Periodicity, Period 3 - A Level Chemistry
Explain the (anomalous) dips in first ionisation Energy between: Group 2 -> 3 (Mg -> Al) Group 5 -> 6 (P -> S)
- Al outer electrons in 3p sub shell whereas Mg outer electrons in the 3s sub shell - Electrons in the 3p subshell are slightly easier to remove because the 3p electrons are higher in energy and are also slightly shielded by the 3s electrons - Phosphorus has 3 electrons in 3p orbitals -> no pairs - Sulfur has 4 electrons in 3p orbital -> sulfur has an electron pair in 3p orbital - This leads to repulsion - So electron is easier to remove
Reaction of Sulfur with oxygen - Observations - Equation
- Burns with a blue flame - Gives off misty fumes - Pungent (acidic) gas - S (s) + O₂ (g) → SO₂ (g)
What block is Si in and why? What block is V in and why?
_ P block - Highest energy electron in p orbital - D block - Highest energy electron in d orbital
Describe the trend in melting point across period 3
Al has a stronger BP than Na & Mg due to more delocalised electrons, stronger attraction, etc. - Initially increases as bonding goes from metallic to giant covalent Giant covalent has a higher MP due to the necessity of breaking many strong covalent bonds - There is then a massive decrease at Si -> P as the molecules become simple molecular, weak inter-molecular forces / VdW between molecules easy to overcome
Aluminium Oxide Reaction with Acid - Ionic Equation - E.g. with Sulfuric Acid Reaction with Alkali - Ionic Equation - E.g. with NaOH Nature of Oxide
Al₂O₃ + 6H⁺ → 2Al³⁺ + 3H₂O Al₂O₃ + 3H₂SO₄ → Al₂(SO₄)₃ + 3H₂O Al₂O₃ + 2OH⁻ + 3H₂O → 2Al(OH)⁻₄ Al₂O₃ + 2NaOH + 3H₂O →2NaAl(OH)₄ Amphoteric = Reacts with both acids and bases / can act as both an acid and alkali
Phosphorus Oxide Structure? Reaction with Water - What happens? - Equation pH
Covalent Molecular Acidic Oxide - Reacts with water to form H₃PO₄ P₄O₁₀ + 6H₂O→ 4H₃PO₄ pH 0
MgO reaction with acid → what is generally formed? - Equation with hydrochloric acid - Equation with nitric acid - What happens to form the water? Give the equation
Forms a salt & water MgO + 2HCl → MgCl₂ + H₂O MgO + 2HNO₃ → Mg(NO₃)₂ + H₂O O²⁻ + 2H⁺ → H₂O (Oxide ion accepts protons from the acid to form water)
Describe and explain the trend of atomic radius of elements across group 3
- As you go across period three *the atomic radius decreases* - This is due to *atomic number increase* -> more protons - Therefore *stronger attraction between nucleus electron(s) in outer electron orbital - *nuclear charge increases* - Nucleus pulls electrons towards it, so *atomic radius decreases* (- shielding is the same)
Reaction of Phosphorus with Oxygen - Observations - Equation
- Burns with a bright white flame - Gives white solid smoke - P₄ (s) + 5O₂ (g) → P₄O₁₀
Reaction of Si with Oxygen - Observations - Equation
- Burns with a white flame - To give white powder - Si (s) + O₂ (g) → SiO₂ (s)
Reaction of Al with oxygen - Observation - Equations
- Burns with a white flame - Gives white solid smoke 4Al (s) + 3O₂ (g) → 2Al₂O₃ (s)
Sulfur Trioxide Structure / Properties (2) Reaction with water: - Observations / What happens - Equation pH?
- Colourless liquid - Simple covalent - Produces hydrochloric acid (H₂SO₄) - SO₃ + H₂O → H₂SO₄ 0
Describe trend in electronegativity as you go across period 3
- Electronegativity increases - More protons - Therefore stronger nuclear charge (atomic radius smaller) - Therefore easier to attract a pair of electrons in a covalent bond
Reaction of Na with water - Observations - Equation - What is formed?
