3.1.1 Atomic Structure

Question 1

What are atoms made up of?

Answer 1

Protons
Neutrons
Electrons

Question 2

What is the relative mass and relative charge of a proton?

Answer 2

Relative mass = 1

Relative Charge = +1

Question 3

What is the relative mass and relative charge of a neutron

Answer 3

Relative mass = 1

Relative Charge = 0

Question 4

What is the relative mass and relative charge of an electron?

Answer 4

Relative Mass = 1/2000

Relative Charge = -1

Question 5

What is the mass number?

Answer 5

Total number of protons and neutrons in the nucleus

Question 6

What is the Atomic Number?

Answer 6

Number of protons in the nucleus - it identifies the element

All atoms of the same element have the same number of protons

Question 7

What is the number of electrons in a neutral atom?

Answer 7

Number of electrons is the same as the number of protons (Atomic Number)

Question 8

How do you find out the number of neutrons?

Answer 8

Mass number minus Atomic Number

Question 9

What are Isotopes?

Answer 9

Atoms of the Same Element with Different Numbers of Neutrons

Question 10

Define Isotopes

Answer 10

Isotopes of an element are atoms with the same number of protons but different number of neutrons

Question 11

What decides the chemical properties of an element?

Answer 11

Number and arrangement of electrons

Question 12

Why do Isotopes of an element have different physical properties?

Answer 12

Physical properties tend to depend on the mass of the atom

Question 13

What is the Relative Atomic Mass (Ar)?

Answer 13

Average mass of an atom of an element on a scale where Carbon-12 is 12

Question 14

What is Relative Isotopic Mass?

Answer 14

Mass of an atom, of an isotope, of an element on a scale where an atom of Carbon-12 is 12

Question 15

What is Relative Molecular Mass (Mr)?

Answer 15

The average mass of a molecule on a scale where an atom of Carbon-12 is 12

Question 16

How do you find out the Relative Molecular Mass (Mr)?

Answer 16

Add up the relative atomic mass values of all the atoms in the molecule
e.g.
Mr of C2H6O = (2x12) + (6x1) + 16 = 46

Question 17

Why is Relative Atomic Mass not usually a whole number?

Answer 17

It is an average.

Question 18

What is the Relative Isotopic Mass of Chlorine (e.g.)?

Answer 18

35

Question 19

What is the Relative Atomic Mass of Chlorine (e.g.)?

Answer 19

35.5

Question 20

What can a Mass Spectrometer tell you?

Answer 20

Relative Atomic Mass (Ar), Relative Molecular Mass (Mr) and Relative Isotopic Abundance

Question 21

What are the 4 things that happen during Time of Flight (TOF) Mass Spectrometry?

Answer 21

1) Ionisation - Ionising sample by Electrospray Ionisation or Electron Impact Ionisation
2) Acceleration - positively charged ions are accelerated by an electric field so that they all have the same kinetic energy (lighter ions move faster than heavier ones)
3) Ion Drift - Ions enter region with no electric field, so they drift through. Lighter ions drift faster than heavier ones
4) Detection - as lighter ions travel @ higher speeds in drift region, reach detector in less time than heavier ions. Detector detects charged particles and a mass spectrum is produced

Question 22

What is Electrospray Ionisation?

Answer 22

Sample is dissolved and pushed through small nozzle at high pressure.
High voltage is applied to it, causing each particle to gain an H+ ion (proton)
Sample is turned into a gas made up of +ve ions

Question 23

What is Electron Impact Ionisation?

Answer 23

Sample is vaporised and an ‘electron gun’ is used to fire high energy electrons at it. This knocks one electron off each particle, so they become +1 ions

Question 24

What is a Mass Spectrum?

Answer 24

Mass/Charge plotted against Abundance

Question 25

How do you work out Relative Atomic Mass from a Mass Spectrum in 3 Steps?

Answer 25

1) For each peak, read the % abundance from y-axis and relative atomic mass from x-axis. Multiply them together to get the total mass for each isotope
2) Add up these totals
3) Divide by 100

Question 26

How can Mass Spectrometry be used to identify Elements?

Answer 26

Elements with different isotopes produce more than one line in a mass spectrum because the isotopes have different masses.
This produces characteristic patterns which can be used as ‘fingerprints’ to identify certain elements

Question 27

How can Molecules be identified by Mass Spectrometry?

Answer 27

1) Molecular ion, M+, is formed in the mass spectrometer when one electron is removed from the molecule
2) This gives a peak in the spectrum with a mass/charge ratio equal to the Relative molecular mass of the molecule
3) This can be used to help identify an unknown compound

Question 28

What are electron shells made up of?

Answer 28

Sub-shells and Orbitals

Question 29

What is the term used for the number of a shell?

