Atomic Structure and Radioactivity - SS1 Physics Past Questions and Answers - page 1

An atom consists of three main subatomic particles: protons, neutrons, and electrons. Protons have a positive charge and are located in the nucleus at the centre of the atom. Neutrons have no charge and also reside in the nucleus. Electrons have a negative charge and orbit around the nucleus in energy levels or electron shells. Protons and neutrons contribute to the mass of the atom, while electrons are much smaller and have negligible mass.

The atomic number of an element represents the number of protons in the nucleus of an atom. It uniquely identifies an element because each element has a distinct number of protons. For example, hydrogen has an atomic number of 1, indicating it has one proton, while helium has an atomic number of 2, indicating it has two protons. The atomic number determines the element's position on the periodic table and its chemical properties.