Atomic structure Flashcards
What is the relative charge and mass of protons?
Protons
Relative charge: 1+
Relative mass: 1
What is the relative charge and mass of neutrons?
Neutrons
Relative charge: 0
Relative mass: 1
What is the relative charge and mass of electrons?
Electrons
Relative charge: 1-
Relative mass: 1
What does an atom consist of?
- nucleus containing positively charged protons and neutral charged neutrons
- negatively charged electrons orbit nucleus in energy levels/shells
What is the maximum number of electrons that each shel can hold?
1st shell - 2 electrons
2nd shell - 8 electrons
3rd shell - 18 electrons
4th shell - 32 electrons
How many orbitals are there in each sub-shell?
s sub-shell: 1orbital
p sub-shell: 3 orbitals
d sub-shell: 5 orbitals
f sub-shell: 7 orbitals
What is the highest energy electron?
- Electron furthest away from the nucleus
———-> highest energy electron (f)
s, p, d, f
What is the electron configuration of Argon?
1s2 2s2 2p6 3s2 3p6
What is the electron configuration of Al2+?
1s2 2s2 2p6 3s1
What is the electron configuration of F-?
1s2 2s2 2p6
What are the 2 exceptions of the d-block atoms? Explain why
Chromium: 1s2 2s2 2p6 3s2 3p6 4s1 3p5
- more stable with a half full d sub-shell
Copper: 1s2 2s2 2p6 3s2 3p6 4s1 3d10
- more stable with a full d sub-shell
What are the exceptions of d-block ions? Explain why
Fe2+: 1s2 2s2 2p6 3s2 3p6 3d6
- Electrons lost from 4s sub-shell
- 4s – first in – first out
Cu2+:
1s2 2s2 2p6 3s2 3p6 3d9
- 4s sub-shell empties first
Does the 3d sub-shell or 4s sub-shell have higher energy?
3d sub-shell
What is an orbital?
A region around the nucleus that can hold up to 2 electrons
Define first ionisation energy
The amount of energy needed to remove one mole of electrons from one mole of atoms in the gaseous state
What is the equation for the 1st ionisation energy of boron?
B (g) —-> B+ (g) + e-
What is the equation for the 3rd ionisation energy of magnesium?
Mg2+ (g) —-> Mg3+ (g) + e-
What is the general trend of atomic radius across period 3? Explain why
- Atomic radius decreases
- As nuclear charge increases
- Shielding stays the same
- So greater attraction between outer electrons and nucleus
What is the general trend in ionisation energies across period 2? Explain why
-General increase
- Nuclear charge increases
- Atomic radius increases
- Shielding stays the same
What 2 elements deviate from the general trend in ionisation energies across period 2? Explain why
Boron: 1s2 2s2 2p1
- outer electron removed from 2p sub-shell
- 2p sub-shell is higher in energy
- so less energy required to remove outer electron
Oxygen: 1s2 2s2 2p4
- outer electron removed from 2p sub-shell from a paired orbital
- less energy required to remove outer electron
- due to electron pair repulsion
What is the trend in ionisation energies down a group? Explain why
- Decrease in ionisation energies
- Increase in atomic radius
- Due to increased shielding
- Weaker attraction between outer electrons and nucleus
What are the 3 factors that influence ionisation energies? Explain why/how
N D S
Nuclear charge:
- Increase in nuclear charge
- stronger attraction between outer electrons and nucleus
- Increases ionisation energies
Distance from nucleus/atomic radius:
- decrease in atomic radius
- stronger attraction between outer electrons and nucleus
- increases ionisation energies
Shielding
- decreased shielding
- stronger attraction between outer electrons and nucleus
- increases ionisation energies
What is the general trend in ionisation energies across period 3? Explain why
- General increase
- Increase in nuclear charge
- Decrease in atomic radius
- Same shielding
- So greater attraction between outer electrons and nucleus
What 2 elements deviate from the general trend of 1st ionisation energies in period 3?
Aluminium and Sulfur
Explain why Aluminium has a lower 1st ionisation energy than Magnesium
Al: 1s2 2s2 2p6 3s2 3p1
Mg: 1s2 2s2 2p6 3s2
- Outer electron of Al is taken from the 3p sub-shell whereas the outer electron of Mg is taken from the 3s sub-shell
- 3p sub-shell is higher in energy than the 3s sub-shell therefore less energy is required to remove the outer electron
Explain why Sulfur has a lower 1st ionisation energy than Phosphorous
S: 1s2 2s2 2p6 2s2 3p4
P: 1s2 2s2 2p6 3s2 3p3
- Outer electron of Sl is taken from a 3p paired orbital whereas the outer electron of P is taken from a 3p unpaired orbital
- Less energy is required to remove the electron from S due to electron pair repulsion
State and explain the trend in atomic radius down a group
- Atomic radius increases
- Due to increase in shielding
What is meant by atomic number?
