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Chemistry > Atomic Structure > Flashcards

Atomic Structure Flashcards

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1
Q

Describe the Bohr model:

A
  • Protons and neutrons are found in the centre of the atom called the nucleus.
  • Electrons orbit around the nucleus in shells or energy levels.
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2
Q

Mass of subatomic particles:

A

Protons: 1
Neutrons: 1
Electrons: 1/1840

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3
Q

Charge of subatomic particles:

A

Protons: 1+
Neutrons: 0
Electrons: 1-

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4
Q

Definition of atomic number:

A

Number of protons

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5
Q

Definition of mass number:

A

Total number of protons and neutrons

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6
Q

Definition of an Ion:

A

An atom that has lost or gained an electron so has a +/- charge

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7
Q

Cation: + ion

A

An atom has lost electrons so that there are more protons than electrons

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8
Q

Anion: - ion

A

An atom has gained electrons so there are more electrons than protons

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9
Q

Definition of an Isotope:

A

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

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10
Q

Why do isotopes of the same element have similar chemical properties?

A

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

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11
Q

Evidence to support Bohr’s model:
Rutherford’s experiment

A

-Rutherford fired He2+ ions at a sheet of gold foil
-When the He2+ ions arrived at the back of the atom he concluded that most of the atom was empty space.
-A very small number of the He2+ ions where detected at the side of the atom
-He concluded that the atom must have a small positive nucleus.

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12
Q

Definition of Ionisation Energy:

A

Amount of energy needed to remove a mole of electrons from a mole of atoms, in the gaseous state.

Units: kJ mol-1

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13
Q

Eg: Write down the equation for the 3rd ionisation energy of Potassium
(2m)

A

K 2+ (g) → K 3+ (g) + e-

INCLUDE STATE SYMBOLS FOR 2ND MARK

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14
Q

Factors that will influence IE:
1) Nuclear Charge

A

-More protons
-Stronger attraction to nucleus
-More energy to remove outermost electron

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15
Q

Factors that will influence IE:
2) Distance from the nucleus

A

-Electron closer to nucleus
-Stronger attraction to nucleus
-More energy to remove outermost electron

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16
Q

Factors that will influence IE:
3) Shielding

A

-Electron on shell further from the nucleus
-More shielding
-Weaker attraction
-Less energy to remove outermost electron

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17
Q

Successive ionisation energies:

A

A single atom can be ionised to form a 1+ ion. This ion can then be ionised again to form a 2+ ion. This process can be repeated until all the electrons have been removed from the atom.

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18
Q

Describing IE levels:
Eg: Boron - Group 4

A

-IEs 1-3 increase because each electron is being removed from a more positive ion each time. (The attraction between the electrons and the protons becomes stronger as there are less electrons being attracted by the same number of protons)

-The 4th electron is removed from a shell closer to the nucleus and so is much more strongly attracted to the nucleus therefore a significantly higher amount of energy is required to remove the 4th electron

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19
Q

Why is the second ionisation energy of Boron higher than the first?

A

The second electron is removed from an ion that already has a positive charge

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20
Q

Eg: The following data shows the first seven successive ionisation energies of a period 3 element. State which element it is and explain your reasoning.

Data: IE
1st - 2947
2nd - 3683
3rd - 4837
4th - 5929
5th - 14839
6th - 15538

A

-the largest increase is between the 4th and 5th ionisation energies
-the 5th electron is on the shell closer to the nucleus
-The element must have 4 electrons on its outer shell
·-in period 3 this must be Silicon

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21
Q

Why is Li a bigger atom than Be?

A

Both atoms have the same number of shells

They have the same shielding

But Be has more protons

So it attracts the outer most electrons more strongly

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22
Q

Why is Li a bigger atom than He?

A

Li has an extra electron shell and is further away from the nucleus

The outer electron is more shielded

The outer electron is less strongly attracted to the nucleus

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23
Q

Why is Li a bigger atom than F?

