13.2.4 Define the term ligand.

Ligand- an ion or small polar molecule that is attracted to transition metal ions because it has an electron pair that it can donate to the central metal ion.

Examples)

NH3
    _
Cl
     _
CN
     _
OH

H2O

13.2.3 Explain the existence of variable oxidation number in ions of transition elements.

• all transition elements can show an oxidation state of +2

• But you also need to know these: 

Cr (+3, +6)
Mn (+4, +7)
Fe (+3)
Cu (+1)

13.2.2 Explain why Sc and Zn are not considered to be transition elements.

• they both do not have partially filled d-subshells
• only have one oxidation state; where as transition metals have variable oxidation states

13.2.1 List the characteristic properties of transition elements.

• higher melting points 
• harder and denser than group 1 and 2 metals 
• variable oxidation number
• form complex ions
• most compounds are colored 
• are able to act as catalysts
• no significant change in atomic radii due to repulsion between 4s and 3d orbitals 

13.1.2 Describe the reactions of chlorine and the chlorides referred to in 13.1.1 with water.

Simply:

• NaCl/MgCl2 dissolves into its ions when water is added.
• AlCl3undergoes hydrolysis.
• SiCl4 and PCl3/PCl5 form acidic solutions:

In more detail and also extra notes:

CHLORIDES 

Reactions with water:

·     Sodium chloride dissolves readily due to polar water molecules being able to pull oppositely charged ions out of the lattice; NaCl forms a neutral solution;

·     magnesium chloride and aluminium trichloride form acidic solutions as their small highly charged cations (high charge density) attract water molecules (to form complexes)  some of which give up their hydrogen ions to other water molecules surrounding the complex.

               [Mg (H₂O)₆]²⁺+  H₂O    ¬®       [Mg(H₂O)₅ OH] ⁺ + H₃O⁺

               [Al (H₂O)₆]³⁺  + H₂O    ¬®         [Al (H₂O)₅ OH] ²⁺  + H₃O⁺

    

      in addition, AlCl₃ also forms HCl when it reacts with water:

                AlCl₃ (s)   + 3H₂O    ¬®       Al (OH)₃     +  3HCl (=fumes)  (exothermic  reaction)

·     simple molecular chlorides all react rapidly with water to form hydrochloric acid.

                           

                SiCl₄ (l)  +4H₂O (l)   ®    Si(OH)₄ (s)  +   4HCl  (g)                 

                PCl₅  (l)  +  4H₂O    ®    H₃ PO₄ (aq)   + 5HCl  (g)      (= HCl fumes)(exo)

                Cl₂ (g)  +   H₂O    ®    HClO   +   HCl  

OXIDES

Reactions with water

• ionic oxides are soluble and react with water to form alkaline solutions (hydroxides) with a decreasing pH when going to the right of the period (basic oxides);

         Na₂O (s)  +   H₂O (l)     ¾®  2Na⁺   (aq) +2OH^-  (aq)     /2NaOH (aq)

         MgO (s)  +   H₂O (l)     ¾®    Mg²⁺   (aq)  + 2OH^-  (aq)     /Mg(OH)₂ (aq)

•  aluminium oxide is amphoteric:

         reaction with acid:      Al₂ O₃ (s)  + 6HCl (aq)   ¾®  2AlCl₃(aq) + 3H₂O (l)

         reaction with alkali:     Al₂ O₃ (s)  + 2NaOH (aq)  ¾®  2NaAlO₂ (aq) +H₂O (l)

                                                                                                                   (sodium aluminate)

• silicon dioxide does not dissolve in or react with water ( water remains neutral) but it can react with sodium hydroxide which is why it is considered an acidic oxide;

           SiO₂ (s)  +   2NaOH (aq)¾®  Na₂SiO₃(s) +H₂O (l)

                             

• simple molecular oxides are soluble in water and react to form strong acidic solutions like phosphoric and sulphuric acid. HClO, hypochlorous acid, is a weak acid.

            P₄ O₁₀ (s)  + 6H₂O (l)     ¾®  4H₃PO₄   (aq) 

            SO₂ (g)  +H₂O (l)     ¾®  H₂SO₃   (aq) 

            Cl₂O (l)  +    H₂O     ¾®  2HClO  (aq)  

13.1.1 Explain the physical states (under standard conditions) and electrical conductivity (in the molten state) of chlorides and oxides of the elements in Period 3 in terms of their bonding and structure.

