Elements and compounds

In a nutshell

Elements are made up of the same type of atom. These elements are represented in the periodic table by one or two letters. A compound is formed when two different types of atoms are bonded together.

Elements

Definition

An element is made up of a single type of atom only. The type of atom is determined by the number of protons the atom contains in its nucleus. Atoms of the same element will have the same number of protons and therefore the same atomic number.

Example

A carbon atom contains six protons in its nucleus. Therefore, all of the atoms in the element carbon will contain six protons.

Elements in the periodic table

The periodic table is made up of elements. In total, the periodic table consists of $118$ different types of elements. Each element is represented in the periodic table by either one or two letters.

Chemistry; Atomic structure and the periodic table; KS4 Year 10; Elements and compounds

Examples

The element aluminium is represented in the periodic table by the symbol Al.

The element potassium is represented in the periodic table by the symbol K.

Compounds

Definition

A compound is formed when two or more different types of atoms join together and react to form a chemical bond. Compounds are formed from a reaction between two or more different elements.

Formulas to display compounds

To show compounds formulas are used. Formulas are made up from the symbols of each element (from the periodic table) that react together to form the compound. The formula of a compound will represent the proportion of each element that makes up the compound.

Example

The compound water is formed by reacting the elements hydrogen (symbol = $H$ ) and oxygen (symbol = $O$ ) together. A water molecule contains two hydrogen atoms and one oxygen atom, so the formula for water is $H_2O$ .

Note: Brackets might be used along with little numbers outside of them to multiply several types of atoms held within the brackets.

Example

Brackets are used in magnesium nitrate, $Mg(NO_3)_2$ . Using the multiplication of the number of each type of nitrogen ( $N$ ) and oxygen ( $O$ ) atom inside the bracket by two, there is one magnesium atom, two nitrogen atoms and six oxygen atoms.