5 visitors online
Guests: 5
Registered: 0
Homework → Science → Chemistry → Elements, Mixtures & Compounds
All substances are made from tiny particles called atoms. They are the smallest particle that can exist. Atoms when they join together form molecules.
Elements are made from only one type of atom. There are just over 100 elements known to man, some of which end in the letters .....ium. Eg. potassium, magnesium and aluminium. All the elements are listed in the "Periodic Table", shown below:
Metals and non-metals: The elements in the Periodic Table are classified as being either metals or non-metals. Both of these groups have certain properties that distinguish them. Below is a list that illustrates the differences between them.
| 88 metals | 21 non-metals |
| Conduct electricity | Poor conductors of electricity |
| Conduct heat | Do not conduct heat well |
| Strong | Not strong |
| Shiny | Very dull |
| Malleable | Very brittle |
| Sonorous | |
| Ductile | |
| High melting points | Low melting points |
| High densities | Low densities |
| Metals make alloys | |
| Sometimes magnetic | Never magnetic |
| Are basic | React with oxygen |
| Make oxides when reacting with oxygen | Non-metal oxides are acidic |
Mixtures are composed of more than one type of atom that have just been physically mixed together but not chemically combined. Mixtures can be separated back into their elements by fairly simple methods.
Air is a mixture of many different gases. These are the following:
- Nitrogen - 78%
- Oxygen - 21%
- Water Vapour - 0.45%
- Carbon Dioxide - 0.05%
- Noble or Inert gases (mainly Argon, but also Neon, Krypton, Xenon and Helium) - 0.5%
The part of the mixture that has been disolved is called the solute and the part that does the disolving/makes it disolve is the solvent. If a substance is able to dissolve in another, it is described as being soluble, while if it cannot disolve it is insoluble.
Suspensions
These are mixtures where the solid does not dissolve in the liquid but instead floats around, in "suspension". E.g. muddy water.
Compounds are made from more than one type of atom that have chemically reacted together in a fixed ratio. This means that one molecule has a set number of each atom joined together. E.g. Water (symbol H20) has a ratio of 2 hydrogen atoms to every oxygen atom.
The endings of some names help us to know what elements compounds are made from.
Examples:
...ate means that it contains oxygen. So copper carbonate has copper carbon and oxygen.
...ide means that it is only the elements mentioned in the chemicals name. Copper oxide therefore contains copper and oxygen.
It is usually difficult to separate the elements contained in a compound. The properties of a compound are different from the properties of the elements it is made up from.