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 (isotopic mass) 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 - extra inner shells shield outer electrons from attraction of the 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
The decrease in ionisation energy provides evidence that electron shell exist

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 2/3 between group 5 and 6?

Answer 20

Decrease between NITROGEN AND OXYGEN (group 5 and 6)
- in oxygen , there are a pair of electrons in the 2px 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 as the frequency increases

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
( 2 electrons in the same orbital must have opposite spins)

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

Question 28

Second ionisation energy?

Answer 28

Energy required to remove one mole of electrons from one mole of gaseous +1 ions to form one mole of +2 gaseous ions

Question 29

How do successive ionisation energies provide evidence for the existence of quantum shell and the group to which the element belongs to ?

Answer 29

Graph of successive ionisation energies can be used : Count how many electron removed before the first big jump to **determine group no.**( if one electron removed must be in group 1) Can also predict **electronic structure** by counting the no. Points before each big jump to find no. Electrons in each shell Each big jump indicates a electrons are on a **new shell** (big jump bc electrons closer to nucleus) + within each shell **successive ionisation energies increase** as electrons are removed from increasingly + ion /there’s less repulsion between remaining electrons so electrons are held more strongly to nucleus

Question 30

What does a line spectrum show ?

Answer 30

The frequencies of light emitted when electrons drop down from a higher energy level to a lower one - these frequencies appear as coloured lines on a dark background

Question 31

How do electrons move down electron shells (or quantum shells)?

Answer 31

In the ground state, electrons are in the lowest possible energy levels. Electrons can be excited to higher energy levels further from the nucleus by **absorbing energy** from their surroundings. As electrons drop back down from higher to lower energy levels, they emit **electromagnetic radiation at specific frequencies** The energy levels are **discrete**, meaning electrons cannot exist between them and can only transition in these fixed jumps.

Question 32

Why does each element give rise to a unique spectrum?

Answer 32

Each element a has unique electron configuration , so the set of frequencies emitted is different for each element

Question 33

Emission spectrum for hydrogen?

Answer 33

Electron drop to n=1 level - produce series of lines in ultraviolet region Electrons drop to n=2 (2nd energy level) series of lines will appear in visible part of spectrum Electrons drop to n=3 even - series of lines will appear in infrared region

Question 34

What does the quantum shell model of atom propose?

Answer 34

1. Electrons are confined to fixed shells at specific distances from the nucleus 2. Each shell has a defined energy and electrons cannot exist between shells 3. Electrons must absorb or emit electromagnetic radiation to move between shells. 4. The discrete nature of the shells means the emitted radiation has fixed frequencies.

Question 35

How does the emission spectra support the quantum shell model?

Answer 35

- Spectra has **distinct lines for different energy levels** rather than a continuous spectrum - indicates that energy levels are discrete (and electron must **jump** from energy level to next with no in between stage) - Each line represents a **specific electronic transition** between two energy levels, with the frequency determined by the energy difference.

Question 36

How many p orbitals are there?

Answer 36

3 Px, Py, Pz Have dumbbell shapes and they’re at right angle to one another