atomic emission spectra

Question 1

what is emission spectrum ( line spectrum )?

Answer 1

heating atoms of a pure element- in gaseous or vapor state- to high temperatures or exposing them to a low pressure inside an electrical discharge tube

Question 2

device to examine this radiant light

Answer 2

spectroscope

Question 3

why is it called line spectrum?

Answer 3

because it is composed of limited number of restricted coloured lines separated by dark areas

Question 4

why is the line spectrum a defining characteristic for each element?

Answer 4

because there are. no two elements with the same line spectrum, and this is due to the difference in the atomic number from one element to another

Question 5

what was the element that emitted the line spectrum and how many colours appeared ?

Answer 5

hydrogen, four colours
Violet Blue Green Red

Question 6

Bohr’s atomic model

Answer 6

atomic spectra is considered the key which solved the puzzle of the atomic structure

Question 7

Bohr’s postulates
(points that agree with Rutherford’s postulates)

Answer 7

1.a positively charged nucleus exists in the center of the atom
2.the number of negative electrons equals the number of positive protons inside the nucleus
3.during the revolving of the electron around the nucleus, a centrifugal force arises which is equivalent to the attraction force of the nucleus on the electron

Question 8

Bohr’s new postulates
what is a stable atom?

Answer 8

is the state of atom when its electrons energy is the least

Question 9

Bohr’s new postulates
what does the electrons orbit the nucleus in?

Answer 9

definite allowed energy levels

Question 10

Bohr’s new postulates
what is a complete jump?

Answer 10

electrons move from an energy level to another via complete jump

Question 11

Bohr’s new postulates
what is the principle quantum number?

Answer 11

each energy level is expressed by an integer number called the principle quantum number and the electron revolves in the lowest allowed energy level in its ground state

Question 12

Bohr’s new postulates
what does the definite allowed energy depend on?

Answer 12

the distance between its energy level and the nucleus

Question 13

Bohr’s new postulates
what happens to the energy level when its radius increases?

Answer 13

the energy of any level increases as its radius increases

Question 14

Bohr’s new postulates
what is a quantum?

Answer 14

is a quantity of energy gained or lost when the electron is transferred from an energy level to another energy level

Question 15

Bohr’s new postulates
what happens to the electron when it gains energy?

Answer 15

the electron jumps temporarily to a higher energy level

Question 16

Bohr’s new postulates
what is an excited atom?

Answer 16

is the state of the atom after gaining a quantum of energy, through heating or electrical discharge

Question 17

why is the amount of energy required to transfer an electron between the different energy levels are not equal?

Answer 17

because the distance and the difference in energy between them are not equal

Question 18

why does the quanta required to transfer an electron from an energy level to another decreases as we go farther from the nucleus?

Answer 18

because the energy gap decreases as we go farther from the nucleus

Question 19

what happened despite the great efforts of Bohr to formulate his atomic model?

Answer 19

the quantitive calculations of his theory didn’t match all the experimental results

Question 20

advantages of Bohr’s atomic model

Answer 20

1) it explained the hydrogen spectral lines
2) it introduced the idea of quantized energy to determine the electron energy in different energy levels in the atom

Question 21

drawbacks of Bohr’s atomic model

Answer 21

1) it failed to explain the spectrum of any other element except hydrogen which is the simplest electronic system, where is contains one electron only
2) it considered the electron as a negative charged particle only and ignored its wave properties
3)it presumed that it is possible to determine precisely both location and speed of the electron at the same time
4)it described the electron as a particle moving in a circular planar orbit, later was proved that the hydrogen atom has three dimensional coordinates

Question 22

the dual nature of electron

Answer 22

the electron is a material particle which has wave properties

Question 23

Heisenberg’s uncertainty principle

Answer 23

the determination of both the velocity and position of an electron at the same time is practically impossible and this is subjected to the laws of probability

Question 24

Schrödinger’s equation

Answer 24

1) Determine the allowed energy levels
2)define the regions of space around the nucleus, where it is probable to find the electron in each energy level

Question 25

electron cloud

Answer 25

region f space around the nucleus, in which the electron probably exists in all directions and distances (dimensions)

Question 26

orbital

Answer 26

region within the electron cloud which has high probability of finding the electron