Atomic Structure Flashcards
what are the 3 subatomic particles
proton , neutron , electron
proton - relative charge and mass
+1 , 1
neutron - relative charge and mass
0 , 1/1836
electron - relative charge and mass
-1 , 1
position of electrons, neutrons and protons in the atom
protons + neutrons = nucleus
electrons = orbitals
define mass number
total number of protons in nucleus of an atom
define atomic number
total number of protons in nucleus of an atom
all atoms of the same element have the same number of ______
protons
how can you work out no. of neutrons
mass no. - atomic no.
electron no, is same as proton to make neutral atom
how to make ions
loss or gain of electrons
define isotope
atoms with the same no. of protons but different no. of neutrons.
isotope properties
-chemical + physical
- same chemical properties as same electronic configuration as regular atoms
- slightly varying physical properties due to different masses. - eg different densities and rates of diffusion
dalton’s atomic model
19th century
solid spheres, different spheres made up different elements
thompson’s atomic model
1897
believed an atom must contain even smaller, negatively charged particles (electrons).
solid spheres –> plum pudding model
rutherford’s atomic model
+ experiment
1909
gold foil experiment - fired alpha particles (+vely charged) at thin sheet o gold - most alpha particles passed straight through gold atoms, very few deflected back.
if plum pudding true, most alpha particles would be deflected back
model - tiny +ve nucleus in centre, surrounded by “cloud” of -ve electrons.
most of atom is empty space
bohr’s atomic model (4 principles)
+ fault w rutherfords
rutherfords model was false as if there was a cloud of electrons, they would spiral down into the nucleus and the atom would collapse.
principles:
- electrons only exist in fixed orbits/shells
- each shell has a fixed energy
- electromagnetic radiation is omitted or absorbed when a an electron moves between shells
- since fixed shell energy, radiation has fixed frequency
revelations about atomic model after bohr
found not all electrons in same shell had same energy –> subshells
whats a time of flight mass spectrometer
machine used to analyse elements or compounds
elements:
- find relative abundance of its isotopes
- relative atomic mass
compounds:
- relative molecular mass of a molecule
name stages of TOFMS
- ionisation
- electrospray ionisation or
- electron impact ionisation - acceleration
- ion drift
- detection
condition needed for TOFMS
under a vacuum or else air particles would ionise and register on the detector
when is electrospray ionisation typically used and when is electron impact ionisation typically used?
electron impact used for elements and substances with low formula mass. Electron impact can cause larger organic molecules to fragment.
electrospray used preferably for larger organic molecules. The softer conditions prevent fragmentation
electron impact ionisation
- A Vaporised sample is injected at low pressure
- An electron gun fires high energy electrons at the sample
- This Knocks out an outer electron
- Forming +ve ions
E.g. Ti –> Ti+ + e–
electrospray ionisation
- The sample is dissolved in a volatile, polar solvent
- injected through a fine hypodermic needle giving a fine mist or aerosol
- the tip of needle has high voltage where the sample molecule (M) gains a proton/H+ from the
solvent - Eg. M(g) + H+ MH+(g)
- The solvent evaporates away while the MH+ ions move towards a negative plate
acceleration
KE = ½ mv^2
KE = kinetic energy of particle (J) m = mass of the particle (kg) v = velocity of the particle (ms–1)
- +ve ions accelerated by electric field that gives same KE to all ions
- lighter ions have greater acceleration
- this is because since they all have the same KE, velocity is dependant on mass
