Structure of atom ppt by shiva prasad class 9th a

STRUCTURE OF ATOMS

Done by :-shiva prasadclass:9th A

ThomsonCarbon atomRUTHORFO

RD

Bhor

PRESENTATION OUTLINECharged particles in

matter Structure of atomNucleus of atomElectronsThomsan's model of an

atomRutherford’s model of an

atomDrawbacks of

Rutherford’s model of an atom

Bohr’s model of an atom

NeutronsDistribution of

Electrons in different shells

Atomic structureValencyAtomic number

and Mass number IsotopesIsobars

CHARGED PARTICLES IN MATTER

Atoms have three types of sub atomic particles. They are electrons, protons and neutrons.

Electrons are negatively charged (e-), protons are positively charged (p+) and neutrons have no charge (n).

The mass of an electron is 1/2000 the mass of a hydrogen atom. The mass of a proton is equal to the mass of a hydrogen atom and is taken as 1 unit. The mass of a neutron is equal to the mass of a hydrogen atom and is and is taken as 1 unit.

STRUCTURE OF ATOMAtoms 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

STRUCTURE OF ATOM

NUCLEUS OF THE ATOMAn 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.

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.

Protons Atoms are made of extremely tiny particles called protons, neutrons, and electrons. Protons and neutrons are in the center of the atom, making up the nucleus. Electrons surround the nucleus. Protons have a positive charge. Electrons have a negative charge.

Rules determining the no. of sub – atomic particles

The number of protons, neutrons, and electrons in an atom can be determined from a set of simple rules. The number of protons in the nucleus of the atom is equal to the atomic number (Z). The number of electrons in a neutral atom is equal to the number of protons. The mass number of the atom (M) is equal to the sum of the number of protons and neutrons in the nucleus. The number of neutrons is equal to the difference between the mass number of the atom (M) and the atomic number (Z).

Difference between protons and electrons protons electrons

protons have positive charge electrons have negative charge

Protons are significantly heavier electrons are comparatively light in weight

protons are significantly larger in size

Electrons are comparatively smaller in size.

protons remain in the nucleus. Electrons can move to other atoms

protons are present in the nucleus clouds.

Electrons are present in shells

In a nuclear explosion, the atom’s nucleus (center) is split. Neutrons are released, and hit other nuclei, setting off a chain reaction. The result is a big release of energy in a blast of heat, light, and radiation.

ATOMIC BOMB

MODEL’S OF ATOM

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

Ruthorford’s modelAn 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. 

Drawbacks of Ruthorford’s model

Any particle in a circular orbit would undergo acceleration and during acceleration the charged particle would radiate energy. So the revolving electrons would lose energy and fall into the nucleus and the atom would be unstable. We know that atoms are stable.

BHOR’S MODEL

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

RUTHORFORD BHOR ‘S MODEL

DISTRIBUTION OF ELECTRONS IN DIFFERENT SHELLS

The distribution of electrons in the different shells was suggested by Bhor and Bury. The following are the rules for filling electrons in the different shells.

The maximum number of electrons in a shell is given by the formula 2n2 where n is the number of the shell 1, 2, 3 etc. First shell or K shell can have = 2n2 = 2 x 12 = 2x1x1 = 2 electrons Second shell or L shell can have = 2n2 = 2 x 22 = 2x2x2 = 8 electrons Third shell or M shell can have = 2n2 = 2 x 32 = 2x3x3 = 18 electrons Fourth shell or N shell can have = 2n2 = 2 x 42 = 2x4x4 = 32 electrons and so on. The maximum number of electrons that can be filled in the outermost shell is 8. Electrons cannot be filled in a shell unless the inner shells are filled

The following rules are followed for writing the number of electrons in different energy levels or shells:-

i) The maximum number of electrons present in a shell is given by the formula 2n2, where ‘n’ is the orbit number or energy level index, 1,2,3,…. Hence the maximum number of electrons in different shells are as follows:first orbit or K-shell will be = 2 × 12 = 2, second orbit or L-shell will be = 2 × 22 = 8, third orbit or M-shell will be = 2 × 32 = 18, fourth orbit or N-shell will be = 2 × 42= 32, and so on.

(ii) The maximum number of electrons that can be accommodated in the outermost orbit is 8.

(iii) Electrons are not accommodated in a given shell, unless the inner shells are filled. That is, the shells are filled in a step-wise manner. Atomic structure of the first eighteen elements is shown schematically in Fig. 4.4.