A

Both atoms have the same number of shells

They have the same shielding

But F has more protons

So it attracts the outer most electrons more strongly

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24
Q

Why is Li+ a smaller ion than F-?

A

A Li+ ion only has one shell

Its electron are closer to the nucleus and there is less shielding

So the outer electrons are more strongly attracted

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25
Q

Which element has the highest IE?

A

Helium has the highest 1st IE of all elements because:
-It has more protons than Hydrogen and only one shell so has the same shielding as Hydrogen

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26
Q

General trend in 1st IE across a Period:

A

The 1st IE will increase

There are more protons in the nucleus (nuclear charge increases)

The shielding remains the same

27
Q

Electron shells:

A

The 1st shell is closest to the nucleus, and each shell further is numbered 2nd, 3rd, 4th etc in succession

Within each shell there are sub-shells (s, p, d), and within each sub-shell we find orbitals.

28
Q

Maximum number of electrons in each shell:

A

1st - 2
2nd - 8
3rd - 18
4th - 32

29
Q

Definition of an orbital:

A

An orbital is a region within an atom that can hold up to two electrons with opposite spins.

30
Q

S and P orbital shape

A

S - Spherical shape
P- Dumbbell shape

31
Q

Highest energy electron

A

Outer most electron on an atom or ion is the highest energy electron because it is the furthest from the nucleus

32
Q

Electron Configuration:
Eg - Xenon

A

1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6, 5s2, 4d10, 5p6

33
Q

Electron Configuration meaning

A

First number represents shell/energy level of electron
Letter represents sub shell of electron
Last number refers to number of electrons in that sub shell

34
Q

When electrons surround a nucleus, there are 3 rules for how to allocate electrons to orbitals:

A

1) Orbitals of lower energy are always filled first
2) Atomic orbitals of same energy fill single first before electrons pair up
3) No orbital can have more than 2 electrons

35
Q

Rule for exception for electron configuration

A

d block elements are more stable when they have a full or exactly half full sub shell

36
Q

Exception 1 for electron configuration: Chromium

A

Expected: 1s2 2s2 2p6 3s2 3p6 4s2 3d4
Correct: 1s2 2s2 2p6 3s2 3p6 4s1 3d5

37
Q

Exception 2 for electron configuration: Copper

A

Expected: 1s2 2s2 2p6 3s2 3p6 4s2 3d9
Correct: 1s2 2s2 2p6 3s2 3p6 4s1 3d10

38
Q

Exception 3 for electron configuration: d block ions

A

When d block elements form positive ions, electrons are removable from the 4s sub shell first and not the 3d sub shell

Example: Fe(2+) ion
Iron: 1s2 2s2 2p6 3s2 3p6 4s2 3d6
Iron(2+): 1s2 2s2 2p6 3s2 3p6 3d6
(2 e- REMOVED FROM 4S SUB SHELL FIRST)

39
Q

Transition metal ions: Electron configuration

A

4S
First in
First out

40
Q

Trend in ionisation energy across a period
Eg: Period 2

A

1) General increase in IE across Period 2
2) this is because across Period 2 there is a greater nuclear charge (more protons)
3) and same amount of shielding
4) so a greater attraction between nucleus and outer electron

41
Q

Period 2
Be + B configuration

A

1) first electron removed from Be is from a 2s sub level
2) first electron removed from B is from a 2p sub level
3) 2s sub level is lower in energy than 2p
4) therefore less energy is needed to remove the electron from B

42
Q

Period 2
N + O configuration

A

1) first electron removed from N is from a 2p sub level and is unpaired
2) first electron removed from O is also from a 2p sub level but is from a paired orbital
3) this means O has a lower IE due to electron pair repulsion
4) therefore less energy is needed to remove electron from O

43
Q

Trends in IE down a group

A

IE decreases down the group
Atomic radius increases as number of shells increases
More shielding
Weaker attraction between nucleus and outer electron

44
Q

Why does atomic radius decrease from left to right across a period

A

Nuclear charge (proton number) increases
Greater attraction between electrons and nucleus
Amount of shielding stays the same

