Chemistry - Period 3: Sodium to Argon + Group II Elements

Explain the trend in atomic radius going from left to right in Period 3

The successive addition of a proton, successively increases the effective nuclear charge of the nucleus which strengthens the electrostatic forces between the nucleus and the valence electrons — bringing them closer

Explain the trends in ionic radius going from left to right in Period 3 (2)

From Na to Si and from P to Cl, there is a decrease due to the increase in nuclear charge

From Si to P there is an increase due to the addition of a new energy level

Explain the trends in electronegativity going from left to right in Period 3 (2)

The general increase in nuclear charge correlates with higher effective nuclear charge, making it easier for the atom to attract electrons to itself

A higher charge density due to the increase in nuclear charge and decrease in atomic radius correlates with higher nuclear charge, making it easier for the atom to attract electrons to itself

Explain the trends in melting point going from left to right in Period 3 (4)

From Na to Al, there is an increase in melting point due to the increase of the charge of the nuclei which strengthens the metallic bonds within their lattice which require more energy to be broken as you progress from the monovalent Na to the trivalent Al

From Al to Si, there is a stark increase in melting point as Si forms a 3-D lattice containing tetrahedral covalently bonded Si atoms which require a significant amount of energy to break

From Si to P, there is a significant decrease as P molecules are held together by van der Waals forces

From P to Ar, the melting point pertains to the amount of bonds each atom forms in their molecular form — more bonds requiring more energy to break

Describe the trends in electrical conductivity in Period 3 going from left to right (4)

From Na to Al, there is an increase in electrical conductivity due to the increase in delocalized electrons which carry charge throughout the metallic structure

From Al to Si, there is a significant decrease in electrical conductivity as Silicon’s electrons only delocalize under specific conditions to a very limited extent

From P to Cl, there is no zero electrical conductivity as there are no free delocalized electrons in their structures that can carry charge due to the strength of the covalent bonds within each molecule

Ar does not exhibit electrical conductivity because its electrons are held strongly in a stable third energy level

Explain the trends in density @STP of Period 3 elements going from left to right (4)

From Na to Al, there is an increase in density as the size of the atoms decrease but the mass increases. The increase in density can also be accredited to a strengthening in electrostatic forces between cations and mobile electrons due to the increase in nuclear charge

From Al to Si, there is a decrease in density as the lattice of Si is very open

From Si to Ar, there is a general decrease in density as their structures become less compact due to the wek van der Waal forces which get progressively weaker

Describe the reactions each Period 3 element has with oxygen (7)

Na burns with an orange flame in air to produce a mixture of sodium oxide and sodium peroxide

Mg burns with a white flame in air to produce magnesium oxide

Aluminium burns to produce aluminium oxide

Silicon burns in a strong flame to form silicon dioxide

Phosphorus burns vigorously with a pink white flame to form tetra-phosphorus trioxide and phosphorus pentoxide

Sulphur burns in air on gentle heating with a blue flame to form sulphur dioxide and sulphur trioxide

Chlorine does not react directly with oxygen

Describe the relationship between the oxidation state of Period 3 oxides and the valency of the element

The oxidation states of the highest Period 3 oxides is proportionate to the amount of valence electrons each atom has

Describe the reactions the Period 3 oxides have with water (3)

Sodium oxide and magnesium oxide react with water to form their respective hydroxides

Aluminum oxide and silicon dioxide do not react with water

Phosphorus, sulfur and chlorine oxides react with water to form acidic solutions

Describe the acid/base character of the Period 3 oxides (3)

The oxides of sodium and magnesium are basic

Aluminium oxides is amphoteric

The oxides of silicon, phosphorus, sulphur and chlorine are all acidic

Describe the type of bonds present in Period 3 oxides (3)

Oxygen forms ionic bonds with sodium, magnesium and aluminium

Oxygen forms a giant covalent structure with silicon

Oxygen forms a simple molecular structure with phosphorus, sulphur and chlorine

Describe the reactions of Period 3 elements which chlorine (7)

