Atomic Structure

Question 1

What is the relative mass and relative charge of a proton?

Answer 1

Relative mass:1
Relative Charge: +1

Question 2

What is the relative mass and relative charge of a neutron?

Answer 2

Relative mass: 1
Relative charge: 0

Question 3

What is the relative mass and relative charge of an electron?

Answer 3

Relative mass: 1/1840
Relative charge: -1

Question 4

What are isotopes?

Answer 4

Atoms with the same number of protons but different number of neutrons

Question 5

Why do isotopes have similar chemical properties?

Answer 5

They have the same electronic structure

Question 6

What can mass spectrometer be used for?

Answer 6

To determine all the isotopes present in a sample of an element and to therefore identify elements.

Question 7

What’s a condition for mass spectrometer?

Answer 7

Need to be under a vacuum otherwise air particles would ionise and register on the detector

Question 8

Explain ionisation? Electron impact

Answer 8

Vaporised sample is injected at low pressure
An electron gun fires high energy electrons at the sample
This knocks out an outer electron
Forms a positive ions with different charge

Question 9

Explain ionisation? Electro spray Ionisation

Answer 9

Sample dissolved in a volatile polar solvent
Injected through a fine needle giving a fine mist or aerosol
Tip of needle has high voltage
At tip of needles the sample molecule gains a proton from solvent forming
Solvent evaporates away while MH+ ions move towards negative plate

Question 10

What is electron impact used for?

Answer 10

Elements and substances with low formula mass, can cause larger organic molecules to fragment

Question 11

What can electro spray ionisation be used for?

Answer 11

Larger organic molecules, the softer conditions of this technique mean fragmentation does not occur

Question 12

Explain acceleration in mass spectrometer?

Answer 12

Positive ions are accelerated by electric field
To a constant kinetic energy
KE= 1/2 n v squared
KE= kinetic energy of particles
M= mass of particle
V= velocity of the particle

Question 13

What does the velocity of the particle depend on?

Answer 13

It’s mass, lighter particles have a faster velocity and heavy particles have a slower velocity

Question 14

Explain the flight tube in mass spectrometer?

Answer 14

Positive ions with smaller m/z values will have the same kinetic energy as those with larger m/z and will move faster
Heavier particles take longer to move through drift air
Ions are distinguished by different flight times
( t= d/v)
T= time of flight
D= length of flight tube
V= velocity of the particle

Question 15

Explain detection in mass spectrometer?

Answer 15

Ions reach the detector and generate a small current, which is fed into a computer of analysis. Current is produced by electrons transferring from the detector to the positive ions. Size of current is proportional to abundance of species

Question 16

How do you work out time of flight?

Answer 16

1.) find mass of one ion: mass of one mole (small number next to element) divided by avogadros constant
2.) convert into kg from grams (divide by 1000)
3.) do the length times the square root of mass of one ion divided by 2 times the kinetic energy
You then get your answer

Question 17

How do you calculate relative atomic mass?

Answer 17

Isotopic mass x % abundance divided by 100
Number above bar times small number next to element divided by 100

Question 18

How do you calculate Relative Atomic mass using relative abundance?

Answer 18

Isotopic mass x relative abundance divided by total relative abundance

Question 19

Why have mass spectrometers been included in planetary space probes?

Answer 19

So elements on other planets can be identified

Question 20

What is the peak with the largest m/z due to?

Answer 20

The complete molecule and will be equal to the molecular mass MR of the molecule, this is called the parent ion or molecular ion

Question 21

What happens to the peaks in a mass spectrometer done with electron impact ionisation?

Answer 21

The molecule will often break up and give a series of peaks caused by fragments

Question 22

What happens to the molecule if its put through a mass spectrometer with electron pray ionisation?

Answer 22

Fragmentation will not occur and there will be one peak equal to the mass of the mH ion, you subtract 1 from the Mr of the molecule.

Question 23

What are electrons arrangement into?

Answer 23

Principle energy levels 1,2,3,4… 1 is closest to nucleus

Question 24

What are principle energy levels split into?

Answer 24

Sub energy levels
S holds 2 electrons
P holds up to 6
D holds up to 10
F holds up to 14

Question 25

Principle level related to its sub-level 1,2,3,4

Answer 25

1: sub level: 1s
2: sub level: 2s, 2p
3: sub level: 3s, 3p, 3d
4: sub level: 4s,4p,4d,4f

Question 26

How do you write electronic structure using letters and numbers?

Answer 26

Number of main energy level name of type of sub level number of electrons in sub level

Question 27

What happens when a positive ion is formed?

Answer 27

Electrons are lost from the outermost shell

Question 28

What block on the periodic table loses ions in there 4s before their 3d?

Answer 28

Block d

Question 29

What is the first ionisation energy? Equation?

Answer 29

The enthalpy change when one mole of gaseous atoms forms one mole of gaseous ion with a single positive charge.
H—-> H+ + E-

Question 30

What is second ionisation energy? Equation?

Answer 30

Enthalpy change when one mole of gaseous ions with a single positive charge forms one mole of gaseous ions with a double positive charge
Ti+ ——-> Ti2+ + e-

Question 31

What are factors that affect ionisation energy?

Answer 31

1.) attraction of the nucleus (more protons in the nucleus the greater the attraction)
2.) the distance of the electrons from nucleus (the bigger the atom the further the outer electrons are from the nucleus and the weaker the attraction to the nucleus)
3.) shielding of the attraction of the nucleus (an electron in an outer shell is repelled by electrons in complete inner shells, weakening the attraction of the nucleus)

Question 32

Why are successive ionisation energies always larger?

Answer 32

Second ionisation energy of an element is always bigger than the first.
When first electron is removed a positive ion is formed
Ion increases attraction on remaining electrons so energy required to remove next electron is larger

Question 33

What is periodicity?

Answer 33

Repeating pattern across a period

Question 34

Why do first ionisation energies decrease down a group?

Answer 34

The outer electrons are found in shells further from the nucleus and are more shielded so the attraction of the nucleus becomes smaller

Question 35

Why is there a small drop from P to S?

Answer 35

When the second electron is added to the 3P orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove

Question 36

Define ionisation energies?

Answer 36

Energy required to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous ions

Question 37

Ionisation energy equation?

Answer 37

O (g) ——> O+(g) + e-
Mg (g) ——-> MG+ (g) + e-

Question 38

What changes between the 1st ionisation energy and the 2nd?

Answer 38

It turns from turning 1 mol of gases out atoms to 1 ion of gases out atoms to form 2+ of gaseous ions

Question 39

What happens when you increase the charge of the nucleus?

Answer 39

The ionisation energy increases

Question 40

What happens when you increase distance from nucleus?

Answer 40

Ionisation energy decreases

Question 41

What happens when you increase shielding?

Answer 41

Ionisation energy decreases