Atomic structure and the periodic table

Question 1

Explain how you would plan an investigation to identify copper, magnesium and iron by comparing their reactivity.

Answer 1

• Place all the metals into separate beakers with the same volume of dilute acid
• Measure temperature change with a thermometer
• Copper will have no/little temperature change
• Magnesium will increase in temperature more than iron
• Order of: magnesium, iron copper
• Keep initial temperature of acid constant

Question 2

Why is it dangerous for sodium to come into contact with water?

Answer 2

The reaction would be very explosive as sodium is a very reactive G1 metal

Question 3

Explain why it’s better to separate metals in argon rather than in air.

Answer 3

Argon is inert (as it has a full outer shell). A metal could react with oxygen in the air after being separated.

Question 4

Why does cobalt form different coloured compounds?

Answer 4

It is a transition metal and has ions with different charges.

Question 5

Compare the physical and chemical properties of G1 and TM.

Answer 5

Physical:
- TM higher m.p whereas G1 lower m.p
- TM harder than G1 - G1 are soft metals
Chemical:
- TM less reactive than G1 - G1 very reactive
- TM form ions with different charges whereas G1 only forms +1
- TM form coloured compounds whereas G1 only form white/colourless compounds
- TM used as catalysts but G1 are not

Question 6

Identify the equipment used for fractional distillation.

Answer 6

Bunsen burner , (boiling) flask, fractionating column, thermometer , condenser with a water jacket, collection beaker

Question 7

Suggest how flammable mixtures should be safely heated during distillation.

Answer 7

Heat using a water bath.

Question 8

Explain the trend in reactivity of group 1 metals with water.

Answer 8

Reactivity increases down the group as the atom has more shells so forces of attraction between the outer electron and the nucleus are weaker as the outer shell is further away from the nucleus. Therefore, the outer electron is more easily lost.

Question 9

Explain why the RFM of chlorine is not a whole number.

Answer 9

It is averaged out by using isotopes.

Question 10

Describe observations when G1 react with water (increasing in reactivity down the group)

Answer 10

-> metal hydroxide and hydrogen formed
- Metal floats and melts into a ball getting smaller, eventually disappears
- May release a flame: lithium red, sodium orange, potassium lilac
- Effervescence (H2 gas)

Question 11

Give two reasons why Mendeleev put iodine in the same group as chlorine.

Answer 11

• Both react in similar ways as have similar properties
• Both diatomic

Question 12

Describe how the number of protons and electrons are used to place elements in the modern periodic table.

Answer 12

Elements are arranged in increasing atomic/proton number. The number of electrons determines the period the element is in as periods correspond to the number of occupied shells and group as groups are the number of electrons in an atoms outer shell.

Question 13

Explain why chlorine is more reactive than iodine.

Answer 13

Chlorine has a lower RMM so less shells. Therefore, chlorines outer shell is closer to the nucleus so there are stronger forces of attraction for an outer electron so an electron is more easily gained to complete the outer shell.

Question 14

How can you tell a solution is a mixture not a compound?

Answer 14

The elements/compounds are not chemically combined and are not in fixed proportions.

Question 15

Explain why b.p increases down G7.

Answer 15

Relative molecular mass increases. Intermolecular forces between molecules increase so a greater amount of energy required to overcome them.

Question 16

Compare the periodic table by Newlands, Mendeleev and the modern periodic table.

Answer 16

-Newlands: ordered in increasing atomic weight, didn’t leave gaps and some elements in groups didn’t have similar properties (law of octaves)
-Mendeleev: also arranged in increasing atomic weight but left gaps and predicted properties so elements in groups had same properties
-Modern: arranged in order of increasing atomic number with similar properties grouped together
-All ordered elements in groups

Question 17

Explain the difference in reactivity in group 1 and group 7.

Answer 17

Group 1 reactivity increases down the group, alkali metals have 1 electron in their outer shell so as move down group atom gains more shells so outer electron is more easily lost due to weak forces of attraction with the nucleus whereas group 7 reactivity decreases down the group. Halogens have 7 electrons in their outer shell so as move down group RMM increases and atom gains more shells so an outer electron is less easily gained due to weaker forces of attraction with an outer electron and nucleus.

Question 18

Why is a fume cupboard used for halogens?

Answer 18

They are toxic gases.

Question 19

Why was Mendeleevs table more widely accepted?

Answer 19

Predicted properties of missing elements. When the elements were discovered they matched the properties he predicted.

Question 20

Describe observations when G1 react with chlorine.

Answer 20

• Flame release
  -> Li crimson red Na orange K lilac
• White solid compound forms

Question 21

Describe observations when G1 react with oxygen

Answer 21

Metal oxides formed
Burn vigorously (may release a flame)

Question 22

What is atomic weight now known as?

Answer 22

Relative atomic mass

Question 23

Explain why alloys are harder than metals

Answer 23

Atoms are different sizes so the layers are distorted meaning the layers slide over each other less easily

Question 24

What do chemical reactions normally involve?

Answer 24

• always involve the formation of one or more new substances
• detectable energy change

Question 25

Describe how to separate rock salt into dry sand and pure crystals

Answer 25

• Grind mixture with pestle and mortar then add distilled water and mix with a glass rod
• Filter sand with filter paper and filter funnel (sand is insoluble) and leave to dry/ dry in a drying oven
• Pour remaining solution into an evaporating basin and gently heat until point of crystallisation
• Leave solution to cool and for crystals to form
• Filter and dry crystals with filter paper

Question 26

Give one reason why an element may not be immediately accepted in the periodic table

Answer 26

Must be peer reviewed

Question 27

Explain why argon does not form compounds in terms of electrons

Answer 27

Full outer shell of electrons as is in G0. Doesn’t need any more electrons to become stable so is inert.

Question 28

Explain why periodic tables placed iodine before tellurium but then Mendeleev swapped them around

Answer 28

Periodic tables initially ordered in strict increasing atomic weight and iodine has a lower atomic weight than tellurium. Mendeleev rearranged to put elements in groups with matching properties that reacted similarly