(1) atomic structure Flashcards
Dalton’s model
- 19th cent.
- Atoms = solid spheres
- Different spheres made up different elements
Thompson’s model
- 1897
- Plum pudding
- Electrons embedded in positive mass
Rutherford’s model
- 1909
- Gold foil experiment
- Tiny + nucleus (most alpha particles went straight through)
- Cloud of - electrons (some alpha particles deflected backwards)
- Most of atom is empty space
Bohr’s model
- Electrons in fixed shells
- Shells have fixed energy
- EMR is emitted/absorbed when electron jumps between shells (has a fixed frequency)
Modern model
- Subshells
Relative Atomic Mass
-The average mass of an atom of an element compared to 1/12th the mass of a carbon 12 atom
Relative isotopic Mass
-The mass of an atom of an isotope of an element compared to 1/12th the mass of a carbon 12 atom
Ar formula
Sum of the product of isotopic masses and relative abundance / 100
Relative Molecular Mass
-The average mass of a molecule compared to 1/12th the mass of a carbon 12 atom
Relative Formula Mass
-Average mass of a formula unit compared to 1/12th the mass of a carbon 12 atom
Electrospray ionisation
- Sample dissolved in polar solvent (water/ethanol)
- Pushed through nozzle at high pressure
- High voltage applied
- Particles gain H+ ion
-(m/z value 1 unit greater on spectrum due to proton)
X(g) + H+(g) -> XH+(g)
Electron impact ionization
- Sampled is vaporized
- High energy electrons fired with electron gun
- Knocks 1* electron off
- *Sometimes more
X(g)-> X+(g) + e-
Acceleration stage
- Ions accelerated by electric field
- All ions have same kinetic energy
- Lighter ions accelerate faster than heavier ones
Ion drift stage
- No electric field
- Lighter ions drift faster
Detection stage
- Lighter ions reach detector first
- Detector records the current created when ion arrives and time taken to travel through spectrometer
- Mass/charge value calculated
Ionisation stage
- So sample can be accelerated by electric field
- So current can be produced at detector
Molecular ion peak
- Tallest peak to the right
- Mr of molecule in sample
- Multiple if sample contains compounds made of different isotopes
4s sub-shell
- Lower energy level than 3d
- Fills before 3d
Hun’s rule
- Electrons fill shells singularly before they start pairing up
Transition metal exceptions
- Chromium and Copper donate a 4s electron to the 3d subshell to be more stable
Transition metal ionization
- Loose their electrons from their 4s subshell before 3d
First ionisation energy
- Energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
- Endothermic
- X(g) -> X+(g) + e-
Nuclear charge
- More protons in nucleus = stronger attraction to valence electrons
Distance from nucleus
- Valence shell electrons further from nucleus = less attraction between the two
Shielding
-More shells between valence shell and nucleus = less attraction
Second ionisation energy
- Higher than 1st ionisation
- Energy required to remove 1 electron from each ion in 1 mole of gaseous 1+ ions to form 1 mole of 2+ ions
Successive ionisation
X(n-1)(g) -> X(n+)(g) + e-
Ionisation down group 2
- Decreasing ionisation energy because distance from atom and shielding increases
Ionisation across periods
- General increase because increasing number of protons so nuclear charge increases
- Drops between groups 2 and 3 show changes in subshells because it gets closer to nucleus
- Drops between 5 and 6 due to electron pair repulsion
Successive ionisation trend (single atom)
- Energy increases within shells because nuclear charge increases
- Jumps happen when new shell is broken into, because closer to nucleus
Proof of shell structure
- Ionisation energies
