Unit 1.2 Basic Ideas about Atoms (Electronic Structure, Ionisation and Spectra)

Question 1

How do electrons in an atom orbit the nucleus?

Answer 1

The electrons in an atom orbit the nucleus in ‘shells’ or ‘energy levels’

The first energy level can hold up to two electrons.

The second energy level can hold up to eight electrons.

Question 2

Energy levels are subdivided into ____________.

Answer 2

Energy levels can be subdivided into ‘orbitals’ which can each hold up to two electrons.

Question 3

What is the condition for the electrons to occupy the same energy level?

Answer 3

To occupy the same orbital, the two electrons must have opposite ‘spins’.

One must be ‘spin up’ and the other ‘spin down’.

Question 4

Define orbital.

Answer 4

A region of space within an atom that can hold up to two electrons with opposite spins.

Question 5

Why can the first energy level hold two electrons?

Answer 5

Because it contains only one orbital.

The orbitals in the first energy level fill before the orbitals of the second energy level.

Question 6

How are orbitals grouped together?

Answer 6

Inside energy levels, orbitals are grouped together in ‘subshells’.

The subshells are called:
s, p, d, f and g
and contain orbitals of the same name.

E.g. the 3x subshell is in the third energy level and contains s orbitals.

Orbitals in different subshells have different shapes.

Question 7

Describe the shape of the s orbital.

Answer 7

s orbitals are spherical.

Every energy level contains one s orbital.

Question 8

Describe the shape of the p orbital.

Answer 8

p orbitals have dumbbell shapes. The second and subsequent energy levels contain 3 p orbitals which have the same shape but point along different axes.

They can be labelled individually as px, py and pz.

Question 9

Describe the shape of the d, f, and g orbitals.

Answer 9

d, f and g orbitals have increasingly complex shapes

Question 10

Describe the arrangement of electrons in energy levels.

Answer 10

Electrons occupy certain fixed energy levels.

Each atom has its own unique set of energy levels which depend on the number of protons and electrons in the atom.

Energy levels in an atom can be numbered from 1 to infinity. 1 is the lowest energy level (closest to the nucleus) and energy level infinity corresponds to the energy of an electron which is not attracted to the nucleus at all.

Energy levels converge as they approach infinity.

Question 11

How many orbitals does the s subshell have?

Answer 11

one s-orbital

The s-subshell can hold 2 electrons

Question 12

How many orbitals does the p-subshell have?

Answer 12

three p orbitals.

The p subshell can hold 6 electrons

Question 13

How many orbitals does the d subshell have?

Answer 13

five d orbitals

The d subshell can hold 10 electrons

Question 14

How many orbitals does the f subshell have?

Answer 14

seven f orbitals

The f orbital can hold 14 electrons.

Question 15

Why must the 4s subshell be filled before the 3d subshell?

Answer 15

Since the different subshells have different energies and the energies of the different levels get closer together with increasing energy level number, the high energy sub-shells of some energy levels soon overlap with the low energy subshells of higher energy levels.

The 4s subshell is at a lower energy level than the 3d subshell, so, must be filled first.

Question 16

List the 3 rules which determine the way in which electrons fill the orbitals.

Answer 16

1. Electrons always fill the lowest energy orbitals first
2. Electrons never pair up in the same orbital until all orbitals of the same energy are singly occupied, and all unpaired electrons have parallel spin.
3. Only two electrons may occupy the same orbital and they must have opposite spin

Question 17

List the number of orbitals for each subshell.

Answer 17

n=1: 1s
n=2: 2s, 2p
n=3: 3s, 3p, 3d
n=4: 4s, 4p, 4d, 4f

Question 18

Tell me the electron configuration of Cr.

Answer 18

1s2, 2s2, 2p6,3s2, 3p6, 3d5, 4s1

Question 19

Tell me the electron configuration of Cu.

Answer 19

1s2, 2s2, 2p6, 3s2, 3p6, 3d10, 4s1

Question 20

In what order are the electrons removed during the process of making ions?

Answer 20

1. Remove outer shell electrons first
2. Remove p electrons first, then s-electrons and then d-electons
3. Remove paired electrons before unpaired electrons in the same subshell.

In most cases, these rules mean electrons are removed from the most recently filled orbital.

However, this is bot true for the elements in the d-block.

Although electrons go in to the 4s subshell before they go in to the 3d, when d-block elements form ions electrons are removed from the 4s subshell first and them from the 3d.

Question 21

What happens if we supply the atom with additional energy?

Answer 21

The electrons can use this energy to jump into higher energy levels.

Question 22

How is additional energy supplied to the atom?

Answer 22

The energy is provided in the form of light energy.

Question 23

What happens when an electron falls from a higher energy level to a lower energy level?

Answer 23

When an electron falls from a higher energy level to a lower energy level, it releases additional energy, again in the form of light energy.

Electrons can only move between energy levels by absorbing or emitting light with exactly the right energy.

Question 24

What does the amount of energy carried by a light wave depend on?

Answer 24

Its frequency and wavelength, hence its colour

Question 25

Tell me the properties of red light.

Answer 25

Red light has a low frequency and a long wavelength and is the lowest energy colour.

Question 26

Tell me the properties of violet light.

Answer 26

Violet light has a high frequency and a long wavelength and is the highest energy colour.

Question 27

What does the emission spectra show?

Answer 27

The light given out from electrons falling from higher energy levels to lower energy levels. They appear as a series of lines, with each line representing the energy gap between a combination of energy levels.

Question 28

What happens if white light is shone onto an atom?

Answer 28

If white light, containing all of the colours of the spectrum is shone onto an atom, the electrons will use only the colours with the exact amount of energy to allow them to jump to higher energy levels.

The rest of the colours will pass through unaffected.

The remaining spectrum (with black lines showing which colours have been absorbed) is called an absorption spectrum.

It is the reverse of an emission spectrum with the lines appearing in the same place.

Question 29

How can the exact energy gap between the energy levels be calculated?

Answer 29

Using the following formulae:

E = hf (where h = plank’s constant, f = frequency of light)
E = hc/f