PRESENTATION OUTLINE• History of atom• What is an atom?• Structure of atom• Nucleus of atom• Electrons• Protons• Neutrons• Thomson’s model of

an atom• Rutherford’s model of

an atom

• Bohr’s model of anatom

• What this particlesconsists of ?

• Atomic structure• Isotopes• Isobars

HISTORY OF THE ATOM

460 BC Democritus develops the idea of atoms

he pounded up materials in his pestle and mortar until he had reduced them to

smaller and smaller particles which he called

ATOMA

He suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOM

Atom, tiny basic building block of matter. All the material on Earth is composed of various

combinations of atoms. An atom consists of a cloud of electrons surrounding a small, dense

nucleus of protons and neutrons.

Atoms are the smallest particles of a chemical element that still exhibit all the chemical

properties unique to that element. A row of 100 million atoms would be only about a centimetre

long.

ATOMS MADE VISIBLEIndividual atoms of the element silicon can be seen in this image

obtained through the use of a scanning transmission electron microscope. The atoms in each pair are less than a ten-millionth of a

millimeter (less than a hundred-millionth of an inch) apart.

Atoms are made of smaller particles, called

electrons, protons, and neutrons. An atom

consists of a cloud of electrons surrounding a

small, dense nucleus of protons and

neutrons. Electrons and protons have a

property called electric charge, which affects

the way they interact with each other and

with other electrically charged particles

An atom consists of a cloud of electrons surrounding a small, dense nucleus of

protons and neutrons. The nucleus contains nearly all of the mass

of the atom, but it occupies only a tiny fraction of the space inside the atom. The diameter of a typical nucleus is only about

1 × 10-14 m (4 × 10-13 in), or about 1/100,000 of the diameter of the entire

atom.

Electrons (e-) were discovered by sir. J.J. Thomson.Electrons are tiny, negatively charged particles around the nucleus of an atom. Each electron carries a single fundamental unit of negative electric charge–1.602 x 10-19 coulomb and has a mass of 9.109 x 10-31 kg. The electron is one of the lightest particles with a known mass. Electrons cannot be split into anything smaller, also electrons do not

have any real size, but are instead true

points in space-that is, an electron

has a radius of zero.

Proton (p+) was discovered by E.Goldstein. Proton has 1 unit mass. Proton Protons have a positive electrical charge of 1.602 x 10-19

coulomb. This charge is equal but opposite to the negative charge of the electron. A

proton’s mass is about 1,840 times the mass of an electron. Protons carry a positive

charge of +1, exactly the opposite electric charge as electrons. The number of protons in the nucleus determines the total quantity

of positive charge in the atom.

Neutron (n) was discovered by Sir James Chadwick. The neutron is slightly heavier than a proton and 1,838 times as heavy as the electron. Neutron, electrically neutral

elementary particle that is part of the nucleus of the atom. The neutron is about

10-13 cm in diameter and weighs 1.6749 x 10-27 kg.

According to Sir Joseph model of an atom, it consists of a positively charged here and the electrons are embedded in it. The negative and the positive charges are equal in

magnitude, as a result the atom is neutral. Thomson proposed that the atom of an atom to be similar

to that of a Christmas pudding

or a watermelon

An atom consists of a positively charged center in the atom called the nucleus.

The mass of the atom is contributed mainly by the nucleus. The size of the nucleus is very small as

compared to the size of the atom. The electrons revolve around the nucleus in well-

defined orbits.

gold foil

helium nuclei

helium nuclei

Bohr agreed with almost all points as said by Rutherford

except regarding the revolution of electrons for which he added

that there are only certain orbits known as discrete orbits

inside the atom in which electrons revolve around the nucleus. While revolving in its discrete orbits the electrons do

not radiate energy.

electrons in orbits

Nucleus

Water Molecule

Hydrogen atom Hydrogen atom

Oxygen atom

the number of protons in an atom

the number of protons and

neutrons in an atom

2

4 Atomic mass

Atomic number

Number Of Electrons = Number Of Protons

CONTD....

Electrons are arranged in Energy Levels or Shells around

the nucleus of an atom.

• first shell a maximum of 2 electrons

• second shell a maximum of 8 electrons

• third shell a maximum of 8 electrons

Isotope, one of two or more species of atom having the same atomic number, hence

constituting the same element, but differing in mass number. The nucleus, and mass number is the sum total of the protons plus the neutrons in the nucleus, isotopes of the same element

differ from one another only in the number of neutrons in their nuclei.

The average mass of naturally occurring copper atoms is equal to the sum of the atomic mass for each isotope multiplied by its isotopic abundance.

For copper, it would be

(62.930 amu x 0.692) + (64.928 amu x 0.308)

= 63.545 amu.

The atomic weight of copper is therefore 63.545 g.

ISOBARSThe total number of nucleons is the

same in the atoms of this pair of elements. Atoms of different

elements with different atomic numbers, which have the same mass

number, are known as isobars.