Unit Atoms, Elements and Compounds.

Brownian motion:

Particles in both liquids and gases (collectively called fluids) move randomly. This is called Brownian motion. They do this because they are bombarded by the other moving particles in the fluid. Larger particles can be moved by light, fast-moving molecules.

Brownian motion is named after the botanist Robert Brown, who first observed this in 1827. He used a microscope to look at pollen grains moving randomly in water. At this point, he could not explain why this occurred.

Crystallization:

The process of crystal forming is called crystallization. Crystals often form in nature when liquids cool and start to harden. Certain molecules in the liquid gather together as they attempt to become stable. They do this in a uniform and repeating pattern that forms the crystal.

Diffusion:

Diffusion is the movement of a fluid from an area of higher concentration to an area of lower concentration. Diffusion is a result of the kinetic properties of particles of matter. The particles will mix until they are evenly distributed.

Chemical Formula

Substances can be divided into pure substances and mixed substances.
Pure substances can be further divided into elements and compounds.

1. Elements are made up of one kind of atom which cannot be broken into simpler substances

2. Compounds are made up of two or more kinds of atoms(elements), chemically combined in a fixed proportion.

Mixtures are made up of two or more kinds of atoms(elements) or compounds or both mechanically mixed in any proportion.
Mixtures are of two kinds : homogeneous mixtures and heterogeneous mixtures.

1. In homogenous mixture composition is uniform and properties are same throughout the mixture.

2. In Heterogeneous Mixture the composition is non-uniform throughout and properties vary throughout the mixture.

Purification of substances:

1. Sedimentation :The process of deposition of a solid material from a state of suspension or solution in a fluid. e.g. obtaining clear water from muddy water.Â

2. Decantation : DecantationÂ is a process for theÂ separation of mixtures, by removing a top layer of liquid from which a precipitate has settled.

3. Filtration: Filtration is the process of removing one substance or material from another by mechanical means. e.g. tea is filtered using a strainer.

4. Evaporation: Soluble solid constituent is separated from its liquid constituent. Solid component remains behind in evaporating dish, liquid component is lost.

5. Distillation: Soluble solid constituent from its liquid constituent. Solid component remains behind in distillation flask and liquid component is collected after condensation

	Created by Chiradeep Varma over 9 years ago

IGCSE Chemistry Note on Unit Atoms Elements and Compounds, created by Chiradeep Varma on 22/05/2017.