Chemical Periodicity Flashcards
How does ionic radius change across period 3?
- It decreases as positive charge increases from sodium to silicon
- It increases dramatically between silicon and phosphorus as phosphorus is an anion
- It decreases as the magnitude of negative charge decreases from phosphorus to chlorine
See the atomic structure deck for deeper explanations
How does melting point change across period 3?
Offer explanations
- It increases for the metals as cationic charge and number of delocalised electrons in the metallic lattices increase
- It sharply increases for silicon as it forms a giant covalent molecule
- It decreases for phosphorus as P₄ is a simple covalent molecule
- It increases a small amount for sulfur as S₈ is a large simple covalent molecule (so has stronger Id-Id forces than phosphorus)
- It decreases for chlorine (Cl₂) and then again for argon as these are smaller simple covalent molecules
How does electrical conductivity change across period 3?
- Conductivity gradually increases from sodium to aluminium due to the increased number of delocalised electrons in the metallic lattices
- It falls dramatically from aluminium to silicon as the molecules become covalent
- From silicon to argon, conductivity is effectively zero (with the exception of silicon, a semiconductor), though the values become even closer to zero as one moves across the period
What is the chemical equation for the reaction between sodium and oxygen and what are the conditions and observations?
All equations in this deck should include state symbols
- 4Na (s) + O₂ (g) → 2Na₂O (s)
- Heat is required
- Burns vigorously with a yellow flame and produces a white solid
What is the chemical equation for the reaction between magnesium and oxygen and what are the conditions and observations?
- 2Mg (s) + O₂ (g) → 2MgO (s)
- Heat is required to ignite
- Burns vigorously with a bright white flame and produces a white solid
What is the chemical equation for the reaction between aluminium and oxygen and what are the conditions and observations?
- 4Al (s) + 3O₂ (g) → 2Al₂O₃ (s)
- The aluminium must be powdered and heated
- Burns quickly with a bright white flame and produces a white powder
What is the chemical equation for the reaction between silicon and oxygen and what are the conditions and observations?
- Si (s) + O₂ (g) → SiO₂ (s)
- The silicon must be powdered and heated strongly
- Burns slowly, producing a red glow and bright white sparkles and forming a white powder
What is the chemical equation for the reaction between phosphorus and oxygen and what are the conditions and observations?
- P₄ (s) + 5O₂ (g) → P₄O₁₀ (s)
- Gentle heating is required
- Burns vigorously with a yellow/white flame, forming a white solid
If there is insufficient oxygen, P₄O₆ forms instead
What is the chemical equation for the reaction between sulfur and oxygen and what are the conditions and observations?
- S (s) + O₂ (g) → SO₂ (g) (or S₈ + 8O₂ → 8SO₂)
- Gentle heating is required
- Burns gently with a blue flame to form a colourless and pungent gas
SO₃ can form after oxidation of SO₂
What is the chemical equation for the reaction between sodium and chlorine and what are the conditions and observations?
- 2Na (s) + Cl₂ (g) → 2NaCl (s)
- Requires some heat
- Burns vigorously with a yellow flame to produce a white solid
What is the chemical equation for the reaction between magnesium and chlorine and what are the conditions and observations?
- Mg (s) + Cl₂ (g) → MgCl₂ (s)
- Requires heat
- Burns vigorously with a bright white flame to produce a white solid
What is the chemical equation for the reaction between aluminium and chlorine and what are the conditions and observations?
- 2Al (s) + 3Cl₂ (g) → Al₂Cl₆ (s)
- Requires heat
- Burns vigorously, producing a pale yellow solid
It may form AlCl₃ and dimerise instead
What is the chemical equation for the reaction between silicon and chlorine and what are the conditions and observations?
- Si (s) + 2Cl₂ (g) → SiCl₄ (l)
- Requires heat
- Reacts mildly (though still exothermically) to form a colourless, volatile liquid
What is the chemical equation for the reaction between phosphorus and chlorine and what are the conditions and observations?
- 2P (s) + 5Cl₂ (g) → 2PCl₅ (l)
- Burns quickly in excess chlorine with a white flame, producing a yellow-white solid
PCl₅ can hydrolyse in moist air to form PCl₃
What is the chemical equation for the reaction between sodium and cold water and what are the conditions and observations?
- 2Na (s) + 2H₂O (l) → 2NaOH (aq) + H₂ (g)
- Reacts vigorously, with the sodium melting into a ball and moving across the water’s surface while releasing hyrogen gas
What is the chemical equation for the reaction between magnesium and cold water and what are the conditions and observations?
- Mg (s) + 2H₂O (l) → Mg(OH)₂ (aq) + H₂ (g)
- Reacts slowly, there may be gentle bubbling and some magnesium hydroxide floating on the surface
When heated strongly, a mixture of magnesium and steam react to form magnesium oxide with the equation Mg (s) + H₂O (g) → MgO (s) + H₂ (g)
What is the variation in the oxidation numbers of period 3 elements in the oxides Na₂O, MgO, Al₂O₃, P₄O₁₀, SO₂ and
SO₃ and why does this trend exist?
- It increases from + 1 to +6 from Na₂O to SO₃
- Oxygen is more electronegative than any period 3 element, so will always have an oxidation state of -2 (as it forms two covalent bonds or accepts two electrons in ionic bonds) while period 3 elements will have a positive oxidation state
- The oxidation number increases as the number of electrons lost to (for metals) or shared with (for non-metals) oxygen increases (so the charge if all bonds were assumed to be ionic increases)
- This is made possible by the number of valence electrons in period 3 elements increasing from 1 to 6 from sodium to sulfur
- This happens alongside the increasing covalent character of the bonds across the period, owing to the increasing electronegativity of the period 3 elements
What is the variation in the oxidation numbers of period 3 elements in the chlorides NaCl, MgCl₂, AlCl₃, SiCl₄ and PCl₅ and why does this trend exist?
- It increases from +1 in NaCl to +5 in PCl₅
- Chlorine is the most electronegative period 3 element and forms single bonds, so will always have an oxidation state of -1
- The number of valence electrons in each period 3 element increases from +1 to +5 from Na to P, increasing the number of electrons that are available for ionic and covalent bonding
- This increases the number of electrons lost to or shared with chlorine, increasing the potential charge of the period 3 elements if all bonds were ionic
- The elements also increase in electronegativity across the period, leading to the formation of covalent bonds instead of ionic
What is the equation of the reaction of Na₂O with water and what is the pH of the solution formed?
- Na₂O (s) + H₂O (l) → 2NaOH (aq)
- Forms a strongly alkaline solution with pH 12-14
Period 3 oxides don’t dissociate in water like period 3 chlorides do because of the reactivity of the O²⁻ ion
What is the equation of the reaction of MgO with water and what is the pH of the solution formed?
- MgO (s) + H₂O (l) → Mg(OH)₂ (aq)
- Forms a weakly alkaline solution with pH 8-10
What is the equation of the reaction of Al₂O₃ with water?
No reaction — Al₂O₃ is insoluble in water
What is the equation of the reaction of SiO₂ with water?
No reaction — SiO₂ is insoluble in water
What is the equation of the reaction of P₄O₁₀ with water and what is the pH of the solution formed?
- P₄O₁₀ (s) + 6H₂O (l) → 4H₃PO₄ (aq)
- Forms a weakly acidic solution with pH 3–4
What is the equation of the reaction of SO₂ with water and what is the pH of the solution formed?
- SO₂ (g) + H₂O (l) ⇌ H₂SO₃ (aq)
- Results in a strongly acidic solution with pH 1-2
