Unit Atoms Elements and Compounds

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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 : Decantation is a

process for the 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