3.1.1 atomic structure (just things not too good at)

Question 1

john dalton

Answer 1

atoms were solid spheres that make up elements, different spheres for each element

Question 2

JJ Thompson

Answer 2

plum pudding model , showing atoms contain electrons

Question 3

Ernest Rutherford

Answer 3

conducted the alpha scattering gold foil experiment to produce nuclear model .
- fired positively charged alpha particles at a very thin sheet of gold
- Ppm suggested : most particles slightly deflected by positive ‘pudding’
- actually : most straight through (most atom is empty space) some deflected (positive centre)

Question 4

Niels Bohr

Answer 4

adapted nuclear model , putting electrons in shells/ orbitals of fixed energy .
- they raised electrons in a ‘cloud’ around the nucleus spiral down into the nucleus , causing it to collapse
- when electrons move to a new shell, electromagnetic radiation ( with fixed energy/ frequency) is emitted (down shells) or absorbed (up shells/ away from nucleus)

Question 5

then

Answer 5

scientists discovered that not all electrons in the same shell have the same energy so refined the model to include sub shells. Not a perfect model but is useful as it is simple and explains many experimental observations e.g. bonding and ionisation energy

Question 6

mass number [A]

Answer 6

total number of protons + neutrons in the nucleus. Nucleons are responsible for almost all the mass as electrons have a tiny mass

Question 7

atomic number [Z]

Answer 7

the number of protons in the nucleus. This also equals the number of electrons in the atom meaning atoms are electrically neutral. The number of electrons in the outer shell of an atom determines the chemical properties of the element , how it reacts and what sort of element it is : its chemical identity. All atoms of the same element have the same atomic number

Question 8

relative atomic mass [Ar]

Answer 8

the average mass of an atom of an element , taking into account its naturally occurring isotopes , relative to 1/12th of the mass of an atom of carbon -12

Question 9

why C-12

Answer 9

too small numbers so relative to C-12 takes into account the percentage abundances of the isotopes

Question 10

how to work it out

Answer 10

Ar = (isotope mass number x % abundance) / sum of % isotope abundance

Question 11

relative isotopic mass

Answer 11

mass of an atom of an isotope relative to 1/12th the mass of an atom of carbon -12 . Always a whole number

Question 12

relative molecular mass [Mr]

Answer 12

average mass of a molecule in relation to 1/12 the mass of a carbon -12 atom

Question 13

how to calculate

Answer 13

Mr = sum of Ar in formula for the molecule

Question 14

isotope

Answer 14

an atom of the same element with the same number of protons (atomic number) and a different number of neutrons (so different mass number)

Question 15

about their properties

Answer 15

• same chemical properties as they have the same electron configuration
• slightly different physical properties as they depend on the mass of the atom e.g. density

Question 16

radioactive?

Answer 16

isotopes can be radioactive if they are unstable (extra protons or neutrons in the nucleus creating extra energy)
- they emit radiation as they decay + the rate of decay is measured by half- life ( the time it takes for half of its radioactivity to decay)
- they have lots of uses e.g. : carbon dating. Carbon -14 isotope is radioactive with a long half life found in all living things . Scientists can work backwards to see how long a living organism has been dead for .

Question 17

time of flight mass spectrometer

Answer 17

powerful instrumental technique that is useful for the accurate determination of relative isotopic masses and relative abundances. it determines the masses of separate atoms/molecules and is used by forensic scientists to help identify illegal drugs. can be used to work out relative atomic masses [Ar] to identify elements and relative molecular masses [Mr] .

It works by forming ions, then separating them according to the ratio of their charge: maths

Question 18

stages of TOFMS

Answer 18

1. ionisation
2. acceleration
3. ion drift
4. detection
5. data analysis

Question 19

ionisation

Answer 19

this is where each atom becomes an ion and can be done one of two ways depending on its mass

Question 20

low molecular mass

Answer 20

ELECTRON IMPACT IONISATION: for compounds with low molecular masses.
- sample is vaporised then high energy electrons are fired at the sample using an electron gun , one electron is knocked off each atom / particle forming a 1+ ion

Question 21

equation

Answer 21

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

Question 22

high relative molecular mass

Answer 22

ELECTROSPRAY IONISATION- for compounds with high relative molecular mass
- sample is dissolved in a volatile solvent + is injected into the ionisation chamber through a hypodermic needle which has a high voltage as is positively charged. The particles gain a proton and become 1+
ions as a fine mist. The solvent evaporates leaving the 1+ ions.

