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STATES OF MATTER - properties of gases and liquids (fluids) and solids

1. Introduction to the three states of matter

Doc Brown's chemistry revision notes: basic school chemistry science GCSE chemistry, IGCSE  chemistry, O level and ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old science students for national examinations in chemistry and also helpful for UK advanced level chemistry students aged ~16-18 and US grades 11-12 K12 honors.

Part 1 Introduction to the three states of matter

You should know that the three states of matter are solid, liquid and gas. Melting and freezing take place at the melting point, boiling and condensing take place at the boiling point. The three states of matter can be represented by a simple model in which the particles are represented by small solid spheres. Particle theory can help to explain melting, boiling, freezing and condensing.

The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance and the nature of the particles involved depends on the type of bonding and the structure of the substance. The stronger the forces between the particles the higher the melting point and boiling point of the substance.

See Part 14. Comparison of latent heat changes in physical changes of state for different types of structure and for more details see  structure and bonding notes.

The strength of the forces between particles depends on the material (structure and type of bonding), the temperature (affects the energy of the particles) and pressure (how close the particles are compressed together e.g. in a gas).

The physical state a material adopts depends on its structure, temperature and pressure.

State symbols used in equations: (g) gas       (l) liquid      (aq) aqueous solution      (s) solid

aqueous solution means something dissolved in water,

a good example of how to use the state symbols correctly is calcium carbonate dissolving in hydrochloric acid:

CaCO3(s)  +  2HCl(aq)  ====>  CaCl2(aq)  +  H2O(l)  +  CO2(g)

(c) doc b (c) doc b (c) doc b

Most diagrams of particles are often 2D representations of their structure and state



e.g. the air mixture around us (including the oxygen needed for combustion) and the high pressure steam in the boiler and cylinders of the steam locomotive. All of the gases in air are 'invisible', being colourless and transparent. Note that the 'steam' you see outside of a kettle or steam locomotive is actually fine liquid droplets of water, formed from the expelled steam gas condensing when it meets the cold air the 'state change' of gas to liquid (same effect in mist and fog formation).


e.g. water is the most common example, but so are, milk, hot butter, petrol, oil, mercury or alcohol in a thermometer.


e.g. stone, all metals at room temperature (except mercury), rubber of walking boots and the majority of physical objects around you. In fact most objects are useless unless they have a solid structure!

In later sections

The basic physical properties of gases, liquids and solids are described in terms of structure, particle movement (kinetic particle theory), effects of temperature and pressure changes, and particle models used to explain these properties and characteristics. Hopefully, theory and fact will match up to give students a clear understanding of the material world around them in terms of gases, liquids and solids referred to as the three physical states of matter.

The changes of state known as melting, fusing, boiling, evaporating, condensing, liquefying, freezing, solidifying, crystallising are described and explained with particle model pictures to help understanding. There is also a mention of miscible and immiscible liquids and explaining the terms volatile and volatility when applied to a liquid.

Some SIMPLE particle pictures of ELEMENTS, COMPOUNDS and MIXTURES in terms of the three states of matter

Particle model diagrams of gases, liquids, solids, elements, compounds, mixtures

Learning objectives for particle pictures and an introduction to the states of matter

Know that matter can exist in a solid, liquid and gaseous state and recognise the state from a given description or picture of a material.

Be able to recognise from particle pictures whether the substance is a solid, liquid or gas and also deduce whether it is a particle picture of a pure element, a pure compound or a mixture of elements or compounds.

All my UK GCSE level (~US grade 8-10) school chemistry revision notes

All my UK advanced level (~US grades 11-12) pre-university chemistry revision notes

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INDEX of all my notes on the states of matter

(GCSE level and advanced pre-university level revision notes)

Detailed notes on the states of matter and their properties

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