s3.1 periodicity

Question 1

what are the names of the groups in the periodic table?

Answer 1

group 1 -> alkali metals
group 2 -> alkaline earth metals
groups 3-12 -> transition metals
group 17 -> halogens
group 18 -> noble gases
La-Lu -> lathanides
Ac-Lr -> actinides

Question 2

how can you deduce the electron configuration of an element based on it’s position on the periodic table?

Answer 2

1s¹ 2s¹
- s block element
- group 1 (number of valence electrons)
- period 2 (highest occupied main energy level)

Question 3

what is periodicity?

Answer 3

trends in properties of elements across a period or down a group.

Question 4

what is electron shielding?

Answer 4

electron shielding occurs when the inner electrons shield the outer electrons from the full attraction of the nucleus.
electron shielding remains constant across a period because the number of shielding electrons is the same across a period.
electron shielding increases down a group because the number of shielding electrons increases down a group.

Question 5

what is effective nuclear charge?

Answer 5

effective nuclear charge is the net positive charge experienced by outer valence shell electrons from the force of attraction between protons in the nucleus and the force of repulsion between inner core electrons.
effective nuclear charge increases across a period.
the effective nuclear charge can be approximated by the following equation, where Z is the atomic number and S is the number of shielding electrons:
Zeff = Z - S

Question 6

what is atomic radius?

Answer 6

the atomic radius is measured as half the distance between neighbouring nuclei.

Question 7

what is the trend in atomic radius across a period?

Answer 7

atomic radii DECREASES across a period:
nuclear charge increases across a period.
electrons are added to the same main energy level - electron shielding remains constant across a period.
the effective nuclear charge increases, so electrons are pulled closer to the nucleus.

Question 8

what is the trend in atomic radius down a group?

Answer 8

atomic radii INCREASES down a group:
- the number of occupied energy levels increases.
- this results in a weaker attraction between the nucleus and the valence electrons (less effective nuclear charge).

Question 9

what are the trends in ionic radius?

Answer 9

ionic radius INCREASES DOWN A GROUP because of the increasing number of occupied energy levels.
ionic radius DECREASES ACROSS A PERIOD for the positive ions, INCREASES for the negative ions, and then DECREASES again.

Question 10

what is the trend in ionic radius across a period?

Answer 10

positive ions:
- smaller in size than their parent atom
- loss of electrons from outermost energy level
- increased attraction between nucleus and valence shell electrons
- decrease in cation radii across a period due to increased effective nuclear charge

negative ions:
- larger in size than their parent atom
- gain of electrons into outermost energy level increases repulsion between electrons
- decreased attraction between nucleus and valence shell electrons
- decrease in anion across a period due to increased effective nuclear charge.

Question 11

what is the trend in ionic radius in isoelectronic species?

Answer 11

the number of protons increases but the number of electrons remains the same.
the attraction between the nucleus and electrons increases, which causes the ionic radius to decrease.

Question 12

what is the trend in ionisation energy down a group?

Answer 12

first IE decreases down a group:
- although the nuclear charge increases, the distance between the nucleus and the valence electron increases
- the shielding by inner shell electrons increases
- the effective nuclear charge is decreasing

Question 13

what is the trend in ionisation energy across a period?

Answer 13

first IE increases across a period:
- nuclear charge increases
- atomic radii slightly decreases
- shielding by inner shell electrons remains the same
- the electrostatic attraction between the nucleus and valence electrons increases

Question 14

what are the exceptions to the trend in ionisation energy across a period?

Answer 14

1. aluminium first IE is lower than that of magnesium because of the shielding effect of the newly filled 3s orbital
2. sulphur first IE is lower than that of phosphorus due to spin-pair repulsion between the newly paired up electrons in one of the p orbitals.
3. there is a rapid decrease in IE between the last element in one period and the first element in the next caused by:
   - increased distance between the nucleus and outer shell electrons
   - increased shielding by inner electrons
   - these factors outweigh the increased nuclear charge

Question 15

what is the trend in electronegativity across a period?

Answer 15

electronegativity values increase across a period:
- nuclear charge increases but electron shielding remains constant. atomic radius decreases across a period
- stronger attraction between the nucleus and the bonding pair of electrons

Question 16

what is the trend in electronegativity down a group?

Answer 16

electronegativity values decrease down a group:
- atomic radius and electron shielding increases
- weaker attraction between the nucleus and the bonding pair of electrons

Question 17

what is the trend in electron affinity across a period?

Answer 17

first electron affinity generally increases across a period:
- nuclear charge increases and electron shielding remains constant
- elements across the period have a higher effective nuclear charge
- stronger attraction between the added electron and the nucleus

Question 18

what is the trend in electron affinity down a group?

