Arrangement of Electrons in the Atom,Model Questions and Solutions

Question 1

What term is used to refer to the condition of the hydrogen atom when its
electron occupies the E 1 level?

Answer 1

Ground state

Question 2

What term is used to refer to the condition of the hydrogen atom when its
electron occupies levels E 2 or higher?

Answer 2

Excited state

Question 3

What causes an electron to leave the E 1 level?

Answer 3

Energy increase e.g. light or

electricity.

Question 4

Why do electrons not remain long in the levels E 2 or higher?

Answer 4

The excited

electrons are too unstable.

Question 5

5. Identify the energy level that produces the visible lines in the atomic emission
   spectrum.

Answer 5

n=2

Question 6

6. How does the modern atomic theory describe the behaviour of electrons?

Answer 6

Electrons move in a wave particle duality.

Question 7

7. Define an atomic orbital

Answer 7

A region in space about the nucleus where there is a high probability of finding an
electron.

Question 8

8. Write the electron configuration for an iron atom

Answer 8

Fe: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6

Question 9

9. Why is it difficult to specify the absolute boundary of an atom?

Answer 9

Heisenbergs uncertainty principle – we can never be sure of the precise location of an electron when it is moving.

Question 10

10. How many orbitals in a carbon atom?

Answer 10

C 1s2 2s2 2p x 1 2p y 1 - four orbitals in carbon.

Question 11

11. Distinguish between a 2p orbital and a 2p sub level

Answer 11

The 2p sub level is made up of 3 orbitals of equal energy

Question 12

12. Why is the main energy levels a calcium atom 2, 8, 8, 2 and not 2, 8, 10?

Answer 12

The 4s sub level is lover in energy than 3d therefore electrons fill the 4s sub level first.

Question 13

13. Give a significant difference between an electron in the 2s orbital and an electron in the 3s orbital

Answer 13

The size. The 3s orbital is bigger than the 2s orbital.

Question 14

14. State the number of sub-levels and orbitals occupied in an argon atom at
    ground state.

Answer 14

Ar 1s2 2s2 2px2 2py2 2pz2 3s2 3px2 3py2 3pz2

Five sub-levels and nine orbitals

Question 15

15. Write the electron configuration of an oxide ion,

Answer 15

O2- O 2- [1s 2 2s 2 2p 6 ] 2-

Question 16

18. State the Pauli exclusion principle

Answer 16

No more than two electrons may occupy an orbital and they must have opposite spin.

Question 17

19. Explain why there are electrons in the fourth main energy level in potassium
    even though its third main energy level is incomplete

Answer 17

The 4s sub level is lower in energy than the 3d sub level

Question 18

16. State the maximum number of electrons that can be accommodated in a p-
    orbital

Answer 18

Two electrons max per orbital (Pauli exclusion principle)

Question 19

21.Give another factor, other than Heisenberg that lead to the modification of Bohr’s
theory.

Answer 19

De Broglies wave particle duality.

Question 20

20.Heisenbergs research lead to the Heisenberg uncertainty principle (1927), which
led to significant modifications of Bohr’s theory. State the Heisenberg
uncertainty theory.

Answer 20

An electron’s position cannot be determined and its velocity known at the same time.

Question 21

22. State Hunds rule of multiplicity

Answer 21

When two or more orbitals of equal energy are available, the electrons occupy them
singly before filling them in pairs.

Question 22

23.Outline Bohr’s atomic theory based on the hydrogen emission spectrum

Answer 22

An electron in hydrogen occupies fixed energy levels. The electron is in its ground state
and when supplied with energy moves up an energy level and is now in an excited
state. It is unstable and falls back to its ground state producing a photon of light.
E 2 - E 1 = hf

Question 23

24.Define energy level

Answer 23

The fixed energy value that an electron in an atom may have.

Question 24

25.Name the visible series

Answer 24

(n = 2) of the line emission spectrum Balmer

series

Question 25

26.Identify the main energy levels involved in the electron transition that gives rise to the first (red) line of the Balmer series in the emission line spectrum

Answer 25

.3 and 2