Grp2, Ionisation Enthalpy, Charge Density

Question 1

Define first ionisation enthalpy of an element

Answer 1

The amount of energy needed to remove one electron from every atom in one mole of separate, gaseous atoms of the element

Question 2

What happens to the 1st ionisation enthalpy values going across a period?

Answer 2

They generally increase

Question 3

Why do 1st ie values generally increase across a period?

Answer 3

Going across a period, more protons are being added to the nucleus. The atoms also have more electrons, but these are going into the same shell so don’t shield each other from the extra positive charge in the nucleus. So the outer electron (that is being removed) is attracted more strongly by the nucleus, hence more energy is required to remove it.

Question 4

Do group 1 elements have the highest or lowest 1st ie values?

Answer 4

Lowest - meaning its easy for them to lose an electron, hence they are very unreactive
(Opposite applies to noble gases)

Question 5

Why is there a dramatic decrease in 1st ie values between Ne—>Na & Ar—>K?

Answer 5

Change in period, therefore there’s an increased distance between the nucleus and outer shell electron, this means more shielding

Question 6

What happens to the 1st ie values down the group?

Answer 6

They decrease down the group (outer electron requires less energy to remove)

Question 7

Why do the ie values decrease down the group?

Answer 7

Going down the group, each atom has more protons in its nucleus, but there is an extra shell of electrons each time, which shields the outer electron from the nuclear charge. And the outer electron is further from the nucleus. So overall the attraction from the nucleus is weaker, hence less energy is needed to remove the electron.

Question 8

Do the successive ionisation enthalpies increase or decrease?

Answer 8

The successive ionisation enthalpies increase always

Question 9

Why do the successive ionisation enthalpies always go up?

Answer 9

Once an electron has been removed from an atom, the same number of protons in the nucleus are now holding fewer remaining electrons so the remaining electrons have greater attraction, meaning the next electron requires more energy to be removed, and so on

Question 10

Why are there sharp rises in successive ionisation enthalpies values?

Answer 10

The big jumps come from every time an electron is taken from the next shell in (outside in), the electron(s) in the outer shell are relatively easy to remove, then there’s a massive jump in ie value as the electron in the next shell in is MUCH closer to the nucleus and MUCH less shielded, therefore there is a greater attraction and more energy is required to remove it

Question 11

What type of bonding will group 2 element do?

Answer 11

Ionic (they lose an electron/s to form positive ionic compounds)

Question 12

Why do the g1 & 2 elements get more reactive down the group?

Answer 12

It takes less energy for the atoms to lose their outer shell electrons bc:
- more shells
- outer electrons are further from the nucleus (weaker attraction from nucleus)
- more shielded by inner shells
- less energy needed to lose electrons

Question 13

Which of the corresponding group 1/2 elements is more reactive & why?

Answer 13

Each group one element is more reactive then its corresponding graph 2 element because it takes more energy to lose 2 electrons rather then just one

Question 14

Which 3 factors affect ie values?

Answer 14

• distance of the electron from the nucleus
• shielding by inner electrons
• number of protons in the nucleus

Question 15

True a false: as you go across a period atomic radius increases so 1st ie decreases

Answer 15

False - as you go acrossthe atomic radius decreases, the number of protes increases so it actually becomes harder to remove the outermost electron

Question 16

As you go across a period, does the atomic radius increase or decrease?

Answer 16

The atomic radius decreases across the period. All the cuter electrons are in the same energy level so approx. The same distance from the nucleus. However as you go across there are mere protons so a stronger force of attraction

Question 17

Describe and element to compare the thermal stability of MgCO3 and CaCO3 and give the expected observations. Explain this difference using charge density

Answer 17

A fixed amount of carbonate is heated and the gas given off passes down a delivery tube and is bubbled through limewater. MgCO3 is least thermally stable so the limewater would turn cloudy more quickly than the CaCO3. Mg2+ is smaller than Ca2+ so has a higher charge density and polarises the carbonate ion more readily so it’s less thermally stable

Question 18

What do group 2 metals produce when they react with water?

Answer 18

Metal hydroxide &hydrogen

Question 19

What’s the trend down the group for atomic radius & why (group 2)?

Answer 19

Atomic radius increases down each group bc electrons in shells further from nucleus

Question 20

What’s the trend in ionic size down the group & why?

Answer 20

Increases down the group, nuclear charge exceeds the electronic charge

Question 21

What do you get when group 2 metals burn in oxygen?

Answer 21

Solid white oxides

Question 22

What happens when group 2 metals react with water?

Answer 22

They form metal hydroxides which dissolve & turn the solutions strongly alkaline

Question 23

What’s the trend in solubility of metal hydroxides down group 2?

Answer 23

Hydroxides get more soluble down the group ( therefore oxides form more strongly alkaline solutions ↓ the group)

Question 24

Why do s block metals have low first ie values compared to other elements in the same period?

Answer 24

They have relatively low nuclear charges

Question 25

what’s the difference in solubility trends for singly charged neg ions (e.g OH) & doubly charged neg ions (e.g CO3) down group 2?

Answer 25

singly charged neg ions increase in solubility, doubly charged neg ions decrease down the group

Question 26

what’s an alternative term for describing compounds with very low solubilities (like magnesium hydroxide)?

Answer 26

sparingly soluble

Question 27

What is thermal decomposition?

Answer 27

thermal decomposition is when a substance breaks down when heated

Question 28

What do g2 elements decompose to form?

Answer 28

the oxide and carbon dioxide

Question 29

If a substance takes lots of heat to break down, is is more or less thermally stable than a substance that takes a little heat to break down?

Answer 29

more heat req to break down = more thermally stable

Question 30

how does thermal stability vary down g2?

Answer 30

thermal stability increases down the group

Question 31

why does thermal stability increase down g2?

Answer 31

carbonate ions are large anions and can be made unstable by the presence of a cation (such as a g2 metal ion), the cation draws the electrons on the carbonate ion towards itself (polarises it). this distorts the carbonate ion, the greater the distortion, the less stable the carbonate ion.
large cations cause less distortion than small ones, as they have a lower charge density. so the further down the group, the larger the cations, the less distortion caused and the more stable the carbonate anion