Inorganic 1 - periodicity and group 2

What happens to atomic radius across period 3?

The atomic radii decrease because number of protons increases, so nuclear charge increases. Shielding remains similar, so the outer electron is more strongly pulled to the nucleus (stronger electrostatic force of attraction) so decrease across the period.

What happens to the melting and boiling points of the metals in period 3?

It rises across the three metals because of the increasing strength of the metallic bonds. The number of electrons which each atom can contribute to the delocalised sea of electrons increases. The atoms also get smaller and have more protons as you go from Na to Al, which means that the electrostatic attraction between the nucleus and sea of electrons increases, increasing melting point.

Describe the melting point of Silicon in period 3:

Silicon has a high melting point because it is a giant covalent structure, and the many strong covalent bonds must be broken which requires a lot of energy.

Describe the melting points of Phosphorous, Sulfur and Chlorine:

Phosphorous, sulfur, and chlorine are simple molecular substances with only van der Waals attractions between molecules, so their melting points are lower than the first 4 elements in period 3. The size of the melting point is affected only by the size of the molecule - for P, it contains P4 molecules, you don’t have to break any covalent bonds, only van der Waals so m.p. is low. Sulfur has S8 rings, so there are more electrons, so van der Waals attractions are stronger, so m.p is higher than P. Chlorine has the lowest m.p. as it is a smaller molecule so van der Waals are weaker.

Describe the melting point of Argon:

It is made of single Argon atoms, so there are only very weak van der Waals as the atoms are difficult to polarise, so melting point is very low (lowest in period 3)

Trend in first ionisation energy going down group 2?

Decreases, because the atomic radius increases so the outer electron is further from the nucleus so it takes less energy to lose the electron.

What is the trend in melting points of group 2 elements?

They have metallic structures so the melting point is high. Going down the group the electrons in the sea of delocalised electrons are further from the positive nucleus as the ions increase in size, so the electrostatic forces between the electrons and nucleus decreases, so melting point decreases down the group.

What happens to the solubility of group 2 hydroxides going down the group?

The hydroxides become more soluble - Mg(OH)2 is almost insoluble and Ba(OH)2 dissolves to produce a highly alkaline solution

How is Magnesium hydroxide used in medicine?

Used as an indigestion remedy to neutralise excess stomach acid which causes heartburn, indigestion. Also used in agriculture to neutralise acidic soil.

How do group 2 metals react with water?

React in a redox reaction to produce a metal hydroxide and hydrogen. The metal hydroxide forms an alkaline solution. The metals are oxidised as electrons are lost. This is a very slow reaction

How can the reaction of group 2 metal with water be sped up, and what happens in this reaction?

Steam can be used as it provides the reaction with extra energy, and when steam is used the Mg burns with a bright white flame to form hydrogen and magnesium oxide, a white powder.

What is the equation for the reaction of Mg with water?

Mg + 2H2O → Mg(OH)2 + H2

What is the reaction for Mg with steam?

Mg + H2O → MgO + H2

What happens to the solubility of group 2 sulfates?

Group 2 sulfates decrease in solubility down the group, so MgSO4 is the most soluble and Barium sulfate is the least.

How is barium sulfate used in medicine?

Used as barium meals as a medical tracer as it allows internal organs to be imaged. It is toxic if it enters the blood, but it can’t be absorbed due to its insolubility.

How is Magnesium used in the extraction of Titanium?

Titanium is a strong, low density useful metal used in aerospace but can’t be extracted with Carbon as it forms Titanium carbide. So, TiO is reacted with Carbon and chlorine to form TiCl4 which is reduced to Ti in a displacement reaction with Magnesium.

What are some uses of Calcium hydroxide and calcium oxide?

Calcium hydroxide used to treat acidic soil in agriculture, as it neutralises acids so provides optimum pH for plants. CaO is used to make building mortar and neutralise soil acids. It also reacts with Sulfur dioxide to remove it from factory pollutants and prevent it being released to the atmosphere. Gases pass through a scrubber containing CaO which reacts with acidic SO2.

Equation for reaction of CaO to remove flue gases?

CaO + SO2 → CaSO3 (calcium sulfite)

How is barium chloride used to test for sulfate ions?

The solution is acidified with HCl or nitric acid, which removes other anions like carbonate that could form a white precipitate so the test is specific to sulfate, and then BaCl2 is added, and if SO4 ions are present a white precipitate of barium sulfate is formed.

How does Magnesium react with water?

Vigorous reaction with steam, no reaction with water

How does Ca react with water?

Reacts moderately, forms a hydroxide

How do Sr and Ba react with water

Reacts rapidly to form a hydroxide

Do group 2 metals react vigorously with HCl

Yes

what happens to the pH of solutions formed from the reaction of group 2 oxides with water going down the group?

they become more alkaline because the solubility of hydroxides also increases, so the concentration of OH- ions increases

how are Barium ions tested for

adding sulfuric acid in the form of Na2SO4

What are the two equations for extraction of Ti by Mg?

TiO2 + 2Cl2 + 2C → TiCl4 + 2CO

TiCl4 + 2Mg → Ti +2MgCl2