Glossary of scientific terms page 1

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Acid.

A substance that has a pH value of less than 7. Strong acids have a pH of 1-2, moderate acids have a pH of 3-4 and weak acids have a pH of 5-6. Acids are generally corrosive unless well diluted. Edible acids (also called common acids) taste sour. Examples of common acids are ethanoic acid (in vinegar), citric acid (in citrus fruits) and ethanedioic acid (in rhubarb).  Common acids are generally moderate to weak whilst mineral acids such as sulphuric acid (chemical formula H2SO4), hydrochloric acid (chemical formula HCl) and nitric acid (chemical formula HNO3) are strong acids. Acids react with some metals (above lead in the reactivity series), metal carbonates, metal oxides and metal hydroxides (these are usually water soluble and are called alkalis). When an acid and alkali are mixed, they neutralise each other). For further information see the chemical changes page - not yet available but coming soon.

Adaptation.
A feature of a plant or animal that makes it suited to its lifestyle e.g. some snakes have evolved organs that act as sensitive heat detectors  so they can find their prey at night.

Alkali.

Chemically opposite to an acid. An alkali is a base that will dissolve in water. They react with acids to form a metal salt and water. You can recognise an alkali from its second name - hydroxide e.g. sodium hydroxide or calcium hydroxide. They are corrosive and you should always wear safety goggles when you are using them. They feel soapy on your skin. They are used to make soap. Cheap soaps are made by boiling animal fat (which contain acids like stearic acid) with sodium hydroxide. More expensive soaps are made from vegetable oils e.g. palmolive soap is based on palmitic acid. Moisturising soap often contains a chemical called glycerine as well. They are also used in many other applications such as paper making and textile manufacture.

Alkane.

This is the main kind of chemical compound in oil. Virtually all of a sample of crude oil will be made from alkanes. Alkanes are hydrocarbons (chemicals that are made only from hydrogen and carbon). They are made from chains of carbon atoms joined together, with hydrogen atoms attached to each carbon as well. Smaller chain alkanes evaporate more easily, ignite more easily and are less viscous (more runny) than longer chain alkanes. Shorter chain alkanes are therefore useful as fuels, petrol (gasoline) is octane, this has 8 carbons in its chain. The alkanes have a general formula of CnH2n+2. This means that for every  carbon arom, there are twice that number + 2 hydrogen atoms. For example, if there are 10 carbon atoms in a particular alkane,there will be (2 x 10) + 2 = 22 hydrogen atoms. For petrol, there will be 18 hydrogens, so the formula will be C8H18. Each carbon atom has 4 chemical bonds to it, each hydrogen has 1. Each bond in an alkane is a covalent bond. When an alkane is burnt, the carbon atoms oxidise to carbon dioxide (thought to contribute to global warming) and the hydrogen atoms oxidise to form water vapour.

Alkene.

When long chain alkanes are 'cracked' using heat and a catalyst, they form shorter chain alkanes and one or more alkenes. An alkene is like an alkane but contains a double covalent bond between one or more pairs of carbon atoms. The alkenes have a general formula of CnH2n. This means that for every  carbon arom, there are twice that number of hydrogen atoms. For example, if there are 10 carbon atoms in a particular alkene,there will be (2 x 10)  = 20 hydrogen atoms. Alkenes are more reactive than alkanes because of the double bond. At GCSE, you can imagine the bond as being strained and therefore easier to break. At A-level, you will find out about different types of covalent bond (pi bonds and sigma bonds) that will explain this reactivity in a different way. As with alkanes, each carbon atom in an alkene has 4 chemical bonds to it, each hydrogen has 1.  When an alkene is burnt, the carbon atoms oxidise to carbon dioxide (thought to contribute to global warming) and the hydrogen atoms oxidise to form water vapour.


Anion.

An ion that has a negative charge. Anions are attracted to the anode during electrolysis.
Anions end up at the anode during electrolysis where they are discharged. They lose one or more electrons and become neutral atoms. A loss of electrons is called oxidation. Anions are therefore oxidised during electrolysis.
For GCSE you need to be aware that non-metals form anions. The atoms of elements do this during chemical bonding or during electrolysis when they gain one or more electrons. For each electron they gain, the atom of the element ends up with one negative charge for example, oxygen gains 2 electrons so an oxide ion has two negativecharges. Note how the name of the anion is different to the name of the original element. Work out the naming rule yourself!

Anode.

