3.1.1 - Atomic Structure Flashcards
1
Q
Relative mass for an electron
A
1/1840
2
Q
What letter represents the mass number?
A
A
3
Q
What letter represents the atomic number?
A
Z
4
Q
What holds electrons and protons together in atom?
A
Electrostatic forces of attraction
5
Q
Why is the strong nuclear force stronger than electrostatic forces?
A
It overcomes repulsion between protons in nucleus
6
Q
What decides the chemical properties of an element?
A
The number & arrangement of electrons
7
Q
Why do isotopes have the same chemical properties? (2)
A
They have same electron configuration and the chemical properties depend on electrons
8
Q
Isotopes have ___ _____ physical properties
A
slight different physical properties
9
Q
Why do isotopes have slight different physical properties?
A
Physical properties depend on mass of atom
10
Q
19th century: What did John Dalton say atoms were?
A
- Solid spheres
- Different spheres made different elements
- All atoms of an element have the same mass
11
Q
1897: What did J.J. Thomson discover and what did it show?
A
- Discovered the electron
- Showed atoms weren’t solid and indivisible
- (Model known as ‘plum pudding model’ - negative electrons embedded in a positive ball of charge)
12
Q
1909 - Ernest Rutherford: What did he find out?
A
Conducted the golden foil experiment:
- Fired positively charged alpha particles at a very thin sheet of gold
- Particles passed straight through gold & only small no. of particles were deflected backwards (pulm pudding model said = alpha particles would be deflected by the positive ‘pudding’ in atom)
- = developed into nuclear model of atom
- Tiny positive nucleus surrounded by ‘cloud’ of negative electrons - most of atom is empty space
13
Q
What was Niels Bohr’s model & discovery?
A
- Model: where electrons exist in shells or orbits of fixed energy
- Discovered: When electrons move between shells, electromagnetic radiation (with fixed energy or frequency) is emitted/absorbed
14
Q
What have modern day scientists discovered & so what did they do?
A
- Electrons in same shell ≠ same energy
- Bohr model = wrong ∴ they refined it & added sub-shells
- (Isn’t perfect model but it’s simple and explains many experimental observations e.g. bonding & ionisation energy trends)
15
Q
Define Relative Isotopic Mass
A
Mass of an atom of an isotope of an element on a scale where an atom of carbon-12 is 12
16
Q
Define Relative Molecular Mass (Mr)
A
Average mass of a molecule on a scale where an atom of carbon-12 is 12
17
Q
What does a mass spectrometer do and how?
A
- It determines the mass of separate atoms (or molecules)
- Works by forming ions from sample and then separating them according to the ratio of their charge to their mass
18
Q
Name the 6 things that happen when a sample is squirted into time of flight (TOF) mass spectrometer
A
- Vacuum
- Ionisation
- Acceleration
- Ion Drift
- Detection
- Data Analysis
19
Q
Describe the step vacuum in mass spectrometry (TOF)
A
Whole apparatus is kept under a vacuum to prevent ions produced from colliding with air molecules
20
Q
Name the two ways you can ionise your sample in mass spectrometry (TOF)
A
2 methods:
- Electrospray ionisation
- Electron impact ionisation
21
Q
Describe the method electrospray ionisation
A
- A high voltage is applied to a sample in a polar solvent
- Sample molecule, M, gains a proton forming MH+
22
Q
Describe the method electron impact ionisation
A
- Sample is bombarded by high energy electrons
- Sample molecule loses an electron = become +1 ions (M+)
23
Q
Describe the step acceleration in mass spectrometry (TOF)
A
Positively charged ions are accelerated by an electric field (attracted to negatively charged plate) so = they all have same kinetic energy
24
Q
Describe the step ion drift in mass spectrometry (TOF)
A
- Ions enter region with no electric field so they just drift through it
- Lighter ions will drift faster than heavier ions
25
Describe the step detection in mass spectrometry (TOF) & state how abundance is measured
* Lighter ions travel at higher speeds = reach detector in less time than heavier ions
* Positive ions collected at detector
* Causing current to flow / detected electrically
* Abundance measured: idea that current depends on number of ions hitting detector
26
Describe the step data analysis in mass spectrometry (TOF)
Signal from detector is sent to a computer which generates a mass spectrum
27
What does the y-axis of mass spectrum represent?
Abundance of ions
28
What does the height of each peak give on the mass spectrum?
Relative isotopic abundance
29
If the sample is an element, what does each line represent on the mass spectrum?
A different isotope of the element
30
What does the x-axis on the mass spectrum represent?
'mass/charge' ratio (m/z)
31
Describe how to work out the relative atomic mass from mass spectrum (4)
1. Spectrum gives relative abundance (of isotopes) & m/z (mass/charge ratio)
2. Multiply m/z by relative abundance for each isotope
3. Sum these values
4. Divide by the sum of the relative iostopic abundances
32
Describe how you can use mass spectrometry to identify elements
You can see if the sample being analysed has the same relative abundances of isotopes
33
Explain how you use mass spectrometry to identify molecules
mass/charge ratio (of peak) = relative molecular mass of molecule
34
Each shell is given a number called ____ \_\_\_\_ \_\_\_\_\_
principal quantum number
35
The further away a shell is from nucleus, the _____ its energy & the ____ its principal quantum number
higher its energy + larger its principal quantum number
36
37
2 electrons in each orbital...
spin in opposite directions
38
Electron configuration: Give 2 examples of transition metals behaving unusually
Chromium (Cr) & copper (Cu) = donate 1 of their 4s electrons to 3d sub-shell
39
Write the electron configuration for chromium
40
Write the electron configuration for copper
41
Groups 4-7 can _______ electrons when they form _____ \_\_\_\_
Groups 4-7 can _share_ electrons when they form _covalent_ _bonds_
42
Why are the gases in Group 0 inert?
