Atomic structure Flashcards
Relative atomic mass
the weighted mean of the mass of an elements atoms
to 1/12 the mass of carbon-12
Relative isotopic mass
the mass of an atom of an isotope
relative to 1/12 the mass of carbon-12
1st stage of mass spectrometry
ionisation
- particles are ionised via bombardment with high energy electrons
- generates positive ions
2nd stage of mass spectrometry
ions are accelerated by an electric field
3rd stage of mass spectrometry
deflection
- ions pass through strong magnetic fields
- lighter ions are deflected more
4th stage of mass spectrometry
detection
- ions are detected electronically as currents
- size of current indicates abundance
How is the mass of an isotope detected using time of flight
- all ions are accelerated so they have equal kinetic energy
KE = 1/2MV2 - ions with different velocities will have different masses
- velocity can be calculated using time and distance
What is the first ionisation energy definition
the energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
Equation for 1st ionisation energy
X(g) -> X+(g) + e-
Factors that affect ionisation energies
- nuclear charge
- distance of outer electrons from nucleus
- shielding
What is the trend in ionisation energies across a period
increases
- greater nuclear charge so greater attraction between electrons and nucleus
What is the trend in ionisation energies down a group
decreases
- more shells so shielding and distance between nucleus and electrons increases
How many electrons does each quantum shell hold
1st - 2
2nd - 8
3rd - 18
What shape are s orbitals
spherical
What shape are p orbitals
dumbbell shaped
What is an orbital
an area in space that has a 95% chance of finding an electron
Explain why the 1st ionisation energy of group 2 is less than that of a group 3
the outermost electron from a group 2 is removed from an s subshell rather than a p subshell which is closer to the nucleus
Explain why the 1st ionisation energy decreases from phosphorus to sulfur
in sulfur the p electros are paired for the first time
- repulsions are set up between paired electrons
- this reduces energy needed to remove the electron
Which groups are in the s block
groups 1 + 2
Which groups are in the p block
groups 3 - 8
Which groups are in the d block
transition metals
How can you identify the group of an element from ionisation energies
big jumps in ionisation energies indicate that an electron is being removed from a subshell closer to the nucleus
group 1 - jump between IE 1 and IE 2
What is periodicity
chemical trends that repeat across periods
Which properties show periodicity
- melting and boiling points
- atomic radius
Why does melting and boiling points increase from group 1 - 3
metals which bond metallically
group 1 - 1e- per atom delocalised
group 2 - 2e- delocalised
results in stronger attraction between delocalised electrons and + ions
- requires more energy to overcome
Why are melting and boiling points the highest in group 4
form giant covalent structures
- strong covalent bonds between atoms
Why does melting and boiling points decrease in group 5 - 7
simple molecular substances with weak intermolecular forces
Why is there a slight increase in the melting and boiling points of phosphorus and sulfur
phosphorus tends to be p4
sulfur is s8
What is atomic radius
distance from the centre of nucleus to the boundary of the electron cloud
- difficult to determine
What are the two ways to find atomic radius
- covalent radius
- van der waal’s radius (two atoms touching eachother rather than overlapping)
Why does atomic radius decrease along a period
nuclear charge increase so greater attraction to electrons, so the electron cloud is pulled in tighter
- attraction to nuclear far outweighs repulsions between electrons
Why does atomic radius increase down a group
more shells
