Chem Topic 1

Question 1

What are the relative masses and charges of subatomic particles

Answer 1

Mass: Charge
Proton 1 1
Neutron 1 0
Electron 1/1840 -1

Question 2

What do the atomic number and mass number of an element signify?

Answer 2

atomic number = proton/electron
mass number= proton + neutron

Question 3

Define isotope

Answer 3

same element with the same number of protons different number of neutrons

Question 4

How do the chemical and physical properties of isotopes compare?

Answer 4

Same chemical properties due to electron arrangement.
different physical properties due to masses

Question 5

Define; relative atomic mass and relative molecular mass

Answer 5

relative atomic mass: average mass of one of its atom where carbon 12=12
molecular average mass of a molecule on a scale where carbon 12=12

Question 6

Write a general equation to show how you would calculate relative atomic mass when given % abundance

Answer 6

∑(mass x abundance) / 100

Question 7

Write a general equation to show how you would calculate relative atomic mass when given relative abundance

Answer 7

∑(mass x abundance) / ∑abundance

Question 8

What are the 6 stages of a TOF mass spectrometer?

Answer 8

Ionisation, acceleration, ion drift, detection, mass spectrum, data analysis

Question 9

Describe the two types of ionisation and write two different equations to represent the ionisation of chlorine

Answer 9

Electron impact:

The sample is vaporised

Then high energy electrons are fired at it/electron gun

This usually knocks off one electron from each particle forming a 1+ ion.

Cl(g) à Cl+(g) + e-

Electrospray ionisation

The sample is dissolved in a volatile solvent

Then injected through a positively charged capillary needle

Each molecule/particle gains a proton/H+

Cl(g) + H+ à ClH+(g)

Question 10

 Explain why it is necessary to ionize molecules when measuring their mass in a TOF mass spectrometer.

Answer 10

So they can be accelerated and detected

Question 11

Explain how ions are accelerated, detected and have their abundance determined in a time of flight (TOF) mass spectrometer.

Answer 11

The ions are accelerated using an electric field so they have the same kinetic energy. They separate in the ion drift region as the lighter ions have a higher velocity. They are detected by a negative plate. Electrons pass from the plate to the positive ions. This creates a current. The size of the current is proportional to the abundance of the ion.

Question 12

What does Avogadro’s constant represent?

Answer 12

6.022x1023 = the number of particles in one mole

Question 13

Calculate the mass in Kg of one Na+ ion

Answer 13

23/1000 = 0.023

0.023/6.022x1023 = 3.819x10-26

Question 14

On mass spectra of molecules what is the molecular ion? What is the m+1 ion?

Answer 14

The molecular ion represents the molecule’s Mr (for electron impact ionisation). The m+1 ion is the Mr+1 and is created by the natural occurrence of 13C

Question 15

If you were given a mass spectrum for a molecule that was ionised via electrospray ionisation, how would you deduce its Mr?

Answer 15

Find the molecular ion peak value and subtract 1 (as the ion has gained a proton during ionisation)

Question 16

describe Thomson’s and Rutherford’s model of the atom

Answer 16

Thomson’s model = plum pudding, positively charged sphere with negative electrons randomly arranged

Rutherford’s model = positively charged nucleus with negative electrons around the outside

Question 17

Write the full electron configuration of krypton

Answer 17

1s22s22p63s23p64s23d104p6

Question 18

Give the electron configuration of O2- and Ni2+ . What do you need to remember for electron configuration of transition metal ions?

Answer 18

1s22s22p6

1s22s22p63s23p63d8

For transition metal ions, the 4s electrons are removed before 3d

Question 19

How do electrons fill p and d orbitals?

Answer 19

Electrons go into separate orbitals (boxes) to start with and then start to pair up

Question 20

What are the names of the 4 blocks of the periodic table? How do they relate to electron structure?

Answer 20

Groups 1&2 = s block, between groups 2 & 3 = d block, groups 3-group 0 = p block

Question 21

Define first ionisation energy

Answer 21

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of positively charged gaseous ions

Question 22

Write an equation for the first ionisation energy of oxygen (remember gas state symbol)

Answer 22

O(g) à O+(g) + e-

Question 23

What is the general trend of first ionisation energy as you go down a group? Explain your answer

Answer 23

As you go down a group the first ionisation energy decreases. This is because the outer electrons become further from the nucleus and experience more shielding. This means it requires less energy to remove an outer electron because there is greater attraction between the nucleus and outer electrons.

Question 24

What is the general trend of first ionisation energy as you go across a period? Explain your answer

Answer 24

As you go across a period the first ionisation energy generally increases. This is because the nuclear charge increases as there are more  protons, but the shielding remains the same. This means there is a greater attraction between the nucleus and outer electron.

Question 25

What are the 2 exceptions to the general trend of first ionisation energy in period 3? Explain each of them

Answer 25

For aluminium, the electron is removed from the 3p subshell which is at a higher energy than the 3s subshell so it is easier to remove.

In sulfur, two of the 3p electrons are paired. There is some repulsion between paired electrons in the same sub-level. This reduces the force of their attraction to the nucleus, so less energy is needed to remove one of these paired electrons than is needed to remove an unpaired electron from phosphorus.

Question 26

Write equations for the second and third ionisation energies of oxygen

Answer 26

O+(g) à O2+(g) + e-

O2+(g) à O3+(g) + e-

Question 27

What do the ‘big jumps’ in the successive ionisation energies of an element signify?

Answer 27

‘Big jumps’ in successive ionisation energy mean that the electron has been removed from a lower energy level (shell). This will tell you what group the element is in.

Question 28

Atomic number and mass number