Periodicity Flashcards
What is the trend of reactivity with water of the Period 3 elements, Na and Mg?
(equations w/water)
- Sodium (Na) is more reactive than Magnesium (Mg) as it takes less energy to lose one electron to form Na+ than it does to lose two, to form Mg2+.
- More energy (usually heat) is needed for magnesium to react.
- Sodium reacts vigorously with cold water; floating on the surface of the water and melting due to the heat given out, forming a molten ball on the surface, whilst fizzing/efferverscing rapidly producing H2 gas.
- This produces a strongly alkaline solution of NaOH.
2Na(s) + H2O(l) → 2NaOH(aq) + H2(g)
- Magnesium reacts very slowly with cold water. Only a few bubbles of H2 gas are formed after a few days; cannot see any reaction, but forms a weakly alkaline solution; magnesium hydroxide is only sparingly soluble (relatively few OH- ions are produced).
Mg(s) +2H2O → Mg(OH)2(aq) + H2(g)
- This reaction is much faster with heated Mg and steam, yielding magnesium xide and hydrogen.
Mg(s) + H2O → MgO(s) + H2(g)
What are the trends in the reactions of the Period 3 elements Na - S ((Na, Mg, Al, Si, P, S) with oxygen?
- All Period 3 elements (except argon) are fairly reactive.
- Most Period 3 elements react readily with oxygen directly, forming oxides.
- They are all redox reactions as every element starts with an ox. state of 0, which is altered post-reaction.
- Exothermic.
- All oxidised to their highest oxidation state; the same as their group numbers.
However, sulfur is the exception, which forms SO2 (a high temperature and a catalyst are required for SO3). - The more reactive metals (Na, Mg) and the non-metals (P, S) react readily in air, whilst Al and Si react slowly.
Element + Oxygen → Oxide
What is the reaction of the Period 3 element Na, with oxygen?
(trend, equation, what is observed)
- Sodium (Na) burns brightly in air with a yellow flame, forming white sodium oxide, Na2O(s).
- Vigorous
2Na(s) + 1/2O2(g) → Na2O(s)
- Sodium is in group 1; it is oxidised to +1.
What is the reaction of the Period 3 element Mg, with oxygen?
(trend, equation, what is observed)
- Magnesium burns in air with a brilliant white flame, producing a white powder of magnesium oxide, MgO.
- Flame is even more intense if Mg is lowered into a gas jar of oxygen.
- Vigorous
2Mg(s) + O2(g) → 2MgO(s)
- Magnesium, Mg is in Group 2; it has been oxidised to +2.
(oxygen has been reduced)
What is the reaction of the Period 3 element Al, with oxygen?
(trend, equation, what is observed)
- White aluminium powder is heated and lowered into a gas jar of oxygen, burning brightly to give a white powder of aluminium oxiude, Al2O3.
- Slow
4Al(s) + 3O2(g) → 2Al2O3(s)
- Aluminium, Al, is in Group 3; it has been oxidised to +3.
- Aluminium is a reactive metal, but it is always coated with a strongly bonded surface of oxide; this protects it from further reaction.
- Thus aluminium appears to be an unreactive metal and is used for many everyday purposes; saucepans, garage doors, windows frames etc. Even if the surface is scratched, the exposed aluminium reacts rapidly with the air and seals off the surface.
What is the reaction of the Period 3 element Si, with oxygen?
(trend, equation, what is observed)
- Silicon undergoes a similar reaction to Aluminium, and burns in oxygen (oxidises) if heated strongly enough to form a silicon dioxide product.
- Slow
Si(s) + O2(g) → SiO2(s)
- Silicon, Si, is in Group 4; it has been oxidised to +4.
What is the reaction of the Period 3 element P, with oxygen?
(trend, equation, what is observed)
- White phosphorus spontaneously ignites in the air and clouds of white smoke of phosphorous pentoxide, P4O10, are given off.
- Red phosphorous must be heated before it will react with oxygen.
- The above are allotropes of phosphorus; the same element with the atoms arranged differently.
- Spontaneously combusts
P4(s) + 5O2(g) → P4O10(s)
- If the oxygen supply is limited, phosphorus trioxide, P2O3, is also formed.
- Phosphorus is in Group 5; it has been oxidised to +5.
What is the reaction of the Period 3 element S, with oxygen?
