Edexcel IGCSE Chemistry 复习笔记 1.3.1 Atoms: Definitions & Structure

• It is important to understand the terms atom and molecule when referring to atomic structure, elements and compounds

Atoms & Molecules Definitions Table

• Elements are made of tiny particles of matter called atoms
• Each atom is made of subatomic particles called protons, neutrons and electrons
• Their size is so tiny that we can't really compare their masses in conventional units such as kilograms or grams, so a unit called the relative atomic mass is used
• One relative atomic mass unit is equal to one twelfth the mass of a carbon-12 atom.
• All other elements are measured relative to the mass of a carbon-12 atom and since these are ratios, the relative atomic mass has no units
• Hydrogen for example has a relative atomic mass of 1, meaning that 12 atoms of hydrogen would have exactly the same mass as 1 atom of carbon
• The relative mass and charge of the subatomic particles are shown below:

The Mass & Charge of Subatomic Particles Table

• You need to know the following terms to describe the properties and characteristics of atoms

Atomic Structure Key Terms Table