Atomic structure Flashcards
State the meaning of the term isotope
atoms with the same protons, but have a different number of neutrons
Describe how ions are formed in a time of flight (TOF) mass spectrometer. ( 2 marks)
For electron impact
the sample is bombarded by high energy electrons
the sample molecule loses an electron forming M+
For electrospray
A high voltage is applied to a sample in a polar solvent
the sample molecule, M, gains a proton forming MH+
A TOF mass spectrometer can be used to determine the relative molecular mass of molecular substances.
Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer ( 3 marks)
Ions, will interact with and be accelerated by an electric field
and only ions will create a current when hitting the detector
Define the term relative atomic mass.
The average mass of 1 atom of an element compared
1/12 mass of one atom of 12C
Define the term relative atomic mass. ( 2 marks)
The average mass of 1 atom of an element compared
1/12 mass of one atom of 12C
In a mass spectrometer, the relative abundance of each isotope is proportional to the current generated by that isotope at the detector.
Explain how this current is generated. (2 marks)
Electron(s) transferred / flow (at the detector)
(From detector / plate) to the (+) ion
Do not mention the charged plate
State why isotopes of an element have the same chemical properties. ( 1 mark)
They have the same electron configuration
Suggest one reason why particles with the same mass and velocity can be deflected by different amounts in the same magnetic field. ( 1 marks)
Size of the charge (on the ion) / different charges / different m/z
Explain why chromium is placed in the d block in the Periodic Table.
The highest energy electron is in the d subshell
State the relative charge and relative mass of a proton, of a neutron and of an electron.
In terms of particles, explain the relationship between two isotopes of the same element.
Explain why these isotopes have identical chemical properties. ( 7 marks)
- Neutrons Electrons Proton
- charge: 0 -1 +1
- relative mass is 1 1/2000 1
The relationship between two isotopes is that they have the same number of electrons and protons but a different number of neutrons
Have identical chemical properties because they have same electron configuration
Define the term relative atomic mass. An element exists as a mixture of three isotopes.
Explain, in detail, how the relative atomic mass of this element can be calculated from data obtained from the mass spectrum of the element. ( 7 marks)
Relative atomic mass is the mean mass of an atom divided by the mean mass of 1/12 of carbon 12
Spectrum gives (relative) abundance
And m/z
Multiply m/z by relative abundance for each isotope
Sum these values
Divide by the sum of the relative abundances
Define the first ionisation energy ( 1 mark)
amount of energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of 1+ ions
How do you work out relative atomic mass
the sum of isotopic mass x % abundance divide 100
and if you don’t have % then do
the sum of isotopic mass x % abundance divide total relative abundance
What is the trend in ionisation energies across a period
- They increase
- nuclear charge increases
- Shielding stays the same
What is the trend in ionisation down a group
- decreases
- more shielding
- larger atomic radius
