Foundations in chemistry Flashcards
Relative isotopic mass
The mass of an atom of an isotope in relation to 1/12th of the mass of carbon-12
Relative atomic mass
The weighted mass of an atom of an element compared to 1/12th of the mass of carbon-12.
How can the percentage abundance of an isotope be found? What stage?
Using a mass spectrometer,
- ionisation
- accelerator
- deflection
- detection
relative abundances are recorded as peaks on a graph and percentage can be found from these results.
x-axis is atomic mass over charge (m/z) however on most ions in this case the charge is +1 so the x-axis scale is equal to atomic mass.
1st ionisation energy
Energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.
factors that affect ionisation energy.
- atomic radius (larger atomic radius = smaller ionisation energy)
- atomic charge/nuclear attraction (larger atomic charge=greater attraction of electrons = greater ionisation energy)
- electron shielding (inner electrons shield outer electrons from the positive attraction of the nucleus)
Explain the increase in ionisation energies from 1st–>2nd->3rd
Why are some differences much greater than others?
The second electron is being removed from a species with a positive charge. The electrons are pulled closer to the nucleus as more electrons are removed.
Ca –> Ca+ + e-
Ca+ –> Ca2+ + e-
etc.
often there is a large jump between particular ionisation energies in elements. For example in group 2 elements the jump between 2nd and 3rd ionisation energies is larger due to the 3rd electron being in a different shell closer to the nucleus. Atomic radius and electron shielding are smaller values and therefore ionisation energies are larger.
Photo electron spectrum?
Why does peak high not matter?
graph demonstrates the energy required to remove electrons from different energy levels in a atom.
Peak height does not matter as it is relative to the highest peak and it is not an absolute value.
How many orbitals and electrons in each type of subshell?
s-subshell = 1 obital containing two electrons (groups 1/2) p-subshell = 3 orbitals each containing 2 electrons therefore with a maximum of 6 electrons. (groups 3-8) d-subshell = 5 orbitals, maximum of 10 electrons (transition metals)
order of energy levels (subshells)?
1s2s2p3s3p4s3d4p
electrons are always lost from orbital furthest from the nucleus but do not always fill in this order.
Oxidation
Is the loss of electrons
Increase in oxidisation number
Mg –> mg^2+ + 2e-
Reduction
Is the gain of electrons
decrease in oxidisation number
Cl2 + 2e- —> 2Cl-
Oxidising agent
Is a reagent that oxidises (takes electrons from) another species
Reducing agent
Is a reagent that reduces (gives electrons to) another species
Redox
Redox reactions are reactions in which both oxidation and reduction happen
Oxidation number rules
- Uncombined elements have an oxidation number of 0
- group I metals have and oxidation number of +1
- group II metals have an oxidation number of +2
- Flourine toms have an oxidation number of -1
- Oxygen atoms have an oxidation number of -2 except in peroxides when it is -2
- hydrogen has an oxidation number of +1 except in hydrides wen it is - 1
Hydrochloric acid
HCl
Sulfuric acid
H2SO4
Nitric acid
HNO3
Phosphoric acid
H3PO4
ethanoic acid
CH3COOH
Acid definition
An acid is a proton donor, and release H+ ions in aqueous solution, when dissociated
weak acids
Acid that do not dissociate completely, at any one time some of the aid molecules have split into H+ and an appropriate anion and some are still associated.
The weaker the acid is the lower proportion of the acid is dissociated, the less h+ ions are in solution .
normally carboxylic acids
Strong acids
Are always fully dissociated in solution.
Both weak and strong acids can be diluted, but it is the percentage of acid that is dissociated that defines weak or strong acids
normally mineral acids
Bases
Bases are proton acceptors