atomic structure - periodicity

Question 1

how does atomic structure influence the periodic table?

Answer 1

elements in the periodic table are arranged in order of increasing proton number (Z) - the arrangement allows for periodic (by row) variations in their properties to be observed
it can also be understood in terms of electron configuration (groups/blocks)

Question 2

how does Zeff vary with atomic orbital?

Answer 2

orbitals that are further from the nucleus experience lower nuclear attraction due to shielding of lower energy electrons, so Zeff decreases

Question 3

what are the implications of perfect nuclear charge?

Answer 3

this would mean valence electrons always experience nuclear charge of +1

Question 4

what are the implications of no shielding?

Answer 4

valence electrons would experience full Z

Question 5

how does the screening constant affect Zeff

Answer 5

Zeff = Z - S, where S = screening constant
S depends on the degree of penetration of the orbital in question and the screening provided by other core electrons

Question 6

how does Zeff change across a period (L->R)?

Answer 6

Zeff increases because filling of the same n shell and screening of each additional electron is insufficient to overcome the effect of increase in proton number

Question 7

how does Zeff change down a group?

Answer 7

Zeff increases only slightly down the group as proton number increases, but the filling of the next n-shell means electrons are much further from the nucleus

Question 8

when does Zeff decrease?

Answer 8

when an additional electron foes into an orbital with a higher n value

Question 9

how does Zeff relate to valence electrons?

Answer 9

higher Zeff means greater stabilisation of valence electrons

Question 10

what is the purpose of slaters rules?

Answer 10

to estimate screening constant

Question 11

limitations of slaters rules?

Answer 11

-they do not take into account stability from maximising parallel spin
-cannot distinguish between s and p electrons

Question 12

hydrogenic definition

Answer 12

2 body systems containing 1 nucleus + 1 electron
e.g. H, Li+, etc

Question 13

how do rdf graphs change for hydrogenic systems + why?

Answer 13

for hydrogenic systems, maxima of rdf graph moves closer to 0 as +ve charge of system increases, this is because Zeff increases as greater +ve charge = more protons, which means atomic radius is much smaller as Zeff pulls valence electron in, meaning its more likely to be found closer to the nucleus

Question 14

how does orbital energy change across a period?

Answer 14

orbital energies become more stable across a period (L->R) as Zeff increases

Question 15

how does penetrating power of s and p orbitals change as Zeff changes?

Answer 15

ns orbitals are more penetrating than np so ns is lower in energy, and the gap between ns and np increases as Zeff increases

Question 16

radial extension definition

Answer 16

how far the electron cloud of an atomic orbital extends from the nucleus - how spread out the electron is in space

Question 17

what are the main 4 elemental properties associated with periodicity?

Answer 17

ionisation energy
electron gain/affinity
electronegativity
size/atomic radii

Question 18

ionisation energy definition

Answer 18

the energy change when each atom in a gaseous mole of atoms of the element loses one electron, forming a gaseous mole of 1+ ions - always endothermic (+)

Question 19

how many successive IEs can an element have?

Answer 19

each element can have Z successive IEs, where Z = atomic no (no. or protons and therefore electrons)

Question 20

uses of IE?

Answer 20

can be used to predict and rationalise available +ve oxidation states of elements

Question 21

how do successive IEs change?

Answer 21

each successive IE for a single element is greater than the previous as each successive electron is being removed from a progressively more +ve ion and from a shell closer to the nucleus, increasing Zeff so more energy is needed

Question 22

why do successive IEs show abrupt changes?

Answer 22

as electrons are removed from shells closer and closer to the nucleus, this causes a large sudden increase in energy between the removal of the last electron of a higher energy shell and the first electron of a lower energy shell

Question 23

how does IE change gong down a group + why?

Answer 23

IE decreases down a group as:
- number of shells / principle QN / size of electron cloud increases
- as n increases, radial extension increases so electron is less tightly bound
- Zeff slightly increases but is outweighed by the rest

Question 24

how does IE change across a period (L->R)?

Answer 24

IE increases across a period as:
- Zeff and atomic size increases due to increasing Z

Question 25

state + explain the 2 discontinuities to the trends in IE

Answer 25

- IE of B < Be as its easier to remove valence p electron than valence s electron as 2p is at a higher energy level - IE of O < N as Os valence electron is paired and so experiences repulsion - its more favourable to remove electron electron repulsion than remove exchange energy stabilisation from 3 parallel spin electrons

Question 26

electron gain energy definition

Answer 26

energy change when each atom in a mole of gaseous atoms of an element gains 1 electron to form a mole of gaseous 1- ions - can be +ve or -ve 2nd and higher electron gain energy is always endothermic (+), costing energ

Question 27

electron affinity definition

Answer 27

energy released on attachment of an electron to an atom

Question 28

state the relationship between electron gain and electron affinity

Answer 28

electron affinity = -electron gain energy electron gain measures ability of an atom to release energy when it gains electrons, electron affinity is simply the amount of energy released

Question 29

what type of elements have the highest electron affinities?

Answer 29

more electronegative elements (near F) have higher electron affinities

Question 30

what increases the favourability of electron gain energy?

Answer 30

electron gain energy is determined by the LUMO, it becomes more favourable as Zeff increases

Question 31

how does electron gain energy change down a group?

