AS - Atomic structure

Question 1

What is the atomic number?

Answer 1

Number of protons found in the nucleus of an atom

Question 2

What is the relative charge of a proton?

Answer 2

+1

Question 3

What is the relative mass of a proton?

Answer 3

1

Question 4

What is the relative charge of a neutron?

Answer 4

0

Question 5

What is the relative mass of a neutron?

Answer 5

1

Question 6

What is the relative charge of an electron?

Answer 6

-1

Question 7

What is the relative mass of an electron?

Answer 7

1/1840

Question 8

What does an atom consist of?

Answer 8

A nucleus containing protons and neutrons surrounded by electrons.

Question 9

What is the mass number?

Answer 9

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

Question 10

What is the atomic number?

Answer 10

The number of protons in the nucleus.

Question 11

What can be said about the number of protons and electrons for neutral atoms?

Answer 11

They have the same number of protons and electrons.

Question 12

How to atoms form ions?

Answer 12

By losing or gaining electrons.

Question 13

What is an isotope?

Answer 13

Atoms of the same element with the same number of protons but different numbers of neutrons.

Question 14

What determines the chemical properties of an element?

Answer 14

The number and arrangement of electrons.

Question 15

What determines the physical properties of an element?

Answer 15

Tends to depend on the mass of the atom.

Question 16

What can mass spectrometry be used to identify?

Answer 16

Can be used to identify elements, determine relative molecular mass, relative isotopic mass and the relative abundance of isotopes.

Question 17

What are the four stages of mass spectrometry?

Answer 17

1. Vaporisation and ionisation
2. Acceleration
3. Ion drift
4. Detection/data analysis

Question 18

Describe what happens during vaporisation/ionisation.

Answer 18

The sample is dissolved and pushed through a small nozzle at high pressure.

A high voltage is applied to it, causing the particles to lose an electron and turning the sample into a gas made up of positive ions.

Question 19

What happens during acceleration?

Answer 19

The positive ions are accelerated by an electric field (the particles need to be positively charged to be accelerated by the field).

Ions with a lower mass/charge ratio experience a greater acceleration.

Question 20

What happens during ion drift?

Answer 20

When ions leave the electric field they have a constant speed and kinetic energy. They entera region with no electric field and so they drift.

Ions with lower mass/charge ratios drift at higher speeds.

Question 21

What happens during detection?

Answer 21

The detector detects charged particles and an electrical current is produced. This produces a mass spectrum.

Question 22

What is plotted on a mass spectrum?

Answer 22

The y-axis shows the abundance of ions.

The x-axis shows the mass/charge ratio. Since the charge on the ions is mostly +1, you can usually assume the x-axis is simply the relative isotopic mass.

Question 23

If the sample is an element, what does each line on the mass spectrum represent? What does the height of each peak represent?

Answer 23

A different isotope of the element. The height of each peak gives the relative isotopic abundance.

Question 24

How do the electron configurations of chromium and copper differ from the accepted rules? Why?

Answer 24

They donate one of their 4s electrons do the 3d sub-shell. This makes them more stable.

Question 25

What happens to transition metals that is unique, in terms of their electron configurations, when they become positive ions?

Answer 25

They lose 4s electrons before 3d electrons.

Question 26

What is ionisation?

Answer 26

The removal of one or more electrons.

Question 27

Define first ionisation energy.

Answer 27

The energy needed to remove one electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.

Question 28

Why is ionisation an endothermic process?

Answer 28

Because you have to put energy in to ionise an atom or molecule.

Question 29

What is the general equation for first ionisation energy?

Answer 29

X(g) —> X+(g) + e-

Question 30

What is the general equation for second ionisation energy?

Answer 30

X+(g) —> X2+(g) + e-

Question 31

What are the three factors affecting ionisation energy?

Answer 31

1. Nuclear charge
2. Distance from nucleus
3. Shielding

Question 32

What is the general trend in ionisation energies down a group of the periodic table?

Answer 32

They decrease.

Question 33

What is the general trend in ionisation energies across a period of the periodic table?

Answer 33

They increase.

Question 34

Explain the trend in first ionisation energies down group 2.

Answer 34

They decrease.

This is because each element down group 2 has an extra shell compared to the one above, so the extra inner shells will shield the outer electrons from the attraction of the nucleus.

Also, the extra shells mean that the outer electrons are further from the nucleus, so the nucleus’ attraction is greatly reduced.

Both these factors make it easier to remove outer electrons, meaning lower ionisation energy.

Question 35

Explain the general trend in first ionisation energies across period 3, not including the anomalies.

Answer 35

Generally increases.

This is because the number of protons is increasing, meaning stronger nuclear attraction.

Also, all the extra electrons are at roughly the same energy levels meaning there’s little extra shielding effect or extra distance to lessen the attraction from the nucleus.

Question 36

Where do the anomalies occur in the first ionisation energies across period 3?

Answer 36

Between groups 2 and 3 and groups 5 and 6.

Question 37

Explain the drop in first ionisation energy across period 3 between groups 2 and 3.

What does this provide evidence for?

Answer 37

This is between Mg and Al where Al’s first ionisation energy is lower.

Al’s outer electron is in a 3p sub-shell, whereas Mg’s is in a 3s. The 3p orbitals has a slightly higher energy than the 3s orbital so the electron is on average, further from the nucleus. The 3p orbital has additional shielding from the 3s^2 electrons too.

Both these factors override the trend and provide evidence for the theory of electron sub-shells.

Question 38

Explain the drop in first ionisation energy across period 3 between groups 5 and 6.

What does this provide evidence for?

Answer 38

Between P and S where S has a lower first ionisation energy.

The shielding is identical in both atoms and the electron is being removed from an identical orbital.

In P’s case, the electron is being removed from a singly occupied orbital but in S, the electron is being removed from an orbital containing two electrons. The repulsión between the two electrons means that electrons are easier to remove from shared orbitals.

Provided evidence for the electronic structure model.