Atomic structure and periodic table

Question 1

equation to calculate maximum number of electrons in a shell?

Answer 1

max electrons in shell = 2n^2

Question 2

What is mass number and what is its symbol?

Answer 2

symbol = A
The sum of protons and neutrons in an atom

Question 3

What is atomic number (proton number) and what is its symbol?

Answer 3

symbol = Z
Equal to the number of protons in an atom

Question 4

What is an isotope?

Answer 4

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

Question 5

What is relative atomic mass (Ar)

Answer 5

The mean mass of an atom of an element, relative to one twelfth of the mean mass of an atom of the carbon-12 isotope.

Question 6

What is isotopic mass?

Answer 6

The isotopic mass of an isotope relative to one twelfth of the mean mass of an atom of the carbon-12 isotope

Question 7

What is relative molecular mass?

Answer 7

The mean mass of a compound, relative to one twelfth of the mean mass of an atom of the carbon-12 isotope.

Question 8

What happens in a time of flight spectrometry (TOF)?

Answer 8

Records time it takes for ions of each isotope to reach a detector.

Question 9

Describe first stage of TOF

Answer 9

Ionisation - A sample of an element is vapourised and injected into the mass spectrometer where a high voltage is passed over the chamber. This causes electrons to be removed from atoms leaving +1 charged ions in the chamber.

Question 10

Describe second stage of TOF?

Answer 10

Acceleration - These positively charged ions are then accelerated towards a negatively charged detection plate.

Question 11

Describe third stage of TOF?

Answer 11

Iron drift - The ions are deflected by a magnetic field into a curved path. The radius of their path is dependent on the charge and the mass on the ion.

Question 12

Describe Fourth stage of TOF?

Answer 12

Detection - When the positive ions hit the negatively charged detection plate they gain an electron producing a flow of charge. The greater abundance the greater the flow of charge.

Question 13

Describe fifth stage of TOF?

Answer 13

Analysis - These current values are then used in combination with flight times to produce a spectra print-out with the relative abundance of each isotope displayed.

Question 14

What happens if a 2+ ion is produced in TOF?

Answer 14

Will be more affected by magnetic field producing a curved path of a smaller radius. So, mass to charge ratio (m/z) is halved

Question 15

Equation for Ar using TOF data?

Answer 15

Ar = (m/z*abundance)/ total abundance

Question 16

What does the tallest peak correspond to in TOF on a molecule and what is this peak known as?

Answer 16

relative atomic mass and know as the molecular ion peak

Question 17

What is ionisation energy?

Answer 17

The minimum energy required to remove one mole of electrons from one mole of atoms in a gaseous state. Measured in KJ

Question 18

Why does the required energy increase for successive ionisation energies?

Answer 18

Electrostatic force between positive nucleus and outer shell electrons increases. Therefore more energy required to overcome this attraction.

Question 19

What is the trend of first ionisation energies across a period and why?

Answer 19

The first ionisation energy increases due to a decreasing atomic radius and increase in proton number so increased electrostatic attraction.

Question 20

What is the trend of first ionisation energies down a group and why?

Answer 20

First ionisation energy decreases due to an increase in atomic radius and an increase in electron shielding which reduces the effect of electrostatic attraction

Question 21

What does it mean if there is a large increase when plotting successive ionisation energies on a graph and why?

Answer 21

Indicates a change in energy level because the electron is being removed from an orbital closer to the nucleus.

Question 22

What provides the evidence for the existence of quantum shells?

Answer 22

emission spectra

Question 23

What do successive ionisation energies provide evidence for?

Answer 23

Quantum shells and suggests and which group an element belongs to.

Question 24

What provides evidence for the existence for electron subshells?

Answer 24

The first ionisation energy of successive elements.

Question 25

What is an orbital?

Answer 25

A region within an atom that can hold up to two electrons with opposie spins.

Question 26

What are the three rules for writing out electron configurations?

Answer 26

1. lowest energy orbital is filled first
2. Electrons with the same spin fill up an orbital first before pairing begins.
3. No single orbital holds more than 2 electrons

Question 27

What makes an exception to the three rules on electron configuration and why?

Answer 27

If electron spins are unpaired (unbalanced), natural repulsion is produced between electrons making the atom very unstable. Electrons may take a different configuration.

Question 28

what is the electron configuration of chromium?

Answer 28

[Ar] 3d5 4s1

Question 29

What is the electron configuration of copper?

Answer 29

[Ar] 3d10 4s1

Question 30

What is periodicity?

Answer 30

Study of patterns of physical, atomic and chemical properties within the periodic table that repeats regularly.

Question 31

What happens to atomic radius across a period and why?

Answer 31

Decreases due to increased nuclear charge for the same number of electron shells. Therefore outer electrons pulled closer to the nucleus as the increased charge produces a greater attraction.

Question 32

What happens to atomic radius down a group and why?

Answer 32

Increases because with each increment down a group another complete inner shell is added. This increases distance of outer electron from the nucleus reducing the power of attraction. The effect of shielding also gets greater hence the attraction reduces further

Question 33

Describe melting/boiling point tread in period 2

Answer 33

-Li and Be have metallic bonding
-Be > Li due to Be forming cations with +2 and li forming +1
-Boron and carbon form strong covalent bonds so have very high melting a boiling points, higher than Li and Be
-N, O, F and Ne are molecules/atoms held together by weak London forces which require very little energy to overcome so low boiling point and have the lowest in the period

Question 34

Why does B have lower IE than Be?

Answer 34

Electron removed from B is in a higher energy level (2p rather than 2s)