A level Chemistry OCR A- Module 2

Question 1

Define isotope

Answer 1

Atoms of the same element with different number of neutrons and the same number of protons.

Question 2

Why do isotopes have the same chemical properties?

Answer 2

They have the same configuration of electrons.

Question 3

Why do isotopes have different physical properties?

Answer 3

Physical properties depend on the mass of the atom. They have the different masses.

Question 4

What is the relative mass of an electron?

Answer 4

1/2000

Question 5

What is the relative mass of a neutron?

Answer 5

1

Question 6

What is the relative mass of a proton?

Answer 6

1

Question 7

What is the mass number?

Answer 7

The total number of protons and neutrons in the nucleus of an atom.

Question 8

What is the atomic number?

Answer 8

The number of protons in the nucleus of an atom.

Question 9

What does Thomson’s model explain.

Answer 9

Atoms are not solid and indivisible, an atom contains even smaller, negatively charged particles- electrons

Question 10

What was JJ Thomson’s model called?

Answer 10

The plum pudding model- a positively charged sphere with negative electrons embedded in it.

Question 11

What does Rutherford’s model explain?

Answer 11

That the plum pudding model isn’t right; there’s a tiny positively charged nucleus at the centre of the atom surrounded by a ‘cloud’ of negative electrons.

Question 12

How did Ernest Rutherford prove his theory?

Answer 12

He conducted the famous gold foil experiment; they fired alpha particles (positively charged) at an extremely thin sheet of gold. Most of the alpha particles passed straight through the gold atoms and a small number were deflected backwards through more than 90*.

Question 13

Name the scientists who conducted the gold foil experiment?

Answer 13

Ernest Rutherford, Hans Geiger and Ernest Marsden.

Question 14

What modifications were made to Rutherford’s model?

Answer 14

jgv

Question 15

Describe the main features of Bohr’s model?

Answer 15

• Electrons only exist in fixed shells, nowhere in between
• Each shell has a fixed energy
• When an electron moves between shells electromagnetic radiation is emitted or absorbed
• Because the energy of shells is fixed, the radiation will have a fixed frequency

Question 16

What does Bohr’s model explain?

Answer 16

Some elements are inert- noble gases.

Shells of an atom can only hold fixed numbers of electrons, and that an element’s reactivity is due to its electrons.

Question 17

How is evidence used to accept or reject particular models?

Answer 17

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Question 18

Define the relative atomic mass

Answer 18

The weighted mean mass of an atom of an element compared to 1/12 the mass of a carbon-12 atom

Question 19

Define the relative isotopic mass

Answer 19

The weighted mean mass of an isotope compared to 1/12 the mass of an atom of carbon-12

Question 20

How do you calculate the relative isotopic mass of an element?

Answer 20

1. Multiply each relative isotopic mass by its % relative isotopic abundance and add up the results
2. Divide by 100

Question 21

How do you calculate the relative atomic mass from mass spectra?

Answer 21

1. Multiply each relative isotopic mass by its relative abundance and add up the results
2. Divide by the sum of the relative abundances

Question 22

Define relative molecular mass

Answer 22

The