Magnetism and magnetic fields Study Guide

Atoms, the fundamental building blocks of matter, are defined by their atomic number, which is the number of protons in their nucleus. All atoms of a particular element have the same number of protons. For example, every atom of carbon has 6 protons. However, atoms of the same element can have different numbers of neutrons in their nucleus. Neutrons are subatomic particles with no electrical charge, located in the nucleus alongside protons. The total number of protons and neutrons in an atom's nucleus is called its nuclear mass, also known as the mass number. When atoms of the same element (same number of protons) have different numbers of neutrons, they are called isotopes. These isotopes will have different nuclear masses. For instance, carbon-12 has 6 protons and 6 neutrons (nuclear mass = 12), while carbon-14 has 6 protons and 8 neutrons (nuclear mass = 14). Both are carbon atoms because they both have 6 protons, but they are isotopes of carbon due to their differing neutron counts and thus different nuclear masses. This difference in nuclear mass can lead to variations in physical properties, such as density, but generally does not affect chemical properties because chemical reactivity is primarily determined by the number of electrons, which in a neutral atom equals the number of protons.

Every atom is made up of a central nucleus surrounded by electrons. The atomic nucleus is a tiny, dense region at the centre of an atom, and it holds almost all of the atom's mass. This nucleus is primarily composed of two types of subatomic particles: protons and neutrons. Protons are positively charged particles, while neutrons are electrically neutral, meaning they have no charge. The number of protons in an atom's nucleus is called its atomic number, and this number uniquely identifies an element. For instance, all carbon atoms have six protons. Because protons are positively charged and neutrons have no charge, the overall charge of an atomic nucleus is always positive. The magnitude of this positive charge is directly determined by the number of protons it contains. Each element has a characteristic positive charge in its nucleus due to its unique number of protons. For example, an atom of helium, with two protons, will have a nuclear charge of +2, while an atom of oxygen, with eight protons, will have a nuclear charge of +8. This characteristic positive charge is fundamental to understanding how atoms interact and form chemical bonds.