∵ completely filled s & p sub-shells
43
Why does Chromium (Cr) & copper (Cu) donate 1 of their 4s electrons to 3d sub-shell?
∵ they're happier with a more stable full or half-full d sub-shell
44
Define first ionisation energy
Enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms
45
Ionisation is a ________ process ∵ you have to put energy in to ionise atom/molecule
endothermic
46
Write an equation for the first ionisation of oxygen
47
Name 3 rules about ionisation energies
1. Must use gas state symbol (g) ∵ ionisation energies are measured for gaseous atoms
2. Always refer to 1 mole of atoms
3. Lower ionisation energy = easier it is to remove from ion
48
Name 3 factors that affect ionisation energy
1. Nuclear Charge
2. Shielding
3. Distance from Nucleus
49
Describe how nuclear charge affects ionisation energy
More protons in nucleus = more positively charged nucleus is & stronger the attraction for electrons
50
Describe how shielding affects ionisation energy
As no. of electrons between outer electrons & nucleus increases = outer electrons feel less attraction towards nuclear charge
Lessening of pull of nucleus by inner shells is called shielding (or screening)
51
Describe how distance from nucleus affects ionisation energy
Attraction decreases rapidly with distance
(i.e. electron close to nucleus = much more strongly attracted than one further away)
52
What is meant by high ionisation energy?
High ionisation energy = high attraction between electrons & nucleus = more energy needed to remove electron
53
What provides evidence for shells structure of atoms?
Graph of successive ionisation energies
54
Why does successive ionisation energies increase within each shell?
∵ electrons are being removed from an increasingly positive ion = less repulsion amongst remaining electrons ∴ they're held more strongly by nucleus
55
When does big jumps in ionisation energy happen?
When a new shell is broken into = an electron is being removed from shell closer to nucleus
56
Define second ionisation energy
Enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions
57
State the equation for the second ionisation of oxygen
58
State the equation for the *nth* ionisation energy
59
Describe how you can use a successive ionisation energies graph to figure out which group an element belongs to
Count how many electrons are removed before the 1st big jump to find the group number
60
Describe how you can use a successive ionisation energies graph to predict the electronic structure of elements
Working from right to left, count no. of points there are before each big jump to find how many electrons there are in each shell, starting with the first
61
Name 2 trends in first ionisation energy
* 1st ionisation energies of elements down a group of periodic table decrease
* 1st ionisation energies of elements across a period generally increase
62
Explain why ionisation energy decreases down Group 2
1. Atomic radius increases/electron removed further from nucleus
2. As group is descended more shielding = nucleus' attraction reduces
Both of these factors = make it easier to remove outer electrons = lower ionisation energy
63
Explain why ionisation energy increases across a Period (2x)
1. Increased nuclear charge (no. of protons is increases = stronger nuclear attraction)
2. Extra electrons enter roughly same energy level or similar shielding
64
Describe and explain how aluminium provides evidence for the theory of electron sub-shells
1. Aluminium's _outer electron_ = in _3p_ orbital rather than 3s
* ∵ 3p orbital = slightly higher energy than 3s orbital
* ∴ electron is found f_urther from nucleus_
2. _Additonal electron shielding_ - 3p orbital has additional shielding provided by 3s2 electrons
3. Both these factors strong enough to override effect of increased nuclear charge = _ionisation energy drops slightly, easier to remove electron_
65
Drops between Groups __ and __ Is due to Electron \_\_\_\_\_\_
**Drops** between **Groups 5 and 6** Is due to **Electron Repulsion**
66
Describe and explain how phosphorus & sulfur provides more evidence for the electronic structure model
1. (Shielding identical in phosphorus & sulfur atoms + electron is being removed from an identical orbital)
2. In phosphorus's case: electron being removed from singly-occupied orbital
3. But in sulfur: electron removed from _paired electrons in 3p orbital_
4. _Electron repulsion_ between 2 electrons = _electron easier to remove from pair_
67
Explain why the value of the first ionisation energy of neon is higher than that of sodium (2x)
* Electron removed from a level of lower energy or e– removed from 2p rather than from 3s
* Less shielding
68
Write the electron configuration for calcium using noble gas symbols
69
Which of Na+ and Mg2+ is the smaller ion? Explain why (2)
Mg2+
Has more protons with same shielding
70
Magnesium exists as three isotopes: 24Mg, 25Mg & 26Mg
24Mg percentage = 80%
26Mg percentage = 10%
71
Define relative atomic mass of an element.
Average mass of an atom of an element on a scale where an atom of carbon-12 is 12
72
How do you calculate the RAM of an element from its mass spectra?
