Atomic Structure

Question 1

what are the 3 subatomic particles

Answer 1

proton , neutron , electron

Question 2

proton - relative charge and mass

Answer 2

+1 , 1

Question 3

neutron - relative charge and mass

Answer 3

0 , 1/1836

Question 4

electron - relative charge and mass

Answer 4

-1 , 1

Question 5

position of electrons, neutrons and protons in the atom

Answer 5

protons + neutrons = nucleus

electrons = orbitals

Question 6

define mass number

Answer 6

total number of protons in nucleus of an atom

Question 7

define atomic number

Answer 7

total number of protons in nucleus of an atom

Question 8

all atoms of the same element have the same number of ______

Answer 8

protons

Question 9

how can you work out no. of neutrons

Answer 9

mass no. - atomic no.

electron no, is same as proton to make neutral atom

Question 10

how to make ions

Answer 10

loss or gain of electrons

Question 11

define isotope

Answer 11

atoms with the same no. of protons but different no. of neutrons.

Question 12

isotope properties

-chemical + physical

Answer 12

• 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

Question 13

dalton’s atomic model

Answer 13

19th century

solid spheres, different spheres made up different elements

Question 14

thompson’s atomic model

Answer 14

1897
believed an atom must contain even smaller, negatively charged particles (electrons).
solid spheres –> plum pudding model

Question 15

rutherford’s atomic model

+ experiment

Answer 15

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

Question 16

bohr’s atomic model (4 principles)

+ fault w rutherfords

Answer 16

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

Question 17

revelations about atomic model after bohr

Answer 17

found not all electrons in same shell had same energy –> subshells

Question 18

whats a time of flight mass spectrometer

Answer 18

machine used to analyse elements or compounds
elements:
- find relative abundance of its isotopes
- relative atomic mass

compounds:
- relative molecular mass of a molecule

Question 19

name stages of TOFMS

Answer 19

1. ionisation
   - electrospray ionisation or
   - electron impact ionisation
2. acceleration
3. ion drift
4. detection

Question 20

condition needed for TOFMS

Answer 20

under a vacuum or else air particles would ionise and register on the detector

Question 21

when is electrospray ionisation typically used and when is electron impact ionisation typically used?

Answer 21

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

Question 22

electron impact ionisation

Answer 22

• 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–

Question 23

electrospray ionisation

Answer 23

• 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

Question 24

acceleration

KE = ½ mv^2

KE = kinetic energy of particle (J)
m = mass of the particle (kg)
v = velocity of the particle (ms–1)

Answer 24

• +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

Question 25

ion drift

t= d/v
t = time of flight (s)
d = length of flight tube (m)
v = velocity of the particle (m s–1)

Answer 25

• ions enter region w/o electric field
• they drift through at same speed they left
• ions with smaller m/z values (lighter) will have the same kinetic energy as those with larger m/z and will move faster

Question 26

detection

( look into this one)

Answer 26

• lighter ions reach the detector quicker
• this creates a small current when the ions hit it
• when the ions hit the negative detector they gain an electron and are deionised

Question 27

define relative atomic mass

Answer 27

Ar - same as atomic no.

the average mass of an atom of an element on a scale where an atom of carbon-12 is exactly 12

Question 28

define relative isotopic mass

Answer 28

the mass of an atom of an isotope of an element on a scale where an atom of carbon-12 is exactly 12

Question 29

define relative molecular mass

Answer 29

Mr

the average mass of a molecule of a compound on a scale where carbon 12 is exactly 12

Question 30

what is relative formula mass

Answer 30

the average mass of a formula unit of a compound on a scale where carbon-12 is exactly 12

• used for ionic/giant covalent compounds
• work out the same as Mr