A - Period 3 Flashcards
What happens to sodium when it reacts? What does it become?
It loses an electron to form the Na+ ion.
What happens to magnesium when it reacts? What does it become?
It loses 2 electrons to become the Mg2+ ion.
Out of sodium and magnesium, which is more reactive and why?
Sodium - it only has to lose one electron, whereas magnesium has to lose 2. It is easier to lose one electron compared to two, therefore sodium is more reactive.
More energy is needed for magnesium to react.
What happens when sodium reacts with cold water?
It reacts vigorously, forming a molten ball on the surface, fizzing and producing hydrogen gas. It also produces sodium hydroxide, creating a strongly alkaline solution (pH 12-14).
What is the equation for the reaction of sodium with cold water?
2Na(s) + 2H2O(l) —> 2NaOH(aq) + H2(g)
What happens when magnesium reacts with cold water?
It reacts very slowly at room temperature and creates a weaker alkaline solution, than that of the reaction between sodium and cold water (pH 9-10). A thin coating of magnesium hydroxide forms on the surface of the metal. Only a few bubbles of hydrogen gas will form after a few days.
What is the equation for the reaction of magnesium with cold water?
Mg(s) + 2H2O(l) —> Mg(OH)2 (aq)+ H2(g)
What happens when magnesium reacts with steam? Give the equation for this reaction.
Magnesium reacts much faster with steam than cold water, as there is more energy. It burns with a white flame.
The reaction forms magnesium oxide and hydrogen.
Mg(s) + H20(g) —> MgO(s) + H2(g)
What do the period 3 elements (except for argon) form when reacted with oxygen?
Are these reactions exothermic or endothermic?
Oxides.
Exothermic.
What happens when sodium reacts with oxygen in the air?
Give the equation for this reaction.
Sodium reacts vigorously and burns brightly in air, with a yellow flame, to form white sodium oxide.
2Na(s) + 1/2O2(g) —> Na2O(s)
What happens when magnesium reacts with oxygen in the air?
Give the equation for this reaction.
A strip of magnesium ribbon reacts vigorously and burns in air with a bright white flame. It produces a white powder (magnesium oxide).
2Mg(s) + O2(g) —> 2MgO(s)
What happens when aluminium reacts with oxygen in the air?
How can this reaction be sped up?
Give the equation for the reaction.
It burns brightly to give aluminium oxide, a white powder.
The reaction is faster if aluminium is powdered.
4Al(s) + 3O2(g) —> 2Al2O3(s)
How does silicon react with oxygen and what is the product?
Give the equation for the reaction.
Silicon reacts slowly so needs to be heated strongly in oxygen to form silicon dioxide.
Si(s) + O2(g) —> SiO2(s)
What are allotropes?
An element with atoms arranged differently.
Red and white phosphorus are ………… of phosphorus.
Fill in the blank.
Allotropes
How do red and white phosphorus react with oxygen respectively?
Give the equation for the reactions.
Red phosphorus must be heated before it will react with oxygen to form phosphorus (V) oxide.
White phosphorus spontaneously combusts in air with a white flame and produced clouds of white smoke.
P4(s) + 5O2(g) —> P4O10(s)
How does sulfur react with oxygen?
Give the equation for the reaction.
Sulfur powder is heated and lowered into a gas jar of oxygen and burns with a blue flame to form the colourless gas sulfur dioxide.
S(s) + O2(g) —> SO2(g)
How is sulfur trioxide formed from sulfur dioxide?
SO2 reacts with oxygen and a vanadium catalyst to form SO3.
Give the formulae of the metal oxides in period 3. (Sodium, magnesium and aluminium oxides)
Na2O
MgO
Al2O3
Why do the period 3 metal oxides have high melting points?
Because they form giant ionic lattices with strong forces of attraction between positive and negative ions which require a large amount of energy to break.
Why does MgO have a higher melting point than Na2O?
Mg forms 2+ ions and forms stronger forces of attraction with negative ions compared to sodium which forms 1+ ions.
