1.1 Atomic Structure Flashcards
Atomic number
Number of protons in the nucleus of an atom
Mass number
Number of protons and neutrons in the nucleus of an atom
Isotopes
Atoms of the same element (same number of protons) with a different number of neutrons
What is a mass spectrometer used for?
Calculating the relative atomic mass of an element or the relative molecular mass of a compound.
What are the 4 stages of a TOF mass spectrometer?
- Ionisation
- Acceleration
- Separation of ions
- Detection
Why is the spectrometer kept in a vacuum?
To prevent ions that are made from colliding with molecules in the air.
Mass spectrometer
What are the two methods of ionisation?
- Electron impact
- Electrospray ionisation
Mass spectrometer
How does electron impact ionisation work?
- Sample is vapourised and injected into spectrometer
- High energy electrons fired from an electron gun
- Electron is knocked from each particle
- Positive ions formed
Mass spectrometer
What is an electron gun?
A hot wire filament that releases high energy electrons.
Mass spectrometer
What is the charge of the ions formed?
1+
Mass spectrometer
How are the positive ions accelerated?
With an electric field
Mass spectrometer
How are the ions separated?
Lighter ions travel through the spectrometer faster than heavier ions
Mass spectrometer
How are the ions detected?
Each ion gains an electron - this generates a current
Mass spectrometer
How is the abundance of each ion determined?
It is proportional to the current produced.
The greater the abundance, the greater the current.
Mass spectrometer
Why is the sample ionised?
So it can be accelerated and detected
Relative isotopic mass
The mass of an isotope relative to 1/12th the mass of an atom of carbon-12
Relative atomic mass (Ar)
Weighted average mass of all isotopes of an element / 1/12 mass of one atom of carbon-12
What order do the energy levels fill up?
1s–>2s–>2p–>3s–>3p–>4s–>3d–>4p
Electron configuration for chromium (Cr)?
1s²2s²2p⁶3s²3p⁶3d⁵4s¹
Electron configuration for copper (Cu)?
1s²2s²2p⁶3s²3p⁶3d¹⁰4s¹
(First) Ionisation energy (chemistry)
The energy needed to remove one mole of electrons from one mole of atoms in the gaseous state.
Why do successive ionisation energies increase?
- Attraction of the outer electrons and nucleus increases (same number of protons for fewer electrons)
- Large increase where outer electron is in a new main shell (closer to nucleus with less shielding)
Which shell are electrons lost from first in period 4 transition metals?
4s
Mass spectrometer
How does electrospray ionisation work?
- Sample dissolved in a volatile polar solvent
- Injected through a hypodermic needle which gives a fine mist
- Tip of needle is attached to positive terminal of a high voltage supply
- Particles gain a protons from the solvent
What is a polar solvent?
A solvent with molecules with an area of more positive charge and an area of more negative charge.
Volatile
Easy to turn into a vapour
Why is a volatile solvent used for electrospray ionisation?
So that all of it evaporates leaving only the positive ions of the sample
What is the mass of the ion formed with electrospray ionisation?
Mass of ion = mass of element/compound + 1
What is the mass of the ion formed with electron impact ionisation?
Mass of ion = mass of element/compound
m/z
Mass/charge
(Z is usually +1 so x-axis is relative isotopic mass)
What are the units of ionisation energy?
KJ mol⁻¹
