 # Definition Of Atoms And Mocules

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Atoms and Mocules
I. Aim:
- To determine the definition of atoms and molecules and the difference of those notions.
- Understanding isotopes, atomic mass, and molecular mass.
- Understanding mole concept and molar mass.

III. Definitions:
1. Atoms:
According to Dalton’s atomic theory, atoms are the basic units of matter and the defining structure of elements. Atoms are made up of three parts: protons (positively charged), neutrons (uncharged) and electrons (negatively charged).
For example: Sodium ( ) has 11 protons, 12 neutrons and 11 electrons.
2. Molecule:
Molecules form when two or more atoms form chemical bonds with each other. It doesn’t matter if the atoms are the same or are different from each other.
For example:
3. Isotopes:
For example: There are 5 isotopes of nickel in the nature, including: , , , , .
4. Atomic mass:
Atomic mass is the mass of an isotope of an element measured in units base on 1/12 the mass of the cacbon -12 atom. The atomic mass is equal to total mass of protons and neutrons ( Because the mass of electrons is insignificant )
For example: There are 5 isotopes of nickel in the nature, including: (67.78%), (26.16%), (1.25%), (3.66%), (1.15%).
Therefore,

Thus, average atomic mass of nickel will be 58.8127 u
5. Molecular mass:
Molecular mass is a number equal to the sum of atomic masses of the atoms in a molecule.
For example: The molecular mass of = 12 + 1 x 4 = 16.0 u
6. Mole concept:
Mole is defined as the amount of a substance, which contains the same number of chemical units as there are atoms in exactly 12 grams of pure cacbon. A mole represents the quantity of material, which contains one Avogadro’s number ( ) of chemical units of any substance.
For example: one mol of sodium ions ( ) = ions
7. Molar mass:
Molar mass is the mass of one mole of a substance .
For example: How many grams are there in 5 mol of benzene ( )
Molar mass of benzene ( ) = 78.0
Aim:
- To Study about types of chemical reactions such as combination, decomposition, displacement and double displacement.
- Find out about oxidation and reduction (redox reactions).

II. Definitions:
1. Combination reactions:
Combination reactions are reactions in which two reactants combine to form one product.
For example: when a metal undergos a combination reaction with oxygen, a metal oxide is formed. 2. Decomposition reactions:
Decomposition reactions are those in which one compound breaks down to form two or more products.
For example: Applying heat and electric in aluminothermic reaction: 3. Displacement reactions:
Displacement reactions are those in which an element reacts with a compound to form a new compound and release a different element.
For example: Highly pure silicon for computer chips is produced through a displacement reaction. In this reaction, hydrogen reacts with silicon tetrachloride to form hydrogen chloride and release silicon. 4. Double displacement reactions:
Double displacement reactions are those in which two compounds exchange ions to form two new compounds.
For example: In the reaction of copper sulphate and hydrogen sulphide, copper sulphide and sulphuric acid are

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