1.1 Atomic structure

Question 1

What are the names and capacities of the 4 orbitals

Answer 1

• S orbital: can hold 2 electrons
• P orbitals (in 3s): can hold 6 electrons
• D orbitals (in 5s): can hold 10 electrons
• F orbitals (in 7s): can hold 14 electrons

Question 2

Describe the plum pudding model of the atom

Answer 2

Atom consists of a sphere of positive charge with small negative charges distributed evenly in it (electrons).

Question 3

Describe the electron shell model of the atom

Answer 3

• Atom consists of a small, dense central nucleus surrounded by orbiting electrons in shells.
• Discovered by alpha scattering experiment.

Question 4

What is an isotope

Answer 4

Atoms of the same element with the same atomic number, but a different number of neutrons, resulting in a different mass number.

Question 5

What is relative atomic mass

Answer 5

The average mass of all isotopes of an element compared to 1/12th the mass of an atom of carbon-12.

Question 6

How does time of flight mass spectrometry work

Answer 6

• It records the time it takes for ions of each isotope to reach a detector.
• Using this, spectra can be produced showing each isotope present.

Question 7

Describe electron impact (electron ionisation) ionisation (TOF)

Answer 7

• Sample being analysed is vaporised and high energy electrons are fired at it.
• Electrons come from an ‘electron gun’ which is a hot wire filament with a current running through it that emits electrons.
• This usually knocks off one electron from each particle, forming a 1+ ion.

Question 8

What elements/ substances is electron impact ionisation typically used for

Answer 8

• Elements and substances with a low formula mass.
• This form of ionisation produces 1+ ions known as molecular ions.
• The molecular ion often breaks down into smaller fragments, some of which are detected in the mass spectrum

Question 9

What is the equation for electron impact ionisation

Answer 9

X(g) => X+(g) + e-

Question 10

Describe electrospray ionisation (TOF)

Answer 10

• The sample is dissolved in a volatile solvent (e.g. methanol) and injected through a fine hypodermic needle.
• The tip of the needle is attached to the positive terminal of a high voltage power supply.
• The particles are ionised by gaining a proton (e.g. a H+ ion) from the solvent as they leave the needle, producing XH+ ions.

Question 11

What substances is electrospray ionisation typically used for

Answer 11

• Substances with higher molecular masses, including many biological molecules such as proteins.
• Known as ‘soft’ ionisation and fragmentation rarely takes place.

Question 12

What is the equation for electrospray ionisation

Answer 12

X(g) + H+ => XH+(g)

Question 13

Describe the acceleration stage of TOF mass spectrometry

Answer 13

• The positive ions are accelerated using an electric field so that they all have the same kinetic energy.
• This means that the velocity of each particle depends on its mass (all have the same kinetic energy).
• Lighter ions travel faster (have a higher velocity) than heavier ions.

Question 14

Describe the flight tube stage of TOF mass spectrometry

Answer 14

• The positive ions travel through a hole in the negatively charged plate into a tube.
• The TOF of each particle depends on its velocity.

Question 15

Describe the detection stage of TOF mass spectrometry

Answer 15

• The positive ions hit a negatively charged electric plate.
• This causes the positive ions to be discharged by gaining an electron from the plate.
• This generates movement of electrons, and so an electric current that is measured.

Question 16

What is the electron configuration of Chromium (Cr) - 24 electrons

Answer 16

1s²2s²2p⁶3s²3p⁶4s¹3d⁵

Question 17

What is the electron configuration of Copper (Cu) - 29 electrons

Answer 17

1s²2s²2p⁶3s²3p⁶4s¹3d¹⁰

Question 18

What is first ionisation energy and what equation is used

Answer 18

• The minimum energy required to remove one mole of electrons from one mole of atoms in their gaseous state to form one mole of 1+ ions.
• Measured in kJmol-1.
• E.g. Sodium: Na(g) => Na+(g) + e-

Question 19

When do successive ionisation energies occur

Answer 19

• When further electrons are removed.
• Usually requires more energy because as electrons are removed, the electrostatic force of attraction between the positive nucleus and the negative outer electrons increases.
• More energy is therefore needed to overcome this attraction, so ionisation energy increases.

Question 20

What is the trend in first ionisation energy down a group

Answer 20

• First ionisation energy decreases due to an increasing atomic radius and shielding.
• This reduces the effect of the electrostatic forces of attraction, so less energy is required to remove the outer electrons.

Question 21

What is the trend in first ionisation energy across a period

Answer 21

• First ionisation energy increases due to a decreasing atomic radius.
• This causes greater electrostatic forces of attraction between the positive nucleus and the negative outer electrons, so more energy is required to remove them.

Question 22

Why is the first ionisation energy of aluminium lower than magnesium

Answer 22

• The outer electron in magnesium is in an s sub-shell whereas the outer electron in aluminium is in a p sub-shell.
• The outer electron in aluminium is therefore of higher energy, so less energy is needed to remove it.

Question 23

Why is the first ionisation energy of sulfur lower than phosphorus

Answer 23

• Phosphorus has stable half-filled p orbitals with one electron in each.
• In sulfur, the 4th electron is added to an already occupied p orbital.
• This leads to repulsion between electrons, so less energy is required to remove the outer electron.