Physical Trends:

• Overall decrease in melting and boiling points as the structures change from ionic to simple molecular.  This happens between Mg and Al; metallic chlorides (NaCl, MgCl₂, AlCl₃ ) are solids, non-metal/molecular 
• chlorides are gases (covalent bonding between atoms within molecules but Van Der Waal’s between molecules).  No giant covalent chloride as silicon tetrachloride is a gas;

Conductance:

• good in molten ionic chlorides while poor in the simple molecular chlorides.

Chemical trends

·     the type of bonding formed changes from ionic to covalent;  aluminium trichloride however is now covalently bonded instead of ionic;

·     no chloride for argon as it does not form any compounds as it is a noble gas with full outer shell.

·     there is a regular trend in the empirical formula of the highest chlorides because of the increase in oxidation state from +1 to +5;

     

            NaCl      MgCl₂     Al₂ Cl₆ (=dimer)       SiCl₄         PCl₅        

·     some elements show variable oxidation states; e.g. PCl₅  and PCl₃.

Physical state:

• melting and boiling points: rise to a maximum at SiO₂ and then decline
• ionic compounds (Na₂O, MgO and Al₂O₃) on the left side have relatively high melting and boiling points (high lattice energy); solids at room temperature;
• giant covalent molecular structure like silicon dioxide has the highest melting and boiling points (lattice held together by strongest bond i.e. covalent); solids at room temperature;
• lowest melting and boiling points are for the simple molecular structures (starting from P₄O₆); they are gases at room temperature (weaker dipole-dipole attractions).

Electrical conductivity in molten state:

• changes from good to semi-conductor to poor; this is the case because their structure changes from ionic to simple molecular. 
• None of the conductors will conduct as solids (because no free moving electrons).

Chemical trends:

• the type of bonding between element and oxygen changes from ionic to covalent;  aluminium oxide is still ionic but has quite a strong covalent character whilst silicon dioxide is mostly covalent;
• type of oxide:

_o    basic:   Na₂O      MgO    
_o    amphoteric:  Al₂ O_3 
o    acidic:  SiO₂         P₄ O₁₀        SO₃     Cl₂ O₇ 

• some elements show variable oxidation states; e.g.  P₄ O₁₀ and P₄ O₆ and  SO₃ and  SO₂;
• trend in empirical formula of highest oxide: ratio of  element : oxygen  (X : O) increases from 0.5 to 3.5.

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3.3.2 Discuss the changes in nature, from ionic to covalent and from basic to acidic, of the oxides across period 3.

As you go across period 3, nature of oxides changes from basic to acidic.

Oxide	Acid or base
Na2O	Basic Giant Ionic
MgO
Al2O3 - giant ionic	Amphoteric
SiO2 - giant covalent
P4O10	Acidic Molecular covalent
SO3/SO2
Cl2O7

Amphoteric: 

• posses properties of both acids and bases.
• when it reacts with an acid, it behaves as a base, and vice-versa. 
• tested with aluminum oxide
• When aluminum oxide reacts with an acid such as hydrochloric, aluminum oxide acts as a base.
• Al₂O₃ (s) + 6HCl (aq) → 2AlCl₃ (aq) + 3H₂O (l)
• Now, when aluminum oxide reacts with a base such as Sodium hydroxide, it acts as an acid.
• Al₂O₃ (s) + 2NaOH (aq) + 3H₂O (l) → 2NaAl(OH)₄

Reactions between Na₂O, MgO, P₄O₁₀  and SO₃  and water.

• Na₂O (s) + H₂O (l) →2NaOH (aq)
• Sodium oxide + water → Sodium hydroxide
• MgO (s) + H₂O (l)→ Mg(OH)₂ (aq)
• Magnesium oxide + water → Magnesium oxide
• P₄O₁₀ (s) + 6H₂O (l) → 4H₃PO₄
• Phosphorous (v) oxide + water → Phosphoric (V) acid
• SO₃(l) + H₂O (l) → H₂SO₄(aq)
• Sulfur trioxide + water → Sulfuric (VI) acid.

Across a period 3, there is a change from metallic to non-metallic. 

• Left. ex) Sodium, Magnesium and Aluminium all have the typical properties of metallic substances (E.g. good conductors of electricity), 
• Righ. ex) such as Chlorine and Sulfur are non-metals.

Metals will react to form ionic compounds. 

Non-metals will react to form covalent compounds.