Physical Unit 1.1: Atomic Structure

Question 1

what is the structure of atoms in terms of protons, neutrons & electrons?

Answer 1

atoms have a central nucleus containing protons & neutrons
most of the atom’s mass is concentrated in the nucleus
the diameter nucleus is tiny compared to the whole atom
electrons orbit the nucleus in energy levels/orbitals
orbitals take up most of the atom’s volume
atoms have no charge

Question 2

what is the relative mass & charge of protons, neutrons & electrons?

Answer 2

protons:
relative mass 1
relative charge +1

neutrons:
relative mass 1
relative charge 0

electrons:
relative mass 1/1836 (0.005)
relative charge -1

Question 3

define ion

Answer 3

has a different number of electrons to protons
has a charge

Question 4

define atomic number

Answer 4

number of protons

Question 5

define mass number

Answer 5

number of protons + neutrons

Question 6

define isotope

Answer 6

atoms with the same number of protons & different number of neutrons
(= atoms of the same element with same atomic number & different mass number)

Question 7

what determines the chemical properties of an element?

Answer 7

number & arrangement of electrons

Question 8

how do the chemical & physical properties of different isotopes compare?

Answer 8

isotopes have the same configuration of electrons so have the same chemical properties
isotopes have slightly different physical properties because they depend on the mass of the atom

Question 9

define relative atomic mass

Answer 9

the average mass of atoms of an element relative to 1/12th the mass of a 12C atom

Question 10

define relative isotopic mass

Answer 10

the average mass of atoms of an isotope of an element relative to 1/12th the mass of a 12C atom

Question 11

define relative molecular mass

Answer 11

the average mass of a molecule relative to 1/12th the mass of a 12C atom

Question 12

how does a time of flight mass spectrometer work?

Answer 12

1. ionisation
2. acceleration of ions
3. ion drift
4. detection

Question 13

explain ionisation in a mass spectrometer

Answer 13

electron impact - used for elements & low Mr compounds (smaller)
high energy electrons are fired at the sample from an electron gun
this knocks one electron off each atom/molecule to form 1+ ions
= particles lose an electron

electrospray ionisation - used for high Mr compounds (bigger)
sample is dissolved & injected through a needle at high pressure
a high voltage is applied to the end of the needle where spray is released
the particles gain a proton (H+ ion) as they leave the needle so they become ions
sample turns into a gas of 1+ ions

Question 14

explain the acceleration of ions

Answer 14

positively charged ions are accelerated by an electric field so all ions have the same kinetic energy

Question 15

explain ion drift

Answer 15

separation of ions
ions enter the flight tube
ions with different masses have a different time of flight
lighter ions have a higher velocity so take less time to reach the detector

Question 16

explain detection

Answer 16

positive ions are attracted to the negatively charged detector
e- is transferred from detector to 1+ ion
& produces a current when they hit
the size of the current is proportional to the relative abundance

Question 17

what is the main peak from electrospray ionisation?

Answer 17

Mr + 1
so must subtract 1 to find the Mr

Question 18

how do you find the relative atomic/formula mass from mass spectrometer data?

Answer 18

mass/charge ratio on x-axis
relative abundance on y-axis
(abundance x mass)/total abundance

Question 19

why are there peaks at different mass/charge values?

Answer 19

different isotopes

Question 20

what can a smaller, lighter peak be?

Answer 20

caused by fragments
fragmentation can happen in electron impact ionisation but not electrospray

Question 21

describe the periodic table trends for:
outer electron distance from nucleus
outer electron orbital

Answer 21

see periodic table in atomic structure booklet

Question 22

how are electrons arranged?

Answer 22

in energy levels/shells
which have s, p & d sub-shells
which have orbitals
each orbital can hold 2 electrons that have opposite spins

Question 23

as the number of the shell increases

Answer 23

distance from the nucleus increases

Question 24

define orbital

Answer 24

the region of space that electrons are most likely to be in

Question 25

how are electrons filled up?

Answer 25

electrons enter the lowest energy orbital available
so 4s generally fills up before 3d because it has less energy
electrons prefer to occupy orbitals on their own so only pair up when no empty orbitals of the same energy level are available

Question 26

what electrons are lost to form ions?

Answer 26

electrons in the highest energy levels are lost first
electrons are lost from 4s before 3d because when electrons fill it, 4s goes above 3d
because smaller increase in the electron’s energy required to leave the atom

Question 27

Cr

Answer 27

1s2 2s2 2p6 3s2 3p6 4s1 3d5

Question 28

Cu

Answer 28

1s2 2s2 2p6 3s2 3p6 4s1 3d10

Question 29

define first ionisation energy

Answer 29

the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions

Question 30

define second ionisation energy

Answer 30

the energy required to remove one mole of electrons from one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

Question 31

what is the equation for first ionisation energy?

Answer 31

X(g) –> X+(g) + e-

Question 32

how does distance from the nucleus affect ionisation energy

Answer 32

distance from nucleus/atomic/ionic radius
the smaller the distance from the nucleus, the stronger the electrostatic attraction b/w the nucleus & outer electron
so more energy is needed to remove the outer electron
so the higher the ionisation energy

Question 33

how does nuclear charge affect ionisation energy?

Answer 33

nuclear charge/number of protons
the greater the number of protons/the grater the nuclear charge, the stronger the attraction b/w the nucleus & outer electron
more energy is needed to remove the outer electron
so the higher the ionisation energy

Question 34

how does shielding affect ionisation energy?

Answer 34

shielding - the # of shells b/w the nucleus & outer electron
the greater the shielding, the weaker the attraction b/w the outer electron & nucleus
less energy needed to remove the outer electron
so lower ionisation energy

Question 35

what is the general trend in first ionisation energy down group 1?

Answer 35

ionisation energy decreases bc:
distance from nucleus increases
shielding increases (bc # of shells increases)
so weaker attraction b/w outer electron & nucleus
so less energy needed to remove e-

Question 36

what is the general trend in first ionisation energy across period 3?

Answer 36

ionisation energy increases bc:
distance from nucleus decreases
nuclear charge increases
same shielding

Question 37

what are the anomalies in the trend in ionisation energy across period 3 & explain them?

Answer 37

Al lower ionisation energy than Mg bc:
outer e- for Al is in a p orbital, which is higher in energy than the outer e- in an s orbital in Mg
so less increase in energy needed to remove it

S lower ionisation energy than P bc:
in sulfur, 2 e-s pair up in a p orbital
this causes repulsion b/w the pair of electrons (as they are both -vely charged)
so the electrons require less energy to be lost
this has less of a decrease than b/w Al & Mg

Question 38

successive ionisation energies

Answer 38

the largest difference in successive ionisation energies comes after the group # of the element

Question 39

what is the formula linking mass, Ar & avogadro’s constant?

Answer 39

m = Ar x 10-3/Na

Question 40

m1/t1^2 =

Answer 40

m2/t2^2