(1) Atomic Structure Flashcards
What is the mass and charge of Protons, Neutrons and Electrons?
Proton:
- mass = 1
- charge = +1
Neutron:
- mass = 1
- charge = 0
Electron:
- mass = 1/1840
- charge = -1
Define atomic number.
The atomic number is equal to the number of protons.
Define mass number.
The mass number is equal to the number of protons and neutrons combined.
Define relative atomic mass.
Average mass of 1 atom (of an element)
[divided by]
1/12 mass of one atom of 12C
What are isotopes?
Atoms with the same number of protons but a different number of neutrons.
Do isotopes of the same element have the same chemical properties and why?
Yes
Because they have the same electron configuration
Define First Ionisation Energy.
Energy when one mole of electrons is removed from one mole of gaseous atoms to form one mole of gaseous 1+ ions
Write an equation for the 1st Ionisation Energy for Potassium.
K(g) —> K+(g) + e-
Why is the 2nd Ionisation Energy of S higher than the 1st?
The second electron is removed from an ion that already has a positive charge.
What is the model answer for:
The following data shows the first seven successive ionisation energies of a period 3 element. State which element it is and explain your reasoning.
When approaching a question like this, look for where there are large gaps between the ionisation energies:
Model Answer:
- The biggest jump 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
What is the shape of:
- s orbital
- p orbital
- spherical
2. dumbbell
How many s orbitals are in the s subshell?
How many p orbitals are in the p subshell
How many d orbitals are in the d subshell?
1
3
5
Which orbitals have the lowest energy?
The ones closest to the nucleus.
Rule: The higher the orbital, the higher in energy it is.
Which electron on an atom is highest in energy?
The outer most electron - because it is the furthest away from the nucleus.
What does an energy level diagram look like?
- each box represents an orbital - each hold 2 electrons
- each electron is represented by a half arrow, one pointing up, other pointing down
- the half arrows represent the electrons spinning in different directions
3 rules for how to allocate electrons to orbitals?
- Orbitals of lower energy are always filled first
- Atomic orbitals of the same energy fill singly before electrons pair up
- No orbital can have more than 2 electrons
Why is Sulfur a p-block element?
It’s highest energy electron is in the p subshell.
How do you work out the electronic configuration of an ion?
You remove the electrons from the highest energy orbitals in its normal electronic configuration
Which orbital is lower in energy, 4s or 3d?
What must you remember with these 2 orbitals when writing electronic configuration?
4s
- FIRST IN FIRST OUT
- electrons fill 4s first, then 3d
- electrons are removed from 4s first, then 3d
Rule for writing d-block element configurations?
They are more stable when they have a full, or exactly half full sub shell.
Electronic configuration for Chromium?
1s2 2s2 2p6 3s2 3p6 4s1 3d5
Electronic configuration for Copper?
1s2 2s2 2p6 3s2 3p6 4s1 3d10
Electronic configuration Cu2+?
1s2 2s2 2p6 3s2 3p6 3d9
What is the general trend in Ionisation Energy across a period?
- general increase across the period
- this is because across period 3 there is a greater nuclear charge
- same amount of shielding
- so greater attraction between the nucleus and outer electron
Explain why Aluminium has a lower 1st 1E than Magnesium.
- The first e- removed from Mg is from a 3s sub level.
- The first e- removed from Al is from a 3p sub level.
- The 3s sub level is lower in energy than 3p.
- Therefore less energy is needed to remove the electron from Al.
Explain why Sulfur has a lower 1st IE than Phosphorous.
- The first e- removed from P is from a 3p sub level and is unpaired.
- The first e- removed from S is also from a 3p sub level, but is from a paired orbital.
- This means Sulfur has a lower ionisation energy due to electron pair repulsion.
- Therefore less energy is needed to remove the electron from S.
Trend in Ionisation Energy down a Group?
- atoms get bigger
- more shielding
- weaker attraction from nucleus to electron in outer shell
- ionisation energy decreases down group
State and explain the trend in Atomic Radius down a Group?
Atomic radius increases.
The number of shells increases so the amount of shielding increases.
There is a weaker attraction between the electrons and the nucleus.
State and explain the trend in Atomic Radius across a Period.
Atomic radius decreases.
The nuclear charge increases.
The amount of shielding stays the same.
There is a greater attraction between the electrons and the nucleus.
What two factors does Mass Spectrometer measure?
Measures:
- relative abundance
- mass/charge ratio
Why is the entire machine in a vacuum?
To prevent any of the particles being tested colliding with molecules from the air.
Describe Electron Impact, and give the equation.
High-energy electrons
Fired at sample
From an electron gun
Knock an electron off sample particles forming 1+ ions
X(g) —> X+(g) + e-
Describe Electrospray Ionisation, and give the equation.
Sample is dissolved in a volatile solvent
Then injected through a fine hypodermic needle
Tip of needle is connected to positive terminal of high voltage
Sample particles gain a proton
X(g) + H+ —-> XH+ (g)
Explain why it is necessary to ionise molecules when measuring their mass in a TOF Mass Spectrometer.
Ions will be accelerated by attraction to negative plate
Only ions will accept an electron and generate a current when hitting the detector
How is the ion separated in the flight tube?
Ions travelling at higher speeds (small m/z)move ahead move ahead of those travelling more slowly (large m/z).
How are the ions detected and how is their abundance measured?
Each ion hits the detector
Ion gains an electron
Generates a current
Size of the current is proportional to the abundance of the ion
Referring to KE = 0.5 X M X V^2, what stays constant for all ions in the question?
The kinetic energy.
How do you calculate the mass in kg of a ion?
Mass number divided by 1000, then divided by avagadros constant
Boron has relative atomic mass of 10.8
Boron exists as two isotopes, 10B and 11B.
Calculate the percentage abundance of 10B in this naturally occurring sample of Boron.
20%.
State two differences between the plum pudding model and the model of atomic structure used today.
- New model has a nucleus containing protons and neutrons
- Electrons are now arranged in shells
Sodium fluoride contains sodium ions (Na+) and fluoride ions (F-).
Na+ and F- have the same electron configuration.
Explain why a fluoride ion is larger than a sodium ion.
Fluoride has lower nuclear charge.
Weaker attraction between nucleus and outer electrons.
Write an equation, including state symbols, to represent the process that occurs when the third ionisation energy of manganese is measured.
Mn2+ (g) ⟶ Mn3+ (g) + e−
Chlorine exists as two isotopes 35Cl and 37Cl in the ratio 3:1
Which statement about peaks in the mass spectrum of Cl2 is correct?
A
Peaks at m/z = 70 and 74 in the ratio 3:1
B
Peaks at m/z = 70, 72 and 74 in the ratio 9:6:1
C
Peaks at m/z = 70, 72 and 74 in the ratio 9:3:1
D
Peaks at m/z = 70 and 72 in the ratio 3:1
B
