1.1- Atomic Structure

Question 1

What are the relative charges and the relative masses of the three fundamental particles?

Answer 1

Protons have a 1 relative mass and a 1+ relative charge
Neutrons have a 1 relative mass and a 0 nuclear charge
Electrons have a 1/1840 relative mass and a -1 nuclear charge

Question 2

Explain what the mass number and atomic number is of an element

Answer 2

Mass number is the total number of protons and neutrons in the atom, presented by A

Atomic number is the number of protons in the nucleus, presented by a Z

Question 3

Explain what an isotope is and why they have similar chemical properties

Answer 3

Isotopes are atoms with the same number of protons and different numbers of neutrons.

Isotopes have similar chemical properties because they have the same electronic structure, they may have slightly different physical properties due to a different mass.

Question 4

Explain Electron impact ionisation in a TOF spectrometer, and what would it be used for?

Answer 4

A vaporised sample is injected at low pressure

An electron gun fires high energy electrons at the sample

This knocks out an outer electron

Forming positive ions with different charges

Electron impact is usd for elements that have a low formula mass and not larger organic molecules as they can fragment

Question 5

Explain electron spray ionisation in a TOF spectrometer, and what is it used for?

Answer 5

The sample would first be dissolved in a volatile polar solvent, then injected through a fine needled giving a fine mist or aerosol

The tip of the needle must have a high voltage, and at the tip of the needle the sample molecule M gains a proton, H+ from the solvent forming MH+

The solvent evaporates away while the MH+ ions move towards the negative plate.

Electro spary ionsation is used for larger organic molecules, the softer conditions of this mean the fragmentation does not occur

Question 6

Go through all the four steps in a TOF mass spectrometer and give the conditions it the spectrometer

Answer 6

1. Ionisation- A sample is ionised by either electron impact or electro spray ionisation. This is done to give the sample a positive charge so that it can be accelerated
2. Acceleration- Positive ions are accelerated by an electric field, to a constant kinetic energy, velocity of each particle depends on it’s mass, the lighter particles have a quicker velocity compared to larger particles
3. Flight tube/Ion drift- Large ions and smaller ions have same kinetic energy, heavier particles take longer to travel, the ions are distinguished by different flight times
4. Detection- The ions reach detector and gain an electron to generate a small current, the size of the current is proportional to the abundance of the species

The Mass spectrometer has to be done under a vaccum otherwise air particles would then ionsise and register under the detector

Question 7

Why do some peaks show up at half the m/z raio

Answer 7

Because sometimes 2 electrons may be removed forming an ion with a 2+ charge

Question 8

What is avogadros constant

Answer 8

6.022x10^23

Question 9

What is the formula for RAM

Answer 9

(Isotopic mass x %abundance)/100

(isotopic mass x relative abundance)/total relative abundance

Question 10

Give the different isotopes for chlorine and bromine, also give their percentage abundance

Answer 10

Chlorine- Cl has two isotopes, Cl35(75%) Cl37(25%)

Bromine- Br has two isotopes Br79(50%), Br81(50%)

Question 11

Explain the m/z graph for a molecule that has gone through electron impact ionisation

Answer 11

If a molecule has been put through electron impact then it will often break up and give different fragments, the peak that has the largest m/z is actually the complete molecule and will be equal to the relative molecular mass of the molecule, this is called the molecular ion or the parent ion

Question 12

Explain the m/z graph for a molecule that has gone through electro spray ionisation

Answer 12

There will be one peak that is equal to the mass of the MH+ ion, it will therfore be necessary to subtract 1 to get the Mr of the molecule.

Question 13

Give the 4 different sub energy levels and how many electrons that they can hold

Answer 13

s holds up to 2 electrons
p holds up to 6 electrons
d holds up to 10 electrons
f holds up to 14 electrons

Question 14

Explain the 2 different exceptions in terms of electronic structure in the d block elements.

Answer 14

. d block elements lose their electrons from the 4s orbital first
.d block elements have two exceptions, chromium and copper
. With chromium instead of filling out the 4s orbital fully, an electon is instead put into the 3d orbital to half fill it, which makes it more stable
. With copper the same thing occurs but the 3d orbital if fully filled

Question 15

Give the definition of first ionisation energies and second ionisation energies

Answer 15

First ionisation energies is the enthalphy change when one mole of gaseous atoms forms one mole of gasesous ions with a single postiive charge

Second ionisation energies is the enthalpy change when one mole of gaseous ions with a single positive charge forms when one mole of gasesous ions with a double positive charge

Question 16

What are the factors that affect ionisation energy

Answer 16

. The attraction of the nucleus, the more protons the greater the reaction
. The distance of the electrons from the nucleus, the bigger the atom the further the outer electrons are from the nucleus giving a weaker attraction
. Shielding of the attracttion of the nucleus, an electron shell in the outer shell is repelled by electrons in complete inner shells, weakening the attraction of the nucleus

Question 17

Why are successive ionisation energies always larger

Answer 17

The second ionisation energy is always bigger than the first ionisation energy becuse when the first electron is removed a positive ion is formed, the ion increases the attraction on the remaining electrons and so the energy required to remove the next electron is larger

Question 18

How do you know what group an atom is in from successive ionisation energies

Answer 18

Acording to what group the atom is, there will be a large jump between going from different shells. The ionisation number before the large jump is the group that the atom is in.

Question 19

Why does helium have the largest first ionisation energy

Answer 19

Its first electron is in the first shell closest to the nucleus and has no shielding effects from inner shells, Helium has a bigger ionisation energy than H as it has one more proton

Question 20

Why do the first ionisation energies decrease down a group

Answer 20

As you go down the group the outer electrons are found in shells further from the nucleus and are more shielded so the attraction of the nucleus becomes smaller

Question 21

Why is there a general increase in the first ionisation energiesd across a period

Answer 21

Electrons are being added to the same shell which has the same distance from the nucleus and same shielding effect, the number of protons increases however making the effective attraction of the nucleus greater

Question 22

Why does Na have a lower first ionisation energy that neon

Answer 22

This is because Na will have its outer electron is a 3s shell further from the nucleus and is more shielded, so Na’s outer electron is easier to remove

Question 23

Why is there a small drop from Mg to Al in ionisation energy

Answer 23

Al is starting to fill out the 3p sub shell whereas Mg has its outer electron in the 3s sub shell, the electrons in the 3p subshell are slightly easier to remove because the 3p electrons are higher in energy and are also slightly shileded by the 3s electrons

Question 24

Why is there a small drop from P to S

Answer 24

With sulfur there are 4 electrons in the 3p sub shell, when the second electron is added to the 3p orbital there is slight repulsion between the two negatively charged electrons which makes the second electrons easier to remove

Question 25

What does the graph of second ionisation energies look like

Answer 25

If the graph of second ionisation or each successive element is plotted then a similar pattern to the first ionisation energy is observed but all the elements will have shifter to the left