Topic 2 + 12

Question 1

state one difference in physical properties of isotopes

Answer 1

(isotope with lower mass number) has lower boiling point/melting point/density than (isotope with higher mass number)

DIFFERENT MASS IS NOT ACCEPTED

Question 2

explain why chemical properties of isotopes are the same

Answer 2

because they have the same (either one of these is accepted)
1. electron configuration
2. arrangement of electrons
3. same number of protons AND electrons

Question 3

define the term “isotopes of an element”

Answer 3

atoms of same element with different numbers of neutrons
-> same chemical properties, different physical properties

Question 4

define “empirical formula”

Answer 4

simplest (whole number) ratio of moles of each element present in a molecule

Question 5

define “molecular formula”

Answer 5

actual numbers of moles of each element present in a molecule

Question 6

define “first ionization energy”

Answer 6

energy needed to remove one mole of electron from the ground state of one mole of the gaseous atom

Question 7

explain the large increase between nth and (n+1)th ionization energies

Answer 7

nth electron comes from pth energy level AND (n+1)th electron comes from (p-1)th energy level.
electron in (p-1)th energy level is closer to nucleus therefore is exposed to greater effective nuclear charge

Question 8

explain the general increase in successive ionization energies of element

Answer 8

successive electrons are more difficult to remove because each is taken from more positively charged ion, therefore experiencing increased electrostatic attraction

Question 9

valence electrons

Answer 9

electrons in the outermost shell/energy level of an atom

Question 10

core electrons

Answer 10

electrons that are not valence electrons and do not participate in chemical bonding

Question 11

percentage yield

Answer 11

actual yield / theoretical yield x 100

Question 12

why experimental yield may be greater than theoretical yield

Answer 12

temperature greater than 273K / pressure less than 100kPa

Question 13

line spectrum

Answer 13

shows discrete number of individual lines at specific points in the visible range

Question 14

continuous spectrum

Answer 14

shows all colors/wavelengths/frequencies of visible light

Question 15

atomic number

Answer 15

number of protons

Question 16

mass number

Answer 16

number of protons + neutrons

Question 17

cations

Answer 17

lost electrons, positive charge

Question 18

anions

Answer 18

gained electrons, negative charge

Question 19

mass spectrometer

Answer 19

used to measure the mass of individual atoms,
basically incomprehensible therefore uses relative mass instead,
used to determine the relative atomic mass of an element from its isotopic composition

horizontal axis: mass/charge ratio of different ions on the carbon-12 scale
vertical axis: percentage abundance

Question 20

percent abundance

Answer 20

relative amounts of two isotopes

Question 21

electromagnetic (EM) radiation

Answer 21

comes in different forms of different energy, small portion can be seen as visible light

all EM radiation travels at same speed but have different wavelengths and frequency

Question 22

frequency

Answer 22

number of waves that pass a point in 1 second

Question 23

absorption spectrum

Answer 23

produced when EM radiation is passed through a collection of atoms and some of the radiation is absorbed and used to excite the electrons in the atoms from a low energy level to higher energy level.
transmitted radiation relative to incident radiation can be measured

Question 24

ground state

Answer 24

when electron is in the lowest unoccupied energy level

Question 25

excited state

Answer 25

when electron is in a higher energy level but is unstable

Question 26

photon

Answer 26

one packet of energy (quantum),
particle of light

Question 27

moving electrons

Answer 27

• when an atom falls from excited state to ground state, light of specific frequency (v) is produced
• when an atom moves from ground state to excited state, light of specific frequency is absorbed

Question 28

ionization energy

Answer 28

energy to remove an electron from the ground state of an atom in a mole of gaseous atoms

Question 29

emission spectra

Answer 29

produced when photons are emitted from atoms with excited electrons returning to a lower energy level

Question 30

line emission spectrum of hydrogen

Answer 30

provides evidence for existence of electrons in discrete energy levels which converge at higher energies

Question 31

orbital

Answer 31

• each orbital has defined energy state for given electronic configuration and chemical environment
• can hold two electrons of opposite spin

Question 32

Aufbau principle

Answer 32

states that electrons are placed into orbitals of lowest energy first

Question 33

Cu
(Copper)

Answer 33

exception to Aufbau principle:
[Ar] 4s^1 3d^10
because of full shell stability

Question 34

Cr
(Chromium)

Answer 34

exception to Aufbau principle:
[Ar] 4s^1 3d^5
because of half shell stability

Question 35

losing electrons

Answer 35

• loses paired electrons in an orbital first
• loses electrons in 4s first before 3d

Question 36

limit of convergence at higher frequency

Answer 36

corresponds to the first ionization energy in an emission spectrum

Question 37

hydrogen spectrum

Answer 37

• absorption: lower level -> higher level
• emission: higher level -> lower level
• converges at higher energy level
• UV radiation: absorption when n=1 -> higher level, emission when higher level -> n=1
• visible light: absorption when n=2 -> higher level, emission when higher level -> n=2
• IR: absorption when n=3 -> higher level, emission when higher level -> n=3

Question 38

exceptions to ionization energy trend

Answer 38

1. First ionization energy of boron (B) is less than that of beryllium (Be) <group 2>
   -> for beryllium, first ionization potential electron comes from 2s orbital which is closer to nucleus and experiences higher electrostatic attraction than first electron of boron which comes from 2p orbital
2. First ionization energy of oxygen is less than that of nitrogen <group 15>
   -> for both nitrogen and oxygen, the first electrons come from the 2p orbital, but all electrons of nitrogen in the 2p orbital are unpaired whereas for oxygen there is one set of paired electrons in one of the 2p orbitals. Due to the repulsion between electrons in that orbital, the first electron of oxygen would be easier to remove than that of nitrogen.