Question 23

equation

Answer 23

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

Question 24

acceleration

Answer 24

ions are accelerated using an electric field. the positively charged ions accelerate towards a negatively charged plate. this is so that all the ions have the same kinetic energy. they all have the same kinetic energy, but their velocity will differ as it depends on their mass lighter ions will have a higher velocity than heavier ions.

Question 25

ion drift

Answer 25

ions pass through a hole in the plate into the flight tube where they enter a region with no electric field so they just drift through it towards the detector. ions with different masses have a different time of flight.

Question 26

detection

Answer 26

The detector is a negatively charged plate and a current is produced when the ions hit the plate. the positive ions pick up an electron from the detector causing a current to flow

Question 27

data analysis

Answer 27

The signal from the detector is passed to a computer which generates a mass spectrum

Question 28

if electrospray what to do

Answer 28

the Mr is always 1 less than the highest peak

Question 29

look at chlorine mass spectra

Question 30

TOFMS calculations for a single ion

Answer 30

1) mass of one ion in Kg
2) mass using kinetic energy
3) kinetic energy of one ion
4) time of flight
5) distance of flight tube

Question 31

TOFMS calculations for two ions

Answer 31

1-5
AND
6) TOF of one isotope ions with same kinetic energy
7) velocity of isotope ions with same kinetic energy

Question 32

look at ppt for each step in more depth

Question 33

blocks in periodic table

Answer 33

from left to right
s,d,p

Question 34

electron configuration exceptions chromium

Answer 34

expect it to be 4S^2 3d^4 however, it donates one of its 4s electrons to the 3d sub shell so the 3d sub shell is more stable as its half - full. its configuration is actually 4s1 3d5

Question 35

electron configuration exceptions copper

Answer 35

expect it to be 4s2 3d9 however it donates one of its 4s electrons to the 3d sub shell so the 3d sub shell is more stable as it’s now full. its configuration is actually 4s1 3d10

Question 36

what’s lost first

Answer 36

4s before 3d

Question 37

first ionisation energy

Answer 37

the energy needed to remove 1 electron from each atom of an element in one mole of gaseous atoms to form one mole of gaseous ions with a +1 charge

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

Question 38

second ionisation energy

Answer 38

the energy needed to remove 1 electron from each ion of an element in 1 mole of gaseous +1 ions to form 1 mole of gaseous ions with a +2 charge

X+(g) -> X2+ (g) + e-

Question 39

factors affecting ionisation energy

Answer 39

• atomic radius
• nuclear charge
• shielding

Question 40

atomic radius

Answer 40

the smaller the atomic radius , the higher the first ionisation energy . Because the outer electron is more strongly attracted to the nucleus

Question 41

nuclear charge

Answer 41

the higher the nuclear charge the higher the first ionisation energy because a higher nuclear charge means a smaller atomic radius because there are more protons to attract the outer electrons therefore more attracted to the nucleus

Question 42

shielding

Answer 42

the more shielding the lower the first ionisation energy inner shells repel the outer electrons making them easier to lose

Question 43

tends in ionisation energy across a period

Answer 43

increase
- higher nuclear charge , smaller atomic radius
- outer electrons are more attracted to the nucleus
- shielding is constant

Question 44

trends in ionisation energy down a group

Answer 44

decrease
- larger atomic radius
- increase in shielding as more energy levels are added
- outer electron is less attracted to the nucleus and is therefore easier to lose

Question 45

exceptions in ionisation energy trends between group 2 and 3

Answer 45

• dip in first IE
• mode to a new energy level with higher energy S -> P subshell
• further away from the nucleus and more shielding

Question 46

exceptions in ionisation energy trends between group 5 and 6

Answer 46

• dip in first IE
• in group 5, P subshell has one electron in each orbital, no repulsion
• in group 6 , P subshell has one orbital with 2 electrons in
• the electrons in the same orbital repel each other
• so less energy is needed to remove the outer electron

Question 47

successive ionisation energies look at slide