The Periodic Table

Question 1

During the 19th century, how did scientists attempt classify the elements in the periodic table?

Answer 1

They attempted to classify the elements based on their properties and atomic weights.

Question 2

In 1863 Newlands proposed which theory, and what did it state?

Answer 2

Newlands proposed his theory of octaves that stated, similar properties are repeated every eighth element.

Question 3

How did Newlands arrange the elements in his periodic table?
What was the main problem with Newlands’ table?

Answer 3

He arranged the 62 elements known at the time based on their atomic weights.
After calcium the properties did not match very well within the groups, so other scientists did not accept his ideas.

Question 4

In 1869 Mendeleev produced a better table, what was different about Mendeleev’s table compared to Newlands’ table?

Answer 4

He left gaps in his table for undiscovered elements, therefore the groups of known elements did have similar properties.

Question 5

Why did scientists accept Mendeleev’s ideas more readily?

Answer 5

He was able to predict the properties of the undiscovered elements.
When some of the undiscovered elements were discovered his predictions were proven right.

Question 6

When did scientists find out about protons and electrons?

Answer 6

At the start of the 20th century

Question 7

How are elements arranged in the modern periodic table?

What are the similarities between elements in the same group of the periodic table?

Answer 7

Elements are arranged in order of their atomic number and lined up in vertical groups.
Elements in the same group of the periodic table have the same number of electrons in their outer shell, which means they have similar chemical properties.

Question 8

What are the group 1 elements called and which two substances do they react readily with?

Answer 8

The alkali metals

Air and water

Question 9

Give four properties of the alkali metals?

Answer 9

They are soft solids at room temperature
They have low melting and boiling points that decrease going down the group
They have low densities - lithium, sodium and potassium float on water
They all have one electron in their outer shell, so in reactions they form ionic compounds in which their ions have a single positive charge

Question 10

What are the products when an alkali metal reacts with water?

Answer 10

Hydrogen gas and a metal hydroxide

Question 11

What is formed when an alkali metal reacts with a halogen?

Answer 11

Salts that are white or colourless crystals are formed.

Question 12

Give a word equation for the reaction between an alkali metal and a halogen.

Answer 12

Sodium + Chlorine => Sodium Chloride

Question 13

Why does reactivity increase going down group 1?

Answer 13

Going down the group there are more occupied energy levels and the atoms get bigger
As the atoms get bigger the electron in the outer shell is less strongly attracted by the nucleus.
This is because it is further away from the nucleus and the inner shells of the electrons shield it from the positive charge of the nucleus.
So the outer electron is easier to loose, so elements lower down the group are more reactive.

Question 14

Where are the transition elements located in the periodic table?

Answer 14

Between groups 2 and 3

Question 15

Give three chemical properties of the transition elements.

Answer 15

Except for mercury they have higher melting and boiling points than the alkali metals
They react slowly or not at all with air and water at ordinary temperatures
They form positive ions with various charges

Question 16

Give three properties and one use of transition elements and their compounds.

Answer 16

They are malleable and ductile and good conductors of heat and electricity.
Most are strong and dense
Compounds of transition metals are often brightly coloured
Many of them and their compounds are catalysts for chemical reactions

Question 17

What are the alloys of transition elements often used for?

Answer 17

Building materials

Question 18

What name is given to the elements in Group 7 of the periodic table?

Answer 18

The halogens

Question 19

Describe the melting and boiling points of the halogens?

Answer 19

They have low melting and boiling points that increase going down the group.

Question 20

Why does reactivity decrease as you go down Group 7?

Answer 20

Reactivity decreases going down the group, as the atoms get bigger an electron added to the outermost shell is less strongly attracted to the positive nucleus.
This because it is further away from the nucleus , and the inner shells of electrons shield it from the positive charge of the nucleus.
An electron is less easily attracted into the outer shell, so elements lower down Group 7 are less reactive.

Question 21

What will happen if a more reactive halogen is added a less reactive halogen in an aqueous solution of a halide compound?

Answer 21

The more reactive halogen is able to displace the less reactive halogen from the solution.