atomic struc. (phys I)

Question 1

orbital

Answer 1

a region in space where there is a 95% chance of finding an electron

Question 2

describe the current nuclear model

Answer 2

• electrons in diff. orbitals
• protons + neutrons in nucleus

Question 3

name all orbitals & shapes of orbitals

Answer 3

•S orbitals —> sphere
•Px orbitals —> on x-axis
•Py orbitals —> on y-axis
•Pz orbitals —> protudes out of axis

Question 4

no. of orbitals and outer electrons in the shells

Answer 4

-1st shell —> 1s orbital —> holds 2 electrons
-2nd shell —> 1s & 3p orbitals —> holds 8 electrons
-3rd shell —> 1s, 3p & 5d orbitals —> holds 18 electrons

Question 5

‘Mr’ definition

Answer 5

average mass of 1 molecule of a substance / 1/12th the mass of an atom of 12C

Question 6

‘Ar’ definition

Answer 6

average mass of 1 atom of an element / 1/12th the mass of an atom of 12C

Question 7

Ar (equation) =

Answer 7

(%A x massA) + (%B x massB) / total abundance

Question 8

time of flight mass spec. —> 1) ionisation

Answer 8

• ‘electron impact collision’ - sample vapourised & bombarded with electrons —> an electron is knocked off each particle —> form +ve ions
  (used for elements & low Mr compounds)
• ‘electrospray ionisation’ - sample dissolved in volatile solvent —> solvent injected into mass spec. using thin, hypodermic needle —> needle connects to + terminal of D.C supply —> + droplets —> evaporate into + ions
  (used for high Mr compounds)

Question 9

formula for electrospray ionisation

Answer 9

X (g) + H^+ –> XH^+ (g)

Question 10

formula for electron impact collision

Answer 10

X (g) + e^- –> X^+ (g) + 2e^-

Question 11

tof mass spec —> 2) acceleration

Answer 11

• +ve H ions attracted towards -vely charged plates, accelerating towards them at same K.E
• velocity depends on mass —> lower mass = higher speed

Question 12

tof mass spec —> 3) ion drift

Answer 12

+ve ions pass through hole in -vely charged plate & move into the flight tube (towards detector)

Question 13

tof mass spec —> 4) detection

Answer 13

• +ve ions hit -vely charged detector plate, gaining an electron, causing a current to flow —> plate connected to p.c n produces mass spec

Question 14

peaks on tof mass spec

(what causes the peaks?)

Answer 14

-larger peaks —> due to isotopes
-mini peaks —> due to 13C or 2H

Question 15

formula for mass spec.
(two ions)

Answer 15

m1/t1 = m2/t2
(m in kg)
(t in secs)

Question 16

finding velocity

Answer 16

V = square root of ( (2 x K.E) /m )
(mass in kg)

Question 17

the ‘first ionisation enthalpy’ is defined as…

Answer 17

the enthalpy change when each atom in 1 mole of gaseous atoms loses one electron to form 1 mole of gaseous 1+ ions

Question 18

reasons for some elements having greater I.E’s than others

Answer 18

• general increase across periods —> nuclear charge increases —> similar shielding —> nuclear attr. to outer electron becomes stronger —> harder to lose electron & ionise atom
• some sublevels have lower energies than others —> more energy needed to remove electron in lower sublevel —> greater I.E (Al to Mg)

Question 19

reasons for some elements having lower I.E’s than others

Answer 19

• easier to remove when in further shell —> eg. 3S instead of 2S —> more shielding—> less nuclear attraction—> less energy needed to remove electron
• slight repulsion between electron pairs —> less energy needed to remove electron (P to S)

Question 20

2 reasons why it’s necessary to ionise the isotopes of an element before they can be analysed in a TOF mass spec.

Answer 20

1. ions can be accelerated by the electric field
2. ions create a current when hitting the detector