GCSE Chemistry (Combined) WJEC

Elements as Substances

Understanding Elements

• An element is a substance that cannot be broken down into simpler substances by chemical reactions. They are made up of one type of atom only.
• Atoms are the smallest unit of an element. They are made up of subatomic particles: protons, neutrons, and electrons.
• Protons carry a positive charge, neutrons carry no charge (they are neutral), and electrons carry a negative charge.
• The number of protons in an atom (the atomic number) determines the type of element it is.

Classifying Elements

• Elements can be classified as metals, non-metals, or metalloids (also called semi-metals) based on their physical and chemical properties.
• Metals are typically solid at room temperature (with the exception of mercury), shiny, good conductors of heat and electricity, and malleable.
• Non-metals can be solid, liquid or gas at room temperature, they are poor conductors of heat and electricity and are not malleable.
• Metalloids have properties intermediate between those of metals and non-metals.

The Periodic Table of Elements

• The Periodic Table is an organised arrangement of elements in rows and columns.
• Elements are arranged in increasing atomic number from left to right and top to bottom. This arrangement reflects the repeating pattern of chemical properties of the elements.
• Each horizontal row is called a period and each vertical column is called a group. Elements in the same group generally have similar chemical properties.
• The Periodic Table is divided into several blocks: the s-block, p-block, d-block, and f-block, which can further categorise elements based on the outermost electrons of their atoms.

Chemical Symbols

• Each element has a unique chemical symbol consisting of one or two letters. The first letter is always capitalised and the second (if present) is always lowercase.
• These symbols are a standardised shorthand way of representing elements in chemical reactions and compounds. For example, the symbol for hydrogen is H and for oxygen is O.

Chemical Reactions and Elements

• In a chemical reaction, atoms are rearranged to form new substances. The starting substances are called reactants and the end substances are called products.
• In all chemical reactions, the total number of each type of atom in the reactants equals the total number in the products. This principle is known as the law of conservation of mass.
• Chemical reactions are usually accompanied by energy changes. The energy can be released (exothermic reaction) or absorbed (endothermic reaction) during the reaction process.