Chemistry Unit 2 Revision

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What are compounds
Substances in which atoms of two or more elements are chemically combined
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All compound want what?
To have the structure of the noble gases (Full outer shell)
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Atoms that loses electrons become..
Positively charged ions
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Atomes that gain electrons become..
Negatively charged ions
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What are the Group 1 elements?
Alkali Metals which all react with non-metal elements to form ionic compounds in which the metal ion has a single positive charge
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What are the Group 7 elements?
The halogens. All react with the alkali metals to form ionic compounds in which the halide ions have a single negative charge.
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What is an ionic compound?
Is a giant structure of ions. Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions. These forces of act in all directions in the lattice.
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What is it called when atoms share pairs of electrons?
Covalent bonds
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An example of a giant covalent structure is?
Diamond and Silicon Dioxide
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In a metal atom the electrons in the highest occupied energy levels are delocalised, what does this mean?
Free to move through the whole structure. This corresponds to a structure of positive ions with electrons between the ions holding them together by strong electrostatic attractions.
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How strong are the forces between covalent molecules? (intermolecular forces)
Weak intermolecular forces of attraction meaning that they have very low melting and boiling points because the molecules are easily parted from each other
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Why can metals be bent and shaped?
Layers of atoms which can easily slide over each other
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What are delocalised electrons?
These are electrons which come from the outer shell and are free to move through the whole structure and so metals are good conductors of heat and electricity
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What are substances which have relatively low melting and boiling points?
Substances that consist of simple molecules
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Why do simple molecules have low melting and boiling points?
Have weak forces between the molecules (inter-molecular forces). It's these inter-molecular forces that are overcome, not the covalent bonds, when the substance melts or boils
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Can substance that consist of simple molecules conduct electricity?
No because the molecules do not have an overall electric electric charge
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Describe the structure of an ionic compound
Giant ionic lattices in which there are strong electrostatic forces in all directions between oppositely charged ions. These compounds have high melting and boiling points because of the large amount of energy needed to break the many bonds
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Why do ionic compounds conduct electricity when melted or dissolved in water?
The ions are free to move and carry the current
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Give examples of giant covalent structures
Diamond, graphite and silicon dioxide
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Why is diamond very strong?
Each carbon atom forms 4 covalent bonds with other carbon atoms in a giant covalent structure
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Why is graphite soft and slippery?
Each carbon atom bonds to 3 others forming layers. The layers are free to slide over each other because there are no covalent bonds between the layers
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Why does graphite conduct heat and electricity?
On electron from each carbon atom is delocalised, so therefore for allows it to
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What is fullereness??
Form of carbon. With different numbers of carbon atoms. Can be used for drug delivery into the body, in lubricants, as catalysts and in nanotubes for reinforcing materials
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How does a metal conduct heat and electricity?
The delocalised electrons in their structures
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Why can metals be bent or shaped?
Metals are made of layers of atoms which can slide over each other
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What are shape memory alloys?
They return to their original shape after being deformed
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What does the properties of polymers depend on?
What they're made from and what conditions they're made in
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What do thermosoftening polymers consist of?
Individual tangled polymer chains
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What do thermosetting polymers consist of?
Polymer chains with cross-links between them so that they don't melt when they're heated
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What are the relative masses of protons, neutrons and electrons?
Proton=1, Neutron=1, Electron=0
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What is the mass number?
The total number of protons and neutrons in an atom
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What is an isotope?
Atoms of the same element can have different numbers of neutrons
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What is the relative formula mass (Mr)
The sum of the relative atomic masses of the atoms in the numbers shown in the formula
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Why is an instrumental method good at detecting elements and compounds?
Accurate, Sensitive, Rapid and are particularly useful when the amount for a sample is very small
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How can additives be identified in food?
Chemical analysis. Artificial colours can be detected and identified by paper chromotography
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Describe the process of Gas Chromatography (instrumental method)
Gas chromatography allows the separation of a mixture of compounds, the time taken for a substance to travel through the colum can be used to help identify the substance. The outcput from the gas chromatography column can be linked to a mass spectrum
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What does a mass spectrometer do?
Be used to identify the substances leaving the end of the column and give the relative molecular mass of each of the substances separated
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/In a chemical reaction why might it not be possible to obtain the calculated amount of product
The reaction may not go to completion because it is reversible. Some of the product may be lost when it is separated from the reaction mixture. Some of the reactants may react in ways different from the expected reaction.
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What is the yield?
The amount of a product obtained
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What are the 2 equations for measuring the rate of reaction?
Amount of reactant used/ Time or Amount of product formed/time
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When can chemical reactions occur?
When reacting particles collide with each other and with sufficient energy.
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What is the activation energy?
The minimum amount of energy particles must have to react
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How can you increase the rate of reaction?
Increasing the temperature (collide more frequently), Increasing the pressure (increases the frequency of collisions), increasing the concentration of reactants, Increasing the surface area of the solid reactants
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Why are catalysts important in increasing the rates of chemical reactions used in industrial processes?
To reduce the cost
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What is an exothermic reaction?
Transfers energy to the surroundings (combustion)
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What is an endothermic reaction?
Takes in energy from the surroundings (thermal decomposition)
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Is a reversible reaction exothermic or endothermic?
In one direction it's endothermic and in the other it's exothermic. The same amount of energy is transferred in each case
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What can produce soluble salts when reacting with acids?
Metal, Insoluble bases and Alkalis
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How can a salt solution change to a solid salt?
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Acid + Metal -> Salt + Hydrogen
Metals react with acids to give salts
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What does ammonia dissolve in water to produce?
An alkaline solution. This is used to produce ammonium salts (important fertilizers)
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What do Hydrogen ions make a solution?
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What do hydroxide ions make a solution?
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How do your break an ionic substance into elements?
Electrolysis. Passing an electric current through ionic substances that are molten.
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What happens during electrolysis?
Positively charged ions move to the negative electrode (cathode) and the negatively charged ions move to the positive electrode (anode0
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What does OILRIG stand for?
Oxidation Is Loss, Reduction Is Gain
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What can reactions at electrodes be represented by?
Half Equations
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How is aluminium manufactured?
The electrolysis of a molten mixture of aluminium oxide and cryolite. Aluminium forms at the cathode and oxygen at the anode. The anode is made of carbon, which reacts with the oxygen to produce carbon dioxide
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What does the electrolysis of sodium chloride solution produce?
Hydrogen and chlorine. Sodium hydroxide solution is also a produced. These are important reagents for the chemical industry
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What are 2 uses of electroplating?
Decoration and Conduction
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Card 2


All compound want what?


To have the structure of the noble gases (Full outer shell)

Card 3


Atoms that loses electrons become..


Preview of the front of card 3

Card 4


Atomes that gain electrons become..


Preview of the front of card 4

Card 5


What are the Group 1 elements?


Preview of the front of card 5
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