Atomic Structure (CDS) Flashcards
What is the equation used to calculate the relative atomic mass?
(mass of isotope x abundance) + (mass of isotope x abundance) / total abundance
What is meant by the relative atomic mass of an element?
The average mass of an atom compared to 1/12 of the mass of an atom of carbon-12
How many decimal places is RAM to?
1
What are the two isotopes of bromine and their abundance?
Br-79 = 50% Br-81 = 50%
What are the two isotopes of chlorine and their abundance?
Cl-35 = 75% Cl-37 = 25%
What will the distribution of bromine isotopes be like on a graph?
1:2:1
What will the distribution of chlorine isotopes be like on a graph?
9:6:1
What is an ion and how are they formed?
A charged particle formed when atoms lose or gain electrons
What type of ions do metals form?
Positive
What type of ions do non metals form?
Negative
What is an isotope?
An atom of an element with the same proton and electron number but different neutron numbers
What is the mass number of an element?
Total number of protons and neutrons
What is the atomic number of an element?
Total number of protons
The number of which subatomic particle identifies an element?
Protons
Will two different isotopes of the same element have the same mass number? Why/Why not?
No, because mass number is total protons and neutrons and isotopes have different neutron numbers
Will two different isotopes of the same element have the same atomic number? Why/Why not?
Yes, elements are identified by their atomic number
What decides the chemical properties of an element?
Its electron configuration
Why do isotopes have the same chemical properties?
They have the same electron configuration
Why do ions have different chemical properties?
They have different electron configurations
Why can isotopes have slightly different physical properties?
Physical properties depend more on the mass of the atom and they have different masses
How can you work out the number of neutrons an atom has?
Mass number - atomic number
Describe JJ Thomson’s model of the atom
Plum pudding, positive cloud with negative plums dotted about
Describe Dalton’s model of the atom
Atoms were solid spheres. Each element was made of a different type of atom
Describe Rutherford’s model of the atom
Nuclear model, most of the atom was empty space, most of the mass was concentrated in the dense positively charged nucleus in the centre, cloud of electrons surrounding it
Describe Bohr’s model of the atom
Same as Rutherford, except he proposed electrons orbited in fixed shells as a cloud would cause the atom to collapse
Explain how the alpha scattering experiment proved Thomson’s model wrong
- Proved most of the atom was empty space, so could not be a positive cloud
- Proved most of the mass was concentrated in the centre
- Proved electrons lived around the outside of the atom not dotted about randomly
Explain the key difference between Rutherford’s and Bohr’s model of the atom
Rutherford proposed electrons existed in a cloud around the atom, Bohr proposed they were in fixed shells
Explain the key differences between Dalton and Thomson’s model of the atom
Thomson proposed the idea of different charges in the atom, Dalton believed they were solid spheres
What happens when electrons move shells?
Electromagnetic radiation is emitted/absorbed
What is meant by the relative isotopic mass of an element?
The mass of an isotope compared to 1/12 of the mass of an atom of carbon-12
What is meant by the relative molecular mass of an element?
The average mass of an molecular compared to 1/12 of the mass of an atom of carbon-12
What is meant by the relative formula mass of an element and what type of compounds is it used for?
The average mass of a formula unit compared to 1/12 of the mass of an atom of carbon-12. It is used for ionic or giant covalent compounds
What are the stages of time of flight mass spectrometry?
- Ionisation
- Acceleration
- Flight Tube
- Detection
What are the two methods of ionisation used in ToF mass spectrometry?
Electrospray Ionisation and Electron impact Ionisation
Describe the steps of electrospray ionisation:
- Sample is dissolved in a volatile solvent and is pushed through a fine hypodermic needle
- Tip of the needle is attached to positive terminal of a power supply
- Each particle gains a H+ ion/proton
- Solvent is removed leaving a sample of gaseous H+ ions
Describe the steps of electron impact ionisation:
- Sample is vaporised
- Electron gun fires high energy electrons at it, knocking off electrons and creating 1+ ions
Describe the difference between the two methods of ionisation and the mass spectra they will produce:
Electrospray ionisation gives particles a proton and so the true mass of the atom will be one unit higher than its actual mass. However, Electron impact knocks off an electron so the value on the mass spectrum will be its true mass.
