CH1: Atomic structure

Question 1

Relative mass and charge of subatomic particles?

Answer 1

PROTON : +1 1
NEUTRON : 0. 1
ELECTRON : -1. 1/1836

Question 2

What is an ions?

Answer 2

• when atoms either gain/lose electrons causing them to be charged

Question 3

What are isotopes?

Answer 3

Atoms of the same element with the same atomic number, but different number of neutrons (so different MASS number)

Question 4

How are chemical properties of isotopes effected?

Answer 4

• not effected
  Isotopes of same element show same chemical characteristics
• because same electrons configuration on outer shells - determining chemistry of atom

Question 5

How and why are physical properties different for isotopes ?

Answer 5

• isotopes have different number of neutrons
• leads to differences in mass, density, mp and BP

Question 6

What is relative isotopic mass?

Answer 6

Mass of an atom of that isotope relative to 1/12 of a carbon-12 atom
E.g relative isotopic mass of oxygen is 15.99… but rounded to 16

Question 7

What is mass spectrometry?

Answer 7

Used to identify different isotopes/find overall relative atomic mass of an element (Ar)

Question 8

Relative atomic mass?

Answer 8

Mean mass of an atom relative to 1/12th of carbon 12 atom.

Question 9

Relative molecular mass?

Answer 9

Mean mass of a molecule of a compound, relative to 1/12th of a carbon12 atom

Question 10

Difference between relative molecular mass and Relative formula mass?

Answer 10

Relative formula mass is similar to Mr but used for compounds with GIANT STRUCTURES

Question 11

How to calculate relative atomic mass?

Answer 11

Ar = (abundance x mass) + (abundance2 x mass2 ) / total abundance

Question 12

How does Time Of Flight (TOF) Mass Spectrometry work?

Answer 12

• records time taken for ions of each isotope to reach detector
  1) IONISATION : electrons are removed from atoms, leaving them with +1 charge
  2) ACCELERATION- positive ions are accelerated towards negatively charged detection plate
  3) DEFLECTION - ions are deflected by a magnetic field into a curved path - the radius of their path depends on CHARGE and MASS of ion
• smaller mass/higher + charge = deflected most
  Larger mass = deflected least
  4) DETECTION- when + ions hit negative detection plate, they GAIN an electron , producing current/signal
• GREATER the abundance , GREATER the current/intensity of signal

Question 13

How is Ar calculated from mass spectrometer ?

Answer 13

(M/z x abundance ) / total abundance

Question 14

What is ionisation energy?

Answer 14

Amount of energy needed to remove one mole of electrons from one mole of GASEOUS atoms of an element to form one mole of gaseous ions

Question 15

What is the first ionisation energy?

Answer 15

Energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions

Ca (g) → Ca+ (g) + e-

Question 16

Trend in ionisation energy across a period?

Answer 16

INCREASES

• nuclear charge increases (increasing at action of valence electrons to nucleus)
  —> DECREASES ATOMIC RADIUS
  Outer electrons are more ATTRACTED to nucleus
  (MORE ENERGY NEEDED )
• shielding is constant

Question 17

Trend in ionisation energy down a group?

Answer 17

DECREASES
- shielding increases - decreased attraction between outer electrons and nucleus
- atomic radius increases - decreased attraction
(Overall VALENCE ELECTRONS ARE LESS ATTRACTED TO NUCLEUS , SO LESS ENERGY NEEDED)

Nuclear charge increases, but other 2 factors outweigh effects of nuclear charge

Question 18

Why do successive ionisation energies increase?

Answer 18

• Removing an electron from an increasingly positive ion is more difficult than from a neutral atom

Ionisation energies increase as you remove an electron, because of :
- increased nuclear charge
- decreased shielding

When big jumps in ionisation energy —> means it is moving shell

Question 19

What are the dips in the ionisation energy trend across PERIOD 2/3 between group 2 and 3?

Answer 19

DECREASE between BERYLLIUM AND BORON (group 2/3)
- as the outer electrons in boron is in 2p shell, which further from nucleus than 2s shell of beryllium
- 2p shell is higher in energy and s shell shields p shell - needs less energy to lose electron

DECREASE between MAGNESIUM and ALUMINIUM
- outer electron on aluminium is on 3p shell, which is further from nucleus than the 3s shell of magnesium

Question 20

Why are there dips in the ionisation energy trend ACROSS A PERIOD between group 5 and 6?

Answer 20

Decrease between NITROGEN AND OXYGEN (group 5 and 6)
- in oxygen , there are 2 electrons in the 2p orbital , so the repulsion between those electrons makes it easier to remove an electron

Decrease between PHOSPHOROUS AND SULFUR (group 5/6) P3
- spin pair repulsion in the 3p orbital of sulfur

Question 21

How do electrons move from shell to shell?

Answer 21

ABSORB ENERGY - move up
EMIT ENERGY - move down

Question 22

What is convergence?

Answer 22

When set of lines get closer tgt towards one end of line emission spectrum

Question 23

Aufbau principle?

Answer 23

Electrons go into the orbital with lowest available energy level first

Question 24

Hund’s rule?

Answer 24

Electrons only occupy orbitals on their own/ only pair up when no empty orbitals of same energy available

Question 25

How does the electronic configuration of Cr and Cu differ from others?

Answer 25

Instead of having a pair of electrons in 4s shell - there is only 1
- the remaining electron is donated to 3d shell

Question 26

Why does mass spectrometer need to be operated under a vacuum?

Answer 26

Prevent collisions with gas molecules that would deflect the ions

Question 27

Periodicity meaning ? Trend in atomic radius across Period 2/3?

Answer 27

Trend of repeating properties
Atomic radius DECREASE from left to right in P2/3
- increase in positive charge - electrons pulled closer to nucleus : reducing ATOMIC RADIUS