STRUCTURE OF AN ATOM

MADE BY:SOURAV SEMALTI

IX-C 40

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

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

WHAT IS 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.

STRUCTURE OF ATOM

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

NUCLEUS OF THE ATOM

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.

ELECTRONSElectrons (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.

PROTONS 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.

NEUTRONSNeutron (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.

THOMSON’S MODEL OF AN ATOM

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

BHOR’S MODEL OF AN ATOM

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.

BHOR’S ATOM

electrons in orbits

Nucleus

WHAT DO THIS PARTICLES CONSIST

OF ?

Water Molecule

Hydrogen atom

Hydrogen atom

Oxygen atom

ISOTOPESIsotope, 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.

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