C2: The Periodic Table

Question 1

Why is the periodic table called the periodic table?

Answer 1

Periodic - occurring at regular intervals.
In the table, elements with similar properties occur at regular intervals.

Question 2

Why do elements in the same groups react in similar ways?

Answer 2

They have the same number of electrons on their outer shells.

Question 3

Describe Dobereiner’s Triads

Answer 3

Dobereiner noticed elements with similar properties occurred in threes.
From this, scientists began to wonder whether elements could be arranged in a logical order.

Question 4

Describe Newlands’ Octaves

Answer 4

Newlands arranged elements in order of increasing atomic weight, and noticed that every 8th element reacts in a similar way.

Question 5

What are the problems with Newlands’ octaves?

Answer 5

By always sticking to the exact order of atomic weight, sometimes elements were grouped together when they had very different properties, meaning his law was not taken seriously by other scientists.

Question 6

Describe Mendeleev’s table

Answer 6

He started by arranging all the elements in order of increasing atomic weight.
He then switched the order of specific elements, so they fit the pattern of the same group.
He then realised that some elements had not been discovered, so he left gaps in his periodic table where he thought an element was missing.
He also predicted the properties of undiscovered elements based on the other elements in the same groups. These were discovered several years later and matched his predictions. Because of that, other scientists now accepted that his table was correct.

Question 7

What are the differences between the modern periodic table and Mendeleev’s periodic table?

Answer 7

The elements are arranged in order of atomic number ( increasing number of protons) - when Mendeleev developed his table, protons had not been discovered, so he ordered the elements in order of increasing atomic weight.
Modern table has noble gasses - which were not fully discovered when Mendeleev published his table.

Question 8

What is the problem with ordering elements in order of atomic weight?

Answer 8

Elements can appear in the wrong order due to the presence of isotopes.

Question 9

What are the properties of Group 0 elements?

Answer 9

Inert - highly unreactive
Have a full outer shell
Extremely low b.p. (lower than room temp) - all gasses

Question 10

Why are noble gasses so unreactive?

Answer 10

All noble gasses have full outer energy levels, meaning they are stable and will not react.

Question 11

Where are the metals found in the periodic table?

Answer 11

Left and the centre of the table (squiggly line down from boron)

Question 12

How can metals be divided?

Answer 12

Left side - highly reactive metals
Centre - less reactive transition metals

Question 13

How do metals react?

Answer 13

Lose electrons to form a full outer shell.
Giving them the same electronic structure as a group 0 element. (?)

Question 14

What ions do all metals form?

Answer 14

Positive ions.

Question 15

What are the properties of Group 1 metals (alkali metals)?

Answer 15

All have 1 outer electron in their outer shell.
Soft
Highly reactive - reactivity increases going down the group
Low density

Question 16

How do the alkali metals react with oxygen?

Answer 16

React rapidly with oxygen to form a metal oxide.

Question 17

How do the alkali metals react with chlorine?

Answer 17

Rapidly, form metal chloride e.g. lithium chloride (LiCl)

Question 18

How do alkali metals react with water?

Answer 18

React rapidly with water, with increasing reactivity going down the group.
We can see effervescence (fizzing) - gas (H) is produced.
Universal indicator turns purple as an alkaline solution is formed.
Metal moves around
Metal floats.
Flame - potassium
Produce metal hydroxides + hydrogen

Question 19

Why do alkali metals get more reactive down the group?

Answer 19

There is a greater distance between the negative outer electron and the positive nucleus, resulting in less attraction between the two. This means that the outer electron is easier to lose.

Question 20

What are the properties of Group 7 elements (Halogens)?

Answer 20

Have 7 electrons in their outer shell
Diatomic
M.p. and b.p. increases going down the group
Molecules get bigger going down the group
Form covalent compounds when reacting with other non-metal atoms
All have a 1- charge.
A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.

Question 21

Why does the reactivity of halogens decrease going down the group?

Answer 21

Going down the group, elements have more outer shells, and therefore more nuclear shielding (also greater distance between outer energy level and nucleus). This means that it is harder for the positive nucleus to attract a negative electron to form a full outer shell, and therefore results in a lower reactivity.

Question 22

Describe how a more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt

Answer 22

e.g. sodium bromide + fluorine

Question 23

What are the properties of transition metals?

Answer 23

Dense