3.1.1 Atomic Structure Knowledge

Question 1

what is the relative mass of a proton?

Answer 1

1

Question 2

what is the relative mass of a neutron?

Answer 2

1

Question 3

what is the relative mass of an electron?

Answer 3

1/1840

Question 4

what is the relative charge of a proton?

Answer 4

1+

Question 5

what is the relative charge of a neutron?

Answer 5

0

Question 6

what is the relative charge of an electron?

Answer 6

1-

Question 7

what is the atomic number?

Answer 7

total number of protons in an atom

Question 8

what is the mass number?

Answer 8

total number of protons and neutrons in a nucleus

Question 9

what is an isotope?

Answer 9

an atom with the same number of protons but different number of neutrons

Question 10

why do isotopes have similar chemical reactions?

Answer 10

isotopes of the same element have the same chemical properties because they have the same electron configuration

Question 11

what is a positive ion?

Answer 11

cation

Question 12

what is a negative ion?

Answer 12

anion

Question 13

when was the Solid Sphere model invented?

Answer 13

1803

Question 14

who invented the Solid Sphere model?

Answer 14

John Dalton

Question 15

summarise the solid sphere model

Answer 15

• All matter is composed of extremely small particles called atoms.
• Atoms of a given element are identical in size, mass, and other properties. Atoms of different elements differ in size, mass, and other properties.
• Atoms cannot be subdivided, created, or destroyed.

Question 16

when was the plum pudding model invented?

Answer 16

1904

Question 17

who invented the plum pudding model?

Answer 17

jj thomson

Question 18

summarise the plum pudding model

Answer 18

• electrons embedded in a uniform sphere of positive charge.
• The positive matter was thought to be jelly-like.
• The electrons were somewhat mobile. As they got closer to the outer portion of the atom, the positive charge in the region was greater than the neighbouring negative charges and the electron would be pulled back more toward the centre region of the atom.

Question 19

when was the nuclear model invented?

Answer 19

1911

Question 20

who invented the nuclear model?

Answer 20

ernest rutherford

Question 21

summarise the nuclear model

Answer 21

a small and dense positively charged nucleus surrounded by a cloud of electrons.

Question 22

when was the planetary model invented?

Answer 22

1913

Question 23

who invented the planetary model?

Answer 23

niels bohr

Question 24

summarise the planetary model

Answer 24

small positive nucleus with electrons orbiting the nucleus in energy shells

Question 25

when was the quantum model invented?

Answer 25

1926

Question 26

who invented the quantum model?

Answer 26

erwin schrodinger

Question 27

summarise the quantum model

Answer 27

the electron is a wave and tries to describe the regions in space, or orbitals, where electrons are most likely to be found.

Question 28

describe the process and findings of the gold foil/alpha particle experiment

Answer 28

1. Rutherford fired He^2+ ions at a sheet of gold foil 2. When the He^2+ ions arrived on the other side, he concluded that most of the atom is empty space 3. A very small number of the He^2+ ions were detected on the same side as the source. He concluded that the atom must have a small, positive nucleus

Question 29

define first ionisation energy

Answer 29

the amount of energy required to remove one mole of electrons from one mole of atoms in the gaseous state, units kJ mol^-1

Question 30

what element has the highest 1st IE? and why?

Answer 30

Helium has the highest 1st IE of all elements; it has more protons than Hydrogen and only one shell so the same shielding as Hydrogen

Question 31

does nuclear charge increase or decrease down a group?

Answer 31

increase

Question 32

does nuclear charge increase or decrease across a period?

Answer 32

increase

Question 33

does atomic radius increase or decrease across a period?

Answer 33

decreases - no. shells stays the same but nuclear charge increases

Question 34

does atomic radius increase or decrease down a group?

Answer 34

increase - no. shells increases so amount of shielding increases

Question 35

does shielding increase or decrease down a group?

Answer 35

increases - no. shells increases

Question 36

does shielding increase or decrease across a period?

Answer 36

stays the same - no. shells stays the same

Question 37

does first ionisation energy increase or decrease down a group? why?

Answer 37

decreases: - atoms increase in atomic radius, due to more shells - more shielding - weaker attraction from nucleus to electron in outer shell ⇒ less energy required to remove

Question 38

does first ionisation energy increase or decrease across a period?

Answer 38

generally increases - exceptions are Boron and Oxygen in P2, and Aluminium and Sulphur in P3

Question 39

what are 3 key factors that influence ionisation energy?

