STRUCTURE OF AN ATOM

MADE BY:NIHARIKA S PANDEPRIYANKA S PAWAR

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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 an atom

• What this particles consists 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

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

STRUTURE OF ATOM

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.

WAVE ASPECT OF ELECTRONS

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

RUTHERFORD’S MODEL OF AN

ATOMAn 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

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

ATOMIC STRUCTURE

the number of protons in an atom

the number of protons and neutrons in an atom

He

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

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.

HYDROGEN ISOTOPES

FOR EXAMPLEThe 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.

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