3.1.1-3 - Atomic Structure, AoS + Bonding

Question 1

what is meant by ‘electronegativity’?

Answer 1

ability of an atom to attract the electron density of a covalent bond towards itself

Question 2

what happens to electronegativity down the group?

Answer 2

electronegativity decreases
- due to increased shielding, meaning the distance between the nucleus + outer electron is greater

Question 3

what happens to electronegativity across the period?

Answer 3

electronegativity increases
- nuclear charge increases

Question 4

what is meant by ‘polarity’?

Answer 4

unequal sharing of electrons in a bond

Question 5

how do London forces arise?

Answer 5

• uneven distribution of electrons within an atom. This results in a slightly negative and slightly positive
  charge on either side of the atom
• induces a temporary dipole; temporary dipole induces other dipoles on a neighbouring atom/molecule

Question 6

why is solid ice less dense than water?

Answer 6

• lattice structure of hydrogen bonds (very rigid + more stable)
• bonds push the water molecules further apart, which lowers the density

Question 7

what’s the bond angle of a linear molecule and why?

Answer 7

180; 2 bonding pairs of electrons around the central atom which repel as far as possible equally

Question 8

what’s the bond angle of a trigonal planar molecule and why?

Answer 8

120; 3 electron pairs around the central atom which repel as far apart as possible equally

Question 9

what’s the bond angle of a tetrahedral molecule and why?

Answer 9

109.5; 4 electron pairs around the central atom which repel as far apart as possible equally

Question 10

what’s the bond angle of a trigonal bipyramidal molecule and why?

Answer 10

120 + 90; 5 electron pairs around the central atom which repel as far apart as possible equally

Question 11

what’s the bond angle of an octahedral molecule?

Answer 11

90; 6 electron pairs around the central atom which repel as far apart as possible equally

Question 12

what’s the bond angle of a pyramidal molecule and why?

Answer 12

107; there are 3 bonding pairs and 1 lone pair of electrons around the central atom; lone pairs repel more than bonding pairs

Question 13

what’s the bond angle of a non-linear molecule and why?

Answer 13

104.5; 2 bonding pairs and 2 lone pairs around the central atom - lone pairs repel more than bonding pairs

Question 14

what is meant by ‘relative atomic mass’?

Answer 14

the weighted average mass of an atom of an element, relative to 1/12th the relative atomic mass of an atom of carbon-12

Question 15

how do you prepare a standard solution?

Answer 15

• weigh the required mass of solid in a weighing boat using a balance
• transfer the solid into a beaker using distilled water to wash it out - preventing any solid remaining in the sample bottle
• reweigh the sample bottle and work out the difference
• add distilled water to the beaker to dissolve the solid (small volume of water) + use a stirring rod to stir
• transfer the dissolved solution into a 250cm3 graduated volumetric flask using a funnel, rinsing contents of the beaker and stirring rod with distilled water into the flask
• add more distilled water, fill up the solution to 250cm3, using a dropping pipette for the last few drops. making sure the bottom of the meniscus is touching the line marking 250cm3.
• invert the volumetric flask several times

Question 16

what are the stages of a time of flight mass spectrometer?

Answer 16

1. ionisation
2. acceleration
3. ion drift
4. magnetic field
5. detection

Question 17

describe how electrospray ionisation works

Answer 17

• sample dissolved in volatile substancce pushed through small needle at high pressure/voltage
• each particle gains H+ ion; sample turned into gas

Question 18

what’s the equation for electrospray ionisation?

Answer 18

X(g) + H+ -> XH+(g)

Question 19

describe how electron impact ionisation works

Answer 19

• sample is vapourised + high energy electrons are fired at it
• knocks 1 electron off each particle and they become 1+ ions

Question 20

what’s the equation for electron impact ionisation?

Answer 20

X(g) + e -> X+(g) + 2e

Question 21

describe the acceleration step in TOF mass spectrometry

Answer 21

• positive ions attracted to negatively charged plate + accelerated towards it, so they have the same KE
• lighter ions move faster than heavier ions

Question 22

describe the detection step in TOF mass spectrometry

Answer 22

• ions with same charge reach detector
• lighter ions have higher velocity to reach detector first
• positive ions pick up electron; electric current generated

Question 23

how do you find the mass of an ion

Answer 23

(RAM X10 to the -3)/AVC

Question 24

how does IE change across a period?

Answer 24

• increases across the period because nuclear charge increases
• causes atomic radius to fall as outer shell is pulled closer to the nucleus
• distance between nucleus + outer electrons decreases
• shielding remains similar
• becomes harder to remove an electron so more energy is needed

Question 25

how does IE change down the group?

Answer 25

• no. of protons in the atom inc, so nuclear charge increases
• atomic radius inc. due to more shielding
• distance between nucleus and outer electron inc.
• meaning less energy is required to remove the outer electron
• so IE DECREASES