Trends+in+chemical+properties

//Having looked at the trends in the physical properties across periods or down the groups of the periodic table we can now look at the trends in chemical properties across groups 1 and 7 of the periodic table. //

**//Group 1—The Alkali metals //**  Na ---> Na + + e - Eg. K + H 2 O ---> KOH + H 2 2K (s) + I 2 (g) ---> 2KI (s) 2Na (s) + Cl 2 (g) ---> 2NaCl (s)  = **//Group 7—The Halogens //** = Cl 2 + 2e - ---> 2Cl -  For example:  Cl 2 (aq) + 2KI (aq) ---> I 2 (aq) + 2KCl (aq) // And the ionic equation is as follows: //  Cl 2 (aq) + 2I - (aq) ---> I 2 (aq) + 2Cl - (aq)
 * These are metals which are very soft and malleable.
 * Alkali metals usually react by losing their outershell electron and thus forming an ion with a single positive charge.
 * The alkali metals are highly reactive metals which become even more reactive as you go down the group. They become more reactive because the ionization energy decreases down the group so it becomes even more easier for the atom to lose its outershell electron and thus take part in a reaction.
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Alkali metals react with water to form a metal hydroxide solution and hydrogen gas.
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">The alkali metals also react with non-metals such as halogens (elements in group 7) to from ionic compounds:
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">These are reactive non-metals.
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">They exist in the form of diatomic molecules e.g. (Fluorine exists as F 2, not F, Chlorine exists as Cl 2 not Cl, etc)
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Halogens usually gain an electron to from an anion with a single negative charge: (Once a halogen atom has formed an ion, its ion is called a halide ion)
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">The reactivity of the Halogens decreases as you go down the group. This is because the electronegativity decreases down the group so it becomes harder for an atom to attract an electron towards itself in order to form an ion.
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">The halogens undergo displacement reactions. That means that halogens atoms which are higher up the series (the more reactive ones) can displace those which are lower down (the less reactive ones) form their compoundes.

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Chlorine is more reactive than Iodine (it is higher up in the group) so it can displace the iodide ions from the compound. //<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">However, the opposite of this can’t happen because iodine is less reactive than chlorine so it can’t displace chlorine from its compounds. // <span style="font-family: Tahoma,sans-serif; font-size: 14pt;"> I 2 (aq) + 2Cl - (aq) ---> (not possible)

//<span style="font-family: Tahoma,sans-serif;">A displacement reaction is one a more reactive element replaces a less reactive one from the compound. Using the above example; //


 * [[image:ibchem4u/Cl--KI.png caption="We have one Chlorine molecule and a potassium iodide compound."]] || [[image:Cl-kicks-KI.png width="318" height="203" caption="Chlorine atom kicks out the Iodide ion from its compound. Thus potassium chloride is formed."]] ||

= **//<span style="font-family: Tahoma,sans-serif;">Trends in the oxides of period 3 elements //** =

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Period 3 elements range from sodium (Na) to Argon (Ar).

//<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">All of these elements form oxides (except Argon, since it’s a noble gas): //

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">**Na** (sodium) forms **Na 2 O** (sodium oxide)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">**Mg** (magnesium) forms **MgO** (Magnesium oxide)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">**Al** (aluminium) forms **Al 2 O 3 ** (aluminium oxide)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">**Si** (silicon) forms **SiO 2 ** (silicon dioxide)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">**P** (phosphorus) forms **P 4 O 10 ** (phosphorus (V) oxide)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">**S** (Sulphur) forms **SO 3 ** (sulphur trioxide)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">**Cl** (Chlorine) forms **Cl 2 O 7 **

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">**Ar** (Argon) forms no oxides

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">These oxides can be classified as being //basic// or //acidic//.

__//<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Usually metal oxides are basic while non-metal oxides are acidic. //__

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Na and Mg oxides (Na 2 O and MgO) are basic; this means that when they dissolve in water, they form an alkaline solution:

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Na 2 O (s) + H 2 O (l) ---> 2NaOH (aq)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">MgO (s) + H 2 O (l) ---> Mg(OH) 2 (s)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">However, although //Aluminium// is a metal, its oxide is //amphoteric//, that means that its oxide can react with both acids and bases.

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">The oxides of Si (SiO 2 ), P (P 4 O 10 ), S (SO 3 ) and Cl (Cl 2 O 7 ) are acidic. That means that their oxides dissolve in water to from an acidic solution:

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">P 4 O 10 (s) + 6H 2 O (l) ---> 4H 3 PO 4 (aq)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">SO 3 (g) + H 2 O (l) ---> H 2 SO 4 (aq)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">( you need to know the four equations which are present here above)

By the end of this lesson you should be able to:
 * Discuss the chemical properties of group 1 and group 7 elements
 * Know that Alkali metal react with water and halogens
 * Know that halogens undergo displacement reaction where they replace a halide ion, below them in the group, from its compound.
 * Know how the oxides of elements in group 3 change from basic to acidic.
 * Know the reactions of oxides of sodium, magnesium, phosphorus and sulfur with water.


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