Chemistry Unit 1.

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What is an element?
A substance that is made of only one sort of atom.
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What is the chemical symbol for oxygen?
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What is the chemical symbol for sodium?
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What are atoms small central nucleus made up of?
Protons and neutrons surrounded by electrons.
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What is a proton's electrical charge?
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What is a neutron's electrical charge?
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What is an electron's electrical charge?
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In an atom, what is the number of electrons equal to in the nucleus?
The number of protons.
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What do all atoms of a particular element have the same?
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What is an atomic number?
The number of protons in an atom of an element.
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What is a mass number?
The sum of the protons and neutrons in an atom.
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What do electrons do?
Occupy particular energy levels. Each electron in an atom is at a particular energy level (in a particular shell). The electrons in an atom occupy the lowest available energy levels (innermost available shells).
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What do elements in the same group in the periodic table all have?
The same number of electrons in their highest energy level (outer electrons) and this gives them similar chemical properties.
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What are elements in Group 0 called?
Noble gases. They are unreactive because their atoms have stable arrangements of electrons and eight electrons in their outer energy level, except for helium, which has only two electrons.
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When elements react, what happens?
Their atoms join with other atoms to form compounds.
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What do reactions in elements involve?
Giving, taking or sharing electrons to form ions or molecules.
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What do compounds formed from metals and non-metals consist of?
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What do compounds formed from non-metals consist of?
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What are the atoms in molecules held together by?
Covalent bonds.
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In a chemical reaction, why is the mass of the products equal to the mass of the reactants?
Because no atoms are lost or made during a chemical reaction.
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What is limestone mainly composed of?
The compound calcium carbonate (CaCO3) and it is quarried and can be used as a building material.
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What does calcium carbonate make when it is decomposed by heating (thermal decomposition) ?
Calcium oxide and carbon dioxide.
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What do the carbonates of magnesium, copper, zinc, calcium and sodium do in a similar way?
Decompose on heating.
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When calcium oxide reacts with water what does it produce?
Calcium hydroxide, which is an alkali that can be used in the neutralisation of acids.
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What does limewater react with carbon dioxide to produce?
Calcium carbonate.
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What is limewater used a test for?
Carbon dioxide which turns limewater cloudy.
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What do carbonates react with acids to produce?
Carbon dioxide, a salt and water.
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What is limestone damaged by?
Acid rain.
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What is limestone heated with clay to make?
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What is cement mixed with sand to make?
Mortar and with sand and aggregate to make concrete.
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What do ores contain to make it economical to extract the metal?
Enough of the metal.
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How are ores extracted?
From mines and may be concentrated before the metal is extracted and purified.
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Where are metals found?
Unreactive metals such as gold are found in the Earth as the metal itself but most metals are found as compounds that require chemical reactions to extract the metal.
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Where can metals that are less reactive than carbon be extracted from?
Their oxides by reduction with carbon, for example iron oxide is reduced in the blast furnace to make iron.
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How are metals that are more reactive than carbon, such as aluminium, extracted?
By electrolysis of molten compounds. The use of large amounts of energy in the extraction of these metals makes them expensive.
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How can copper be extracted from copper-rich ores?
By heating the ores in a furnace (smelting). The copper can be purified by electrolysis. The supply of copper-rich ores is limited.
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Why are ways of extracting copper from low-grade ores being researched?
To limit the environmental impact of traditional mining. Copper can be extracted by phytomining, or by bioleaching.
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How can be copper obtained from solutions of copper salts?
By electrolysis or by displacement using scrap iron.
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Which elements cannot be extracted from their oxides by reduction with carbon?
Alluminium and titanium.
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Why are current methods of extraction expensive?
Because there are many stages in the process and large amounts of energy are needed.
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Why should we recycle metals?
Because extracting them uses limited resources and is expensive in terms of energy and effects on the environment.
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What is an alloy?
A mixture or solid solution composed of a metal and another element.
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How much iron does iron from the blast furnace contain?
About 96%. The impurities make it brittle and so it has limited uses.
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What is most irons converted into?
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What are steels?
Alloys since they are mixtures of iron with carbon. Some steels contain other metals.
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Properties of low carbon steels?
Easily shaped
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Properties of high carbon steels?
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Properties of stainless steels?
Resistant to corrosion.
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What happens to pure copper, gold, iron and aluminium that are too soft for many uses?
They are mixed with small amounts of similar metals to make them harder for everyday use.
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What are the elements in the central block of the periodic table known as?
Transition metals.
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Properties of transition metals?
Like other metals they are good conductors of heat and electricity and can be bent or hammered into shape. They are useful as structural materials and for making things that must allow heat or electricity to pass through them easily.
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Properties of copper?
Good conductor of electricity and heat, can be bent but is hard enough to be used to make pipes or tanks and does not react with water.
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What do the properties of copper make it useful for?
Electrical wiring and plumbing.
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What makes aluminium and titanium useful metals?
Low density and resistance to corrosion.
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What is crude oil a mixture of?
A very large number of compounds.
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What does a mixture consist of?
Two or more elements or compounds not chemically combined together. The chemical properties of each substance in the mixture are unchanged. It is possible to separate the substances in a mixture by physical methods including distillation.
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What do most of the compounds in crude oil consist of?
Molecules made up of hydrogen and carbon atoms only (hydrocarbons). Most of these are saturated hydrocarbons called alkanes, which have the general formula CnH2n+2.
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What is the process of fractional distillation?
The crude oil is evaporated and its vapours allowed to condense at different temperatures in the fractionating column. Each fraction contains hydrocarbon molecules with a similar number of carbon atoms.
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Why can the substances in crude oil be seperated using fractional distillation?
Because they have different boiling points.
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What do some properties of hydrocarbons depend on and why?
The size of their molecules because e properties influence how hydrocarbons are used as fuels.
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What are the trends of properties of hydrocarbons?
Boiling points, viscosity and flammability.
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What do most fuels, including coal, contain?
Carbon and/or hydrogen and may also contain some sulfur. The gases released into the atmosphere when a fuel burns may include carbon dioxide, water (vapour), carbon monoxide, sulfur dioxide and oxides of nitrogen. Particulaltes may also be released.
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What does the combustion of hydrocarbon fuels release?
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During combustion what happens to the carbon and hydrogen in the fuels?
They are oxidised.
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What causes acid rain?
Sulfur dioxide and oxides of nitrogen.
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What causes global dimming?
Solid particles.
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What can be removed from fuels before they are burned?
Sulfur, eg in vehicles.
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can be removed from the waste gases after combustion, for example in power stations.
Sulfur dioxide.
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What are biofuels, including biodiesel and ethanol, made from?
Plant material.
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What can hydrocarbons be cracked to produce?
Smaller, more useful molecules.
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What does the process of cracking involve?
Heating the hydrocarbons to vaporise them. The vapours are either passed over a hot catalyst or mixed with steam and heated to a very high temperature so that thermal decomposition reactions then occur.
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What do the products of cracking include?
Alkanes unsaturated hydrocarbons called alkenes. Alkenes have the general formula CnH2n.
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What do alkenes turn from orange to colourless in a reaction?
Bromine water.
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What are some of the products of cracking useful as?
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