Electron structure

Question 1

First ionisation energy definition

Answer 1

The minimum energy needed to remove one mole of electrons from one mole of atoms in their gaseous state to form one mole of 1+ ions (also in their gaseous state)

Mg(g) —> Mg+(g) + e-

Question 2

Successive ionisation energies definition

Answer 2

the energy that is required to remove the electron one after the other

Question 3

Factors that affect ionisation energy

Answer 3

Factors that affect ionisation energy

Atomic radius
* as atomic radius increases, electrostatic force of attraction between nucleus and outer electrons decreases

Charge on the nucleus
- greater number of protons results in a greater force of attraction between outer electrons and the nucleus

Shielding
- electrons in the outer shell are repelled by electrons in inner shells
- this shielding affect reduces the attraction between the nucleus and outer electrons

Question 4

Ionisation energy across a period

Answer 4

Moving across a period the overall trend is that first ionisation energy increases, however there are exceptions
- nuclear charge increases as number of protons increases
- therefore increasing the attraction between the nucleus and outer electrons
- therefore the atomic radius also decreases across a period
shielding
- in elements from the same period, the electron is being removed from the same electron shell
- therefore the shielding effect is similar for each element

Question 5

The exceptions to the general trend of ionisation energy across a period

Answer 5

Third
- the third element in a period is in a higher energy subshell than the first and second
- therefore it takes less energy to remove the outer electron

Sixth
- the sixth element in a period’s outer subshell (p) has 4/6 electrons
- meaning one of the orbitals contains a pair of electrons which repel each other
- therefore it takes less energy to remove an electron than if they were in seperate orbitals

Question 6

First ionisation energy moving down a group

Answer 6

Moving down a group first ionisation energy decreases.

• moving down a group, the atomic radius increases, therefore the outer electron is further away from the nucleus
• the number of internal energy levels increase, therefore more shielding between the nucleus and the outer electrons
• therefore less energy is needed to remove the outer electron

(nuclear charge does increase, however it is offset by the previous factors)

Question 7

What do successive ionisation energies tell us about how electrons are arranged in an atom?

Answer 7

Gradual increase in ionisation energy
- each time an outer electron is removed, the remaining electrons in the outer shell are pulled slightly closer to the nucleus
- greater attraction between nucleus and outer electrons
- requires more energy to remove

Large increases in ionisation energy
- the next electron is in a lower energy shell which experiences much less shielding
- greater attraction between nucleus and outer electrons
- requires a lot more energy to remove an electron

Question 8

Using ionisation data to identify an element

Answer 8

-the number of removed electrons with gradually increasing ionisation energy before a large jump tells us the number of electrons in the outer shell of the element

Question 9

How does first ionisation energies for successive elements provide evidence for electron sub-shells?

Answer 9

Any large leaps in ionization energy indicate a transition between different subshells as removing an electron from a lower energy subshell requires more energy

Question 10

what is an electron at a level?

Answer 10

a cloud of negative charge

Question 11

the number of electrons that the first four quantum shells can hold

Answer 11

1st Shell 1s 2
2nd Shell 2s, 2p 2 + 6 = 8
3rd Shell 3s, 3p, 3d 2 + 6 + 10 = 18
4th Shell 4s, 4p, 4d, 4f 2 + 6 + 10 + 14 = 32

how to calculate:
2n^2 (where n is the quantum shell number)

Question 12

what is an orbital

Answer 12

a region within an atom that can hold up to two electrons with opposite spins

Question 13

shapes of s orbitals and p orbitals

Answer 13

s orbitals are spherical
p orbitals are dumbell shapes

Question 14

the number of electrons that occupy s, p and d-subshells

Answer 14

s subshell - 2
p subshell - 6
d subshell - 10

Question 15

rules for filling subshells

Answer 15

rules for filling subshells:
-orbitals in the lowest energy are filled first
-up to 2 electrons can be in the same orbital but they must have opposite spins
-if there is an orbital with the same energy (e.g s,p,d) put electrons into individual orbitals before pairing them, because electrons in the same orbital repel

Question 16

order to fill and write out subshells

Answer 16

order of filling
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10

order of writing:
1s^2 2s^2 2p^6 3s^2 3p^6 3d^10 4s^2

electron configuration is always written in the order of the electron shells, not the order of filling

Question 17

why is the 4s subshell filled before the 3d?

Answer 17

the energy of the 4s subshell is less than the energy of the 3d subshell
> and subshells are filled from smallest energy to largest

Question 18

exceptions to the order of filling subshells

Answer 18

chromium (24 e)
* expected: 1s^2 2s^2 2p^6 3s^2 3p^6 3d^4 4s^2
* actual : 1s^2 2s^2 2p^6 3s^2 3p^6 3d^5 4s^1

copper (29 e)
- expected: 1s^2 2s^2 2p^6 3s^2 3p^6 3d^9 4s^2
- actual : 1s^2 2s^2 2p^6 3s^2 3p^6 3d^10 4s^1

in these two cases the 4s subshell only has one electron so that the 3d subshell can be either half full or full

this is because the 3d subshell is more stable when it is either half filled or full

Question 19

Electronic configuration of ions

Answer 19

The same but taking into account it has lost/gained electrons

Question 20

How is the periodic table divided into blocks?

Answer 20

Four blocks - s (group 1&2), d (transition metals), p (non-metals) and f (not needed)

Each block is named after the subshell containing the highest energy electron for the elements in that block

Question 21

Shorthand electron configuration

Answer 21

Uses the nearest before noble gas and replaces the innter shells electron config.

e.g. sodium - 1s^2 2s^2 2p^6 3s^1
-closest noble gas = neon - 1s^2 2s^2 2p^6

can be represnted [Ne] 3s^1

Question 22

D-block elements shorthand electron configuration

Answer 22

In the case of d-block elements, we show the d-subshell in the shorthand electron config because electrons in the d-subshell can be involved in chemical reactions

Question 23

D-block elements electronic configuration of ions

Answer 23

-4s subshell fills before the 3d subshell because it has a lower energy
-Once the 4s subshell contains electrons, it now has a higher energy than the 3d subshell
-This means when d-block elements lose electrons the electrons are always lost from the 4s subshell before the 3d
g

Question 24

How does electronic configuration determine the chemical properties of an element?

Answer 24

It determines how readily it will react