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on May 6, 2020
Atom, Molecule, Element and Compound
An atom is the smallest particles of an element which can exist independently
An element is any substance that exist in a free and not combine state
A compound is any substance that exist or formed from two or more elements chemically combined together
A molecule is a group of atoms of the same or different elements joined in simple proportion
Some elements have single atom in their molecule while some like Oxygen 
and hydrogen 
have two atoms in their molecules i.e 1 molecules of oxygen contain two atoms of oxygen while 1 molecule of carbon contain 1 atom. Ozone 
molecule contain 3 atom of oxygen.
PROVES THAT MATTER ARE MADE UP OF MOLECULES
- Brownian Motion : Robert Brown observe a direct effect of the movement of molecules in May 1827. He was able to observe it through a microscope and find out that there is some tiny particles in the water. He found out that this particles are in constant motion and the path of the motion is zigzag form.
This zigzag form of motion is called Brownian motion .See fig 1 above
Another example of Brownian motion is seen in a smoke particles suspended in air
Brownian motion is of two important
- Is an evidence for molecules existence of substances which are too small to be seen directly.
- Is an evidence that molecules are in continual motion
2. Law of definite proportion
This law state that when two or more elements combined together to form a compound , they do so in a simple ratio and in the same proportion by weight.
For example the compound of carbon-dioxide 
was formed from 12 parts of carbon and 32 parts of oxygen
3. Diffusion
Diffusion is a process whereby molecules of liquid or gases move from area of high concentration to an area of low concentration. The speed with which the molecules moves depend on their mass and the temperature.
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