1. Concept of Basic
Chemistry

2. Objectives
After this session, the students are expected to be able to:
explain the difference between atom, molecule and material
3. explain chemical reaction
2. explain the law of conservation of mass
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3. Atomic theory Dalton’s atomic theory:
1. All matters are composed of atoms which are indivisible
2. All the atoms given of an element are alike in weight and in all other respect
3. The atoms of different elements are difference of weights
4. Atoms are indestructible and preserve their identities in all chemical reactions
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4. The nature of element
The proportion by weight of the elements present in any chemical compound are entirely independent of the manner in which the compound is prepared
If two elements A and B combine to form the two-atoms molecule
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5. Molecule
If two elements A and B combine to forms various compounds and if the weight of element A in each compound is kept constant, then the weights of element B present in these compounds will be in the ratio of small integers
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6. Molecule
For example that water is a binary compound of hydrogen and oxygen and the relative weights of the two elementary atoms are 1 : 7
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7. Material If two compounds are mixture become a material
For example mixture of iron powder with sulfur become a new material
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8. Chemical Equation
Any chemical reaction can be represented by an equation that shows as all reactants and products and their physical states
The physical states are shown by the use of the letters s, l, g for solid, liquid and gas respectively
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9. Chemical Equation
These letters are placed in brackets after the appropriate chemical formula
For example, the decomposition of ammonium nitrate can be represented as :
NH4NO3 (s) → N2O (g) + 2 H2O (l) …(1)
This equation states that 1 mol of solid NH4NO3 reacts to give 1 mol of gaseous N2O and 2 mol of liquid water
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10. Chemical Equation
Substances that are presented in aqueous solution can be indicated by the use of ‘aq’ for aqueous, as in the equation :
Ag+ (aq) + Cl– (aq)  AgCl (s) …..(2)
This equation states that 1 mol of Ag+ in aqueous solution and 1 mol of Cl– in aqueous solution react to give 1 mol of solid AgCl
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11. Law of Conservation of Mass
The above examples are balanced equation. This means that the same number of atoms of each element appears on each side of equation
For example, the first equation has three oxygen atoms on the left side and three on the right
This is in agreement with the
Law of Conservation of Mass
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12. Electrolytes
Many substances when dissolved give solution that conduct electricity readily, whereas other do not
Those substances that give conducting solutions are called electrolytes and now are known to give free ions in solution
Solvents like water, alcohols and various organic substances dissolves many electrolytes readily
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13. Stoichiometry Definition :
Stoichiometry is the study of the quantitative relations between amounts of reactants and amounts of products in chemical reactions
It allows us to calculate how much of one chemicals is needed to form another
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14. Chemical reaction Characteristic of chemical changes:
* Temperature changes
(Exoterm & Endoterm)
*Colour change
* Precipitated formation
* Gases formation
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15. Physical changes Melting Freezing Sublimation Condensation Evaporation
Deposition
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