(trend, equation, what is observed)
- Sulfur is heated and lowered into a gas jar of oxygen, where it burns with a (pale) blue flame and forms the colourless gas sulfur dioxide, SO2.
(a little SO3 also forms) - Burns steadily
S(s) + O2(g) → SO2(g)
- Sulfur makes SO2; its oxidation state is +4, which is not correspondent to its Group number, but wotevs lol.
How do the physical properties (bonding and structure) of the (highest) oxides of the Period elements Na - S affect melting points?
- The metal oxides;
- Na2O, MgO and Al2O3, all have high melting points* as they form *giant ionic lattices, with bonding that extends throughout the compound.
The strong forces of attraction between each ion means a lot of heat energy is required to break the bonds and melt them. - MgO has a higher melting point than Na2O as it forms 2+ ions, thus bonding is stronger than the 1+ ions in Na2O.
- Al2O3 has a lower boiling point than expected as it exhibits some covalent character; the Al3+ ions form a very small ion with a large positive charge and so can approach closely to the O2- and distort its electron cloud.
- The non-metal oxides;
- Silicon dioxide (SiO2) has a giant macromolecular (covalent) structure, with covalent beonding extending throughout the structure, hence a greater melting point that the other non-metal oxides.
Many strong covalent bonds must be broken for melting. - Phosphorus and sulfur oxides (P4O10 and SO2) have relatively low melting points as they form simple molecular structures; the molecules are bound by weak intermolecular forces which take little energy to overcome. They are seperate covalently-bonded molecules with weak van der Waals and dipole-dipole forces.
What is the reaction of Na2O and water?
(equation + explain in terms of bonding present)
- The ionic oxides of the metals Na and Mg (both basic oxides; basic because it contains the oxide ion, O2- which is a very strong base with a high tendency to combine with hydrogen ions) dissolve in water to form hydroxides.
- Strongly alkaline solution (due to NaOH)
- More alkaline than Mg(OH)2 due to its greater solubility.
- pH 14
Na2O(s) + H2O(l) → 2NaOH(aq)
- Sodium oxide is composed of ions; contains the oxide ion O2- which is a very strong base (strongly attracts protons) thus readily reacts with water to produce hydroxide ions; a strongly alkaline solution.
What is the reaction of MgO and water?
(equation + explain in terms of bonding present)
- Ionic oxides Na and Mg form hydroxides; MgO is a simple basic oxide; basic due to the oxide ion, but the oxide is not as free thus not as alkaline.
- Sparingly soluble, produces a weaker alkaline solution.
- pH = 9
MgO(s) + H2O(l) → Mg(OH)2(aq)
- Magnesium oxide is composed of ions; contains oxide ions but produces less alkaline solution due to its lesser solubility.
What is the reaction of P4O10 and water?
(equation + explain in terms of bonding present)
- Simple covalent oxides of the non-metals (right side) of phosphorus and sulfur form acidic solutions
- Phosphorus pentoxide reacts violently with water to produce an acidic solution of phosphoric(V) acid.
- Ionises to form the acidic solution.
- pH = 0-1
P4O10(s) + 6H2O(l) → 4H3PO4(aq)
- Phosphorous pentoxide is a covalent molecule that reacts with water to form acid solutions.
What is the reaction of SO2 and water?
(equation + explain in terms of bonding present)
- Simple covalent non-metal oxides (right side), phosphorus and sulfur, form acidic solutions.
- Sulfur dioxide is fairly soluble in water, reacting to give an acidic solution of sulfurous acid (sulfuric(IV) acid).
- pH = 2-3
SO2(g) + H2O(l) → H2SO3(aq)
- Sulfur oxides are covalent molecules that react with water to form acid solutions.
What is the reaction of SO3 and water?
(equation + explain in terms of bonding present)
- Simple covalent non-metal oxides (sulfur and phosphorus) form acidic solutions.
- Sulfur trioxide reacts violently with water to produce sulfuric acid (sulfuric(VI) acid).
- pH = 0-1
SO3(g) + H2O(l) → H2SO4(aq)
- Sulfur oxides are covalent molecules that react with water to form acid solutions.
What is the reaction of SiO2 and water?
(equation + explain in terms of bonding present)
- The giant macromolecular (covalent) structure of silicon dioxide means that it is insoluble in water; water does not affect this type of structure.
- pH = 7
