Atomic structure

Question 1

What is element

Answer 1

1) Substances that cant be broken down into simpler substances by a chemical reaction

Question 2

Dalton model of atoms

Answer 2

1) observed in 19th century
2) First person to assign chemical symbols to element s
3) We can understand how elements react together to make new substances called compounds .
4) he noticed elements always combine in fixed ratios

Question 3

What did JJ Thomson model suggested ?

Answer 3

1) Electrons are part of atoms
2) He observed stream of - charged electrons, when high voltage was applied to a metal
3) Due to neutrality of atom, he suggested that electrons must be scattered in a positively charged sponge like substance.

Question 4

Rutherford’s model of an atom

Answer 4

1) he tested Thomson’s model.
2) he fired alpha particles at a piece of gold foil
3) Alpha particles= helium nuclei.
4) If Thomson’s model was true then large number of particles should have passed straight through or get stuck in the positive sponge.
5) Most of the alpha particles did pass through but some were repelled and bounced back
6) Large no of deflected particles led to the conclusion that atom is mainly empty space.
7) Large deflections= + alpha particles collide with and are repelled by a dense , + charged nucleus
8) small no of alpha particles bounced back= nucleus is very small.

Question 5

What is the relative mass of electron

Answer 5

5 X 10^-4

Question 6

Bohr model of hydrogen.

Answer 6

1) pictured H atoms as a small solar system
2) The electrostatic attraction between the sub atomic particles prevent the electron from leaving the atom.
3) Without neutrons, protons would repel each other and nucleus would fall apart.
4) An electron moves into an orbit or higher energy level further from nucleus when an atom absorbs energy.

Question 7

What does Z represent ?

Answer 7

1) Atomic number

2) No of protons.

Question 8

What does ‘A’ represent ?

Answer 8

1) Mass number

2) Protons+neutrons.

Question 9

What are isotopes

Answer 9

Atoms of same element with different mass numbers.

1) Similar chemical properties
2) Difference in mass lead to different physical properties.

Question 10

What is relative atomic mass

Answer 10

average mass of an atom of the element taking into account all the isotopes and their relative abundance, compared to one atom of Carbon-12.

Question 11

What does no of lines represent in mass spectrum ?

Answer 11

No of isotopes present

Question 12

Does all electromagnetic radiations travel at the same speed (c)

Answer 12

YES

Question 13

Wavelengths of different colors of visible light

Answer 13

Red light>orange > yellow> green> blue> pink.

Question 14

Increasing wavelength of electromagnetic spectrum,

Answer 14

Gamma rays< X-rays < UV< visible light< IR < Mirco waves< radio waves

Question 15

Absorption spectrum

Answer 15

shows the radiation absorbed as atoms move from a lower to higher energy level.

Question 16

Emission spectrum

Answer 16

when an atom moves from a higher to a lower level.

Question 17

How much energy is released for one transition ?

Answer 17

1 photon (packet of energy) is released for each electron transition.

Question 18

Why line emission spectrum is not quantized ?

Answer 18

1) electron cant change their energy in continuous way

2) it can only change its energy in discrete amounts. +

Question 19

Different electromagnetic radiations related to energy levels

Answer 19

When electrons fall to
n=1 — UV radiations are released = Lyman series
n=2—- Visible light= Balmer series
n=3—- IR radiations or higher energy levels= Paschen series.

Question 20

Disadvantages of Bohr model

Answer 20

1) Failed to predict the spectral lines of atoms with more than one electron
2) Assumes electrons trajectory can be precisely described- which is impossible

Question 21

What is Heisenberg uncertainty principle ?

Answer 21

We cant know where an electron is at any given moment in time.

Question 22

what are atomic orbitals ?

Answer 22

1) Solution to Schrodinger wave equation

2) Region around an atomic nucleus in which there is a 90% probability of finding the electron.

Question 23

Whats the difference between 3 2p orbitals

Answer 23

1) Only orientation in space

2) They have same energy

Question 24

Confusion between the energy of 3d and 4s

Answer 24

3d falls below 4s for elements with atomic number greater than 20

Question 25

Whats Pauli exclusion principle ?

Answer 25

1) no more than 2 electrons can occupy any one orbital

2) If 2 electrons are in the same orbital they must spin in opposite directions.

Question 26

Whats 2n^2

Answer 26

Each main level can hold 2n^2 no of electrons

Question 27

Whats Aufbau principle ?

Answer 27

States that electrons are placed into orbitals of lowest energy first

Question 28

Whats Hund’s Rule ?

Answer 28

If more than 1 orbital in a sub level is available, electrons occupy different orbitals with parallel spins.

Question 29

no of orbitals at nth energy level

Answer 29

n^2

Question 30

How transition metals form ions ?

Answer 30

They lose electrons from 4s sub level first and then from 3d.
however 3d is filled after 4s

Question 31

Unusual configuration of Chromium(Cr) and Copper (Cu)

Answer 31

Cr= 3d^5 4s^1 --- it should be 4s^2, 3d^4
Cu= 3d^10 4s^1---- it should be 4s^2 3d^9

Question 32

Why chromium has 3d^5 4s^1 configuration ?

Answer 32

1) 4s and 3d are close in energy
2) half filled d orbital is relatively stable as it minimizes electrostatic repulsion.
3) 6 singly occupied orbitals.

Question 33

Whats first ionization energy ?

Answer 33

Energy needed to remove 1 mole of electrons from the ground state of 1 mole of the gaseous atoms.

Question 34

What does successive ionization energies suggest

Answer 34

Gives an evidence for sub levels present.

Question 35

Whats convergence limit ?

Answer 35

Frequency at which spectral lines converge -ionise

Question 36

Mass spectrometry steps

Answer 36

1) Vaporization
2) Ionization
3) acceleration
4) Deflection
5) Detection