iGCSE Chemistry Edexcel

Atomic Structure and the Periodic Table

Atomic Structure

• All substances are made up of atoms, which are incredibly small particles.
• Atoms consist of three types of particles: protons, neutrons, and electrons.
• Protons and neutrons are found in the atom's nucleus, while electrons orbit the nucleus in electron shells.
• Protons have a positive charge, electrons have a negative charge, and neutrons have no charge.
• An atom is overall neutral because it has an equal number of protons and electrons, meaning their charges cancel each other out.
• The Atomic Number of an atom is the number of protons it has. This number is unique to each element.
• The Mass Number or Atomic Mass of an atom is the combined number of protons and neutrons.
• Atoms of the same element can have a different number of neutrons. These are called isotopes.

Electron Configuration

• The arrangement of electrons in an atom is known as the electron configuration.
• The first shell can hold up to 2 electrons, and the subsequent shells can each hold up to 8 electrons.
• The arrangement of these electron shells affects the chemical reactivity of the atom.

The Periodic Table

• The Periodic Table is a system of categorising elements based on their atomic structure.
• Elements are listed in order of increasing atomic number.
• Elements in the same column, or group, have similar properties and the same number of electrons in their outer shell.
• Periods are the rows on the table, and the number of the period represents the number of electron shells in the atoms of the elements in that row.
• Metals are found on the left side of the table, and non-metals on the right.
• The transition metals are the block of elements in the middle of the table.
• The elements in Group 0, the far right-hand column, are known as the noble gases. They are very unreactive as they have full electron shells.
• The elements in Group 1, on the far left hand-side, are known as alkali metals. They are very reactive, as they have one electron in their outer shell that is easily lost in reactions.
• Group 7 elements are known as halogens and are very reactive non-metals.