Relative electrical charges of subatomic particles — AQA GCSE Chemistry

Atoms contain protons, neutrons and electrons. Protons have a relative charge of 1⁺, electrons have a relative charge of 1⁻, and neutrons have no charge. In a neutral atom, the number of electrons equals the number of protons, so the positive and negative charges balance exactly. For example, a carbon atom has six protons and six electrons, giving six positive charges and six negative charges, so the overall charge is zero. If the numbers were unequal, the atom would become a charged ion. This balance explains why atoms are electrically neutral and why the nucleus, although positive, does not make the whole atom charged.

The atomic number is the defining count of protons in an atom's nucleus. Because each proton carries a relative charge of 1⁺, the atomic number also equals the positive nuclear charge and, in a neutral atom, the number of electrons. For example, every carbon atom has six protons, so its atomic number is 6; a neutral carbon atom therefore has six electrons arranged around the nucleus. The atomic number identifies the element and fixes its position in the periodic table. It is not the same as mass number, which counts protons plus neutrons. In the nuclear model, protons and neutrons occupy a tiny central nucleus while electrons occupy shells. Reading a periodic table entry, the smaller whole number is usually the atomic number.

Every atom of a given element has an identical proton count, and this fixed number is the atomic number. For example, all chlorine atoms contain 17 protons, whether they are chlorine-35 or chlorine-37; the isotopes differ only in neutron number. Because protons carry relative charge 1⁺, the nuclear charge is the same for all atoms of that element. The proton number does not change in chemical reactions; atoms gain, lose or share electrons instead. This constancy is why the periodic table can be arranged by increasing atomic number and why elements have consistent chemical identities. In the nuclear model, the nucleus contains these protons together with neutrons, while electrons occupy shells around it.

The proton count is the distinguishing feature between elements: hydrogen atoms have 1 proton, helium atoms have 2, lithium atoms have 3, and so on. Because each proton carries relative charge 1⁺, changing the proton number changes the nuclear charge and therefore the element's identity. This is why the modern periodic table is ordered by increasing atomic number rather than by atomic mass. For example, argon and potassium are placed by proton number even though their mass numbers reverse the order. In the nuclear model, the nucleus contains the protons and neutrons, and the proton number defines which element the atom is. Different proton numbers mean different elements with different chemical and physical properties.

The nuclear model describes an atom as a tiny, dense, positively charged nucleus surrounded by electrons in shells. The nucleus contains protons, each with relative charge 1⁺, and neutrons, which have no charge; together they give the nucleus almost all of the atom's mass. Electrons carry relative charge 1⁻ and occupy shells at relatively large distances from the nucleus, so most of the atom is empty space. For example, a sodium atom has 11 protons and 12 neutrons in its nucleus, with 11 electrons in shells around it. The model explains why atoms are neutral overall and how ions form when electrons are gained or lost. It does not include a fixed scale diagram, so descriptions should focus on relative charge, mass and position.