C2 The Periodic Table

Question 1

How and why is the modern periodic table different from Mendeleev’s?

Answer 1

In the modern periodic table, elements are arranged in order of atomic (proton) number. Back then protons hadn’t been discovered yet so Mendeleev ordered the elements in his table in order of atomic mass. However this meant that elements could be in the wrong order due to the presence of isotopes.

Also the modern periodic table contains group 0 (noble gases), which hadn’t been discovered during Mendeleev’s time.

Question 2

How did Mendeleev develop the first modern periodic table?

Answer 2

He arranged all the elements in increasing atomic weight, however he would switch the order of some elements so they fitted the same patterns of other elements in the same group. He also left gaps in his table for undiscovered elements. Several years later new elements were discovered and they matched the properties that Mendeleev predicted.

Question 3

Which scientist developed the first modern periodic table?

Answer 3

Dimitri Mendeleev

Question 4

Why was Newlands’ law of Octaves disregarded by other scientists?

Answer 4

By always sticking to atomic weight, some elements grouped together had totally different properties

Question 5

What was Newlands’ law of Octaves?

Answer 5

He arranged elements in increasing atomic weights and saw that every 8th element reacted in a similar way.

Question 6

What was Johann Döbereiner’s theory of “Triads”?

Answer 6

• He thought that elements with different properties occurred in threes.

e.g. Sodium Lithium and Potassium all react rapidly
with water.
Or Chlorine Bromine and Iodine were all reactive
non metals

Question 7

Give 3 uses of transition metals

Answer 7

Iron - mixed with other elements to make steel

Copper - Electrical wires, water pipes

Gold - Malleable and shiny

Question 8

What is the only transition metal that is a liquid at room temperature?

Answer 8

Mercury

Question 9

Are transition metals more or less reactive than group 1 metals

Answer 9

Much less

Question 10

Do transition metals have low or high densities?

Answer 10

High

Question 11

Do transition metals have low or high melting and boiling points?

Answer 11

High

Question 12

Are transition metals hard or soft?

Answer 12

Hard

Question 13

Describe the properties of the transition elements

Answer 13

• Hard and strong (iron)
• High melting and boiling points
  ( except mercury which is a liquid at room temp)
• High densities
• Not very reactive; much less than group 1
• Form ions with different charges
• Form coloured compounds
• Can be used as catalysts
• Malleable

Question 14

Cl2 + 2KBr ——– 2KCl + Br2

[ What type of reaction is this? ]

Answer 14

A displacement reaction, a more reactive halogen is displacing a less reactive one from an aqueous solution

Question 15

Explain why reactivity decreases down group 7

Answer 15

There’s a greater distance from the nucleus down the group, and the outer electrons are shielded by the internal shells. This means that there is less attraction to the positive nucleus, and the outer energy level is unlikely to receive an electron.

(Why Cl2 is more reactive than F2)

Question 16

What is a displacement reaction?

Answer 16

A more reactive element displacing “pushing out” a less reactive element from a compound

Question 17

“Reactivity _______ down group 7”

[Fill in the blank}

Answer 17

Decreases

Question 18

Are group 7 metals toxic?

Answer 18

Yes

Question 19

Do group 7 elements have high or low melting and boiling points?

Answer 19

Low

Question 20

Are group 1 metals good or poor conductors of electricity?

Answer 20

Good

Question 21

Describe the properties of the Halogens

Answer 21

• Toxic
• Non metal
• Poor conductors of heat and electricity
• Diatomic (bonded covalently)
• Very reactive
• Reactivity decreases down the group
• Low melting and boiling points

Question 22

What is electron shielding?

Answer 22

An outer electron’s attraction to the nucleus being reduced due to a shielding effect from the inner shells

Question 23

Explain why reactivity increases down group 1

Answer 23

As you go down the group, the atoms get larger, and the outermost electron experiences less electrostatic attraction towards the positive nucleus as the distance between the outer electron and nucleus increases.
The outer electron also experiences an electron shielding effect.

Question 24

Do group 1 metals have high or low densities?

Answer 24

Low

Question 25

Are group 1 metals soft or hard?

Answer 25

Soft

Question 26

Do group 1 metals have high or low melting and boiling points?

Answer 26

Low

Question 27

Why are the group 1 metals stored in oil?

Answer 27

It stops them from reacting with moisture in the air

Question 28

Describe properties of the group 1 alkali metals

Answer 28

• Very reactive
• Low densities
• Soft
• Low melting and boiling points
• React vigorously with water and halogens
• Good conductors of electricity and heat

Question 29

Name properties of the noble gases

Answer 29

• Highly unreactive
• Full outer shells
• Monatomic

Question 30

Explain, in terms of electronic structure, why fluorine is the most reactive element in group 7 (3)

Answer 30

• Fluorine is the smallest atom
• And therefore experiences the smallest electron
  shielding effect between the nucleus and outer shell
• So it can gain an electron to its outer shell more
  easily

Question 31

What did Niels Bohr discover?

Answer 31

That electrons orbit the nucleus in energy levels (shells)

Question 32

Explain how James Chadwick’s work on the atom led to a better understanding of isotopes (3)

Answer 32

• Chadwick proved the existence of neutrons
• Isotopes have the same proton number but a
  different neutron number
  (Improving understanding of atoms)

Question 33

What happens to the melting point as you move down group 7?

Answer 33

It increases

Question 34

What are the states of all the halogens at room temperature?

Answer 34

Fluorine - Gas
Chlorine - Gas
Bromine - Liquid
Iodine - Solid
Astatine - Solid

Question 35

What does iodine form when heated?

Answer 35

A purple vapour

Question 36

What happens to the boiling point of each noble gas as you go down the group?

Answer 36

It increases

Question 37

What are the properties of non metals?

Answer 37

• Form negative ions
• Brittle
• Poor electrical and thermal conductors
• Low melting and boiling points

Question 38

How did knowledge of protons and electrons allow chemists to place elements in the correct order? (3)

Answer 38

• Number of protons = number of electrons
• Number of shells gives the period
• Reactions/chemical properties depend on outer
  electrons

Question 39

Why did many chemists disagree with Mendeleev’s table in 1869?

Answer 39

• It had metals and non metals in the same group
• Group 1 contained copper and silver (were unreactive)
• Mendeleev left gaps (many chemists believed that there
  were no more elements to discover)
• Mendeleev reversed the order (for some elements)

Question 40

How did Mendeleev know that some elements remained undiscovered?

Answer 40

When elements were arranged consecutively they would be in the wrong groups/ properties wouldn’t correspond

Question 40

How did Mendeleev know that some elements remained undiscovered?

Answer 40

When elements were arranged consecutively they would be in the wrong groups/ properties wouldn’t correspond

Question 41

Describe what would be seen in a reaction between sodium and chlorine

Answer 41

• Flame
• (white) solid forms
• colour of gas / chlorine
  disappears / fades