Topic 1 Flashcards
What is the structure of an atom?
A nucleus containing protons and neutrons surrounded by electrons in electron shells.
What are the relative mass and charges of protons, neutrons and electrons?
What is an atomic number and Mass number?
Atomic / Proton number - Amount of Protons OR Electrons
Mass Number = Amount of Protons AND Electrons
How to find the number of each subatomic particle
12 - 6 = 6 Neutrons
6 = 6 Protons
6 = 6 Electrons
What are isotopes?
Isotopes are atoms of the same element but different numbers of neutrons.\
- Same chemical properties ← same electron configuration
- Different Physical Properties ← different isotopic mass
What is relative isotopic mass?
Mass of an atom of an isotope compared to 1/12th of a carbon atom
What is relative atomic mass?
Ar is the weighted mean mass of an atom of an element compared to 1/12th of a carbon atom
(We use carbon because of the mass of carbon is 12)
How do you calculate Ar from isotopic abundances?
- Multiply each isotopic abundance with the isotopic mass
- Add up all the results
- Divide by 100
What is a Mass Spectrometer?
Devices that find out what samples are made up of by measuring their masses
How does a mass spectrometer work?
Ions are sent at a high speed and are deflected and depending where they are detected on the electromagnet you are able to see the mass as
A moving force will be deflected if a force of a higher strength makes contact in another direction
What is step 0 in mass spec?
Step 0 - Preparation
- Samples must be vaporised to be GASEOUS
- Mass spec must be in a Vacuum to avoid collision with air molecules
What is step 1 is mass spec
Step 1 - Ionisation
- Electrons are knocked off the atoms using a electron gun
- This then turns the atom into a ion
Example H(g)→ H(g)+
What is step 2 in mass spec
Step 2 - Acceleration
- Positively charged plates launch the ions
- Negatively charged plates then accelerate the ions
- This is done to ensure all ions have the same kinetic energy
All this is done in an electric field
What is step 3 in mass spec
Stage 3 - Deflection
- A Magnetic field then deflects the ions
- Separation of ions occur because the more charged an ion is the more its deflected
What is step 4 in mass spec?
Stage 4 - Detection
- The beams of electrons are then detected electronically
- This is recorded through Mass charge ratio (M/z)
How do you analyse mass spectra?
- Height of each peak = relative isotopic abundance
- The m/z of each isotope is the isotopic mass
How do you work out relative atomic mass Ar from mass spectra?
How do you predict the mass spectra of diatomic molecules?
When chlorine is ionised you get unstable chlorine ions
Cl2→Cl2+
The unstable ions then get fragmented where the atoms can’t be accelerated so their lost
Cl2+→Cl + Cl+
This means that Cl+ ions will be detected and give out lines at 335 and 37
HOWEVER some Cl2+ ions will also be detected meaning that there will be peaks at:
70 = 35 + 35
72 = 35 + 37
74 = 37 + 37
How to calculate relative formula mass
This only works because the molecular ion is the sum of all the relative molecular masses
What is ionisation energy?
Ionisation energy is the energy required to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
What is successive ionisation energy?
The energy required for the removal of the second electron form the ion such as that 1 mole of gas with +1 ion gives +2 ions
What factors effect ionisation energy?
Nuclear Charge
More protons ⇒ more positively charged nucleus ⇒ stronger attraction ⇒ harder to remove electron
Ionic radii
Electron shells further away ⇒ higher ionic radii ⇒ less attraction ⇒ easier to remove electron
Electron Shielding
More electron shells (shielding) ⇒ less attraction to nucleus ⇒ easier to remove electron
Why is there a general increase in first ionisation energy?
(across a period)
Across a period first ionisation energy increases:
- Electron number increase (increasing nuclear charge)
- Shielding would stay the same
- Ionic radii would decrease
- Meaning overall first ionisation energy increases
Why is there a general decreases in ionisation energy down a group?
First ionisation energy decreases down a group:
- Electron number increases (no increase in nuclear charge as…)
- Shielding increases
- Atomic radii increases (reducing the nuclear charge)
- Meaning that overall first ionisation energy decreases
