EDEXCEL GCSE Chemistry - Unit 2 - Topic 2

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What is a compound?
A compound is two or more different atoms that are chemically bonded together.
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What is ionic bonding?
Positive and negative ions are held together by electrostatic attraction. This is called ionic bonding. Compounds held together by ionic bonding are called ionic compounds.
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What happens when atoms form ions?
When atoms form ions, they give or receive electrons to gain a full outer shell of electrons.
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What does the electronic configuration of an atom tell us?
The electronic configuration of an atom tells us what type of ion it will form.
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What type of ion will oxygen form?
Oxygen 2.6 will gain two electrons to fill up the second shell, so there are eight electrons. It forms an O2- ion.
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What type of ion will magnesium form?
Magnesium 2.8.2 will lose two negative electrons so that the full second shell becomes the outer shell. It forms an Mg2+ ion.
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How does the name of an atom change when it becomes an ion?
Negative ions change the ending of their element name to -ide, for example a fluorine atom become fluoride ion.
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What are cations?
Metal atoms lose electrons to form positively charged ions called cations.
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What are anions?
Non-metal atoms gain electrons to form negatively charged ions called anions.
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How are monoatomic ions formed?
Monoatomic ions are formed from atoms of only one element.
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Describe monoatomic anions.
Monoatomic anions have the same name as their atoms but with the ending changed to -ide. A chlorine atom becomes chloride ion.
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Describe monoatomic cations.
Monoatomic cations have the same name as the element from which they were made. A sodium atom becomes sodium ion.
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How are polyatomic cations formed?
Polyatomic cations are formed from atoms of more that one element. The different symbols show the different elements from which they are formed.
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What happens to the charges when ionic compounds form?
When ions join to form ionic compounds, the total number of negative charges always equals the total number of positive charges. This means that the number of positive and negative ions is not necessarily the same.
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What does the chemical formula of an ionic compound show?
It shows how many and which type of ions the compound contains.
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What is the structure of ionic compounds?
The ions in an ionic compound are arranged in a regular way, called a lattice structure. The ions in sodium chloride pack together in a box-like arrangement. This means they often form crystals.
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What are the physical properties of ionic compounds?
Ionic compounds have high melting and boiling points, are brittle and hard, conduct electricity only when dissolved or molten, may be soluble in water.
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Why do ionic compounds have high melting points?
Ionic substances form giant lattice structures with strong electrostatic forces of attraction between the oppositely charged ions. A large amount of energy is needed to break strong ionic bonds, so the melting point is high.
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Which two conditions must be met for a substance to conduct electricity?
A substance must contain charged particles and these particles must be free to move. Ionic substances conduct electricity when molten or dissolved because the charged ions are able to move towards oppositely charged electrodes.
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Why do ionic substances not conduct electricity when solid?
They do not conduct electricity when solid because the ions are not able to move.
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What is a precipitation reaction?
A reaction that results in an insoluble product.
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How can a pure sample of an insoluble salt be made?
1. Mix solutions of the reactants 2. Filter to separate the insoluble salt 3. Wash the residue in the filter paper to remove impurities 4. Allow to dry
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How can we test for carbonate?
To test for a carbonate, add dilute acid. If a gas bubbles off, test it with limewater. If the gas turns the limewater cloudy then the gas is carbon dioxide and the carbonate is confirmed.How
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What is the general equation for the reaction of an acid with a carbonate?
acid + carbonate --> salt + water + carbon dioxide
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How can we test for sulphate ions?
To test for sulphate ions, add hydrochloric acid and barium chloride solution. If a white precipitate forms then the solution contains sulphate ions.
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What is the word equation for the reaction of sulphate ions with barium chloride?
sulphate ions (aq) + barium chloride (aq) --> barium sulphate (s) + chloride ions (aq)
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How can we test for chloride ions?
To identify aqueous chloride ions, a few drops of dilute nitric acid are added to the sample solution, which is then shaken. A few drops of silver nitrate solution are then added. A white precipitate of silver chloride forms if sample has Cl- ions.
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What is the word equation for the reaction of chloride ions with silver nitrate?
chloride ions (aq) + silver nitrate (aq) --> silver chloride (s) + nitrate ions
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How is emission spectroscopy used?
Emission spectroscopy can be used to detect the presence of individual elements.
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What does each element produce when heated?
Each element produces a unique and characteristic spectrum when heated, like a chemical fingerprint.
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What can the emission spectrum of an unknown substance be compared with?
The emission spectrum of an unknown substance can be compared with standard spectra of elements to see which one it matches. This led to the discovery of rubidium and caesium.
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What can spectroscopy detect?
The method can detect very small amounts and can also measure the quantity of each element.
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Card 2

Front

What is ionic bonding?

Back

Positive and negative ions are held together by electrostatic attraction. This is called ionic bonding. Compounds held together by ionic bonding are called ionic compounds.

Card 3

Front

What happens when atoms form ions?

Back

Preview of the front of card 3

Card 4

Front

What does the electronic configuration of an atom tell us?

Back

Preview of the front of card 4

Card 5

Front

What type of ion will oxygen form?

Back

Preview of the front of card 5
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