- Fizzes, floats on water, skids across surface, etc. - Alkali solution is formed (can be tested) 2Na (s) + 2H₂O (l) → 2NaOH (aq) + H₂ (g)
Phosphorus Oxide Reaction with alkali e.g. NaOH - What happens - Equation Nature of Oxide?
- Forms Phosphate salts 12NaOH + P₄O₁₀ → 4NaPO₄ + 6H₂O Acidic
Silicon oxide Reaction with Alkalis: - What happens - Equation with NaOH Nature of oxide
- Forms Silicates - Slow at room temp - SiO₂ (s) + 2NaOH (aq) → Na₂SiO₃ (aq) + H₂O (l) - Acidic
Describe & Explain the general trend in first ionisation energy across period 3
- Generally the first ionisation energy increases across the group - Due to more protons -> stronger nuclear charge / stronger attraction between nucleus and outer shell electrons - Therefore more energy required to remove outer electron(s)
Silicon oxide Structure Reaction with water: - What happens pH
- Giant / Macromolecular Covalent - White powder Doesn't dissolve, very strong covalent bonds 7
Sulfur Dioxide Reaction with alkali - General ionic equation - Equation with NaOH Nature of Oxide
SO₂ + 12OH⁻ → SO₃²⁻ + H₂O SO₂ + 2NaOH → Na₂SO₃ + H₂O Acidic
Reaction of Mg with oxygen - Observation - Equation
- Intense white light - White solid formed 2Mg (s) + O₂ (g) → 2MgO (s)
Aluminium Oxide Structure & Appearance Reaction with water pH
- Ionic, Amphoteric Oxide - White solid Insoluble -> very high lattice enthalpy 7
MgO Structure? Solubility? Reaction with water - What is formed - Equation? pH?
- Ionic, basic oxide, lattice structure - White solid - Slightly / sparingly soluble -> relatively high lattice enthalpy - Forms Mg(OH)₂ MgO + H₂O → Mg(OH)₂ 9 - Mg(OH)₂ is only slightly soluble in water as its lattice is stronger so fewer free OH⁻ ions are produced and so lower pH
Reaction of Mg with Cold Water - Observations - Equation pH? Equation for Mg with steam & difference
- Reacts very slowly with cold water Mg (s) + 2H₂O (l) → Mg(OH)₂ (s) + H₂ (g) 9 or 10 - weakly alkaline - Reacts much more steadily with steam Mg (s) + H₂O (g) → MgO (s) + H₂ (g)
Sulfur Dioxide Structure / Properties (3) Reaction with water - What happens? - Equation pH?
- Simple Covalent - Colourless gas - Pungent gas (weak) Sulfuric Acid produced SO₂ + H₂O → H₂SO₃ 3
Sulfur Trioxide Reaction with alkali - What happens - General Ionic equation - Equation with NaOH Nature of Oxide?
- Sodium Sulfate formed + water SO₃ + 2OH⁻ → SO₄²⁻ + H₂O SO₃ (g) + 2NaOH → Na₂SO₄ + H₂O Acidic
Why is the melting point of S₈ is greater than that of P₄?
- S₈ is the larger molecule - More electrons - Higher chance of distortion in electron cloud - Stronger / More VdW forces
Reaction of Na with Oxygen - Observations - Equation
- Yellow Flame - White solid formed - (Na reacts when exposed to air) 2Na (s) + ½O₂ (g) → Na₂O (s)
Na₂O Structure / Comments Reaction with Water - Observations / What happens - Equation pH?
Ionic basic oxide - (vigorous exothermic reaction) - Colourless solution of NaOH formed Na₂O + H₂O → 2NaOH pH 13
Equation for Mg reacting with steam
Mg (s) + H₂O (g) → MgO (s) + H₂ (g)
What happens when Na₂O reacts with an acid? What is produced? Equations(2) HCl H₂SO₄ Nature of Oxide?
Produces a salt and water Na₂O + 2HCl → 2NaCl + H₂O Na₂O + H₂SO₄ → Na₂SO₄ + H₂O Basic