Answer 18

first electron affinity decreases down a group:
- less exothermic
- elements further down have a larger atomic radius, with outer valence shells further away from the nucleus plus increased shielding
- weaker effective nuclear charge between the added electron and the nucleus

Question 19

what is the trend in melting point across a period?

Answer 19

a general increase then a decrease

Question 20

what is melting point like in metals Na - Al?

Answer 20

melting point increases due to the increasing strength of metallic bonding caused by the larger number of delocalised electrons contributing to the ‘electron cloud’ - larger charge and smaller size of ions gives rise to a larger charge density

Question 21

what is melting point like in non-metals Si - Ar?

Answer 21

much lower melting points as they are simple covalent molecules. melting point depends on the weak intermolecular london forces. the larger the molecule the greater the london forces.

sulphur - melting point rises slightly as the molecule is bigger so has slightly stronger london forces
chlorine - melting point falls slightly as the molecule is smaller

Question 22

what is metallic character?

Answer 22

metallic character is the tendency of an element to lose electrons and form positive ions. metals tend to lose their outer electrons to form positive ions and non-metals tend to gain electrons to form negative ions.

Question 23

what is non-metallic character?

Answer 23

non-metallic character is the tendency of an element to accept electrons and form negative ions. non-metallic character increases from left to right across a period and decreases down a group in the periodic table

Question 24

what is the trend in metallic character?

Answer 24

ionisation energy is the energy required to remove the outermost electron from a neutral. the lower the ionisation energy, the greater the tendency that element has for electron loss and therefore having greater metallic character. this means that elements lower down to the left of the periodic table have the greatest metallic character.

Question 25

what is the trend in reactivity down group 1?

Answer 25

reactivity increases down group 1. alkali metals react by losing their one valence electron to form positive ions. the atomic radius increases down a group as the number of occupied energy levels increases. ionisation energy decreases so reactivity increases.

Question 26

what is the reaction of lithium and water?

Answer 26

2Li(s) + 2H2O(l) → 2LiOH(aq) + H2(g) solid floats and moves slowly on the surface, gently fizzing

Question 27

what is the reaction of sodium and water?

Answer 27

2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) solid melts to create a molten ball that floats and moves more quickly on the surface, fizzing

Question 28

what is the reaction of potassium and water?

Answer 28

2K(s) + 2H2O(l) → 2KOH(aq) + H2(g) solid melts to create a molten ball that quickly ignites and produces a lilac flame

Question 29

what is the trend in non metallic character?

Answer 29

electron affinity is the energy change that occurs when an elements gains an electron. the higher the electron affinity, the greater the tendency that element has for electron gain and therefore has greater non metallic character. this means that elements higher up to the right of the periodic table have the greatest non metallic character.

Question 30

what are halogens?

Answer 30

group 17 (halogens - salt formers) are very reactive non metal elements. they are coloured - f2 is a pale yellow gas, cl2 is a yellow green gas, br2 is a reddish brown liquid, i2 is a purple solid.

Question 31

what is the trend in state down the halogens?

Answer 31

they show a change from gases (f2, cl2), to liquid (br2) to solid (i2) as the molar mass increases down the group which results in stronger intermolecular forces between the molecules. iodine sublimes to form a purple gas.

Question 32

what is the trend in reactivity down the halogens?

Answer 32

reactivity decreases down the group. the halogens react by gaining one electron to form negative ions. as the atomic radius increases down the group, the attraction for the electron decreases.

Question 33

what are displacement reactions?

Answer 33

halogens readily undergo displacement reactions. an example of this reaction is cl2 with kbr. Cl2 (aq) + 2KBr (aq) → Br2 (aq) + 2KCl (aq) in this reaction, cl2 is the diatomic halogen and kbr is the ionic compound made up of the metal ion k+ and a non metal halide ion br-. the extra electron that the non metal ion br- has is transferred to the halogen to form the cl- ion. this results in each halogen atom in cl2 gaining an electron and each halide ion losing an electron.

Question 34

what is the bonding continuum in period 3 oxides?

Answer 34

pure covalent bonding and ionic bonding can be considered to be opposite ends of a bonding continuum. compounds of metallic and non metallic elements show this continuum in their bonding.

Question 35

what is acid base character?

Answer 35

the acid base character of the oxides provides evidence of chemical trends in the periodic table. the broad trend is that oxides change from basic through amphoteric to acidic across a period. aluminium oxide is amphoteric which means that it can act as both a base and an acid.

Question 36

what is the acid base nature of Na₂O?

