Metals and non-metals — AQA GCSE Chemistry

Metals are elements that lose electrons when they react, forming positive ions. For example, sodium loses one electron to form Na⁺, and magnesium loses two electrons to form Mg²⁺. This loss of electrons is oxidation, and it happens because metals have relatively few electrons in their outer shell, so losing them gives a stable electron arrangement. The resulting positive ion has more protons than electrons. This behaviour links to other metal properties such as conduction and malleability, but the defining test in this section is the formation of positive ions during reaction. When a metal reacts with a non-metal, electrons transfer from metal to non-metal, producing positive metal ions and negative non-metal ions in an ionic compound.

Non-metals are elements that do not form positive ions. Instead, when they react they gain electrons to form negative ions, or they share electrons in covalent bonds. For example, chlorine gains one electron to form Cl⁻, and oxygen gains two electrons to form O²⁻. This happens because non-metals have relatively full outer shells, so gaining electrons is energetically favourable and gives a stable arrangement. The resulting negative ion has more electrons than protons. In reactions with metals, non-metals accept the electrons that metals lose, forming ionic compounds. Some non-metals, such as carbon and hydrogen, mainly form covalent bonds rather than ions, but they still do not form positive ions in these reactions.

The periodic table contains over one hundred elements, and most of them are metals. Metals occupy the large block on the left, centre and lower part of the table, including Groups 1, 2 and the transition metals, while non-metals form a much smaller region towards the top right. This matters because the physical and chemical behaviour you meet in later topics, such as conduction, malleability, reaction with acids and formation of positive ions, applies to the majority of elements. For example, iron, copper, sodium and calcium are all metals, whereas oxygen, chlorine and sulfur are non-metals. Recognising that metals dominate the table helps you predict properties and interpret trends rather than learning each element separately.

Metals occupy the left-hand side and the lower portion of the periodic table. Group 1 metals such as lithium, sodium and potassium sit on the far left, Group 2 metals such as magnesium and calcium sit next to them, and the large central block contains the transition metals such as iron, copper and zinc. Moving down a group, metallic character becomes more pronounced, so elements lower in a group behave more typically as metals. This positional pattern lets you predict properties: an element on the left or low down is likely to conduct electricity, be malleable and form positive ions. For example, sodium in Group 1 and iron in the transition block are both clearly metallic, whereas elements towards the top right are not.

Non-metals occupy the upper right region of the periodic table. Group 0 noble gases such as helium, neon and argon sit on the far right, Group 7 halogens such as fluorine, chlorine and bromine sit just to their left, and Group 6 includes oxygen and sulfur. Elements towards the top right generally lack metallic properties: they are poor conductors of electricity, often brittle as solids, and tend to form negative ions or share electrons in covalent bonds. Hydrogen is a non-metal even though it appears at the top left, which is a useful exception to remember. Position therefore allows prediction: an element high and to the right is likely to be a non-metal with low conductivity and a tendency to gain or share electrons.

This outcome asks you to connect three ideas. First, metals and non-metals differ in physical properties such as conductivity, malleability and melting point, and in chemical behaviour such as forming positive or negative ions. Second, an element's position in the periodic table reflects its atomic structure, because elements are arranged in order of atomic number, so proton number determines the number of electrons and therefore the group and period. Third, chemical reactions depend on the arrangement of electrons, especially the outer shell: Group 1 metals lose one electron readily, Group 7 non-metals gain one electron, and Group 0 elements have full outer shells and are unreactive. For example, sodium (2,8,1) reacts vigorously because it can lose its single outer electron, while chlorine (2,8,7) gains one electron to form a 1⁻ ion.