The positive electrode in electrolysis. It attracts negatively charged ions (anions).
For GCSE you need to know that when these ions reach the anode they lose electrons to the electricity supply and turn into neutral atoms.
When an ion loses electrons, we say that it has been oxidised.

Atom.

If you hit a piece of rock with a hammer, it will obviously break. How far can you go? Using a hammer, you could pulverise the rock into dust but no smaller. If you use chemicals, you can break down the dust into even smaller particles. The smallest particles that you can get are called atoms. They are so incredibly tiny that you cannot see them, even with the help of a very powerful microscope. Scientists believe that atoms exist because they explain a lot about how chemicals behave. There is plenty of indirect evidence for atoms (as you will have learnt in school). A good picture for you to keep in your mind is that atoms are rather like small, hard balls. This doesn't explain everything about how atoms behave but it is a good start. At GCSE you will need to know a better model. Atoms can be smashed into smaller fragments using particle accelerators. Atoms are found to break into 3 other particles - protons, neutrons and electrons. The protons and neutrons make up the nucleus of an atom and the electrons orbit this in areas called shells (also called orbitals or energy levels). At A-level, you will find out about even smaller particles that make up the protons and neutrons. These are called quarks. I will stop there otherwise this one topic will fill the glossary on its own!

Base.

A base is a compound which is an oxide or  hydroxide of a metal. Bases neutralise acids, forming a salt and water. Soluble bases are called alkalis. Copper oxide and aluminium hydroxide are examples of bases.


Basalt.

A type of igneous rock that is formed from lava. This means that it has come from a volcano and has solidified on the surface of the Earth. It will have cooled much more quickly than an igneous rock that has been formed deep within the Earth's crust and will therefore have smaller crystals. This sort of lava comes from volcanoes that are formed where plates are moving apart from each other (constructive plate boundaries). Volcanoes that erupt Basalt are generally called quiet volcanoes. Basalt is a very runny sort of lava. Good examples of where basalt is formed are the Hawaiian Islands, Iceland and the Mid-Atlantic ridge.


Cation.

An ion that has a positive charge. Cations are attracted to the cathode during electrolysis.
Cations end up at the cathode during electrolysis where they are discharged. They gain one or more electrons and become neutral atoms. A gain of electrons is called reduction. Cations are therefore reduced during electrolysis.
For GCSE you need to be aware that metals form cations. The atoms of elements do this during chemical bonding or during electrolysis when they lose one or more electrons. For each electron they lose, the atom of the element ends up with one positive charge for example, magnesium loses 2 electrons so a magnesium ion has two positive charges.

Cathode.

The negative electrode in electrolysis. It attracts positively charged ions (cations).
For GCSE you need to know that when these ions reach the cathode they gain electrons from the electricity supply and turn into neutral atoms. These are often seen as a coating on the cathode. When an ion gains electrons, it is said to have been reduced.

Compound.

A compound is a substance that can be broken down into simpler substances. Another way of putting it is that a compound is a substance that is made of two (or more) elements that are chemically joined together. Yet another way of defining a compound is to say that is is made from two or more different types of atom that are chemically joined together. Either way, the crucial thing is that the atoms of the different elements in a compound are chemically joined together. If they are not it is simply a mixture. The number of atoms in a particular compound is always the same. If you take several samples of the compound called water, you will find that it always contains two hydrogen atoms joined to one oxygen atom. In a mixture, the proportions of the different elements will be different for different samples.

Discharge.

 This means to remove the charge from an ion during electrolysis. See anion and cation for details of how this happens.

Electrolysis.

Electrolysis is the process of splitting up a chemical compound into simpler substances. For electrolysis to work, the compound has to be ionically bonded (made up from positive and negative ions) and in the liquid state (either melted or dissolved in water).

Electrolyte.

An electrolyte is a liquid that will conduct electricity. There are two ways of making an electrolyte. You can either melt an ionically bonded compound or, if it is soluble, dissolve it in water.  

Element.

An element is a substance that can not be broken down into any simpler substances. An example is to compare water (which is a compound) with iron (which is an element). You can get water to break apart into two simpler substances (using electricity). These two substances are hydrogen and oxygen. No matter how hard you try, or what chemical or electrical processes you carry out, iron will just not split into anything simpler.  You can recognise if a substance is an element from it's symbol and/or it's formula. If the symbol appears on the periodic table, then what you are looking at is an element. Water has the formula H2O and iron has the formula Fe. H2O does not appear on the periodic table but Fe does. In the formula H2O, The symbol H stands for hydrogen and the symbol O stands for oxygen. Both of these appear on the periodic table so water is made of two elements, joined together. This is in fact the definition of a compound. Even if you do not really understand about atoms, you can still play a word game to decide if you have an element or not - if the formula contains two or more capital letters, the substance is not an element, it is a compound. For those who do understand about atoms more, an element contains only one type of atom. Iron therefore will contain only iron atoms and as you already know, it is an element.