Composition of Atoms of First Eighteen ElementsName of element Symbol Atomic

NumberNumber ofProtons

Number ofNeutrons

Number ofElectrons

DistributionOf ElectronsK L M N

Valency

Hydrogen H 1 1 - 1 1 - - - 1Helium He 2 2 2 2 2 - - - 0Lithium Li 3 3 4 3 2 1 - - 1Beryllium Be 4 4 5 4 2 2 - - 2Boron B 5 5 6 5 2 3 - - 3Carbon C 6 6 6 6 2 4 - - 4Nitrogen N 7 7 7 7 2 5 - - 3Oxygen O 8 8 8 8 2 6 - - 2Fluorine F 9 9 10 9 2 7 - - 1Neon Ne 10 10 10 10 2 8 - - 0Sodium Na 11 11 12 11 2 8 1 - 1Magnesium Mg 12 12 12 12 2 8 2 - 2Aluminium Al 13 13 14 13 2 8 3 - 3Silicon Si 14 14 14 14 2 8 4 - 4Phosphorus P 15 15 16 15 2 8 5 - 3,5Sulphur S 16 16 16 16 2 8 6 - 2Chlorine Cl 17 17 18 17 2 8 7 - 1Argon Ar 18 18 22 18 2 8 8 - 0

VALENCY Valency is the combining

capacity of an atom of an element.

The electrons present in the outermost shell of an atom are called valence electrons.

If an atom’s outermost shell is completely filled, they are inert or least reactive and their combining capacity or valency is zero.

Of the inert elements Helium atom has 2 electrons in the outermost shell and the atoms of other elements have 8 electrons in their outermost shell. Atoms having 8 electrons in their outermost shell is having octet configuration and are stable.

If an atom’s outermost shell is not completely filled it is not stable. It will try to attain stability by losing, gaining or sharing electrons with other atoms to attain octet configuration.

The number of electrons lost, gained or shared by an atom to attain octet configuration is the combining capacity or valency of the element

Eg :- Hydrogen, Lithium, Sodium atoms can easily lose 1 electron and become stable. So their valency is 1. Magnesium can easily lose 2 electrons. So its valency is 2. Aluminiun can easily lose 3 electrons. So its valency is 3. Carbon shares 4 electrons. So its valency is 4.

Fluorine can easily gain 1 electron and become stable. So its valency is 1. Oxygen can easily gain 2 electrons. So its valency is 2. Nitrogen can easily gain 3 electrons. So its valency is 3.

Atomic structure of the first eighteen elements

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

Atomic number and Mass number Atomic number (Z)

The atomic number of an element is the number of protons present in the

nucleus of the atom of the element.

All the atoms of an element have the same atomic number.

Eg :- Hydrogen – Atomic number = 1 (1 proton)

Helium - Atomic number = 2 (2 protons)

Lithium - Atomic number = 3 (3 protons)

Mass number (A) The mass number of an element is the

sum of the number of protons and neutrons (nucleons) present in the

nucleus of an atom of the element. The mass of an atom is mainly the mass

of the protons and neutrons in the nucleus of the atom.

Eg :- Carbon – Mass number = 12 (6 protons + 6

neutrons) Mass = 12u Aluminium – Mass number = 27 (13 protons + 14

neutrons) Mass = 27u Sulphur – Mass number = 32 (16 protons + 16

neutrons) Mass = 32u

The first ever image of a hydrogen bond

Isotopes Isotopes are atoms of the same element having

the same atomic numbers but different mass numbers.

Eg :- Hydrogen has three isotopes. They are Protium, Deuterium (D) and Tritium (T).

H H H Protium Deuterium Tritium Carbon has two isotopes. They are :- C C Chlorine has two isotopes They are :- Cl Cl

11

11

32

12614

35 3717 17

6

1 1 1 3

21

Isobars Isobars are atoms of different elements having different

atomic numbers but same mass numbers. These pairs of elements have the same number of nucleons. Eg :- Calcium (Ca) – atomic number - 20 and Argon (Ar) –

atomic number 18 have different atomic numbers but have the same mass numbers – 40.

Iron (Fe) and Nickel (Ni) have different atomic numbers but have the same atomic mass numbers – 58.

20 18

40 40

58 58

2726 Fe

Ca Ar

Ni

Isobars Isotopes

they have same mass number but different atomic number

They have the same atomic number but different mass number

Number of electrons are different in isobars

Same number of protons but different number of neutrons

They have different chemical properties

They have identical chemical properties

They are atoms of different elements

They are atoms of the same element

Difference between isotopes and isobars

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DONE BY

SHIVA PRASAD Class 9th A