Chemistry Definitions G-L
Chemistry Definitions of words beginning with the letters G to L.
G
Gas One of the three states of matter. In a gas, the particles are a long way apart and are able to move freely. The particles bounce off each other and off the walls of the container. A gas cannot hold its own shape and will fill any container in which it is put.
Glass It is made from sodium carbonate, limestone and sand. Other materials can be added to give the glass special properties.
Global dimming There is some evidence that the production of particulates during the combustion of fossil fuels is causing the sun's rays to be reflected away from the Earth.
Global warming Many people are worried that the average temperature of the Earth is increasing. Some scientists believe that this is nothing to worry about because the Earth's average temperature has always been changing both up and down. Other scientists are very worried because they believe that the temperature is rising too fast and will not go down again after a time.
If global warming becomes serious, the sea levels will rise (as more ice melts at the North and South Poles. There will be climate change too (because the wind and sea currents will change).
Grain This is a tiny piece of rock. They are usually rounded because they have been greatly weathered.
Granite This is an igneous rock that has large crystals. It has formed slowly as the molten rock (magma) cooled inside other rock. Compare it with basalt.
Greenhouse effect and greenhouse gas The Sun's energy is trapped by the Earth's atmosphere. It is said to be a contributor to global warming. Many gases can cause global warming but carbon dioxide and methane are the most talked about. If people use a lot of energy that has been provided by burning fuels, they are responsible for releasing large amounts of carbon dioxide into the atmosphere.
In recent years, the term "carbon footprint" has been used to try to help people understand that we all have a share in this problem.
H
Heat conductor (thermal conductor) A substance that can allow heat to pass through it easily. Metals are good heat conductors. The bottom of a frying pan is made of metal so that the heat from the cooker can reach the food very easily.
High-alloy steel Some steels contain up to 25% of other elements. Stainless steel is an example of a high alloy steel (it contains large amounts of nickel and chromium).
High melting point Substances with high melting points have strong attractions between their particles. Metals (in general) have high melting points and so do ionic compounds and macromolecules.
Humus This is a component of soil. Humus is the mixture of rotting vegetation and animal remains. A compost bin will provide a source of humus for a gardener.
Hydrocarbon A hydrocarbon is a chemical that contains ONLY hydrogen atoms and carbon atoms. The main source of hydrocarbons is crude oil. This is mostly alkanes (hydrocarbons with only single bonds). The hydrocarbons in crude oil are separated by fractional distillation into groups that have similar boiling points.
Hydrogen This gas is produced when a metal reacts with an acid. Hydrogen gas has a very low density. It burns with a squeaky pop. This is the test for hydrogen.
I
Indicator A substance which takes on a different colour depending on the pH of a solution.
Common indicators include litmus (red in acid, blue in alkali) and phenolphthalein (colourless in acid, pink in alkali). Many natural substances can act as an indicator (eg red cabbage, blackcurrant juice)
Full-range indicator and universal indicator are mixtures of different indicators. The mixtures ae carefully designed to give a gradual colour change from acid to alkali. They are available as solutions or papers which can be matched to a colour chart to tell you the pH.
Ion An atom or group of atoms that has gained or lost one or more electrons.
J
Jelly Sometimes, when thinking about solids, liquids and gases, you come across substances that don't fit one particular category.
A jelly is a bit like a solid (to some degree, it holds it own shape). A jelly is a bit like a solid (it wobbles).
K
K Potassium !
Ka Although not part of GCSE, you may see this if you look at data about weak acids. A large value of Ka means that although the acid is weak (only partly dissociated in water) it is one of the stronger weak acids.
Kevlar This material is manufactured for use in bulletproof vests and many other applications because it is strong.
L
Lava This is molten rock that is on the surface of the Earth. It flows from volcanoes. Molten rock inside the Earth is called magma.
Limestone A form of sedimentary rock. It is made from the compacted bony remains of dead sea creatures. It is mostly calcium carbonate.
Limewater This is known mainly as the test for carbon dioxide gas. Limewater is a clear (not cloudy), colourless (not coloured) solution of calcium hydroxide. If carbon dioxide is present, the limewater forms a white precipitate of calcium carbonate.
Interestingly, if a lot of carbon dioxide is used, the limewater milkiness fades (because calcium hydrogen carbonate is formed which is soluble).
Liquid A state of matter. It has a fixed volume but no fixed shape.
Loam A type of soil. It is a good mixture of sand, clay and humus. Gardeners try to make their soil a good loam so that their plants grow well.
Low-alloy steel Some steels contain only a small amount of other elements (<5%) but it is enough to modify the properties to fit the requirement.
Low boiling point A substance with a low boiling point has only weak forces between its particles. It turns into a gas at fairly low temperatures. Remember that its boiling point might be so low that it boils below room temperature.
Low melting point A substance with a low melting point has only weak forces between its particles. It turns into a liquid at fairly low temperatures. Remember that its melting point might be so low that it melts below room temperature.
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