1. EXPLORING THE NATURE OF MATTER

2. DIVERSITY OF OBJECTS IN NATURE  Nature has an unlimited variety of living and non-living objects

3. UNDERSTANDING THE BASIC CONSTITUENTS  Scientists have been trying from a long time to understand the composition of different objects.  One of the scientists who have made great contribution in this direction is -John Dalton

4. Dalton’s Findings  Law of Constant Proportions: Dalton found that no matter which sample of a particular substance was chosen, the proportion by weight of its elementary constituents remained the same. Dalton found that no matter which sample of a particular substance was chosen, the proportion by weight of its elementary constituents remained the same. e.g. Water taken from any place is composed of Hydrogen and Oxygen. The proportion in it by weight of hydrogen and oxygen is always 1:8.

5. Dalton’s Findings Contd…  Law of Multiple Proportions: Whenever two elements combine to form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers. In Water H 2 0, 1g of Hydrogen combines with 8g of oxygen In Hydrogen Peroxide H 2 0 2, 1g of Hydrogen combines with 16g of oxygen The ratio of oxygen combining with the same amount i.e. 1g of hydrogen is 8:16 or 1:2 between water and hydrogen peroxide- a small integral ratio.

6. Dalton Proposed the following..   All matter is made of very tiny indivisible particles called atoms.   An element is a substance that has the same kind of atoms in it i.e., all atoms of an element are identical.   Atoms of an element combine in many ways to create the variety and complexity we see around

7. Examples of Elements  Hydrogen  Oxygen  Silver  Copper

8. RELATIONSHIP BETWEEN ELEMENTS, ATOMS AND MOLECULES

9. Atoms  Atom consists of electrons, protons and neutrons.

10. Atomic Mass  Atomic mass of an atom is the sum of the masses of its protons and neutrons.  For example, Mercury has atomic mass =80+120 = 200 atomic mass units (a.m.u.)

11. Atomic Number  Atomic number of an atom is only the number of protons the atom has.  For example, the atomic number of mercury(Hg) is 80.

12. Arrangement of Electrons around the Nucleus  Electrons move around the nucleus in shells or orbits.

13. Number of electrons in each shell  The first i.e. the innermost shell can take on only two electrons  Maximum eight electrons can move in the second shell. Neon

14. Shells contd..  The next shell can take maximum of 8 electrons.  Beyond this, the size of shells increases, thus they have smaller shells called sub-shells

15. Order of filling shells  The shells are filled from innermost to the outermost. SodiumMagnesium Neon

16. Inertness  When a shell gets filled, the atom becomes chemically inert.  Helium, Neon, Argon have their shells full, so they are chemically unreactive.