Arrangement of electrons In Atoms

Question 1

Define energy level.

Answer 1

Energy level is the fixed/discrete amount of energy of an electron.

Question 2

Define ground state.

Answer 2

The ground state is when all electrons are in the lowest available energy level-most stable state of an atom.

Question 3

Define excited state.

Answer 3

An excited state occurs when electrons absorb enough energy to be promoted to higher energy levels - it is an unstable state and electrons release energy to drop back down.

Question 4

Give two ways electrons in an atom can be excited.

Answer 4

Heating the element.

Passing an electric current through the element.

Question 5

What is an atomic/line emission spectrum?

Answer 5

An atomic emission spectrum is a series of coloured lines that correspond to the specific frequencies of light emitted when electrons in an element are excited.

Question 6

Explain how the visible line spectrum of hydrogen arises and proves the existence of energy levels.

Answer 6

Ground State: Electron n=1.
Element heated-excited state-promoted to level greater than n=2
Temporary and unstable state falls back to n=2.
This energy is emitted as a photon of light of definite frequency equal to the difference between the energy levels. This frequency shows as a particular colour on the emission line spectrum.

Question 7

Formula for energy/frequency of emitted photon.

Answer 7

E2 - E1 = hf

Question 8

What name is given to the visible region of frequency? Which energy level do they drop to?

Answer 8

The Balmer series. All drop to energy level n=2.

Question 9

What name is given to the invisible infra-red region? What level do they fall to?

Answer 9

Paschen Series. All drop to energy level n=3.

Question 10

What name is given to the invisible ultra-violet region? What level do they fall to?

Answer 10

Lyman Series. All drop to energy level n=1.

Question 11

Why is there no yellow line in the hydrogen emission spectrum?

Answer 11

There is no corresponding electron transition in hydrogen that would produce light of frequency that gives a yellow colour.

Question 12

What are flame tests? Why is it useful?

Answer 12

Heating an element in a bunsen burner will cause that element to produce a characteristic colour.
The element can therefore be identified.

Question 13

Give two reasons why different elements have different atomic emission spectra.

Answer 13

1. Different metals have different transitions between their energy levels.
2. Different metals have different number of electrons.

Question 14

List and explain briefly, three uses of a knowledge of energy levels in everyday life.

Answer 14

• Atomic Absorption Spectrometry (AAS) If white light is passed through an element sample certain light frequencies will be absorbed. Same lines as a line spectrum but they are black marks on the full spectrum.
• Sodium streetlights use sodium vapour in an excited state.
• Fireworks use particular elements to give off their characteristic colours.

Question 15

The Heisenberg Uncertainty Principle.

Answer 15

It is not possible to ascertain both the position and the momentum of an electron in an atom simultaneously.

Question 16

Define energy sub level.

Answer 16

A group of atomic orbitals that all have the same energy.

Question 17

Define dual wave particle nature.

Answer 17

Light and matter exhibit properties of both waves and particles.

Question 18

Define atomic orbitals.

Answer 18

The region in space around the nucleus of an atom in which electrons are likely to be found.

Question 19

Aufbau principle

Answer 19

Electrons occupy the lowest available energy level.

Question 20

Pauli exclusion principle.

Answer 20

No more than two electrons can occupy an orbital, and this they can only do if they have opposite spin.

Question 21

List three uses of AAS

Answer 21

• Identifying elements present in distant stars.
• Detecting the presence and concentration of heavy metals in water.
• Detecting gunshot residue on clothes in forensics

Question 22

What was Bohr’s model of an atom?

Answer 22

• An atom consists of a small dense area called the nucleus.
• Electrons are tiny particles that revolve around the nucleus in fixed orbits.
• An electron in any one orbit has a definite amount of energy.

Question 23

Describe four limitations of Bohr’s theory.

Answer 23

1. Energy levels were found to consist of further sub levels.
2. Bohr’s explanation only worked for hydrogen emission spectrum and failed to explain many of the lines in other emission spectra.
3. Electrons were found to have properties of particles and waves.
4. The exact position and velocity of an electron cannot be measured at the same time so they cannot be described as travelling in fixed paths.

Question 24

Characteristics of s-orbital and s-sub level.

Answer 24

There is one s-orbital in a s-sub level.
Each s-orbital can hold two electrons.
Therefore an s-sub level can hold two electrons.
S-orbital spherical in shape.

Question 25

Characteristics of p-sub level.

Answer 25

There are three p-orbitals in each p-sub level.
Each p-orbital can hold two electrons.
Therefore a p-sub level can hold six electrons.
P-orbital dumb-bell in shape.

Question 26

Characteristics of d-orbital.

Answer 26

There are 5 d-orbitals in a d-sub level.
Each d-orbital can hold two electrons.
Therefore a d-sub level can hold 10 electrons.
D-orbital complex in shape.

Question 27

Give two differences between an atomic orbit and an atomic orbital.

Answer 27

Orbit-Electrons travel in fixed paths.
Orbital-Electrons have wave properties, has a high probability of being found there.
Orbit-Has a maximum capacity of 2, 8, 18 electrons.
Orbital-Has a maximum capacity of 2 electrons.

Question 28

Give two differences between the 4s orbital and the 3p orbital.

Answer 28

The electron in the 4s orbital has a greater energy than the electron in the 3p orbital.
The electron in the 4s orbital has a high probability of being found within a spherical shape.
The electron in the 3p orbital has a high probability of being found within a dumb-bell shape.

Question 29

State Hund’s Rule.

Answer 29

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

Question 30

Write the s, p configuration of copper and chromium.

Answer 30

Copper: 1s(2) 2s(2) 2p(6) 3s(2) 3p(6) 4s(1) 3d(10)
Chromium: 1s(2) 2s(2) 2p(6) 3s(2) 3p(6) 4s(1) 3d(5)

Question 31

Give one piece of evidence for the existence of energy levels.

Answer 31

Atomic emission spectrum

Question 32

Describe how to carry out a flame test.

Answer 32

Using a platinum needle hold the metal salt to be tested into the hottest part of the bunsen burner flame and note the colour observed. Between each new metal salt clean the platinum needle by dipping it in hydrochloric acid.

Question 33

Colour for lithium.

Answer 33

Crimson.

Question 34

Colour for sodium.

Answer 34

Yellow.

Question 35

Colour for potassium.

Answer 35

Lilac.

Question 36

Colour for barium.

Answer 36

Green.

Question 37

Colour for strontium.

Answer 37

Red.

Question 38

Colour for copper.

Answer 38

Blue-green