PREPARED BY

LEKSHMI.S.GPHYSICAL SCIENCEREG NO: 13357003BNVCTE,THIRUVALLAM

All matter is made up of atoms.Atoms of an element are identical.Each element has different atoms.Atoms can engage in a chemical reactions.Atoms can neither be created nor be destroyed.Atoms are indivisible.

Atomic Theory

John Dalton(1776-1884)

atom has a positively charged central part (nucleus)

Electrons are distributed around nucleus

Mass of an atom is concentrated at nucleus.

Compared with total volume of an atom, the volume of nucleus is meager

Rutherford’s Atomic Model

Ernest Rutherford (1871-1937)

Solar system Rutherford‘s atom model

Planetary model of atom

Bohr's Model of the Atom

Niels Bohr

1913

Bohr's Model of the Atom

electrons orbit the nucleus like planets orbit the sun

Bohr's Model of the Atom

electrons fills the orbits closest to the nucleus

e.g. fluorine:#P = 9

#e- = 9

#N = 10

9P10N

each orbit can hold a specific maximum number of electrons

Shell maximum no: of electrons

1 - K2 - L3 - M4 - N

Bohr's Model of the Atom

2

818

32

Bohr’s Model

Nucleus

Electron

Orbit

Energy Levels

What is the structure of an atom?

• Nucleus - center of the atomHome of Protons and NeutronsHas a positive charge• Proton

Has a relative mass of 1Has a positive (+) chargeDetermines the atomic numberFound inside the nucleus

What is the structure of an atom?

• NeutronHas no (0) chargeHas a relative mass of 1Found inside the nucleus

What is the structure of an atom?

• ElectronHas a negative (-) chargeFound outside the nucleus

• Rutherford atom model - electrons are around the nucleus

• Bohr model – electrons are in specific energy levels called shells

How are p, n, e related?

• No: protons = No: electrons• No: protons = atomic number• No: protons + No:neutrons = mass number• No: neutrons=mass no: - atomic no:

ATOMI C STRUCTUREATOMI C STRUCTURE

the number of protons in an atom

the number of protons and neutrons in an atom

HeHe22

44Atomic mass

Atomic number

number of electrons = number of protons