Chemistry Topic 3 - Periodicity

How are the elements in the periodic table arranged?

in increasing atomic number, periods are rows, groups and columns and table is split into s,p,d,f blocks according to the highest occupied sub-level

What group make up the alkali metals?

group 1

What groups make up the transition metals?

group 3-12

What group makes up the alkaline earth metals?

group 2

What groups make up the S block?

groups 1 and 2

What section of the periodic table makes up the D block?

transition metals

What group makes up the noble gases?

group 18

What elements are metalliods?

B, Si, Ge, As, Sb, Te

What group makes up the halogens?

Group 17

What groups make up the P block?

groups 13-18

What groups make up the f block?

lathanoids and actinoids

Define Electronegativity

the ability of an atom to attract a pair of electrons towards itself in a shared covalent bond.

How does electronegativity change down a group?

electronegativity decreases down a group as shielding increases and nucleus’ power of attraction gets weaker.

How does electronegativity change across a period (left to right)?

electronegativity increases across a period as shielding stays the same but proton number increases, making nucleus’ power of attraction greater.

Define Atomic Radius

the radius of an a atom

How does atomic radius change down a group?

atomic radius increases down a group as shielding increases

How does atomic radius change across a period?

atomic radius decreases across a period as shielding stays the same but atomic number increases, causing electrons in atom’s energy levels to be attracted more closely to nucleus, making the atom denser.

Define ionisation energy

the energy required to remove one mole electron from one mole of a gaseous atom M(g) → M+(g) + e-

How does ionisation energy change going down a group?

ionisation energy decreases down a group

How does ionisation energy change across a period?

ionisation energy generally increases across a period but there are exceptions

Define electron affinity

The amount of energy released when one mole of electrons is gained by one mole of atoms of an element in the gaseous state to form one mole of gaseous ions. M(g) + e- → M-(g)

How does electron affinity change going down a group?

generally electron affinity decreases going down a group and becomes less exothermic - but beware of exceptions. The size of the atom increases, weakening the attraction between the nucleus and the added electron, making the addition of an electron require more energy.

How does electron affinity change across a period?

the general trend is that electron affinity increases across a period and becomes more exothermic - there are exceptions

Why are radii of positive ions smaller than their atomic radii?

M and M+ have the same number of protons and therefore the same amount of nuclear attraction, however M+ has on fewer electron so less electron-electron repulsion, making the electrons pulled closer together and therefore creating a smaller atomic radii.

Why are the radii of negative ions larger than their atomic radii?

X and X^- have the same number of protons so their nuclear attraction is the same, however X- has an extra electron so there is greater electron-electron repulsion, making the electrons spread further apart, increasing the ionic radii.

Why is there a sudden decrease in electron affinity from F to Cl?

From F to Cl, a huge decrease in electron-electron repulsion occurs as F is a very small atom with a lot of electron electron repulsion whereas Cl is a larger atom that has less electron electron repulsion.

Define a metallic structure

a structure consisting of a regular lattice of positive ions in a sea of delocalised electrons

What features do most elements capable of forming metallic structures have?

a low ionisation energy - meaning they can form positive ions easily

Define a Basic Oxide (e.g Na2O)

a basic oxide is an oxide that will react with an acid to form a salt and, if soluble in water, will produce an alkaline solution

Define an amphoteric oxide (e.g. Al2O3)

an amphoteric oxide is an oxide that reacts with both acids and bases

Define an acidic oxide (e.g. SO2)

an acidic oxide is an oxide that reacts with bases/alkalis to form a salt and, if soluble in water, will produce an acidic solution

Describe how oxides change across a period

oxides change from basic to amphoteric to acidic across a period

Give the formula of the oxide, nature of element and nature of oxide for Sodium

Na2O, metal, basic

Give the formula of the oxide, nature of element and nature of oxide for Magnesium

MgO, metal, basic

Give the formula of the oxide, nature of element and nature of oxide for Aluminium

Al2O3, metal, amphoteric

Give the formula of the oxide, nature of element and nature of oxide for Silicon

SiO2, non metal, acidic

Give the formula of the oxide, nature of element and nature of oxide for phosphorus

P4O10, non metal, acidic

Give the formula of the oxide, nature of element and nature of oxide for Sulfur

SO2, SO3, non metal, acidic

Write the chemical equation for the reaction between sodium oxide and water

Na2O(s) + H2O(l) → 2NaOH(aq)

Write the chemical equation for the reaction between Magnesium Oxide and water

MgO(s) + H2O(l) → Mg(OH)2(aq)

Write the chemical equation for the reaction between Phosphorus oxide and water

P4O10(s) + 6H20(l) → 4H3PO4(aq)

Write the chemical equation for the reaction between Nitrogen dioxide and water

2NO2(g) + H2O(l) → HNO2(aq) + HNO3(aq)

Write the chemical equation for the reaction between sulfur (2) oxide and water

SO2(g) + H2O(l) → H2SO3(aq)

Write the chemical equation for the reaction between sulfur (3) oxide and water

SO3(g) + H2O (l) → H2SO4 (aq)

What two oxides contribute to acid deposition in the form of acid rain?

nitrogen and sulfur oxides

Describe the reactions of group 1 (alkali metals)

all group 1 elements have one outer shell electron so virtually all reactions involve the loss of this outer shell electron to form the positive M+ ion. Group 1 metals rapidly react with water and react with halogens to form salts. Reactivity increases down the group.

