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Elements and compounds
ELEMENTS: substances that cannot be chemically broken down into simpler substances
COMPOUNDS: pure substances made from two or more elements chemically combined together.
Chemical reactions and physical changes
DECOMPOSITION: a compound breaks down to form two or more substances
SYNTHESIS: the substance is formed by the combination of two or more substances
In chemical reactions:
new chemical substances are formed
usually the process is not easily reversed
energy is often given out
In a physical change:
substances involved do not change identity
they can be easily returned to original by physical processes ike cooling and evaporation
Atomic theory
Dalton suggested that:
a pure element is composed of atoms
the atoms of each element are different in size and mass
atoms are the smallest particles that take part in a chemical reaction
atoms of different elements can combine to make molecules of a compound
A chemical language
Dalton suggests that each element should have its own symbol.
The kinetic model of matter
all matter is made up of very small particles (different substances contain different types of particles such as atoms and molecules).
the particles are moving all the time (the higher the temperature, the higher the average energy of the particles). The faster they are moving, the higher the temperature
the freedom of movement and the arrangement of particles is different for the three states of matter
The pressure of the gas is produced by the atoms of molecules of the gas hitting the walls of the container. The more often the particles collide, the greater the pressure.
DIFFUSION: fluids are made of moving particles
Gases diffuse to fill the space available to them.
Diffusion is important for our sensing of the world around us.
not all gases diffuse at the same rate
DISSOLVING: spreading the solute particles throughout the liquid
Atoms and molecules
Molecules consist of atoms of different elements bonded together.
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