Thus the symbol for nickel is written Ni and not NI. A symbol may be one letter or two the convention is to write a second letter as a small letter. This information may give clues to how one chemical compound may react with another.Įvery element is assigned a symbol (see table 2 periodic table of the elements), which is different from that of all the other elements. Symbols give as much information as possible, but are simple and quick to use. Formulae may also be used to describe the way that atoms in a molecule are grouped together. But to separate or change a single chemical substance (break the bonds between atoms in a molecule), a chemical reaction is required.Ĭhemical symbols are used as a way of describing chemicals in terms of formulae, which are complete descriptions of molecules in terms of the constituent atoms. For example, a mixture of salt and sand can be separated by dissolving the salt in water, leaving the sand behind.
As each element has unique mass, differences in mass need to be taken into account when calculating the correct quantity of each substance (see Atomic mass).Ī mixture may be separated into its constituents by some physical or mechanical means. The smallest unit of a compound or element that still behaves as that compound is called a molecule.Ĭontinuing with the example above using chemical terminology, one atom of carbon can react with four atoms of hydrogen to form one molecule of methane.Īs atoms and molecules are infinitesimally small, reactions are usually worked out using mass (grams or kilograms). Atoms are made from sub-atomic particles (protons, neutrons and electrons) the number of these present in the atom determines which element it is, and therefore the chemical and physical properties it possesses.Īs mentioned above, one unit (or one atom) of carbon can react with four units (four atoms) of hydrogen to form one unit of methane. It cannot be divided any further except in nuclear reactions. The smallest possible unit of an element is called the atom.Īn atom is the smallest unit of an element that still behaves in the same way as (has the properties of) that element. The simplest and smallest of these compounds is methane, which is made up of one unit of carbon and four units of hydrogen. For example, simple fuels are referred to as hydrocarbons this is because they are compounds made up of the elements carbon and hydrogen. However, most will be bonded together with other elements these substances are called compounds. Some elements exist in this elemental state, for example hydrogen, oxygen, iron and gold. Less than 100 of these fundamental materials can be found naturally, although a handful of additional elements have been synthesised in laboratories. Elements cannot be separated into simpler substances. Substances may be solids, liquids or gases, in living or non-living systems, but they all have one common factor: they consist of chemicals.Īll matter is made from a limited number of fundamental materials these are known as elements. Chemistry is the science of the composition of substances, their properties and reactions with each other.
0 kommentar(er)
