Periodicity and group 2

Question 1

What does the atomic number tell us about an element?

Answer 1

Number of protons in an atom

Question 2

How is mass number calculated?

Answer 2

Number of protons + number of neutrons

Question 3

Define relative atomic mass

Answer 3

Average mass of all isotopes of an element compared to 1/12 the mass of am atom of carbon12

Question 4

What is an isotope of an element?

Answer 4

Different forms of the same element, containing the same number of protons but different numbers of neutrons. They still have the same chemical properties.

Question 5

Name the number of orbitals

Answer 5

1s2 2s2 2p6 3s2 3p6 4s2 3d10

Question 6

Does 3D or 4s have a higher energy?

Answer 6

3D

Question 7

What is an orbital?

Answer 7

A region around the nucleus that can hold up to two electrons

Question 8

What would be the relationship between 2 electrons in the same orbital in terms of their spin?

Answer 8

Have opposite spin as repel each other as both negative

Question 9

Explain why chromium does not fit the trend for electronic configuration

Answer 9

It only has one electron in its 4s orbital before filling 3D

Question 10

Explain why cooper does not follow the trend for electronic configuration

Answer 10

It only has one electron in its 4s orbital before 3d

Question 11

What are the two types of ionisation for a mass spectrometer? How do they differ?

Answer 11

1) electron impact- electron gun knocks odd one electron from each particle to form each 1+ ion
2) electron spray- sample dissolved in volatile solvent and injected through a fine needle which is attached to a high voltage, it gains a proton producing XH+ ions

Question 12

When would you use the different types of ionisation in a mass spec?

Answer 12

Electron impact is used for substances with a low formula mass
Electron spray is used for substances with a high molecular mass

Question 13

Describe how a time of flight mass spec works

Answer 13

Acceleration- positive ions attracted towards a negatively charged plate
Ion drift- ions pass through hole in plate, form a beam with constant kinetic energy, travel along tube to detector. Time of flight is therefore directly proportional to the square root of mass
Detection- positive ions pick up electrons, current flows m/z value and time of flight recorded. Largest current from most abundant ions

Question 14

Define first Ionisation energy

Answer 14

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions

Question 15

Explain the graph of first ionisation energy of group 3

Answer 15

Increases across group 3 because of increase in nuclear charge, decreased atomic radius and same electron shielding means more energy is needed to remove first electron.
Dips at Al because outer electron is in a 3p orbital which has a higher energy than 3s
Dips at S because one 3p orbital contains two electrons and there is a repulsion between the paired electrons

Question 16

Describes ionisation energy down group 2

Answer 16

Decreases because number of filled electron shells increases down the group so increased shielding so increases atomic radius so weaker force between electrons and nucleus

Question 17

How does reactivity with water change as you go down group 2?

Answer 17

Mg least
Ba most
Because outer electrons are further away from nucleus and more electron shielding so electrons are lost more easily

Question 18

Write an equation for the reaction of Ba and water

Answer 18

Ba + 2H2O -> Ba(OH)2 + H2

Question 19

Equation between Mg and steam

Answer 19

Mg + H2O -> MgO + H2

Question 20

What is the trend in hydroxide solubility down group 2?

Answer 20

Increases down the group
Mg(OH)2 is almost insoluble
Ba(OH)2 creates a strong alkaline solution

Question 21

What is the trend in sulphate solubility down group 2?

Answer 21

Decreases down group
MgSO4 is soluble
BaSO4 is insoluble

Question 22

Trend in melting point down group 2

Answer 22

Decreases because sea of delocalised electrons is further away from nucleus so weaker metallic bonds

Question 23

What is the trend in atomic radius down group 2

Answer 23

Increases as there are more occupied shells

Question 24

What is Ca(OH)2 used for

Answer 24

Neutralise soil

Question 25

What is Mg(OH)2 used for

Answer 25

Antacid to treat indigestion

Question 26

What is a use of BaSO4

Answer 26

Barium meals to outline gut in X-rays