Answer 39

nuclear charge distance from the nucleus shielding

Question 40

why do IE's 1-3 of Boron increase slowly, then a jump on the 4th?

Answer 40

- IEs 1-3 increase slightly because each electron is being removed from a more positive ion each time - This means the attraction between the electrons and protons becomes stronger as there are less electrons being attracted by the same no. protons - the 4th electron is removed from a shell much closer to the nucleus and so is much more strongly attracted, therefore requiring more energy to remove

Question 41

describe the trend of 2nd IE's across a period, in relation to first IEs

Answer 41

After the first IE trend, across a period, each ion/element jumps 1 place left on the graph (e.g. the 2nd IE of Be [so from Be+ to Be2+] is similar to the 1st IE of Li [Li to Li+])

Question 42

Explain the general trend in IEs across P2

Answer 42

- there is a general increase in IE across P2 - this is because across P2 there is a greater nuclear charge and the same amount of shielding - so a greater attraction between nucleus and outermost electron, meaning more energy is required to remove it

Question 43

Explain why Boron is lower in IE than Beryllium, despite coming after it in P2

Answer 43

- the first electron removed from Be is from a 2s sublevel - the first electron removed from B is from a 2p sublevel - the 2s sublevel is lower in energy than 2p - therefore less energy is needed to remove the electron from B (as electron from higher sublevel)

Question 44

Explain why Oxygen is lower in IE than Nitrogen, despite coming after it in P2

Answer 44

- the first electron removed from N is from a 2p sublevel and is unpaired - the first electron removed from O is from a 2p sublevel, too, but it is from a paired orbital - this means O has a lower IE due to electron pair repulsion, therefore less energy is needed to remove the electron from O

Question 45

Explain the general trend in IEs across P3

Answer 45

- there is a general increase in IE across P3 - this is because across P3 there is a greater nuclear charge and the same amount of shielding - so a greater attraction between nucleus and outermost electron, meaning more energy is required to remove it

Question 46

Explain why Aluminium is lower in IE than Magnesium, despite coming after it in P3

Answer 46

- the first electron removed from Mg is from a 3s sublevel - the first electron removed from Al is from a 3p sublevel - the 3s sublevel is lower in energy than 3p - therefore less energy is needed to remove the electron from Al (as electron from higher sublevel)

Question 47

Explain why Sulphur is lower in IE than Phosphorus, despite coming after it in P3

Answer 47

- the first electron removed from P is from a 3p sublevel and is unpaired - the first electron removed from S is from a 3p sublevel, too, but it is from a paired orbital - this means S has a lower IE due to electron pair repulsion, therefore less energy is needed to remove the electron from S

Question 48

why is Mg not lower in IE than Na, DESPITE the electron being from a paired orbital and same subshell?

Answer 48

this is because there is only 1 s orbital, in Mg and Na, compared to the 3 p orbitals in S and P for example, so the electron pair repulsion is outweighed by the nuclear charge

Question 49

Why is Li a bigger atom than Be?

Answer 49

- Both have the same number of shells so they have the same shielding - But, Be has more protons so the nucleus attracts the outermost electrons more strongly

Question 50

Why is Li a bigger atom than F?

Answer 50

- both atoms have the same number of shells so have the same shielding - F has a higher nuclear charge so the nucleus attracts the outermost electrons more strongly

Question 51

Why is Li a bigger atom than He?

Answer 51

- Li has an extra electron shell and is further away from the nucleus - The outermost electron is more shielded which means it is less strongly attracted to the nucleus

Question 52

Why is Li+ a smaller ion than F-?

Answer 52

- an Li+ ion only has one shell so the outermost electrons experience less shielding - This means they are more strongly attracted to the nucleus as they are closer to it

Question 53

give the order of organisation of electron configuration

Answer 53

Energy level ⇒ subshell ⇒ orbital

Question 54

what is an orbital?

Answer 54

a region within an atom where it is most likely to find an electron; can hold up to 2 with opposite spins

Question 55

what shape is an s orbital?

Answer 55

spherical

Question 56

what shape is a p orbital?

Answer 56

dumbbell

Question 57

what does the large number refer to in electron configuration?

Answer 57

the energy level of the electron

Question 58

what does the letter refer to in electron configuration?

Answer 58

the subshell of the electron

Question 59

what does the small number refer to in electron configuration?