How are ions accelerated in ToF mass spectrometry?
The positive ions are attracted by a negative electric plate so they all have the same kinetic energy
What is the equation for Kinetic energy?
KE = 1/2 𝒎𝒗𝟐
KE = Kinetic energy (J)
m = mass of particle (kg)
v = velocity (m s-1)
What is the equation for time of flight?
t = d/v
t= time of flight (s)
d = distance travelled / length of flight tube (m)
v = velocity (m s -1)
Why do different isotopes/particles have different times of flight if they all have the same kinetic energy?
Time of flight depends on velocity, which depends on mass and they have different masses.
𝒗 = √(𝟐𝑲𝑬/m)
How are ions detected in a ToF mass spectrometer?
The detector is a negatively charged plate which causes ions to be discharged when they hit it. The movement of electrons generates a current and the size of the current gives an indication of the abundance of each ion
3 reasons why ToF mass spectrometry takes place in a vacuum
- Avoids the effect of air resistance on velocity
- Avoids air particles being ionised and detected and interfering with mass spectra
- Reduces chance of particles colliding which can cause them to react and neutralise, interfering with the mass spectrum
What do the axes represent on a mass spectrum?
x-axis = mass to charge ratio (m/z)
y-axis = % abundance
What are the 4 types of sub shells?
s, p, d, f
How many electrons can an s sub shell hold?
2
How many electrons can a p sub shell hold?
6
How many electrons can a d sub shell hold?
10
How many electrons can an f sub shell hold?
14
Which sub shells are found in the first energy level?
1s
Which sub shells are found in the second energy level?
2s 2p
Which sub shells are found in the third energy level?
3s 3p 3d
Which sub shells are found in the fourth energy level?
4s 4p 4d
In what order are sub shells filled?
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 4d
What do each of the characters in the notation, 1s^2 represent?
1 - Energy level/principal quantum number
s - sub shell type
2 - number of electrons in shell
What must electrons be doing in order to occupy the same orbital?
Spinning in opposite directions
Rules for working out electron configurations:
- Electrons fill up lowest energy sub shells first
- Electrons fill each orbital in a sub shell before pairing up
- When forming ions, transition metals lose their 4s electron first
- All other metals lose electrons from their highest energy level
Which 2 elements are exceptions to the general pattern on the periodic table in terms of electron configuration and how?
Chromium (Cr) and Copper (Cu), they donate a 4s electron to the 3d shell because they prefer a full or half full d shell
What is the outer configuration of Cr (3d and 4s)?
3d^5 4s^1
What is the outer configuration of Cu (3d and 4s)?
3d^10 4s^1
What is meant by first ionisation energy?
The energy required to remove 1 mole of electrons from one mole of 1+ ions (also in their gaseous state)
What are the factors affecting ionisation energy and how do they affect the force of attraction between the outer electron and the nucleus?
- Nuclear charge - Higher nuclear charge = higher force of attraction
- Atomic radius - Higher atomic radius = weaker force of attraction
- Shielding - More shielding = weaker force of attraction
Describe and explain how 1st ionisation energy changes down the group
1st IE decreases down the group because atomic radius and shielding increases as you move down the group, so the force of attraction between the outer electron and the nucleus is weaker. although nuclear charge increases, this is offset by the other factors
What is the general trend for 1st IE across a period?
It increases as you go across the group
Describe and explain the 2 exceptions to the pattern in 1st IE across a period
- When going from an s to a p orbital IE decreases as the outer e- is in a high energy sub shell and is easier to remove.
- When going from p3 –> p4, IE decreases due to electron pair repulsion
Is the 2nd IE of an element lower or higher than the first and why?
Higher because atomic radius decreases as you remove e- so force of attraction increases
Why is the difference between 6th and 7th IE very high for oxygen?
Oxygen is in group 6 so has 6 outer e-. Once you remove the last outer electron, you move to a closer shell to the nucleus, so the shielding is lower and the atomic radius is lower, therefore the electron is harder to remove.
How to find the mass of a particle from its atomic mass?
(atomic mass/1000) / L
