EXPLORING THE EXPLORING THE NATURE OF MATTERNATURE OF MATTER

DIVERSITY OF OBJECTS IN DIVERSITY OF OBJECTS IN NATURENATURE

Nature has an unlimited variety of Nature has an unlimited variety of living and non-living objectsliving and non-living objects

UNDERSTANDING THE BASIC UNDERSTANDING THE BASIC CONSTITUENTSCONSTITUENTS

Scientists have been trying from a Scientists have been trying from a long time to understand the long time to understand the composition of different objects.composition of different objects.

One of the scientists who have made One of the scientists who have made great contribution in this direction is great contribution in this direction is -John Dalton-John Dalton

Dalton’s FindingsDalton’s Findings Law of Constant Proportions:Law of Constant Proportions:

Dalton found that no matter which sample of a Dalton found that no matter which sample of a particular substance was chosen, the proportion particular substance was chosen, the proportion by weight of its elementary constituents by weight of its elementary constituents remained the same.remained the same.

e.g.e.g. Water taken from any place is composed of Water taken from any place is composed of Hydrogen and Oxygen. The proportion in it by Hydrogen and Oxygen. The proportion in it by weight of hydrogen and oxygen is always 1:8.weight of hydrogen and oxygen is always 1:8.

Dalton’s Findings Contd…Dalton’s Findings Contd…

Law of Multiple ProportionsLaw of Multiple Proportions: Whenever two : Whenever two elements combine to form more than one elements combine to form more than one compound, the different masses of one element compound, the different masses of one element that combine with the same mass of the other that combine with the same mass of the other

element are in the ratio of small whole numberselement are in the ratio of small whole numbers..In Water H20, 1g of Hydrogen

combines with 8g of oxygen

In Hydrogen Peroxide H202, 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.

Dalton Proposed the following..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

Examples of ElementsExamples of Elements

HydrogenHydrogen OxygenOxygen SilverSilver CopperCopper

RELATIONSHIP BETWEEN ELEMENTS, RELATIONSHIP BETWEEN ELEMENTS, ATOMS AND MOLECULESATOMS AND MOLECULES

AtomsAtoms

Atom consists of electrons, protons Atom consists of electrons, protons and neutrons.and neutrons.

Atomic MassAtomic Mass

Atomic mass of an atom is the sum Atomic mass of an atom is the sum of the masses of its protons and of the masses of its protons and neutrons. neutrons.

For example , Mercury has atomic For example , Mercury has atomic mass =80+120 = 200 atomic mass mass =80+120 = 200 atomic mass units (a.m.u.)units (a.m.u.)

Atomic NumberAtomic Number

Atomic number of an atom is only Atomic number of an atom is only the number of protons the atom has.the number of protons the atom has.

For example, the atomic number of For example, the atomic number of mercury(Hg) is 80.mercury(Hg) is 80.

Arrangement of Electrons around Arrangement of Electrons around the Nucleusthe Nucleus

Electrons move around the nucleus Electrons move around the nucleus in shells or orbits.in shells or orbits.

Number of electrons in each shellNumber of electrons in each shell

The first i.e. the innermost shell can The first i.e. the innermost shell can take on only two electronstake on only two electrons

Maximum eight electrons can move Maximum eight electrons can move in the second shell. in the second shell.

Neon

Shells contd..Shells contd..

The next shell can take maximum of The next shell can take maximum of 8 electrons.8 electrons.

Beyond this, the size of shells Beyond this, the size of shells increases, thus they have smaller increases, thus they have smaller shells called sub-shellsshells called sub-shells

Order of filling shellsOrder of filling shells

The shells are filled from innermost The shells are filled from innermost to the outermost. to the outermost.

Sodium MagnesiumNeon

InertnessInertness

When a shell gets filled, When a shell gets filled, the atom becomes the atom becomes chemically inert. chemically inert.

Helium, Neon, Argon Helium, Neon, Argon have their shells full, so have their shells full, so they are chemically they are chemically unreactive. unreactive.