Answer 59

the number of electrons in that subshell

Question 60

describe how orbitals fill up in electron configuration

Answer 60

- orbitals of lower energy are always filled first (closest to nucleus) - atomic orbitals of the same energy fill up singly before electrons pair up (Hund's Rule) - no orbital can have more than 2 electrons

Question 61

how does the block an element is in, relate to its electron configuration?

Answer 61

each element is placed in the position of its highest energy electron; this means the block that the element is in, determines which type of orbital its highest energy electron is in.

Question 62

why are d-block elements more stable when they have a full or, or exactly half full, subshell?

Answer 62

as this is a lower energy configuration

Question 63

what is a mass spectrometer?

Answer 63

machine used to analyse elements or compounds; can accurately determine Ar of atoms or Mr of molecules

Question 64

what 2 factors do mass spectrometers measure?

Answer 64

relative abundance mass/charge (m/z) ratio

Question 65

what are the 4 main steps in TOF mass spectrometry?

Answer 65

ionisation acceleration ion drift detection

Question 66

describe the full process of TOF mass spectrometry

Answer 66

1. Vacuum: the entire machine is a vacuum inside to prevent any of the particles being tested colliding with molecules from the air 2. Ionisation: sample particles gain a positive charge through electron impact or electrospray ionisation 3. Acceleration: the positive ions are attracted to a negatively charged plate and accelerate towards it. The amount they accelerate depends on m/z ratio (high m/z ratios will accelerate to lower speeds than low m/z ratios). Once accelerated, all ions have the same kinetic energy 4. Ion Drift: some ions will pass through a hole in the negatively charged plate, forming a beam of particles which travel along the 'flight tube' towards the detector. Because they are travelling at different speeds, they start to drift further apart. 5. Detection: different m/z ratio ions arrive at the detector at different times due to different velocities. Time of flight is recorded and as each ion hits the detector is gains an electron, generating a current, the size of which is proportional to the number of each type of ion. 6. Data analysis: signal from detector passed to computer which generates a mass spectrum

Question 67

what are the 2 methods of ionisation in a mass spectrometer?

Answer 67

electrospray or electron impact ionisation

Question 68

describe the process of electrospray ionisation

Answer 68

1. sample X is dissolved in a volatile solvent (water or methanol) 2. sample X is injected through a hypodermic needle to produce a fine mist (aerosol) 3. tip of the needle is attached to the positive terminal of a high voltage power supply 4. particles are ionised by gaining a proton (H+ ion) from the solvent as they leave the needle 5. this produces XH+ ions (ions with a single positive charge and a mass of Mr + 1) 6. solvent evaporates while XH+ ions are attracted towards negative plate where they are accelerated

Question 69

describe the process of electron impact ionisation

Answer 69

1. sample being analysed is vapourised 2. high energy electrons are fired at sample from an electron gun (hot wire filament with a current running through it which emits electrons) 3. high energy electrons knock one electron off each particle, forming a 1+ ion 4. 1+ ions are then attracted towards a negative electric plate where they are accelerated

Question 70

what type of element/substance is electron impact ionisation used for and why?

Answer 70

- electron impact ionisation is used for elements/substances with low formula mass - 1+ ion formed is known as a molecular ion; molecular ion often breaks down into smaller fragments, some of which are also detected in the mass spectrum

Question 71

what type of element/substance is electrospray ionisation used for and why?

Answer 71

electrospray ionisation is used for substances with higher molecular mass as fragmentation rarely takes place

Question 72

how do ions separate in the TOF mass spectrometer?

Answer 72

Once accelerated, all ions have same kinetic energy, though they will travel through flight tube at different velocities and reach detector at different times.

Question 73

why may isotopes have slightly varying physical properties?

Answer 73

because they have different masses

Question 74

when would a 24Mg ion have a m/z of 12?

Answer 74

if 2 electrons had been removed from the particle, forming a 2+ ion

Question 75

what should you give in an exam, if asked for the species for a peak in a mass spec?

Answer 75

charge and mass number e.g. 24Mg+

Question 76

With electron impact ionisation, the molecule will often break up and give a series of peaks caused by the fragments. Which peak on the mass spec is the molecular ion peak?

Answer 76

The peak with the largest m/z, however, will be due to the complete molecule and will be equal to the relative molecular mass

Question 77

How do you find the Mr of a molecule that was ionised using electrospray ionisation, from the mass spec?

Answer 77

With electrospray ionisation, fragmentation will not occur; there will be one peak that will be equal to the mass of the MH+ ion. Subtract 1 to get the Mr of the molecule.