Give the symbol equation for the reaction between an alkali metal and water

2M(s) + 2H20(l) → 2MOH(aq) + H2(g)

Give the equation for the reaction between an alkali metal and a halogen

2M(s) + X2(g) → 2MX(s)

Describe the reactions that occur with elements in Group 17

all elements in group 17 have 7 outer shell electrons so usually react by gaining one electron (X-) or forming a covalent compound. Reactivity decreases down the group and displacement reactions are very common.

What is a displacement reaction? (involving halogens)

a displacement reaction involves a reaction between a halogen solution and a solution containing halide ions. The more reactive halogen displaces the halide ion of the less reactive halogen from the solution.

What occurs during this reaction? Cl2 + 2KBr

→2KCl + Br2, chlorine displaces bromide ions and solution turns orange

What occurs during this reaction? Cl2 + 2KI

→ 2KCl + I2, chlorine displaces Iodide ions and solution turns brown

What occurs during this reaction? Br2 + 2KI

→ 2KBr + I2, Bromine displaces iodide ions and solution turns brown

Define Transition Metal

an element which forms at least one stable ion with a partially-filled d sub-shell

Give the electron configuration of Sc (21)

[Ar]4s2 3d1

Is Zinc a transition metal according to the definition?

No Zinc is not a transition metal as it has a complete 3d sub shell

Is Scandium a transition metal according to the definition?

No Sc is not a transition metal according to the definition as it only forms the ion Sc3+ which doesn’t have a 3d sub orbital

Give 5 characteristics of transition metals

1. can exhibit more than one oxidation state 2. form complex ions 3. form coloured compounds 4. act as catalysts in many reactions 5. can exhibit magnetic properties

What oxidation state do all transition metal elements exhibit when the 4s electrons are removed

\+2

How do you calculate the maximum oxidation state exhibited by a transition metal?

add the number of electrons in their 4s and 3d sub orbitals

Why can transition metals have more than one oxidation state?

the 4s and 3d sub orbitals are close in energy and there are no big jumps in the successive ionisation energies when the 4s and 3d electrons are removed

Define Complex Ion

a central transition metal ion surrounded by ligands

Define Ligand

negative ions or neutral molecules which use lone pairs of electrons to bond to a transition metal ion to form a complex ion

What bond is formed between the ligand and the transition metal ion?

a coordinate bond as the ligand donates a pair of electrons to the transition metal ion

Give the formula of neutral ligands

H2O, NH3, CO

Give the formula of -1 ligands

Cl-, CN-, OH-

Define Paramagnetic substances

substances that are attracted by a magnetic field, caused by the presence of unpaired electrons

Define Diamagnetic substances

substances that are repelled slightly by a magnetic field, caused by the presence of paired electrons

Why in transition metals do we remove electrons from the 4s sub orbital before the 3d sub orbital when an ion is formed?

in transition metals the 4s sub shell is at a lower energy than the 3d sub shell so electrons are removed their first as it requires less energy.

True or False Cr is [Ar] 4s1 3d5  not [Ar] 4s2 3d4

True - [Ar] 4s1 3d5 is more energetically stable

What two transition metals have 4s1 instead of 4s2?

Cr and Cu

How are coloured complexes formed?

Complex ions e.g. [Ni(H2O)6]2+ have an incomplete d -sub-shell which splits into two groups with different energies. Certain frequencies of visible light can be absorbed to promote an electron from the lower set of d orbitals to the higher set. Since [Ni(H2O)6]2+ is green, it must absorb the complementary colour red and transmit green.

What complexes are colourless?

any complexes containing Sc3+ or Ti4+ are colourless as they have no electrons in the 3d sub-shell. any complexes containing Cu+ or Zn2+ are also colourless as they have a full 3d subshell.

What can affect the colour of a complex ion?

1. the amount of splitting of the d orbitals - the bigger the difference in energy between the lower and higher set of d-orbitals, the higher the frequency of light absorbed. 2. the identity of the metal (different electron configurations) 3. the oxidation state of the metal (higher charge in ion causes greater splitting) 4. the nature of the ligand (ligands have different splitting powers)

What is the spectrochemical series?

the arrangement of ligands according to how much they split d orbitals.

CN- is after F- in the spectrochemical series. What does this mean?

CN- causes greater splitting of the d orbitals than F- so therefore a higher frequency of light will be absorbed by complexes containing CN- ions.

What factor causes some ligands to split d orbitals more than others?

the charge density of the ligand can explain its splitting power, the higher the charge density the greater the splitting power.