Period 3 Flashcards
What is the trend in atomic radius across period 3?
Decreases, extra protons pull electrons closer, no extra shielding
What is the trend in melting and boiling point across period 3?
Increases up to silicon then decreases
Describe the elements across period 3
- Na, Mg and Al contain metallic bonding and react with dilute acids to form hydrogen and salts.
- Si has a macromolecular tetrahedral structure and is a metalloid (semi-metal)
- P, S and Cl are molecular and typical non-metals, MP and BP depends on their van der waals forces
- Ar exists as individual atoms
Show the equation for sodium and water and explain the reaction
2Na(s) + 2H2O(l) -> 2NaOH(aq) + H2(g)
- This reaction is vigorous as sodium fizzes rapidly on the surface and produces a strongly alkaline solution of sodium hydroxide which has a pH of around 13-14.
Show the equation for magnesium and water and explain the reaction
Mg(s) + 2H2O(l) -> Mg(OH)2 + H2(g)
- This reaction is very slow at room temperature and only a few bubbles of hydrogen gas is formed after a few days. The solution produced is less alkaline than sodium hydroxide because magnesium hydroxide is sparingly soluble with a pH of 10.
Mg(s) + H2O(g) -> MgO(s) + H2(g)
- This reaction is much faster and produces a white powder of MgO
Why are the reaction of water with magnesium and sodium considered redox reactions?
The oxidation state of the metal increases and the oxidation state of hydrogen decreases
Show the equation for sodium reacting with oxygen and state the observation
2Na(s) + 1/2O2(g) -> Na2O(s)
- Burns brightly in air with a yellow flame and forms white Na2O
Show the equation for magnesium reacting with oxygen and state the observation
2Mg(s) + O2(g) -> 2MgO(s)
- Bright white flame, white powdered MgO forms
Show the equation for aluminium reacting with oxygen and state the observation
4Al(s) + 3O2(g) -> 2Al2O3(s)
- Burns brightly, white powdered Al2O3 forms
Show the equation for silicon reacting with oxygen and state the observation
Si(s) + O2(g) -> SiO2(s)
- Heated strongly in oxygen, white powdered SiO2 forms
Show the equation for phosphorus reacting with oxygen and state the observation
4P(s) + 5O2(g) -> P4O10(s)
- Red phosphorus must be heated before reacting with oxygen.
- White phosphorus spontaneously ignites in air, white smoke of phosphorus pentoxide is given off
- If the supply of oxygen is limited, phosphorus trioxide P2O3 is also formed
Show the equation for sulfur reacting with oxygen and state the observation
S(s) + O2(g) -> SO2(g)
- Must be heated and lowered into a glass jar of oxygen
- Burns with a blue flame, colourless SO2 gas forms
- A little sulfur trioxide can form
What are the different types of structure and bonding displayed by the period 3 oxides?
Na - ionic lattice
Mg - ionic lattice
Al - ionic lattice with covalent character
Si - giant covalent
P - simple molecular
S - simple molecular
Why does Al2O3 have covalent character?
Al3+ distorts O2- electron cloud
