3.1.1 Atomic structure Flashcards
What is the relative mass of an electron?
1/1840
What is meant by an isotope of an element?
Why do isotopes have identical chemical properties?
- Elements with same number of protons (atomic number) but different number of isotopes (mass number).
- Chemical properties are controlled by electron configuration, isotopes have same number of electrons.
What property of electrons in represented by the up and down arrows (↑↓)?
Spin of electrons
What two elements are exceptions to the electron configuration rules and why?
Cr: in order to half-fill 3d sub-shell
Cu: in order to fill 3d sub-shell
Why do electrons occupyinng the 2p orbitals have a higher energy than electrons in the 2s oribital?
They are more shielded from the nucleus
What is the first ionisation energy of an atom?
The enthalpy change when one mole of electrons are removed from one mole of gaseous atoms to produce one mole of 1+ ions.
Describe the general pattern of IE across a period and down a group.
Down group: IE decreases as there is more shielding, larger atomic radius and weaker attraction between outer electrons and nucleus, easier to remove outer electron
Across period (L to R): IE increases as nuclear charge increases, stronger attraction between nucleus and electron shells, smaller atomic radius
Explain why the 1st IE of sulfur is less than the value of the 1st IE of phosphorus.
- Electrons begin pairing in S (3p^4)
- Electron repulsions mean less energy is required to remove electron from S than P
Explain why the 1st IE of aluminium is less than the value of the 1st IE of magnesium.
- Outer electron in Mg occupies 3s orbital, outer electron in Al occupies 3p orbital.
- 3p orbital is a higher energy sub-shell so requires less energy to remove electron from 3p than 3s.
- Requires less energy to remove electon from Al
Define the term relative atomic mass of an element.
The weighted average mass of one atom of an element relative to the mass of carbon-12 (defined as exactly 12)
Describe two ways ionisation is achieved in a mass spectrometer.
Electrospray ionisation:
- Mixture dissolved in volatile solvent
- Mixture injected into ToF mass spec throguh a thin needle connected to a high voltage
- Protonation, each molecule gains a proton, producing 1+ ions
Electron impact:
- High energy electrons fired at gaseous atom using electron gun
- Knocks electron off atom to produce +1 ion
Give two reasons why ionisation is neccassary in ToF mass spec.
- Require positive charge so that a current can be produced at negative detector plate (measure abundance)
- Allows ions to be accelerated by electric field
Explain how ions in a mass spectrometer are detected and how their abundance is measured.
- Positive ions collide with negative detector plate
- Electrons transferred from plate to ion, producing an electrical current
- Size of this electrical current is relative to the abundance of the ion
Why is the mass spectrometer kept under vacuum?
- Particles in air would obstruct the path of the ions through the ToF tube.
- This will interfere with the results
Explain how ions are accelerated and seperated by mass in the mass spectometer.
- Positive ions accelerated by an electric field
- All ions have the same KE, but different mass
- Ions with the smallest mass have the higher velocity and will arrive at the detector plate first
