Chapter 3Atomic Structure

(Neither take rest nor be the time waste,

Because life is the test and only heaven is the rest)

Definitions1. Atom: -The building block of the matter that takes part in the reaction.

OR

The smallest component of an element having the chemical properties of the element, consisting of a nucleus and surrounding shells.

2. Nucleus: -the central part of the atom comprising the mass of the atom conferred by protons and neutrons, initially discovered by RUTHERFORD.

3. Shell or energy level: -according to Bohr these are the circular orbits at certain distance from the nucleus where electrons exist.

4. Atomic number (Z): -The number of protons in nucleus is called the atomic number of the element.5. Atomic mass: - The total number of protons and neutrons in nucleus constitute its atomic mass.6. Element: -The simplest matter whose all atoms have same atomic number and can not be further simplified is called element. 7. Crooks discharge tube experiment: - indicates the existence of protons and electrons in the atom

8. Cathode rays: -the rays which consist of electrons and are produced when the current is passed through gases at low pressure are called cathode rays.

9. Properties of cathode rays (electrons):

Discovered by J.J THOSMSON Carry a negative charge equal to 1.6*10-19C=4.803*10-10 Their e/m ratio is 1.76*108 C/g

Their mass is 9.11*10-31 kg = 0.00055a.m.u

They can be deflected by electromagnetic field.

These dont depend upon the material of which the electrode is made nor of the gas which is enclosed inside the tube.

10. The properties of canal rays ( protons):

GOLDSTIEN discovered them.

These rays carry positive charge

They travel in straight line

The value of e/m depends upon the gas enclosed

The mass is 1.67*10-27kg=1.0073amu

They are composed of heavy particles than electrons. 11. The properties of neutrons:

Discovered by CHADVICK.

They are neutral, carrying no charge.

The mass is same as that of proton but slightly heavier. i.e. 1.0087 a.m.u.

It is highly energetic particle.12. Radioactivity: -the spontaneous emission of radiations by certain elements is called radioactivit

13. Isotopes: - Atoms of the same elements, having the same atomic number but the different atomic masses are called isotopes.14. Spectrum: -the band of colors formed through the dispersion of light is called spectrum.15. Electronic configuration: - the arrangement or distribution of electrons in the available orbitals is called electronic distribution.

16. Atomic radius: -the half of the bond length, taken between two homonuclear diatomic molecules. OR the distance from nucleus to the valence electron is called atomic radius.

17. Ionic radius: -the radius of an ion.

18. ion: -the charged atom is called ion

19. Cation: -the positively charged ion is called cation.20. Anion: -the negative charged ion is called anion.21. Ionization potential: -the energy required to make an atom ion is called ionization potential.22. Electron affinity: -the amount of energy released when an electron is added to a neutral gaseous atom to form a negative ion is called electron affinity.

23. Electronegativity: - the force with witch an atom attracts the shared pair towards itself is called electronegativity.

Multiple Choice Questions

1. The first atomic theory was proposed by:

a) Democritusb) Greek Philosophers

c) both a & bd) John Dalton

2. According to modern theory, all elements are made up of small, indivisible, indestructible particles called atoms

a) trueb) false

3. Protons and neutrons were discovered by respectively:

a) J.J Thomson, Chadwick

b) Chadwick, J.J Thomson

c) Goldstein, Chadwick

d) Chadwick, Goldstein

4. Electrons are the constituent of all matter.

a) true b) false

5. The incorrect statement regarding the cathode rays is:

a) material particles

b) e/m ratio is differentc) possess K.E d) N.O.T

6. Electrons do not depend upon the the nature of the cathode and the gas inside the tube.

a) true b) false

7. e/m ratio of electron is:

a) 1.76*108 C/gb)1.76*1011C/gc) 1.602*10-19 C/gd) 1.672*10-27C/g

8. The Charge on electron is:

a) 1.76*108 Cb)1.76*1011C

c) 1.602*10-19 Cd) 1.672*10-27C

9. The charge on proton is:

a) 1.76*108 b)1.76*1011C

c) 1.602*10-19 Cd) 1.672*10-27C

10. 1 a.m.u =?

a) 1.76*108 gb)1.76*1011g

c) 1.602*10-19 gd) 1.672*10-27g

11. Atom was proved divisible particle by:

a) cathode raysb) radioactivity

c) discharge tube exp. d) A.O.T

12. Electron is 1836 times heavier than proton.

a) trueb) false

13. Radioactivity was discovered by:

a) Henry Bequeralb) Rutherford

c) Bohord) J.J Thomson

14. Rutherford used particles in his experiment.

a) particlesb) particles

c) particlesd) A.O.T

15. The -particles deflected back by striking the atom because of the presence of:a) shellsb) nucleus

c) protonsd) electrons

16. Energy is when an electron jumps from higher energy level to lower energy level.

a) absorbedb) released

c) neither absorbed nor released

d) both a & b

17. This of the following particles takes part in the reaction.a) electronb) proton

c) neutrond) A.O.T

18. The correct equation is:

a) E2 - E1 = hb) E2 + E1 = h

c) E2 * E1 = h d) E2 / E1 = h19. Na has:

a) 11 electrons b) 11 protons

c) 12 neutrons d) A.O.T

20. Mass number =

a) protons + electrons

b) protons + neutrons

c) electrons + neutrons

d) no. of protons.21. Atomic number =

a) protons + electrons

b) protons + neutrons

c) electrons + neutrons

d) no. of protons.

22. The positively charged particles in radioactivity are protons.

a) true b) false

23. Isotopes have different number of:

a) electronsb) protons

c) neutronsd) A.O.T

24. Proteum has one proton and no neutron.

a) trueb) false

25. Isotopes are used in the treatment of diseases.

a) trueb) false

26. The formula to find out max number of electrons is:

a) n2b) 2n

c) 2n2 d) N.O.T

27. When n=3 the max electrons in a shell should be.

a) 3b) 6

c) 9d) 18

28. The max. number of electrons in 4th shell is:

a) 4b) 8

c) 16d) 3229. Find the mis match

a) electrons : J.J Thomson

b) protons : nucleus

c) neutrons : atomic mass

d) protons : atomic number

30. The correct statement is:

a) A = Z+Ab) A=Z-N

c) A=N-Zd) Z=A-N

31. Which isotope of oxygen forms ozone

a) O16b) O17c) O18d) O19

Answer Key1D2B3C

4A5A6B

7A8C9C

10D11B12B

13A14B15A

16B17B18A

19D20B21D

22C23A24A

25A26C27D

28D29A30D

31C

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