Electron arrangement

Question 1

How do you calculate the number of electrons in an atom of an element?

Answer 1

Electrons are the same as protons in an atom on element

Question 2

Define the first ionisation energy?

Answer 2

The energy needed to remove 1 electron from each mole of gaseous atoms to form 1 mole of gaseous 1+ ions.

Question 3

Write an equation for the first ionisation energy of lithium

Answer 3

Li_(g)→ Li(g)⁺ + e^-

Question 4

What does a large ionisation energy mean?

Answer 4

The bigger the ionisation energy the harder it is to remove an electron.

Question 5

Which element in period 2 is this?

Answer 5

Carbon.

The big jump between ionisation energies tells you when the next inner shell is being ionised. This means that Carbon is in group 4 as the big jump is between 4 and 5.

Question 6

Identify, from the Period 2 elements lithium to nitrogen, the element that has the largest
atomic radius.

Answer 6

Lithium

The other elements have more protons and as the electrons are all roughly at the same distance will be feeling a stronger force from the nucleus.

Question 7

Write an equation for the second ionisation energy of lithium:

Answer 7

Li_(g) ^{<span>+</span>} → Li_(g)²⁺ + e^-

Question 8

Write an equation for the third ionisation energy of lithium:

Answer 8

Li_{<span>(g</span>)} ²⁺ → Li_(g)³⁺ + e^-

Question 9

What is the general trend in first ionisation energies across a Period 2?

Answer 9

In general it increases because there are more protons in the nucleus as you cross the period but the extra electrons are in the same energy level.

Question 10

What 3 factors affect the size of ionisation energy?

Answer 10

Nuclear charge (number of protons)

Distance from nucleus

Shielding

Question 11

What is shielding (screening)?

Answer 11

A weakening of the attractive force of the nucleus for outer electrons caused by inner electron shells.

Question 12

How does nuclear charge affect ionisation energy?

Answer 12

The more protons in a nucleus the stronger the force of attraction for the outer electrons so the higher the ionisation energy

Question 13

What is the trend of first ionisation energies as you descend a group? Why?

Answer 13

It decreases. Electrons are easier to remove because they are further away from the nucleus and there is shielding (screening) from inner electrons.

Question 14

How does the energy level of an electron affect the ionisation energy?

Answer 14

The greater the energy level the further away the electron is from the nucleus. There is also more shielding from inner electrons. This means the force of attraction of the nucleus is less so the ionisation energy will be less too.

Question 15

Which element in Group II (Be, Mg, Ca, Sr, Ba) has the lowest ionisation energy?

Answer 15

Ba - bottom of group II. outer electron is furthest away from nucleus so experiences lowest force of attraction. There is also screening from inner shells.

Question 16

Why is there a drop between Mg and Al in period 3?

Answer 16

Aluminium’s outer electron is in a 3p subshell. Magnesium’s electron is in a 3s subshell. The p subshell is further away from the nucleus so is easier to remove, so the ionisation energy will be less. There is also more shielding on the p subshell (so easier to remove).

Question 17

Why is there a drop in ionisation energy between Phosphorus and Sulphur in period 3?

Answer 17

P 1s²2s²2p⁶3s²3p³

S 1s²2s²2p⁶3s²3p⁴

Phosphorus’ electron being removed is from a singly occupied p subshell. Sulphur’s electron is being removed from a p subshell containing two electrons. The repulsion between these two electrons (inter-electron repulsion) makes one of them easier to remove.

Question 18

What is a subshell?

Answer 18

a subshell is a smaller division of an energy level

Question 19

What are the different subshells called?

Answer 19

s, p, d, f

Question 20

What does an orbital look like?

Answer 20

an s orbital is a sphere of charge with the nucleus in the center. A p orbital looks like a dumbbell with the nucleus where the lobes meet. There are 3 p orbitals aligned to the x, y and z axis.

Question 21

What is an orbital? How many electrons can they hold?

Answer 21

An orbital is an area of space around the nucleus where you can find electrons. Each orbital can contain two electrons maximum,

Question 22

How many orbital are in each subshell? How many electrons are in each subshell?

Answer 22

s subshell - 1 orbital

p subshell - 3 orbitals

d subshell - 5 orbitals

s subshell - 1 orbital - so 1 x 2 = 2 electrons

p subshell - 3 orbitals - so 3 x 2 = 6 electrons

d subshell - 5 orbitals - so 5 x 2 = 10 electrons

Question 23

In what order do the first 36 electrons fill subshells?

Answer 23

1s

then 2s then 2p

then 3s then 3p

then 4s then 3d then 4p

Question 24

What is each block of the periodic table named after?

Answer 24

The subshell being filled in those elements.

So Chlorine is in p block as its outer electron structure is 3s² 3p⁷

Sodium is in s block as its outer electron structure is 3s¹

Question 25

Carbon has 6 electrons. What is the subshell notation?

Answer 25

1s²2s²2p²

Question 26

Neon has 10 electrons. What is the subshell notation?

Answer 26

1s²2s²2p⁶

Question 27

Potassium has 19 electrons. What is the subshell notation?

Answer 27

1s²2s²2p⁶3s²3p⁶4s¹

Question 28

Draw and write the electron configuration of gallium (Ga). Gallium has 31 protons

Answer 28

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p¹.

Question 29

Which electrons are lost first in d block ions?

Answer 29

When d-block elements form ions, the 4s electrons are lost first.

Question 30

Write the electronic structure for Fe³⁺

Answer 30

Fe is 1s²2s²2p⁶3s²3p⁶3d⁶4s²

so losing 3 outer electrons (4s lost before 3d) makes:

Fe³⁺ 1s²2s²2p⁶3s²3p⁶3d⁵

Question 31

What is the structure of Copper?

What is the structure of Cu²⁺?

Answer 31

Cu is 1s²2s²2p⁶3s²3p⁶3d¹⁰4s¹

Cu²⁺ is 1s²2s²2p⁶3s²3p⁶3d⁹

Remember 4s electrons lost before 3d!