Answer 36

-> ionic -> 'dissolves' in water, then reacts to form solution -> Na₂O + H₂O > 2NaOH -> Na₂O + 2H⁺ > 2Na⁺ + H₂O -> basic

Question 37

what is the acid base nature of MgO?

Answer 37

-> ionic -> 'dissolves' in water, then reacts to form solution -> MgO + H₂O > Mg(OH)₂ -> MgO + 2H⁺ > Mg²⁺ + H₂O -> basic

Question 38

what is the acid base nature of Al₂O₃?

Answer 38

-> ionic -> insoluble due to very high lattice enthalpy -> Al₂O₃ + 6H⁺ > 2Al³⁺ + 3H₂O -> Al₂O₃ + 2OH⁻ > 2Al(OH)₄⁻ + 3H₂O -> amphoteric

Question 39

what is the acid base nature of SiO₂?

Answer 39

-> giant covalent -> insoluble due to lattice of atoms linked by strong covalent bonds -> SiO₂ + 2OH⁻ > SiO₃²⁻ + H₂O (must be hot, conc alkali) -> acidic

Question 40

what is the acid base nature of P₄O₁₀?

Answer 40

-> simple molecular -> reacts violently -> P₄O₁₀ + 6H₂O > 4H₃PO₄ -> P₄O₁₀ + 12OH⁻ > PO₄³⁻ + 6H₂O -> acidic

Question 41

what is the acid base nature of SO₂?

Answer 41

-> simple molecular -> 'dissolves' in water, then reacts to form solution -> SO₂ + H₂O > H₂SO₃ -> SO₂ + 2OH⁻ > SO₃²⁻ + H₂O -> acidic

Question 42

what is the acid base nature of SO₃?

Answer 42

-> simple molecular -> reacts violently -> SO₃ + H₂O > H₂SO₄ -> SO₃ + 2OH⁻ > SO₄²⁻ + H₂O -> acidic

Question 43

what affects the acid base nature of period 3 oxides?

Answer 43

the acidic and basic nature of the period 3 elements can be explained by looking at their structure, bonding and the period 3 elements electronegativity. the difference in electronegativity between oxygen and sodium, magnesium and aluminium is the largest and therefore the electrons will be transferred to oxygen, giving the oxide an ionic bond. the oxides of silicon, phosphorus and sulfur will share the electrons with oxygen to form covalently bonded oxides.

Question 44

what is acid rain?

Answer 44

unpolluted rainwater is naturally acidic with a pH of 5.6. CO₂ + H₂O(l) ⇌ H₂CO₃(aq) acid deposition has a pH of less than 5.

Question 45

how does sulfuric acid contribute to acid rain?

Answer 45

- Sulfur (S) burns in oxygen (O2) to form sulfur dioxide (SO2) - SO2 dissolves in water to form sulfurous acid (H2SO3). - SO2 can react with O2 to form sulfur trioxide (SO3). - SO3 dissolves in water to form sulfuric acid (H2SO4) S(s) + O2(g) → SO2(g) 2SO2(g) + O2(g) → 2SO3(g). SO3(g) + H2O(l) → H2SO4(aq)

Question 46

how does nitrogen monoxide contribute to acid rain?

Answer 46

- Nitrogen (N2) and oxygen (O2) react at high temperatures in internal combustion engines to form nitrogen monoxide (NO). - NO reacts with O2 to form nitrogen dioxide (NO2). - NO2 dissolves in water to form HNO3 and HNO2. N2(g) + O2(g) → 2NO(g) 2NO(g) + O2(g)→ 2NO2(g) 2NO2(g)+ H2O(l) → HNO3(aq)+ HNO2(aq)

Question 47

describe how increasing concentrations of atmospheric CO2 could decrease the pH of ocean water?

Answer 47

O2 dissolves in seawater. CO2(g) ⇌ CO2(aq) The CO2 dissolves in seawater to produce carbonic acid (H2CO3) which is a weak acid. CO2(aq) + H2O(l) ⇌ H2CO3(aq) Carbonic acid (H2CO3) partially dissociates in water to produce H+ (aq). H2CO3(aq) ⇌ H+ (aq) + HCO3-(aq) Increasing concentrations of CO2 shift the equilibrium position to the right, decreasing the pH.

Question 48

what is ionic charge?

Answer 48

ionic charge indicates a numerical quantity of electrons that has been either lost or gained from a species

Question 49

what is oxidation state?

Answer 49

oxidation state is a number assigned to an element showing the number of electrons lost of gained in a compound or ion

Question 50

what is the oxidation states rule about free elements?