Equal to the number of protons
What is meant by mass number?
Equal to the number of protons and neutrons combined
What is meant by an isotope?
- Atoms with the same number of protons and electrons but a different number of neutrons
Why do isotopes of the same element have the same chemical properties?
Because they have the same electron configuration
Describe how a time of flight mass spectrometer works
- Ionisation: particles gain a positive charge by undergoing electrospray/electron impact ionisation
- Acceleration: Positively charged ions attracted to negatively charged plate
- Detection: As each ion hits the detector, an electron is gained which generates a current
- current proportional to the relative abundance (number of each type of ion)
- Data analysis: signal from detector passed onto computer. Mass spectrum generated
Describe electron impact ionisation
- Sample is vaporised
- High energy electrons fired from an electron gun
- Knocking off an electron off each molecule, forming 1+ ions
What is the equation of ionisation of CH4 after undergoing electron impact ionisation?
CH4 (g) —> CH4+ (g) + e-
Describe electrospray ionisation
- Sample is dissolved in a volatile solvent
- Injected through a fine hypodermic needle
- Needle is connected to a positive terminal of high voltage
- Particles ionised by gaining a proton
Why are sample particles ionised?
- So they can accelerate towards the negatively charged plate
- So a current is generated when they hit the detector
How is the ion accelerated?
- Positive ions are attracted to a negatively charged plate
- All ions have the same KE
How are the ions separated in the flight tube?
- Lighter ions (smaller m/z ratio) move ahead of heavier ions (larger m/z ratio)
- Lighter ions travel at faster speed
How are the ions detected?
- Ion hits detector
- Each ion gains electron
- Generates a current
- Size of current proportional to ion abundance
What is the equation for KE?
KE = 1/2mv2
What is the equation for speed/distance/time
v = d/t
Formula to calculate relative atomic mass?
(mass 1 x abundance 1) + (mass 2 x abundance 2) + (mass n x abundance n) / total abundances
State two features of todays atomic structure model that is not shown in Rutherford/plum pudding model
- Nucleus containing protons and neutrons
- Electrons arranged in different energy levels/orbitals
Define the term relative atomic mass
- Average mass of an atom of an element
- Compared to 1/12th the mass of on atom of carbon-12
What is the electron configuration of an atom with only two unpaired electrons?
A - 1s2 2s2 2p3
B - 1s2 2s2 2p4
C - 1s2 2s2 2p6 3s2 2p5
D - 1s2 2s2 2p6 3s2 2p6 4s1 3d5
B - 1s2 2s2 2p4
State in terms of fundamental particles, one similarity and one difference between atoms of Cr50 and Cr53
Similarity:
same number of protons
Difference
different number of neutrons
Give two reasons why it is necessary to ionise isotopes before they can be analysed in a TOF mass spectrometer
- positive ions accelerated by electric field
- Ions hit detector to create a current
Explain the pattern in first ionisation energies of the elements from lithium to neon
- 1st IE increases (generally)
- Increase in nuclear charge
- Same shielding
- stronger attraction between outer electrons and nucleus
Deviation from Be –> B
- B has lower 1st IE
- Outer electron in 2p which is higher in energy than 2s
Deviation from N –> O
- O has lower 1st IE
- 2 paired electrons in 2p
- electron pair repulsion
State and explain trend in 1st ionisation energies of elements in group 2 from magnesium to barium
- General decrease
- Ions get bigger
- Weaker attraction of ion to lost electron
Describe how ions are formed in TOF mass spectrometer
Describe electrospray/electron impact
Outline how TOF mass spectrometer is able to separate two species to give two peaks
- positively charged ions accelerated by electric field
- All ions have same KE
- ions with lower m/z travel faster
- ions with lower m/z reach detector first
suggest why the Mr calculated is different to the one on the periodic table
other isotopes present
state how relative abundance is determined in TOF spectrometer
- each ion gains electron as it hits detector
- relative abundance depends on size of current
give two reasons why it is necessary to ionise isotopes of chromium before they can be analysed by TOF mass spectrometer
- so they can be accelerated to negative plate
- ions create current when hitting detector
identify period 3 element with highest SECOND ionisation energy
sodium
explain why atomic radius decreases across period 3
- increase in nuclear charge
- similar shielding
Identify the element in Period 3, from sodium to chlorine, that has the highest electronegativity.
Chlorine
