Unit 1: Section 1: Atomic Structure Flashcards
Nuclear symbol for mass number, atomic number and element symbol
Mass number: A
Atomic number: Z
Element symbol: X
What are the four basic principles that Niels Bohr proposed for his model of the atom
Electrons only exist in fixed orbitals
Each shell has a fixed energy
When an electron moves between shells electromagnetic radiation is emitted or absorbed
Because the energy of shells is fixed, the radiation will have a fixed frequency
What is relative atomic mass
The average weighed mass of one atom compared to 1/12th the mass of one atom of carbon 12
What is relative isotopic mass
The relative isotopic mass is the mass of an isotope relative to 1/12th of the mass of a carbon-12 atom
What is relative formula mass
The average mass of a formula unit on a scale where an atom of carbon-12 is exactly 12
How do you work out the relative formula mass
Add up the relative formula mass of all the ions that make the compound
What is a mass spectrometer
A machine used to analyse elements or compounds
What information can you derive from mass spectrometry
Relative atomic mass
Relative abundance of its isotopes
Relative molecular mass of a molecule
What are the four things that happen when a sample enters a time of flight mass spectrometer
Ionisation
Acceleration
Ion drift
Detection
Explain the ionisation stage of time of flight mass spectrometry
Sample needs to be ionised before it enters the spectrometer
Two ways to do this is :
- Electrospray ionisation - in this method the sample is dissolved
in a solvent and pushed through a small nozzle at a high
pressure. High voltage is applied to it so each particle gains a
H+ ion. The solvent is then removed leaving a gas made up of
positive ions
- Electron impact ionisation - sample is vaporised and an
electron gun is used to fire high energy particles at it. This
knocks one electron off each particle, so they become 1+ ions
Explain the acceleration stage in time of flight mass spectrometry
Positive ions are accelerated by negatively charged electric field
Lighter ions experience greater acceleration because they experience the same kinetic energy as the heavier ions but they weigh less
Explain the ion drift stage in time of flight mass spectrometry
The ions enter a region with no electric field
They drift through it at the same speed as the speed in the electric field
The lighter ions will therefore drift at a quicker speed
Explain the detection stage in time of flight mass spectrometry
The lighter ions reach the ion detector quicker then the heavier ions
Detector detects the current created when the ions hit it and records how long they took to pass through the spectrometer. This data is then used to calculate the mass/charge values needed to produce a mass spectrum
What are the y and x axis in a mass spectrum
y - % abundance
x - mass/charge
Explain the relationship between the mass/charge ratio and the relative mass of each isotope when the sample has been ionised by electron impact ionisation
Since one electron is being knocked off and turning the sample into +1 ions the mass/charge ratio will be the same as the relative mass of that isotope
Explain the relationship between the mass/charge ratio and the relative mass of each isotope when the sample has been ionised by electrospray ionisation
Since H+ ions are added for each particle to form +1 ions the mass/charge ratio of each peak would be one unit greater than the relative mass of each isotope
How do you work out how many isotopes of the element are present in the sample
Count the amount of peaks in % abundance
How to calculate the relative atomic mass from a mass spectrum
Multiply the relative isotopic abundance (read y axis) by the mass (read x axis) and divide by 100
How do you calculate the relative molecular mass of a molecular ion from a mass spectrum
Find the mass/charge ratio and it is the same as that value
What is a principal quantum number and explain it’s relationship to the nucleus
A measurement of how far a shell is from a nucleus
The further a shell is from the nucleus the larger the principal quantum number is
Explain the relationship between the distance of the shell from the nucleus and the amount of energy
The further a shell is from the nucleus the higher it’s energy
Name the four different sub shells you can have
s, p, d, f
List the different sub shells in each shell up to four shells
1st : 1s
2nd : 2s, 2p
3rd : 3s, 3p, 3d
4th : 4s, 4p, 4d, 4f
What are the different number of orbitals in each sub-shell and what are the maximum electrons that each sub shell can hold
s : 1 Max electrons : 2
p : 3 Max electrons : 6
d : 5 Max electrons : 10
f : 7 Max electrons : 14
What are the three rules when working out electron configuration
Rule 1 : Electrons fill up the lowest energy sub-shells first
Rule 2 : Electrons fill orbitals in a sub-shell singly before they start sharing
Rule 3 : For the configuration of ions from the s and p blocks of the periodic table just add or remove the electrons to or from the highest energy occupied sub-shell
What is the rule regarding the s and d sub-shells
s fills and empties before d
Define relative molecular mass
The average weighed mass of one molecule compared to 1/12th the mass of one atom of carbon 12
Equation for electrospray
M(g)+ H^+(g) –> MH^+(g)
What is the anomaly to electron configuration
Chromium and Copper
They both donate one of their electrons to the 3d sub shell
What is the first ionisation energy
The first ionisation energy is the energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
Write the equation for the first ionisation of oxygen
O(g) -> O+(g) + e-
What state symbol should be used when writing equations for ionisation energy
(g)
Because ionisation energies are measured for gaseous atoms
What is the correlation between ionisation energy and the reactivity
The lower the ionisation energy the easier it is to form a positive ion
What does a high ionisation energy mean
There’s a high attraction between the electron and the nucleus, so more energy is needed to remove the electron
What are the three things that affect ionisation energy
Nuclear charge:
- The more protons in the nucleus the stronger the attraction
between the nucleus and the electrons
Distance from nucleus:
- Attraction falls very rapidly with distance between the nucleus
and the electron
Shielding:
- As the number of electrons between the outer electron and the nucleus increases the attraction decreases
What is second ionisation energy
The second ionisation energy is the energy needed to remove an electron from each ion in 1 mole of gaseous 1+ ions
Write the equation for the second ionisation energy of oxygen
O+(g) -> O2+(g) + e-
Why is the second ionisation energy always higher than the first
Because the atom becomes a positive ion so the attraction is stronger so more energy is needed to remove it
It will also experience less shielding
It is also closer
Write the general equation for successive ionisation
X(n-1)+ (g) -> Xn+ (g) + e-
what is the equation for the fifth ionisation energy of oxygen
O4+ (g) -> O5+ + e-
Describe the ionisation energy trends going down group 2
The first ionisation energy decreases
What is the general trend for ionisation energy when you move across a period
To increase
Number of protons increase so attraction is stronger
What are the two exceptions to the ionisation energy trend across periods
Mg and Al
P and S
Explain why Mg is higher in ionisation energy than Al
Al’s outer electron is in a 3p orbital rather than a 3s
3p is higher in energy than the 3s orbital so the electron (on average) is found further from the nucleus
3p orbital has additional shielding provided by the 3s electrons
Explain why P is higher in ionisation energy than S
In P the electron is removed from a singly-occupied shell
In S it is being removed from a shell with two electrons
The repulsion from two electrons in the same orbital means it is easier to be removed so it has lower ionisation energy