Answer 50

a pure element will have an oxidation state of 0. this is because the distribution of electrons between atoms is the same for atoms of the same element. atoms of the same element will have the same tendency to attract or gain electrons, therefore an oxidation state of zero is used to indicate no degree of electron transfer.

Question 51

what is the oxidation states rule about ions?

Answer 51

ions have an oxidation state equal to the charge of the ion.

Question 52

what is the oxidation states rule about neutral compounds?

Answer 52

oxidation state of all atoms in a neutral compound must sum up to give zero overall.

Question 53

what is the oxidation states rule about polyatomic ions?

Answer 53

oxidation states of atoms in polyatomic ions must add up to give the overall charge of the ion.

Question 54

why do transition metals have high melting points?

Answer 54

like other metals, transition metals have a giant metallic lattice structure. since the 3d and 4s subshells are so close in energy, the transition metals are able to delocalise their d-electrons to form metallic bonds. transition metals have a higher melting point than s and p block metals. the ability to delocalise the d-electrons (increased ionic charge) means that transition metals have a greater electron density

Question 55

why do transition metals have magnetic properties?

Answer 55

magnetism in transition metals is due to the presence of unpaired electrons in the d-subshell. this is called paramagnetism - they are attracted by an external magnetic field. iron, nickel and cobalt form stronger interactions with a magnetic field as they have more unpaired electrons in the d-subshell (ferromagnetism)

Question 56

why do transition metals have variable oxidation states?

Answer 56

since the 4s and 3d subshells are close in energy, electrons from both of these subshells are able to act as valence electrons. electrons are lost first from the 4s subshell, however electrons can also easily be lost from the 3d subshell. this is why transition metals can form more than one positive ion. because of this, roman numerals are used to indicate the oxidation state.

Question 57

why can transition metals form complex ions?

Answer 57

transition metal ions form complexes. the surrounding ligands donates a lone pair of electrons to form a coordinate bond with a central transition metal ion. the chemical formula of complex ions uses square brakcets around the entire complex ion and round brackets around the ligand.

Question 58

what are ligands?

Answer 58

ligands are species with lone pairs of electrons that form coordinate covalent bonds with a central metal ion. examples: :Cl¯, :OH¯, H2O:, :NH3, :CN:¯, :CO ligands use their lone pairs of electrons to form coordinate covalent bonds. they are also lewis bases (electron pair donors).

Question 59

what are coordination compounds?

Answer 59

coordination compounds are made up of a complex ion and counter ions which balance the charge of the complex ion. coordination compounds are neutral because of the counter ions.

Question 60

how do you deduce the charge on the central metal ion in a coordination compound?

Answer 60

if the ligands are neutral (e.g. NH3 is a neutral ligand), the charge on the complex ion is the same as the charge on the central metal ion. if the ligands are negatively charged (e.g. Cl-, subtract the total charge of the ligands from the charge on the complex ion.

Question 61

why do transition metals have catalytic properties?

Answer 61

transition metals and ion are often used as catalysts in chemical reactions. transition metals provide a surface for the reaction to take place and ions lose or gain electrons to form variable oxidation states. this enables them to catalyse certain redox reactions. they can easily be oxidised and reduced again, or reduced and then oxidised again due to the variable oxidation states.

Question 62

what are the different types of catalyst?

Answer 62

1. heterogenous catalyst: a different physical state from the reactants 2. homogenous catalyst: same physical state as the reactants.

Question 63

what are the factors affecting the colour of transition metal complexes?

Answer 63

1. the nature of the transition element 2. the oxidation state 3. the identity of the ligand 4. the stereochemistry of the complex

Question 64

why can transition metals form coloured compounds?

Answer 64

white light is composed of all the wavelengths of the visible spectrum. when light passes through a solution of Cu²⁺ ions, certain wavelengths of light are absorbed and certain wavelengths of light are transmitted. The [Cu(H₂O)₆]²⁺ complex ion appears blue in solution. the colour that is seen is complementary to the colour that is absorbed.

Question 65

why does the d-orbital split in coordination compounds?

Answer 65

crystal field theory states that the properties of complex ions are caused by the splitting of d-orbitals into two sets of different energies. the splitting occurs when ligands approach the central metal ion; this causes repulsion between the lone pairs of electrons on the ligands and the electrons in the five d-orbitals of the central metal ion. the d-electrons are repelling unequally, which causes splitting, with two d-orbitals of higher energy and three d-orbitals of lower energy.

Question 66

how does the splitting of the d-orbital lead to coloured compounds?

Answer 66

electrons can transition between the two sets of d-orbitals by absorbing energy. the energy difference between the two sets of d-orbitals corresponds to the wavelengths of visible light.