Describe the melting point of Al2O3 compared to Na2O and MgO. Why is this the case?
Higher than Na2O but lower than MgO.
The melting point of Al2O3 is lower than expected because the highly charged Al3+ ions distort the oxygen’s electron cloud giving the bonds some covalent character.
How can you predict the covalent character of a bond?
By considering the difference in electronegativities between the two atoms. The larger the difference, the greater the IONIC character of the bond.
Why does silicon dioxide have a higher melting point than the other non-metals in period 3?
It has a giant macro molecular structure where covalent bonding extends throughout the structure. This results in a high melting point as many strong covalent bonds must be broken to melt it.
Why do P4O10 and SO2 and SO3 have relatively low melting points?
They form simple molecular structures where molecules are attracted to each other by weak dipole-dipole and van der Waals forces, which take little energy to break.
The trend in melting points for P4O10, SO2 and SO3 is as follows:
P4O10 > SO3 > SO2
Why is this the case?
Larger molecules have an increase in intermolecular forces. The more intermolecular forces there are, the more energy is required to break these.
What are the basic oxides of the period 3 elements?
Sodium oxide and magnesium oxide.
Why do sodium oxide and magnesium oxide form alkaline solutions?
Because they both contain oxide ions (O2-). When they dissolve in water, the O2- ions accept protons from water molecules to form hydroxide ions, creating an alkaline solution.
Why does sodium oxide react with water to give a more alkaline solution compared with that of magnesium oxide?
Sodium hydroxide is more soluble in water, magnesium hydroxide is sparingly soluble in water so gives a less alkaline solution.
Give the equation and pH of the solution formed when sodium oxide reacts with water.
Na2O(s) + H2O (l) —> 2NaOH (aq)
pH of solution: ~14
Give the equation and pH of the solution formed from the reaction between magnesium oxide and water.
MgO(s) + H2O(l) —> Mg(OH)2(aq)
pH of solution formed: ~9
Describe and explain the solubilities of silicon dioxide and aluminium oxide in water. What do they react with to form?
Both are insoluble in water.
Silicon dioxide is insoluble in water due to its giant covalent structure, however it will react with bases to form salts so is classed as acidic.
Aluminium oxide is insoluble in water due to its partially ionic and covalent character. However it will react with acids and bases to form salts so it is classed as amphoteric (can act as either an acid or base).
What are the acidic oxides of the period 3 elements?
P4O10, SO2 and SO3.
They form acidic solutions, with a pH of ~0-2 (for solutions with a concentration of at least 1.0 mol dm-3). They will dissociate (split into ions) in solution, forming hydrogen ions and a negative ion (sometimes called a conjugate base).
Give the equations of the reaction between phosphorus (V) oxide and water, and the following dissociation reaction that occurs.
P4O10(s) + 6H2O —> 4H3PO4(aq) (phosphoric acid)
H3PO4(aq) —> 3H+(aq) + PO4 3- (aq)
Give the equations for the reaction between sulfur dioxide and water, and the following dissociation reaction that occurs.
SO2(g) + H2O(l) —> H2SO3(aq) (sulfuros acid or sulfuric (IV) acid)
H2SO3(aq) —> 2H+(aq) + SO3 2- (aq)
Give the equations for the reaction between sulfur trioxide and water and the following dissociation reaction that occurs.
SO3(l) + H2O(l) —> H2SO4(aq) (sulfuric (VI) acid)
H2SO4(aq) —> 2H+(aq) + SO4 2- (aq)
What is the general equation for neutralising an acid with a base?
Acid + base —> salt + water
What do the following neutralise?
- Basic oxides
- Acidic oxides
- Amphoteric oxides
- Acids
- Bases
- Acids and bases
What is the structure of the unionised acid of H3PO4?
P in the middle, double bonded to an oxygen atom and has three other single bonds to hydroxyl groups.
What is the structure of the unionised sulfuric acid?
S in the middle, has two double bonds to two oxygen atoms opposite each other and then two single bonds to two hydroxyl groups opposite each other.
