Electron configuration + ionisation energy

Question 1

How are electrons arranged in an atom?

Answer 1

Electrons are arranged in principle energy levels which are split into sub-shells which are split into orbitals.

Question 2

what is an electron orbital?

Answer 2

• an area within an atom where there is high probability of finding an electron
• each orbital has a 3d shape

Question 3

what are the electron sub-shell?

Answer 3

s
p
d
f

Question 4

what are s- orbitals?

Answer 4

• spherical
• every energy level contains one
• s -orbitals can hold 2 electrons

Question 5

what are p -orbitals?

Answer 5

• dumbbell shaped
• only in energy levels 2 or above
• there are 3 in each energy level so 3 x 2 = 6
• they can hold up to 6 electrons

Question 6

what are d- orbitals?

Answer 6

• complex/cross shaped
• in energy levels three or above
• there are 5 in each level so 5x2= 10
• they can hold up to 10 electrons

Question 7

what are f- orbitals?

Answer 7

they can hold up to 14 electrons ( 5 orbitals)

Question 8

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

Answer 8

4s orbital have electrons which have slightly less energy than the electrons in 3d

Question 9

In what order does an atom fill up its sub-shells?

Answer 9

An atom fills up the sub-shells in order of increasing energy
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶

Question 10

why are the electronic structures of d-block elements different?

Answer 10

Conventionally we say that 4s fills before 3d and so we write them in that order.
If you look at the electronic structures below you will see both chromium and copper have an unusual arrangement in having a half-filled 4s sub-shell.
You will also see that when d-block elements form ions they lose the 4s electrons first.
Cr - 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵
Cu - 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

Question 10

What is the electron configuration of Fe³+?

Answer 10

1s² 2s² 2p⁶ 3s² 3p⁶ 4s⁰ 3d⁵
It loses 3 electrons.
First it loses its two 4s electrons and then it loses one 3d electron.

Question 11

what is the first ionisation energy?

Answer 11

the energy required to remove one mole of electrons from one gaseous mole of atoms of an element to form one mole of gaseous 1+ ions.

Question 12

general equation for the first ionisation energy?

Answer 12

X(g) –> X+ (g) + e-

Question 13

what are the main factors that affect ionisation energy?

Answer 13

• nuclear charge
  -distance from nucleus
• shielding
  -orbitals

Question 14

how does nuclear charge affect the ionisation energy?

Answer 14

As the charge increases the ionisation energy increases. This is because the number of protons increase.

Question 15

How does atomic radius ( distance from the nucleus) affect ionisation energy?

Answer 15

As the distance between the nucleus and the highest energy electron increases, the ionisation energy decreases.

Question 16

How does shielding affect ionisation energy?

Answer 16

Electrons are negatively charged so their inner shell electrons repel the outer shell electrons. This repulsion is called the shielding effect. As the shielding increases the ionisation energy decreases.

Question 17

How do orbitals effect ionisation energy?

Answer 17

Two electrons in the same orbital experience some repulsion which offsets the attraction from the nucleus so paired electrons can be removed much more easily.

Question 18

why are successive ionisation energies always larger than first ionisation energies?

Answer 18

• The second ionisation energy of an element is always bigger than the first ionisation energy.
• When the first electron is removed a positive ion is formed.
• The ion increases the attraction on the remaining electrons and so the energy required to remove the next electron is larger.

Question 19

How are ionisation energies linked to electronic structure?

Answer 19

As the number of electrons removed from an element increases, eventually an entire shell of electrons will be removed.
The electron in the next shell will require much greater energy to be removed as it is much closer to the nucleus and has less shielding.

Question 20

Why has helium the largest first ionisation energy?

Answer 20

Its first electron is in the first shell closest to the nucleus and has no shielding effects from inner shells.
Helium has a bigger first ionisation energy than hydrogen as it has one more proton.

Question 21

how does first ionisation energy change down a group?

Answer 21

it decreases down a group because the atomic radius increases so shielding increases

Question 22

Has does first ionisation energy change across a period?

Answer 22

It increases across the period as the atomic radius decreases and the nuclear charge increases.
There is also similar shielding.

Question 23

Why is there a small drop in first ionisation energy from Mg to Al?

Answer 23

• Al is starting to fill a 3p sub shell, whereas Mg has its outer electrons in the 3s sub shell.
• The electron in the 3p sub shell is further from the nucleus, is higher in energy and is also slightly shielded by the 3s electrons.
• This makes the 3p electron slightly easier to remove.