Ar, Atomic Strcuture, Nuclear Fusion

Question 1

Where is most of the mass of an atom concentrated?

Answer 1

The nucleus

Question 2

What are the relative charges and masses of protons, neutrons and electrons?

Answer 2

P - 1, +1
N - 1, 0
E - 1/2000, -1

Question 3

What does the mass number of an element tell you?

Answer 3

The total number of protons and neutrons in the nucleus

Question 4

What does the atomic (proton) number tell you?

Answer 4

The number of protons in the nucleus - this is the same for all atoms of the same element

Question 5

What are isotopes?

Answer 5

Isotopes are atoms of the same element with different numbers of neutrons

Question 6

What dictates the chemical properties of an element?

Answer 6

The number and arrangement of electrons

Question 7

Do isotopes have different chemical or physical properties and why?

Answer 7

Isotopes of the same element have the same chemical properties because they have the same configuration of electrons, but different physical properties (such as densities and rate of diffusion) because they often depend more on the mass of the atom

Question 8

What makes up most of the volume in an atom?

Answer 8

The electron shells

Question 9

How did John Dalton describe atoms?

Answer 9

Solid spheres

Question 10

How did John Dalton describe atoms?

Answer 10

Solid spheres

Question 11

What did JJ Thompson suggest?

Answer 11

The plum pudding model

Question 12

Describe the plum pudding model

Answer 12

A positively charged sphere with negative electrons embedded into it

Question 13

What is the Geiger-Marsden experiment?

Answer 13

Rutherford, Geiger and Marsden fired alpha particles at a thin sheet of gold

Question 14

What happened during the Geiger-Marsden experiment and what did this mean?

Answer 14

They expected most of the alpha particles to be deflected very slightly by the positive ‘pudding’ of the atom, but most particles travelled straight through the gold and a very small number were deflected backwards (more than 90 degrees) - this showed the plum pudding model was incorrect, and so Rutherford created the nuclear model of the atom

Question 15

What is the nuclear model?

Answer 15

• Tiny, positively charged nucleus at the centre of the atom where most of the mass is concentrated
• the nucleus is surrounded by a ‘cloud’ of freely orbiting negative electrons
• most of the atom is empty space

Question 16

How was Rutherford’s nuclear model modified?

Answer 16

• Mosley discovered that the charge of the nucleus increased from one element to another in units of one
• Rutherford then investigated further and discovered protons
• Chadwick discovered the neutron

Question 17

What 4 principles did Bohr propose in his model of the atom?

Answer 17

• electrons can only exist in fixed orbits, or shells, and not anywhere in between
• each shell has a fixed energy
• when an electron moves between shells, electromagnetic radiation is emitted or absorbed
• because the energy of the shells is fixed, the radiation will always have a fixed frequency

Question 18

What else did the Bohr model explain?

Answer 18

Why some elements (the noble gases) are inert - shells of an atom can only hold a fixed number of electrons, and an elements reactivity is due to its electrons. So when it has a full shell, it is stable and does not react

Question 19

Is only one atomic model in use?

Answer 19

No, scientists use whichever model is relevant to what they’re investigating

Question 20

What is the relative atomic mass (Ar)?

Answer 20

The average mass of an atom of an element on a scale where an atom on carbon-12 is 12

Question 21

What is the relative isotopic mass?

Answer 21

The mass of an atom of an isotope of an element on a scale where carbon-12 is 12

Question 22

What is the relative molecular/formula mass (Mr)?

Answer 22

The average mass of a molecule or formula unit on a scale where an atom of carbon-12 is 12

Question 23

What types of compounds are Mr used for?

Answer 23

Ionic or giant covalent

Question 24

Are Ar and relative isotopic masses usually whole numbers?

Answer 24

Ar is an average, so is not usually a whole number
Relative isotopic mass will always be a whole number

Question 25

What information can you get from a mass spectrometer?

Answer 25

Relative atomic mass, relative molecular mass, relative isotopic abundance and molecular structure

Question 26

Explain the 4 steps when a sample is squirted into a mass spectrometer

Answer 26

1. Vaporisation - the sample is turned into gas (vaporised) using an electric heater
2. Ionisation - the gas particles are bombarded with high energy electrons to ionise them. Electrons are knocked off of particles, leaving positive ions
3. Acceleration - the positive ions are accelerated by an electric field
4. Detection - the time taken for the positive ions to reach the detector is measured. This depends on an ion’s mass and charge - light, highly charged ions will reach the detector first, while heavier ions with a smaller charge will take longer. For each sample analysed a mass spectrum is produced

Question 27

What goes on the x and y axes of a mass spectrum?

Answer 27

The y axis gives the abundance of ions (often as a percentage). For an element, the height of each peak gives the relative isotopic abundance
The x axis units are given to a mass/charge ratio. Since the charge on ions is mostly 1+ you can often assume the x axis is simply the relative mass

Question 28

What are the 3 steps for calculating the Ar of an element from the mass spectrum?

Answer 28

1. For each peak, read the % relative isotopic abundance from the y axis and multiply it with the relative isotopic mass from the x axis to get the total mass for each isotope
2. Add up these totals
3. Divide by 100 (because percentages were used)

Question 29

What do you need to change about mass spectrum calculations if the relative abundance is not given as a percentage?

Answer 29

Divide by the total relative abundance instead of 100

Question 30

What is the formula for % relative isotopic abundance?

Answer 30

% relative isotopic abundance = (relative abundance/total relative abundance) x 100