Atomic Structure

Question 1

What is the relative mass of an electron?

Answer 1

5.45 x 10 to the power of -4

Question 2

What is the mass number?

Answer 2

Total number of protons and neutrons.

Question 3

Why does atomic radii increase as you move down a group?

Answer 3

Because there are more electron shells.

Question 4

Why does atomic radii decrease across a period?

Answer 4

Because across a period there are no more shells, but there are successively more protons, giving a greater force of attraction between protons and electrons.

Question 5

What phase must the substance be in when injected into a ToF machine?

Answer 5

Gas or liquid. Solid must be dissolved.

Question 6

What are the two types of ionisation in ToF?

Answer 6

Electron impact and electrospray.

Question 7

During the acceleration phase of ToF, why do lighter particles have a greater velocity than heavier particles?

Answer 7

Because they are both given the same amount of kinetic energy, and a higher mass results in a lower velocity (because of the formula KE = 1/2m(v squared.)

Question 8

How does electrospray ionisation work?

Answer 8

• A high voltage is applied to a sample in a solvent.
• The sample molecule gains a proton (H+) from the solvent
• The solvent evaporates leaving molecules of the sample MH+

Question 9

How does electron impact work?

Answer 9

• The sample is bombarded with high energy electrons
• The sample loses an electron forming M+

Question 10

How are ions detected in a ToF spectrometer?

Answer 10

• When the ions fall on the negative plate of the detector, they gain an electron.
• This causes a charge to flow.
• The more ions that fall, the greater the current.
• All the ions eventually fall on the detector.
• The heavier ions take longer than lighter ions.

Question 11

How many electrons can an orbital hold?

Answer 11

2

Question 12

How many orbitals in an s shell?

Answer 12

1

Question 13

How many orbitals in a p shell?

Answer 13

3

Question 14

How many orbitals in a d shell?

Answer 14

5

Question 15

How many orbitals in an f shell?

Answer 15

7

Question 16

What do the orbitals shapes respresent?

Answer 16

Where an electron can be found 95% of the time.

Question 17

When transition metals form ions, do they lose 4s electrons or 3d electrons first?

Answer 17

4s electrons.

Question 18

What is first ionisation energy?

Answer 18

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

O (g) –> O+ (g) + e-

Question 19

What is the general rule for ionisation energy across a period?

Answer 19

It will increase.

Question 20

Is it easier to remove an s electron or a p electron?

Answer 20

A p electron.

Question 21

What factors affect ionisation energy?

Answer 21

• Nuclear charge (the more protons there are, the more positively charged the nucleus is and the stronger the attraction for the electron –> higher ionisation energy)
• Nuclear distance (electromagnetic attraction decreases rapidly with distance, an electron closer to the nucleus will be more strongly attracted than one further away –> higher ionisation energy)
• Electron shielding (as the number of electrons between outer shell electrons and the nucleus increases, the outer electrons feel less attraction towards the nuclear charge = shielding, more shielding –> lower ionisation energy)