Answer 31

electron gain energy tends to decrease down a group - most -ve values around F arise from incoming electron occupying a p orbital and experiencing a large Zeff - it tends to be more +ve if new electron makes a new filled electron configuration - also very +ve for noble gases as new electrons must be placed in a much higher energy orbital

Question 32

how does electron gain energy change across a period?

Answer 32

electron gain energy increases across a period

Question 33

electronegativity definition

Answer 33

ability of an atom to attract electron density towards itself (rationalises ionicity/covalency of bonds/bond polarity) - not directly measurable and unitless

Question 34

electropositive definition

Answer 34

an element/atom with a low electronegativity

Question 35

what is the most electronegative element?

Answer 35

F, followed by O and N

Question 36

how does electronegativity impact bond polarity?

Answer 36

elements with large electronegativity differences form ionic bonds elements with similar electronegativities form covalent bonds

Question 37

what affects the polarisability of ions?

Answer 37

ions which are larger with higher charges are more polariseable ions which are smaller and singly charged are more polarising

Question 38

what is the most common scale for electronegativity and how was it made?

Answer 38

Paulings electronegativity scale created by comparing bond dissociation enthalpies for heteronuclear diatomics with homonuclear diatomics - BDE for heteronuclear diatomics are greater than for homonuclear diatomics - this is a measure of the ionic character of the heteronuclear bond

Question 39

how does electronegativity change across a period?

Answer 39

it increases across a period as: - Zeff increases and atomic size decreases

Question 40

how does electronegativity change down a group?

Answer 40

it decreases down a group as: - atomic size increases a lot - offsets slight increase in Zeff

Question 41

how does electronegativity relate to oxidation state?

Answer 41

as electronegativity increases, O.S increases

Question 42

how does electronegativity relate to atomic orbitals?

Answer 42

as electronegativity increases, stability of atomic orbitals increases

Question 43

what bonds are formed between metals and non-metals?

Answer 43

ionic bonds - forms hard, non-volatile solids

Question 44

what bonds are formed between non-metals?

Answer 44

covalent bonds - forms volatile molecular compounds

Question 45

what do 2 metals form?

Answer 45

an alloy

Question 46

metalloid definition

Answer 46

elements in between metals and non-metals that show behaviour of both

Question 47

why is it difficult to measure atomic radii?

Answer 47

due to wave-particle duality of electrons, and the fact that electron density doesn't stop at a certain distance from the nucleus, but fades away gradually

Question 48

what affects atomic radii?

Answer 48

Zeff and the environment of the atom / what its bonded to - when atoms pack in solids or form bonds in molecules their nuclei are generally found at characteristic distances from eachother

Question 49

atomic radius definition

Answer 49

1/2 the distance between nuclei of neighbouring atoms in the pure element

Question 50

what are the 4 types of atomic radii

Answer 50

metallic radius - specific for metals in solid state (experimentally determined) covalent radius - specific for non-metal molecules ionic radius - specific for ions in solid state (experimentally determined) van der waals radius - used for noble gases/monoatomics, referring to 1/2 distance of closest approach

Question 51

how does atomic radii change across a period?

Answer 51

atomic radius decreases across a period as: - Zeff increases pulling valence electrons closer to nucleus

Question 52

how does atomic radii change among d-block elements?

Answer 52

it decreases as: - reduction n radial size of transiton metals as d electrons are added, these are very poorly shielded to there is a large increase in Zeff this is the d-block contraction

Question 53

how does atomic radii change down a group?

Answer 53

atomic radii increases down a group as: - QN n increases, electrons occupy higher energy orbitals so rdf maximum shifts right - Zeff slightly increases but electrons arent as tightly held do to increased radial extension

Question 54

give 3 exceptions to trend in atomic radii

Answer 54

Ga and Ge - poor screening ability of 3d shell (d-block contraction) 4f orbitals - poor screening from nuclear charge so atomic radii decreases as Zeff increases (f-block contracton) d-block - while 4d have larger atomic radii than 3d, poor screening of f-orbitals means 4d and 5d elements in the same group have similar radii

Question 55

what affects covalent radii?

Answer 55

- the size of the electron cloud, determined by Zeff, as valence electrons are involved in bonding - theoretically radii should be constant but not true in practice, varies depending on the exact nature of bonding

Question 56

what is the difference between directional and non-directional metallic bonding?

Answer 56

if metals bond using s orbitals = non-directional if metals overlap using p orbitals = directional directional bonding gives a higher melting point and approximates to covalent bonding (this means for metals with higher melting points, metallic and covalent radii are similar)

Question 57

difference between covalent radii and van der waals radii?

Answer 57

van der waals radii tends to be larger than covalent radii as no bonds, so its assumed valence electron clouds do not interpenetrate

Question 58

what assumptions must be made about ionic radi?

Answer 58

- assumes ions are hard spheres -they touch but do not overlap - as cations have lost electrons their radii will be smaller than its atomic radius - as anions have gained electrons their radii will be larger than its atomic radius

Question 59

specifically which types of ionic compounds are used to determine ionic radii?

Answer 59

compounds with charge balances, 1-/1+ or 2+/2-, not 2+/(1-x2)

Question 60

how does coordination number affect ionic radii?

Answer 60

increasing coordination number = increasing radius - this means there are different ionic radii for compounds with different coordination numbers

Question 61

give 3 problems with determining atomic radii

Answer 61

1- size of a singular isolated atom has no real meaning, as this never occurs 2- vast range of environments atom scan be in, e.g. cannot compare ionic and covalent radii as measure is different 3- experimental methods used to determine radii are prone to error