Na burns with an orange flame to form sodium chloride

Mg burns with a white flame to form magnesium chloride

Aluminium burns to form aluminium chloride

Silicon reacts to form silicon chloride

Phosphorus burns to produce phosphorus trichloride and phosphorus pentachloride

Sulfur reacts to form disulfur dichloride

Chlorine does not react with chlorine

Describe the relationship between the oxidation states of the Period 3 chlorides and the valency of the element

The oxidation state is proportionate to the amount of valence electrons each element has except for sulphur

Describe the reactions the chlories have with water (3)

The chlorides of sodium, magnesium and aluminium dissolve in water

The chlorides of silicon and phosphorus react with water to form acidic solutions and fumes of hydrogen chloride gas

The hydrolysis of disulfur dichloride creates several compounds including thionic acid

Describe the bonds present in the Period 3 chlorides (3)

The chlorides of sodium and magnesium are ioonic

Aluminium chloride has covalent bonds (due to high charge density)

The chlorides of silicon, phosphorus and sulphur form simple molecular structures

Describe the reactions of the Period 3 elements with water (6)

Sodium reacts with cold water to form sodium hydroxide and hydrogen gas

Magnesium reacts slowly with cold water to form magnesium hydroxide and hydrogen gas. Magnesium reacts with steam to form magnesium oxide and hydrogen gas

Aluminium powder heated in steam forms aluminium oxide and hydrogen gas

Silicon, Phosphorus and Sulphur do not react with water

Chlorine undergoes a disproportionation reaction with water to form hydrochloric acid and hypochlorous acid

Describe the basicity of Period 3 hydroxides

They are both basic but sodium hydroxide is more alkaline than magnesium oxide because it is more soluble in water

State the uses of common Period 3 compounds (4)

Aluminium hydroxide is used in antacid medication

White phosphorus is used in flares and to kill children in Palestine

Red phosphorus is used on the side of match boxes

Argon is used in fluorescent and incandescent lighting

Describe the trend in atomic radius in Group II as you descend

The addition of an energy level that the electrons occupy increases the distance between the nucleus and the valence electrons. The addition of an energy level also increases the shielding effect which decreases the effect of the nuclear charge on the valence electrons. Hence, increasing atomic radius

Describe the trend in ionization energy in Group II as you descend

An increase in atomic radius and in the shielding effect weakens the electrostatic pull the nucleus has on the valence electrons. Hence, requiring progressively less energy to remove electrons as you descend down the group

Describe the reactions of Group II metals with oxygen

Group II metals burn readily in oxygen to form metal oxides

Describe the reactions Group II metals have with water (4)

Beryllium has no reaction with water

Magnesium reacts with steam to form magnesium oxide and hydrogen gas. Magnesium slightly reacts with cold water to form magnesium hydroxide

Calcium, strontium and barium react with cold water to form metal hydroxides

Describe the reactions of the Group II metals with acids

All Group II metals except Beryllium react with acids to form a salt and hydrogen gas

Explain the solubility of Group II sulphates

Group II sulfates become less soluble as you descend down the group. This occurs due to the enthalpy change of solution, which is equal to the enthalpy change of hydration and reverse enthalpy change of lattice energy, becoming more and more endothermic. This happens because the lattice energy and hydration energy decreases as the cations get bigger stifling the attraction within the lattice and with water molecules. Furthermore, the hydration energy decreases more significantly than the lattice energy which results in the enthalpy change of solution becoming more positive

Describe the trend in thermal decomposition in Group II carbonates/nitrates

Group II carbonates/nitrates are more thermally stable going down the group as larger cations decrease the polarizing effect and distort the electron cloud less — requiring more heat to break the bond

State the uses of common Group II compounds (4)

Magnesium oxide — antacid, laxative, dietary supplement

Calcium carbonate — mortar, stained glass, iron purification

Calcium oxide — mortar, form silicates, remove silicates

Calcium hydroxide — raise pH of soils, process foods and to prepare leather