Topic 1- Atomic Structure

Question 1

What does symbol Z mean?

Answer 1

Proton/atomic number

Question 2

What does symbol A mean?

Answer 2

Mass number

Question 3

Define relative isotopic mass

Answer 3

The mass of an isotope relative to 1/12th of an atom of carbon 12

Question 4

Define relative atomic mass

Answer 4

The mean mass of an atom of an element relative to 1/12th of an atom of carbon-12

Question 5

Name the 5 stages of mass spectroscopy

Answer 5

1. Vaporization
2. Ionisation
3. Acceleration
4. Deflection
5. Detection

Question 6

Vaporization?

Answer 6

The sample has to be in a gaseous form. If not, then a heater is used in order to vaporize it.

Question 7

Ionisation?

Answer 7

The sample is bombarded by a stream of high energy electrons by an electron gun. This knocks out an electron which produces a positive ion.

Question 8

Acceleration?

Answer 8

An electric field is used to accelerate the positive ions towards the magnetic field. The accelerated ions are focused and passed through a slit, this produces a narrow beam of ions.

Question 9

Deflection?

Answer 9

The accelerated ions are deflected into the magnetic field. The amount of deflection depends on the mass of the ion if they are all traveling at the same velocity.

Question 10

Detection?

Answer 10

Ions that reach the detector cause electrons to be released in an ion-current detector.
The number of electrons released is proportional to the number of ions striking the detector.
The detector is linked to an amplifier and then to a recorder, this converts the current into a peak which is shown on a mass spectrum.

Question 11

What does a mass spectrometer measure?

Answer 11

It measures the masses of atoms and molecules, and to find the relative abundance of isotopes in a sample of an element.

Question 12

What is ionisation energy?

Answer 12

The amount of energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous ions.

Question 13

What are the standard conditions in which ionisation energies are measured in?

Answer 13

298K and 101kPa

Question 14

Why is removing an electron from a positive ion harder than from a neutral atom?

Answer 14

As more electrons are removed, the attractive forces increase due to the decreasing shielding and an increase in the proton and electron ratio.

Question 15

What is the size of the first ionisation energy affected by?

Answer 15

1. Nuclear charge
2. Shielding
3. The distance of the outer electron from the nucleus

Question 16

What happens to the ionisation energy across a period and why?

Answer 16

Increases:
- nuclear charge increases which causes the atomic radius to decrease.
- the shielding by inner shell electrons remain the same because electrons are being added to the same shell.

Question 17

What happens to the ionisation energy down a group and why?

Answer 17

Decreases:
- the number of shells increase meaning the atomic radius increases. Shielding weakens the nuclear attraction.
- although proton number does increase, this is outweighed by the increase in atomic radius and sheilding.

Question 18

What are the trends across period 3 elements?

Answer 18

There is a general increase in melting point up till silicon. Silicon has the highest melting point, after silicon, the melting points decrease significantly.

Question 19

Explain the trend across period 3 elements.

Answer 19

Na, Mg, Al- metallic bonding. They form positive ions arranged in a giant lattice in which the ions are held by a sea of delocalised electrons.
Si- covalent bonding. Highest MP due to its giant molecular structure in which each Si atom is held to its neighboring atoms by strong covalent bonds.
P, S, Cl- covalent bonding. These are non metallic elements are exist as simple molecules

Question 20

Explain why the MP starts to increase at first.

Answer 20

Na will donate 1 to the sea of delocalised electrons, Mg will donate 2, and Al 3. So the metallic bonding in Al is much stronger than in Na. This is because the electrostatic forces of attraction between a 3+ ion and the larger number of negatively charged delocalised electrons is much larger compared to a 1+ ion.

Question 21

Explain the trends in conductivity across periods 2 and 3.

Answer 21

The first 3 elements are good conductors because of their giant metallic structures. They have delocalised electrons which are able to move through the structure.
The last 3 elements are poor conductors, they are simple covalent molecules and so have no mobile charge carriers.