How many electrons are in a double bond? A triple bond?

Four electrons (two pairs); six electrons (three pairs).

How is a covalent bond represented in a displayed formula?

A line (one line per shared pair).

Define a dative covalent (co-ordinate) bond.

A shared pair of electrons in which both electrons are supplied by one atom.

How is a dative covalent bond represented?

An arrow pointing from the donor atom to the acceptor.

What does the acceptor of a dative bond need?

An empty orbital to take the pair, e.g. H⁺ or boron in BF₃.

How does NH₄⁺ form?

The lone pair on N in NH₃ is donated to H⁺, forming a dative covalent bond.

How does H₃O⁺ form?

A lone pair on O in H₂O is donated to H⁺ forming a dative bond.

How many shared pairs are in a molecule of ethene?

Six: four C–H single bonds and one C=C double bond (2 pairs).

Why can BF₃ accept a lone pair?

Boron has only six outer electrons, so it can accept a pair to reach eight.

Covalent and dative covalent bondingAQA A-Level Chemistry: Flashcards

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Define a single covalent bond.

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Define a single covalent bond.: A shared pair of electrons between two atoms.
How many electrons are in a double bond? A triple bond?: Four electrons (two pairs); six electrons (three pairs).
How is a covalent bond represented in a displayed formula?: A line (one line per shared pair).
Define a dative covalent (co-ordinate) bond.: A shared pair of electrons in which both electrons are supplied by one atom.
How is a dative covalent bond represented?: An arrow pointing from the donor atom to the acceptor.
What does the donor of a dative bond need?: A lone pair of electrons.
What does the acceptor of a dative bond need?: An empty orbital to take the pair, e.g. H⁺ or boron in BF₃.
How does NH₄⁺ form?: The lone pair on N in NH₃ is donated to H⁺, forming a dative covalent bond.
How does H₃O⁺ form?: A lone pair on O in H₂O is donated to H⁺ forming a dative bond.
Which atom supplies the dative bond electrons in CO?: Oxygen (arrow from O to C).
How many shared pairs are in a molecule of ethene?: Six: four C–H single bonds and one C=C double bond (2 pairs).
Why can BF₃ accept a lone pair?: Boron has only six outer electrons, so it can accept a pair to reach eight.

Exam questions on Covalent and dative covalent bonding

Nitrogen gas from the air is used to make ammonia. Ammonia is then converted into fertilisers that contain the ammonium ion, NH₄⁺.
Explain how an ammonia molecule forms an ammonium ion with a hydrogen ion, H⁺.2 marks
Carbon monoxide, CO, is a toxic gas formed by the incomplete combustion of carbon-containing fuels. A carbon atom has four outer-shell electrons and an oxygen atom has six. In carbon monoxide the carbon and oxygen atoms are joined by a triple bond, and each atom has one lone pair of electrons.
Explain why one of the bonds in carbon monoxide is a dative covalent bond, and state how this bond is represented in a displayed formula.2 marks
Boron trifluoride, BF₃, is a gas in which the boron atom has only six electrons in its outer shell. It reacts with ammonia, NH₃, to form a solid compound with the formula H₃N→BF₃.
Explain how the bond between the nitrogen atom and the boron atom forms.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).