Atomic Structure and the Periodic Table

Question 1

When is filtration used?

Answer 1

Used to separate an insoluble solid from a liquid.

Question 2

Describe filtration.

Answer 2

• place filter paper into the filter funnel
• pour mixture into the filter paper
• liquid passes through thetiny pores in the paper into the beaker
• solid cannot pass through the paper so it is trapped
• now the solid and liquid are seperated

Question 3

When is crystallisation used?

Answer 3

Used to separate a soluble solid from a liquid.

Question 4

Describe crystallisation.

Answer 4

• leave the solution for a couple of days then the water will evaporate
• this will leave behind crystals of the solid
• to speed up the process gently heat the solution
• be careful that the heating does not affect the chemical you are trying to crystallise, some chemicals are broken down by heating

Question 5

What is simple distillation used for?

Answer 5

-used to seperate a liquid from a solid if we want to keep the liquid

Question 6

Describe the simple distillation process.

Answer 6

• place our solution with the liquid and dissolved solid into the round bottom flask
• flask is connected to glass tube which is surrounded by a condenser
• cold water from the tap is continuously running through it keeping the glass tube cold
• start by heating the soltuion e.g. bunsen burner
• liquid starts to evaporate and turns into a vapour
• vapour rises up the glass tube and passes into the condenser
• vapour condenses and turns back into a liquid
• collect liquid in a beaker
• we are left with crystals of the solid in the flask

Question 7

What did the Ancient Greeks believe?

Answer 7

• everything is made up of atoms

- tiny hard spheres that cannot be divided

Question 8

What did scientists discover in 1897?

Answer 8

• atoms contain tiny negative particles
• electrons
• this shows that they aren’t spheres that cannot be divided
• they have an internal structure

Question 9

Alpha-scattering experiment

Answer 9

• take a piece of gold foil as it is only a few atoms thick
• fire alpha particles at the foil
• alpha particles have a positive charge
• most of the particles passed straight through showing that they were mainly empty space
• some were deflected, meaning the centre of the atom must have a positive charge which repelled the particles
• some bounced straight back, meaning the mass of the atom must be concentrated in the centre, informing us on the nucleus

Question 10

Niels Bohr

Answer 10

• electrons orbit the nucleus at specific distances

- his work agreed with the results of experiments of other scientists

Question 11

James Chadwick

Answer 11

• nucleus contains neutrons

- 1923

Question 12

Why do atoms have no overall charge?

Answer 12

The number of electrons is the same as the number of protons.
The positive charges on the protons are cancelled by the negative charges in the electrons.

Question 13

What is the radius of an atom?

Answer 13

0.1nm

1x10^-10m

Question 14

What is the radius of the nucleus?

Answer 14

1x10^-14 m

Question 15

What is an isotope?

Answer 15

Atoms of an element with different numbers of neutrons.

All atoms of the same element have the same number of protons.

Question 16

What are ions?

Answer 16

Atoms that have an overall charge. They have gained or lost electrons.

Question 17

What is relative atomic mass?

Answer 17

The average of the mass numbers of the different isotopes. It is weighted for the abundance of each isotope.

Question 18

Why is it called the periodic table?

Answer 18

Periodic means occurring at regular intervals.

Elements of similar properties occur at regular intervals.

Question 19

What did Dobereiner notice?

Answer 19

Noticed that elements with similar chemical properties often occurred in triads.
E.g. lithium, sodium and potassium all react rapidly with water.

Question 20

Newland’s Law of Octaves

Answer 20

• arranged the elements in order of increasing atomic weight

- he saw that every 8th element reacts in a similar way

Question 21

What was wrong with Newland’s Periodic table?

Answer 21

By always sticking to the same exact order of atomic weight, sometimes elements were grouped together when they had totally different properties.
His law wasn’t taken seriously by other scientists.

Question 22

Mendeleev’s Periodic Table

Answer 22

• started by arranging the elements in order of increasing atomic weight
• he would switch the order of specific elements so they fitted the patterns of the other elements in the same group
• he realised some elements had not been discovered, so he left gaps in the periodic table where he thought an element was missing
• he predicted the properties of the undiscovered elements based on other elements in the same group

Question 23

Why did scientists accept Mendeleev’s Periodic Table?

Answer 23

When the elements were discovered, they matched the properties that Mendeleev had predicted.

Question 24

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

Answer 24

In the MPT, the elements are arranged in order of atomic number.
When Mendeleev developed his table, protons had not been discovered.
The MPT has Group 0 (the noble gases).
These had not been fully discovered when Mendeleev published his table.

Question 25

What is the problem with ordering elements based on atomic weight?

Answer 25

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

Question 26

Noble gases

Answer 26

They are very unreactive because they all have a full outer energy level and are stable.

Question 27

Boiling points of noble gases

Answer 27

All lower than room temperature. | The boiling point increases as the relative atomic masses increase (going down the group)

Question 28

Metals

Answer 28

When metals react, they lose electrons to achieve a full outer energy level. They always form positive ions.

Question 29

Why do elements get more reactive as you move down Group 1?

Answer 29

The outer electron is less attracted to the nucleus and is easier to lose. This is because there is a greater distance between the negative outer electron and the positive nucleus. And the outer electron is shielded from the nucleus by the internal energy levels.

Question 30

How do the melting and boiling points of Group 7 elements change as we move the group?

Answer 30

Fluorine and chlorine are both gases at room temperature. The m.p/b.p points increase as you go down because their relative molecular mass increases. This means the molecules get bigger.

Question 31

What group 7 elements form when they react with non-metals?

Answer 31

Covalent compounds

Question 32

What do group 7 elements form when they react with other metals?

Answer 32

Ionic compounds.

Question 33

Why do Group 7 elements get less reactive as you go down the group? Compare fluorine with chlorine.

Answer 33

Chlorine gains an electron less easily than fluorine. This is because there is a greater distance between the outer electron and the positive nucleus. And there is more shielding by internal electrons. This reduces attraction between the outer electron and nucleus.