C1 Particles

Atoms are neutral because they contain the same number of positive protons as negative electrons.

The arrangement of electrons is often called the electron configuration or electron structure

Electrons are not evenly spread.

They exist in layers known as energy levels or shells

Group number = number of electrons in outer shell

Period number = number of shells containing electrons

The smallest particles that make up a substance are called atoms

The average size of an atom is 1 x 10^-10 m

Ratio of distance to diameter    =      distance between atoms

                diameter of atom

The particle model does not take into account:

• The forces between particles

• The size of particles

• The space between particles
  
  

Changes of state and dissolving are examples of physical changes. 

No new substances are made, and the change is often easily reversed.

During heating, the particles gain energy. This is used to overcome forces of attraction between particles

Ions are charged particles formed when atoms, (or groups of atoms), lose or gain electrons:

positively charged ions (cations) form when electrons are lost

negatively charged ions (anions) form when electrons are gained

Atoms consist of a central nucleus containing protons and neutrons. 

The nucleus is small compared to the size of the whole atom. 

The nucleus is surrounded by electrons in energy levels (also called shells)

Atoms are neutral because they contain the same number of protons and electrons. 

Most of the atom is empty space.