Chemical Properties

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.

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!!

• 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

• The oxides of phosphorous, sulfur and chlorine contain covalent bonds.

• They are molecular covalent• These elements are non-metals (don’t

conduct)

• 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.

Silicon forms an oxide which has a giant covalent structure

• There is also a trend from basic oxides to acidic oxides.

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

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)

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-

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

• 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!

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.