chemical properties. syllabus statements 3.3 chemical properties 3.3.1 discuss the similarities and...
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Chemical Properties
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Syllabus Statements
3.3 Chemical properties • 3.3.1 Discuss the similarities and differences in
the chemical properties of elements in the same group.
• 3.3.2 Discuss the changes in nature, from ionic to covalent and from basic to acidic, of the oxides across period 3.
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Trends across period 3• The elements we are talking about are:• Sodium Na• Magnesium Mg• Aluminium Al• Silicon Si• Phosphorous P • Sulfur S• Chlorine Cl• We ignore Argon because it doesn’t really have
any chemistry!!
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• As we move across the period, we change from metals to non metals.
• Its actually a gradual change and is best illustrated by the way in which elements bond with oxygen.
• Sodium, magnesium and aluminium are metallic. (shiny, conductors etc.)
• They form oxides which contain ionic bonds and which have a giant ionic structure
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• The oxides of phosphorous, sulfur and chlorine contain covalent bonds.
• They are molecular covalent• These elements are non-metals (don’t
conduct)
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• Silicon is a metalloid• From Wikipedia, the free encyclopedia• A metalloid is a chemical element with properties that
are in-between or a mixture of those of metals and nonmetals, and which is considered to be difficult to classify as either a metal or a nonmetal. There is no standard definition of a metalloid nor is there agreement as to which elements are appropriately classified as such.
• The six elements commonly recognized as metalloids are boron, silicon, germanium, arsenic, antimony and tellurium.
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Silicon forms an oxide which has a giant covalent structure
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• There is also a trend from basic oxides to acidic oxides.
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Formula Na2O MgO Al2O3 SiO2 P2O5 SO3 Cl2O7
Type of bonding
Ionic Ionic Highly polar covalent
Polar covalent
Polar covalent
Polar covalent
Polar covalent
Acid/base character
Basic Basic Amphoteric Weakly acidic
Acidic Acidic acidic
Other oxides
Na2O2 P2O3 SO2 ClO2
Cl2O
Amphoteric – a substance which can react with both acids and bases
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Basic oxides• Sodium oxide will dissolve in water to give a
basic solution which contains hydroxide ions• Na2O + H2O 2Na + 2OH-
• Magnesium oxide is only slightly soluble, but will react with acid to make salt + water
• Write the equation for it reacting with Hydrochloric acid. Include state symbols
• MgO(s) + HCl(aq) MgCl2(aq) + H2O(l)
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Amphoteric oxides
• Aluminium oxide is insoluble.• It will react with (and hence dissolve in) both
acids and alkalis
• Al2O3 + 6H+ 2Al3+ + 3H2O
• Al2O3 + 2OH- + 3H2O 2Al(OH)4-
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Acidic Oxides
• Silicon oxide doesn’t really show much behaviour as an acid or a base,
• But it will slowly react with a hot, concentrated alkali (i.e. it shows slightly acidic properties)
• SiO2 + 2OH- SiO32- + H2O
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• The remaining period 3 oxides react fully with water to give acidic solutions.
• P4O10 + 6H2O 4H3PO4
• SO3 + H2O H2SO4
• Cl2O7 + H2O 2HClO4
Note that this is a dimer!
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Syllabus Statements
3.3 Chemical properties • 3.3.1 Discuss the similarities and differences in
the chemical properties of elements in the same group.
• 3.3.2 Discuss the changes in nature, from ionic to covalent and from basic to acidic, of the oxides across period 3.