OCR Gateway Chemistry A - Particles Revision Guide

Particle Theory of Matter

The theory that states that all matter is made up of small particles and is used to explain the physical characteristics of the states of matter.

Melting Point

The temperature at which a substance changes state from solid to liquid.

Boiling Point

The temperature at which a substance changes state from liquid to gas.

Forces of Attraction

The forces that exist between particles and can be overcome by providing energy during a change of state.

Particle Arrangement and Movement

The different arrangements and movements of particles in solids, liquids, and gases.

Properties of Solids

Fixed volume and shape, particles close together, low energy, and cannot be easily compressed.

Properties of Liquids

Fixed volume but variable shape, particles can flow and slip/slide over each other, greater energy than solids, and cannot be easily compressed.

Properties of Gases

No fixed shape or volume, particles are far apart, move quickly without direction, high energy, and can be compressed.

Physical Changes

Changes in states of matter that are easily reversible.

Chemical Changes

Changes in matter that result in the formation of a new substance and are usually not easily reversible.

Limitations of the Particle Model

The particle model fails to consider forces of attraction between particles, size of particles, and the presence of space between particles.

Atom

The smallest part of an element that retains the chemical properties of that element.

Atomic Model

Different models proposed by scientists to explain the structure of atoms.

Mass Number

The total number of protons and neutrons in an atom.

Atomic Number

The number of protons in an atom.

Ion

An atom that has gained or lost electrons, resulting in a positive or negative charge.

Isotopes

Atoms of the same element that have the same atomic number but different mass numbers due to a difference in the number of neutrons.

Subatomic Particles

Protons, neutrons, and electrons that make up an atom.

Calculating Numbers of Subatomic Particles

The process of determining the number of protons, electrons, and neutrons in an atom using the atomic number and mass number.