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3.2.4 Period 3 Elements (Reaction with oxygen: (sodium: yellow flame,…
3.2.4 Period 3 Elements
Reaction with water:
sodium: vigorous reaction; sodium fizzes and floats at top of water, and melts because of heat; pH 13-14
2Na (s) + 2H₂O(l) --> 2NaOH(aq) + H₂(g)
magnesium: slow at room temperature, pH 10
Mg(s) + 2H₂O(l) --> Mg(OH)₂(aq) + H₂(g)
faster with heated magnesium and steam
Mg(s) + H₂O(g) --> MgO(s) + H₂(g)
Reaction with oxygen:
sodium: yellow flame, white sodium oxide
2Na(s) + 1/2 O₂(g) --> Na₂O(s)
magnesium: bright white flame, white magnesim oxide
2Mg(s) + O₂(g) --> 2MgO(s)
aluminium: white aluminium oxide; coated with strong oxide layer which is unreactive
4Al(s) + 3O₂(g) --> 2Al₂O₃(s)
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sulfur: powderis heated; blue flame; colourless sulfur dioxide/trioxide
S(s) + O₂(g) --> SO₂(g)
2SO₂(g) + O₂(g) --> 2SO₃(g)
phosphorus: red phosphorus must be heated first; white phosphorus spontaneously ignites in air; white smoke of phosphorus pentoxide; two allotropes of P
4P(s) + 5O₂(g) --> P₄O₁₀ (+ P₂O₃ if supply of oxygen is limited)
Melting point
metal oxides:
sodium oxide, magnesium oxide, aluminium oxides
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aluminium oxide bonding is ionic but has some covalent character; Al forms small ion with large positive charge; can approach O²⁻ closely and distort its electron cloud
greater the difference of the electronegativities of two compounds, the more ionic the bond
non-metal oxides:
silicon oxide has giant covalent structure; bonding extends throughout entire structure; high melting point
phosphorus and sulfur oxides are separately bonded covalent molecules; phosphorus oxides are solids, sulfur oxides are gases; weak van der Waal forces, and dipole-dipole forces; low melting points
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Elements:
Na, Mg, Al are metallic: shiny, conduct electricity, and react with dilute acids to give hydrogen and salts
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P, S, Cl are non-metals: don't conduct electricity, have low melting and boiling points
Ar is a noble gas: chemically unreactive, exists as separate atoms
all reactions are redox reactions as each element starts off with an oxidation state of zero and after the reaction it ends up with a positive or negative oxidation state
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