45
Q

What is a mass spectrometer

A

A machine that can be used to analyse elements or compounds to accurately determine Ar of atoms or Mr of molecules

46
Q

2 factors that mass spectrometer measure:

A

1) Relative abundance
2) Mass/charge ratio (m/z)

47
Q

Time of flight mass spectrometer: Steps

A

Step 1: Ionisation
Step 2: Acceleration
Step 3: Ion Drift
Step 4: Detection

48
Q

TOF mass spectrometer:
MP1) Vacuum

A

Entire machine is a vacuum inside to prevent any of the particles being tested colliding with molecules from the air

49
Q

TOF mass spectrometer:
MP2) Ionisation

A

Two Methods:
a) Electron impact
b) electrospray ionisation

in both methods, sample particles gain a positive charge

50
Q

TOF mass spectrometer:
MP3) Acceleration

A

Positive ions are attracted to negatively charged plate and accelerate towards it.
High m/z ratio ions will accelerate to lower speeds. Low m/z ratio ions will accelerate to higher speeds
Once accelerated, all ions will have same kinetic energy

51
Q

TOF mass spectrometer:
MP4) Ion drift

A

Some ions will pass through a hole in negatively charged plate. They form a beam of particles and travel along flight tube towards detector.
Due to particles travelling at different speeds, ions drift apart as slower particles can’t keep up with faster ones

52
Q

TOF mass spectrometer:
MP5) Detection

A

Different m/z ratio ions arrive at detector at different times due to different velocities
As each ion hits the detector, it gains an electron
This generates a current
Size of current is proportional to abundance of ion

53
Q

TOF mass spectrometer:
MP6) Data analysis

A

Signal from detector is passed to a computer which generates a mass spectrum

54
Q

Why are sample particles ionised

A

1) so they can be accelerated towards negatively charged plate
2) so they generate a current when they hit the detector

55
Q

How is the ion accelerated

A

1) positive ions attracted to negatively charged plate
2) all ions have same kinetic energy

56
Q

How are ions separated in flight tube

A

Ions travelling at higher speeds (small m/z ratio) move ahead of those traveling more slowly (large m/z ratio)

57
Q

How are ions detected

A

1) each ion hits the detector
2) ion gains an electron
3) generates a current
4) size of current is proportional to abundance of ion

58
Q

Ionisation method 1:
Electron impact

A

Sample is vaporised
High energy electrons are fired from electron gun at sample
An electron is knocked off forming 1+ ion
Ion is attracted towards negatively charged plate and accelerated

Equation:
X (g) → X+ (g) + e-

59
Q

Ionisation method 2:
Electrospray ionisation

A

Sample is dissolved in a volatile solvent and injected through fine hypodermic needle to give a fine mist
Tip of needle is attached to positive terminal of a high voltage power supply
Particles gain a proton
Ions are attracted to negatively charged plate and are accelerated

Equation:
X (g) + H+→XH+ (g)

60
Q

Equation for Ar:

A

Ar = (Mass 1 × Abundance 1) + (Mass 2 × Abundance 2) ÷ Sum of Abundances

61
Q

Equation for Kinetic energy:

A

Kinetic Energy (J) = 1/2 × Mass (kg) × Velocity^2 (m/s2)

62
Q

Rearranging KE equation to find:
a) mass
b) velocity^2

A

m = KE ÷ (1/2 × v^2)

v^2 = KE ÷ (1/2 × m)

63
Q

Equation for time of flight

A

t = d ÷ v

t = d√(m ÷ 2KE)

t - time of flight (s)
d - length of flight tube (m)
v - velocity of particle (m/s-1)
m- mass of particle (kg)
KE - kinetic energy of particle (J)

64
Q

Working out mass of an ion

A

mass ÷ (6.022 × 10^23)

mass units: gmol-1 / kgmol-1

1 gmol-1 = 0.001 kgmol-1

Chemistry (9 decks)

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