Enzyme.

A protein molecule that acts as a catalyst in a biological system. Enzymes occur in both plants and animals. A common misunderstanding is that enzymes are alive - they are not, they are only chemicals. At higher levels, you need to be aware that different enzymes are suited to different conditions. Most are damaged beyond repair by temperatures above about 45 degrees C. This is because in their natural state, they are coiled in a certain way. Heating tends to make them uncoil and so they do not work properly. They are not "killed", you should talk about them being "damaged" or "denatured". We use enzymes for many applications in the field of biotechnology, mainly in the food industry. The classic examples are the use of enzymes in yeast to ferment glucose into alcohol under anaerobic conditions and to produce CO2 to make bread rise.

Equation.

An equation is a chemical reaction written like a sentence, or using symbols and formulae. For example: 'iron reacts with sulphur to form iron sulphide' can be written as:
iron + sulphur ---> iron sulphide
or
Fe + S ---> FeS

Exfoliation.

The correct scientific name for onion skin weathering.

Formula.

A formula is a compound's "symbol". It shows what elements the compound contains and the numbers of each sort of atom. For example, the formula of sulphuric acid is H2S04. This formula tells you that every molecule of sulphuric acid contains two hydrogen atoms, one sulphur atom, and four oxygen atoms.
Elements also have a formula. In most cases it is the same as the symbol. This indicates that the element exists as individual atoms, not chemically joined together e.g. any of the metals. Where the formula of an elements includes a number as well as the symbol, it tells you that the element exists as molecules. An example is N2, nitrogen - it exists as diatomic (2 atoms) molecules. Many of the non metals exist as molecules.  

Freeze-Thaw weathering.

This occurs in areas that are wet and cold. Water gets into cracks in rocks. If that water freezes, it expands. When substances expand, large forces are created. The force of the freezing water expanding pushes the sides of the crack apart by a small amount. This gradually widens the crack and given enough time, the rock cracks apart. This can lead to the formation of screes. A scree is a triangular shaped area of debris that has fallen from rocks near the top of a mountain.

Why not search the internet for pictures information on screes:


Granite.

An igneous rock formed from magma that has cooled deep underground. Since it is insulated by the surrounding rocks, it will have cooled very slowly, allowing large crystals to form.

Igneous (rocks).

Literally means "born of fire". This type of rock is made from magma that has cooled and solidified. It is therefore made from randomly arranged crystals. Extrusive igneous rocks are formed when magma reaches the surface of the Earth and erupts from a volcano. Intrusive igneous rocks are formed when the magma cools and solidifies within the Earth. They only appear at the surface when they are exposed by weathering and erosion. Igneous rocks can have large or small crystals. Those which cool slowly have larger crystals that those that cool faster. Lava cools relatively quickly because the heat is convected away by the air. Lavas (e.g. basalt, rhyolite) therefore have small crystals. Magma that cools in the crust (forming for example granite or gabbro) is insulated by the surrounding rocks. This cools relatively slowly  and therefore has larger crystals that lavas. Igneous rocks are made from minerals that are resistant to weathering. The texture of an igneous rock is interlocking rather than porous and this also helps to make it resistant to the effects of the weather.

Indicator.

In simple terms, an indicator is a substance that is one colour in acids and a different colour in alkalis. They can therefore be used to tell if a liquid is an acid or an alkali. An example is litmus. This is a dye from a tree, in acid it turns red but in an alkali it is blue. Other examples of indicators are phenolpthalein (colourless in acid but red in alkalis, methyl orange (red in acids and orange in alkalis) and bromothymol blue (yellow in acid but blue in alkalis). A very useful indicator is Universal indicator. Not only does this tell you if a substance is an acid or an alkali, it tells you what pH it is, in other words, it gives you the strength reading as well!

Ion.

An ion is an atom or molecule that has been given a positive or negative charge. For example, an oxygen atom with two negative charges on it is called an oxide ion. A hydrogen atom with one positive charge on it is called a hydrogen ion.