EDEXCEL GCSE Chemistry - Unit 2 - Topic 3

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What is a covalent bond?
A covalent bond is formed between non metal atoms, which combine together by sharing electrons.
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Why do atoms share electrons?
Atoms share electrons because they are more stable when they share. The outermot shell of each atom in the molecule fills up with shared electrons. A full outer shell of electrons makes atoms stable.
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Why are atoms held in covalent bonds?
Because the nuclei of two different atoms are both holding onto the same pair of electrons.
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What does the number of covalent bonds that can be formed by an atom depend on?
It depends on how many electrons are needed to complete the outer shell.
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What type of bonds can sometimes form?
Sometimes two atoms share two or three pairs of electrons to form double bonds and triple bonds. Some elements form diatomic molecules - molecules containing two atoms.
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What are some examples of diatomic molecules?
H2, O2, N2, F2, Cl2, Br2, I2.
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Why do covalent compounds not conduct electricity?
Covalent compounds have no free electrons and no ions so they don't conduct electricity.
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Why do covalent substances have low melting and boiling points?
The covalent bonds binding the atoms together are very strong but there are only very weak forces holding the molecules to each other. Therefore, only a low temperature is needed to separate the molecules when they're melted or boiled.
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What does immiscible mean?
Liquids that do not form a solution but separate into two layers.
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Give one example of immiscible liquids.
Oil and water.
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How can we separate immiscible liquids?
Using a separating funnel.
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Describe the method used to separate immiscible liquids.
Put the mixture of liquids into a separating funnel. Open the tap and collect the bottom layer in a beaker. Close the tap when the top layer enters it. Change the beaker then open the tap to collect the top layer.
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What does miscible mean?
Liquids that completely mix together to form a solution.
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Give one example of miscible liquids.
Ethanol and water.
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How can we separate miscible liquids?
By fractional distillation.
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What is chromatography?
A technique for separating the components of a mixture. It works because dissolved substances move at different rates through a piece of paper soaked in a solvent.
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What is the Rf value?
The Rf value is the distance the compound has risen divided by the distance the solvent has risen.
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Other cards in this set

Card 2

Front

Why do atoms share electrons?

Back

Atoms share electrons because they are more stable when they share. The outermot shell of each atom in the molecule fills up with shared electrons. A full outer shell of electrons makes atoms stable.

Card 3

Front

Why are atoms held in covalent bonds?

Back

Preview of the front of card 3

Card 4

Front

What does the number of covalent bonds that can be formed by an atom depend on?

Back

Preview of the front of card 4

Card 5

Front

What type of bonds can sometimes form?

Back

Preview of the front of card 5
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