Element:
An element is a substance that cannot be split into two or more simpler substances by chemical means or by electricity.
Elements can be classified into metals and non-metals.
| Metals | Non-metals |
| Shiny appearance (lustrous) | Dull appearance (non-lustrous) |
| Mostly solids at r.t.p*. | Either gases, volatile liquids or solids with low melting points at r.t.p. |
| ● Malleable
● Sonorous ● Ductile |
Brittle (if solid) |
| High melting points and boiling points. | Generally low melting points and boiling points. |
| Good conductors of heat. | Generally poor conductors of heat. |
| Good conductors of electricity in all states of matter. | Generally poor conductors of electricity. |
Table 4.1. Differences between Metals and Non-metals.
*r.t.p: room temperature and pressure.
Atom:
An atom is the smallest possible particle of an element that can take part in a chemical change.
Compound:
A compound is a pure substance which contains only one type of molecule made up of atoms of more than one element. It is formed when two or more different elements are chemically combined together.
Heat can be used to form compounds. Heat can also be used to break down compounds into elements or simpler compounds. Such a chemical reaction is called thermal decomposition.
Molecule:
A molecule is the smallest particle of a compound and is made up of a group of two or more atoms chemically combined together. The atoms that join to make one molecule can either be same or different.
To show the atoms present in the molecule of a compound, we use its chemical formula, e.g., the chemical formula of water is H2O. It contains the elements Hydrogen (symbol H) and Oxygen (symbol O). The subscript number 2 shows the number of atoms of the element preceding it.
Mixture:
A mixture is not a pure substance, as its components are not chemically combined. It is formed when two or more substances are physically combined.
The differences between mixtures and compounds are listed below:
| Mixture | Compound |
| 1. Component substances can be separated by physical means. | Component substances cannot be separated by physical means. |
| 2. Its physical properties (colour, density, etc) are an average of those of the substances in it. | Its physical properties are individual and not the result of its elements. |
| 3. Normally little or no energy is given out or taken in when a mixture is formed. | Energy is usually taken in or given out when a compound is formed. This is because a chemical reaction takes place here. |
| 4. A mixture’s composition can vary. | A compound’s composition cannot vary. Constituent elements are present in a fixed proportion by mass. |
| 5. Its chemical properties are the result of the substances in the mixture. | Its chemical properties are quite different from those of its elements. |
Table 4.2. Differences between mixtures and compounds.