Answer 29

Principal Quantum Number

Further away shell is from nucleus, higher its energy and the larger its Principle Quantum Number

Question 30

What is the electron structure for Chromium (Cr)?

Answer 30

[Ar], 4s1, 3d5

Question 31

What is the electron structure for Copper (Cu)?

Answer 31

[Ar], 4s1, 3d10

Question 32

How does number of outer shell electrons decide the chemical properties of an element?

Answer 32

1) s block elements (Group 1 & 2) have 1 or 2 outer shell electrons. These are easily lost to form positive ions with an inert gas configuration
2) Elements in Groups 5, 6 and 7 (in the p block) can gain 1, 2 or 3 electrons to form negative ions with an inert gas configuration. Groups 4 to 7 can also share electrons when they form covalent bonds
3) Group 0 (inert gases) have completely filled s and p sub-shells and don’t need to bother gaining, losing or sharing electrons - their full sub-shells make them inert
4) The d block elements (transition metals) tend to lose s and d electrons to form positive ions

Question 33

What is ionisation?

Answer 33

Removal of one or more electrons

Question 34

What is the First Ionisation Energy?

Answer 34

Energy required to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions

Question 35

What are 3 important points about ionisation energies?

Answer 35

1) You MUST use the gas state symbol, (g), because ionisation energies are measured for gaseous atoms
2) Always refer to 1 mole of atoms, as stated in the definition, rather than to a single atom
3) The Lower the ionisation energy, the Easier it is to form an ion

Question 36

What factors affect Ionisation Energy

Answer 36

1) Nuclear Charge
2) Distance from Nucleus
3) Shielding

Question 37

How does Nuclear Charge affect Ionisation Energy?

Answer 37

The More Protons there are in the Nucleus, the more positively charged the nucleus is and the Stronger The Attraction for Electrons

Question 38

How does Distance from Nucleus affect Ionisation Energy?

Answer 38

Attraction falls rapidly w/ distance. An electron close to the nucleus will be much more strongly attached than one further away

Question 39

How does Shielding affect Ionisation Energy?

Answer 39

As # of electrons b/w outer electrons and the nucleus increases, outer electrons feel less attraction towards the nuclear charge. Lessening of pull of the nucleus by inner shells is called Shielding (or Screening)

Question 40

What does a high ionisation energy mean?

Answer 40

There is a high attraction b/w the electron and the nucleus so more energy is needed to remove the electron

Question 41

What is Second Ionisation Energy?

Answer 41

Energy needed to remove 1 electron from each ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions

Question 42

Why do successive ionisation energies increase within each shell?

Answer 42

Because electrons are being removed from an increasingly positive ion - there’s less repulsion amongst the remaining electrons, so they’re held more strongly by the nucleus

Question 43

Why are there big jumps in ionisation energy?

Answer 43

These occur when a new shell is broken into - an electron is being removed from a shell Closer to the nucleus

Question 44

What are the trends in First Ionisation Energies?

Answer 44

1) The 1st Ionisation Energies of elements down a group of the periodic table decrease
2) The 1st Ionisation Energies of elements across a period generally increase

Question 45

Why does Ionisation Energy Decrease down Group 2?

Answer 45

1) Each element down has an extra electron shell compared to the one above, extra inner shells will shield the outer electrons from the attraction of the nucleus
2) Also, extra shell means that the outer electrons are further away from the nucleus, so the nucleus’s attraction will be greatly reduced

Question 46

Why does Ionisation Energy Increase across a Period?

Answer 46

1) General trend is for the ionisation energies to increase
2) Number of protons is increasing = stronger nuclear attraction
3) Extra electrons are roughly @ same energy level, even if the outer electrons are in different orbital types
4) Generally little extra shielding effect or extra distance to lessen attraction from nucleus
5) Small drops between Groups 2 and 3, and 5 and 6.

Question 47

Whys is there a drop in Ionisation Energy between Group 2 and 3?

Answer 47

Drop Shows Sub-Shell Structure

1) e.g. Al’s outer electron is in a 3p orbital rather than a 3s. 3p orbital has slightly higher energy than the 3s orbital
2) 3p orbital has additional shielding provided by 3s2 electrons
3) Both factors strong enough to override effect of increased nuclear charge, resulting in drop of ionisation energy
4) Pattern provides evidence for the theory of electron sub-shells

Question 48

Why is there a drop in Ionisation Energy between Group 5 and 6?

Answer 48

Electron Repulsion

1) Shielding is Identical in the Phosphorus and Sulphur atoms, and the electron is being removed from an identical orbital
2) In Phosphorus’ case, electron is being removed from a singly-occupied orbital. But in Sulphur, the electron is being removed from an Orbital containing two electrons. Repulsion means that electrons are easier to remove from shared orbitals
3) More evidence for the electronic structure model