Atomic Structure (SQA National 5 Chemistry): Revision Note

Structure of the atom

• All substances are made of tiny particles of matter called atoms which are the building blocks of all matter

  • The atom is the smallest part of an element that still retains the properties of that element

• However, atoms themselves are made of even smaller particles called subatomic particles

• The three subatomic particles are:

  1. Protons

  2. Neutrons

  3. Electrons

Location of subatomic particles

• The particles are found in two main areas of the atom:

  • The nucleus:

    • This is the dense core at the centre of the atom

    • It contains the protons and neutrons

    • The nucleus is positively charged

  • Electron shells:

    • These are energy levels that orbit the nucleus

    • They contain the electrons, which move very fast

Atomic structure diagram 

Relative mass & charge

• The actual mass and charge of the subatomic particles are incredibly small

• To make them easier to work with, we use a simplified, relative scale

The relative mass of subatomic particles

• Since the mass of an electron is so small, the mass of an atom is almost entirely contained in the nucleus

The relative charge of subatomic particles

• Overall, atoms are electrically neutral

  • This is because the negative charge of an electron exactly cancels out the positive charge of a proton

• An ion is formed when an atom loses or gains electrons to achieve a full outer shell 

  • If an atom loses electrons:

    • It has more positive protons than negative electrons

    • So, it forms a positively charged ion 

  • If an atom gains electrons:

    • It has more negative electrons than positive protons

    • So, it forms a negatively charged ion