondingIB MYP Sciences: Flashcards

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What is a covalent bond?

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What is a covalent bond?: A shared pair of electrons between two atoms.
Which types of atoms usually form covalent bonds?: Non-metal atoms bonded to other non-metal atoms.
How many shared pairs are in a molecule of H₂?: One.
How many shared pairs are in a CO₂ molecule?: Four, in two double bonds, O=C=O.
How many covalent bonds are in a CH₄ molecule?: Four single bonds, one from carbon to each hydrogen.
What is special about the nitrogen atom in NH₃?: It has three bonding pairs and one non-bonding pair of electrons.
Why do simple molecular substances have low boiling points?: The forces between molecules are weak and need little energy to overcome.
Do the covalent bonds break when a simple molecular substance boils?: No, only the weak forces between molecules are overcome.
Why do simple molecular substances not conduct electricity?: They have no ions and no free electrons.
What is a giant covalent structure?: A huge network of atoms joined by strong covalent bonds.
Why does diamond have a very high melting point?: A lot of energy is needed to break the many strong covalent bonds.
Why does graphite conduct electricity?: Each carbon uses only three outer electrons in bonds, so one electron per atom is delocalised and can move.
Why is graphite soft and slippery?: Its layers can slide over each other.
Name two uses of silica.: Making glass, and as sand in building.

Exam questions on Covalent bonding

Chlorine gas, Cl₂, is added to the water in public swimming pools in Singapore to kill bacteria. A chlorine atom has seven electrons in its outer shell, and a molecule of chlorine contains two chlorine atoms joined by a covalent bond.
Describe, in terms of outer electrons, how the covalent bond forms between two chlorine atoms.2 marks
A fertiliser factory in Gujarat makes ammonia, NH₃, from nitrogen and hydrogen. A nitrogen atom has five electrons in its outer shell and a hydrogen atom has one. Ammonia is a gas at room temperature.
Explain why ammonia has a low boiling point and does not conduct electricity.2 marks
A student in Nairobi compares two forms of carbon, diamond and graphite. She tries to scratch a glass slide with a sample of each. The diamond scratches the glass. The graphite does not scratch the glass and instead leaves a grey mark on it. She also finds that graphite conducts electricity but diamond does not, and both have very high melting points.
Explain why graphite conducts electricity but diamond does not.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).