periodicity

• The Periodic Table: Chemical Periodicity
• Period 3 Elements: Physical Properties
• Period 3 Elements: Structure & Bonding
• Period 3 Oxides & Hydroxides: Acid/Base Behaviour
• Period 3 Chlorides
• Period 3 Elements: Electronegativity & Bonding
• Period 3 Chlorides & Oxides
• Chemical Periodicity of Other Elements
• Going across the period from Na to Si, the ions get smaller due to the increasing nuclear charge attracting the outer electrons in the second principal quantum shell.
• Metals produce positively charged ions (cations) whereas nonmetals produce negatively charged ions (anions).
• Cations have lost their valence electrons which causes them to be much smaller than their parent atoms.
• Silicon has the highest melting point among the Period 3 elements.
• Unlike the melting points, the electrical conductivity of the Period 3 elements shows a clear trend.
• The ionic radii of ions of Period 3 elements decrease as the nuclear charge increases across the period and fewer electrons are gained by the atoms.
• Going across the period, the electrical conductivity of the elements decreases significantly.
• After the Si element, the melting points of the elements decrease significantly.
• Ions of Period 3 elements with increasing positive charge (metals) and increasing of outer electrons across the period have a general increase in melting point.
• Electrical conductivity refers to how well a substance can conduct electricity.
• Anions are larger than their original parent atoms because each atom has gained one or more electrons in their third principal quantum shell.
• The ionic radius is the distance between the nucleus and the outermost electron of an ion.
• The elements in Period 3 gain extra electrons in the same principal quantum shell.
• Fewer electrons result in less shielding of the outer electrons.
• Magnesium reacts extremely slowly with cold water: Mg(s) + 2H O(l) → Mg(OH) (aq) + H (g).
• Hydrogen gas is given off in the reaction of sodium with water.
• The sodium melts into a ball and moves across the water surface until it disappears.
• The solution formed is strongly alkaline (pH 14) due to the sodium hydroxide which is formed.
• Sodium reacts vigorously with cold water: 2Na(s) + 2H O(l) → 2NaOH(aq) + H (g).
• The Period 3 elements therefore have positive oxidation states in their oxides and the oxygen has a negative oxidation state of -2.
• When magnesium is heated, it reacts vigorously with steam (water) to make magnesium oxide and hydrogen gas: Mg(s) + H O(g) → MgO(s) + H (g).
• The oxidation states of the Period 3 elements in their oxides are represented by the formulae of the oxides of the Period 3 elements & their oxidation states table.
• Aluminium oxide does not react or dissolve in water, the oxide layer protects the aluminium metal from corrosion.
• Not all Period 3 oxides react with or are soluble in water.
• Period 3 elements react with oxygen and chlorine.
• Oxygen is more electronegative than any of the Period 3 elements which is why the Period 3 elements will have positive oxidation states and the oxygen a negative oxidation state in the oxides of Period 3 elements.
• The solution formed is weakly alkaline (pH 11) as the formed magnesium hydroxide is only slightly soluble.
• The SiO is seen as a white precipitate and some of the hydrogen chloride gas produced dissolves in water to form an acidic solution.
• Chlorides of Period 3 elements show characteristic behaviour when added to water which can be explained by looking at their chemical bonding and structure.
• The highly charged Al ion becomes hydrated and causes a water molecule that is bonded to the Al to lose an H ion which turns the solution acidic.
• When water is added to aluminium chloride the dimers are broken down and Al and Cl ions enter the solution.
• Sodium & magnesium chloride, NaCl and MgCl, do not react with water as the polar water molecules are attracted to the ions dissolving the chlorides and breaking down the giant ionic structures.