Group II Elements Flashcards
True or false
Group II elements are less electropositive than group I elements
True
True or False
Group II elements are more reactive than group I elements
False
True or false
Group II elements are good reducing agents
True
(Weaker than Group I though)
Why do group II elements have higher melting and boiling points than group I elements?
- Group II metals contribute 2 electrons per atom to their charge cloud. Their atoms carry a bigger charge and have a smaller ionic radii
- Therefore they form stronger electrostatic attraction between the positively charged metal ions and delocalized electrons resulting into stronger metallic bonds that require more heat energy to break
- Group I metals contribute 1 electron per atom to their charge cloud. Their atoms carry a smaller charge and have a bigger ionic radii
- The electrostatic attraction between the group I cations and delocalized electrons is less resulting into weaker metallic bonds that require less heat energy to break resulting into lower melting points
True or false
Group II compounds are less ionic than corresponding group I elements
True
- Group II cations form smaller cations with a bigger positive charge (+2) thus they have a higher charge density and polarizing power
- Group II cations exert a greater polarizing power on anions than group I cations do
(makes it more covalent-like than ionic)
Why are group II salts less soluble than group I salts?
Both the lattice energies of group II salts and hydration energies of group II cations are much higher than those of corresponding group I salts and group I cations respectively
Why does Beryllium show a significant difference in its chemical properties from the rest of the alkaline earth metals?
Very small ionic radius thus high charge density and polarizing power. Therefore it readily distorts the electron cloud of negatively charged ions forming covalent compounds
How do group II metals react with air?
- Burn in oxygen forming white solid metal oxides
- Magnesium and calcium also react with nitrogen in air and form nitrides
How do group II metals react with acids?
- All react with dilute mineral acids forming a salt and hydrogen gas.
- Beryllium is rendered inactive by nitric acid
- Vigor of the reaction increases down the group but for sulphuric acid it reduces after magnesium due to formation of insoluble sulphates.
How do beryllium and magnesium react with concentrated sulphuric acid?
Form a sulphate, sulphur dioxide and water
True or false
Beryllium is rendered inactive by nitric acid
True
This is due to formation of a protective oxide, beryllium oxide that causes the reaction to stop
How do group II metals react with water?
- Beryllium does not react with water
- Magnesium slowly reacts with cold or hot water but vigorously reacts with steam forming magnesium oxide (white solid) and hydrogen gas.
- Calcium, Strontium and Barium react with cold water forming a metal hydroxide and hydrogen gas.
How do group II metals react with alkalis?
- Beryllium reacts with hot concentrated sodium hydroxide (because of its greater polarizing power) forming a soluble complex of tetrahydroxoberyllate ions and hydrogen gas.
- Other elements do not react with alkalis
How do group II metals react with halogens?
- Hot group II metals react with halogens forming white solid metal dihalides
How do group II metals react with hydrogen gas?
- Heated group II metals react with hydrogen gas forming solid metal hydrides
(Hydrides of Be and Mg are covalent while those of Ca, Sr, Ba are ionic)
How are oxides of group II elements prepared?
- Heating metal carbonates or nitrates
- In the case of MgO; passing steam over heated Mg
True or false
All group II oxides except BeO are basic
True
BeO is amphoteric
But all group II oxides (including Be) react with acids forming salt and water only
What is the result of reacting Beryllium oxide with an alkali?
Soluble complex of tetrahydroxoberyllate ion
Why can’t BeO, MgO and CaO form peroxides but Sr and Ba can?
BeO, MgO and CaO cations are too small to form stable lattices while Sr and Ba cations are big enough to form stable lattices
How are hydroxides of group II metals prepared?
- Action of water on their metal oxides
- Action of aqueous sodium hydroxide on soluble salts of the metals
True or false
All group II hydroxides are basic
False
Beryllium hydroxide is amphoteric, the rest are basic
What is the result of reacting group II metal hydroxides and acids?
A salt and water only
True or false
Beryllium hydroxide reacts with alkalis
True
Forms a soluble complex of tetrahydroxoberyllate ions
What is the trend of solubility of group II hydroxides?
Solubility increases down the group
Explain why the solubility of group II hydroxides increases down the group
Down the group, both lattice energy and hydration energy decrease in magnitude but lattice energy decreases more rapidly than hydration energy
Explain why the solubility of group II hydroxides increases down the group
Down the group, both lattice energy and hydration energy decrease in magnitude but lattice energy decreases more rapidly than hydration energy
How are group II sulphates prepared
Action of aqueous sodium sulphate on aqueous solutions of metal salts
Describe and explain the trend in solubility of group II sulphates
Solubility of sulphates decreases down the group
Both lattice energy and hydration energy of group II sulphates decrease but hydration energy decreases more rapidly than lattice energy
How are group II carbonates prepared?
Precipitation by adding aqueous sodium carbonate to an aqueous solution of a group II salt
Describe and explain the trend in solubility of group II carbonates
All are insoluble in water
What is the trend of thermostability of group II carbonates?
Increases down the group
Explanation:
- The ionic radius of group II ions increases from Be2+ to Ba2+, but the ionic charge remains constant
- The ionic character of the carbonates increases down from beryllium carbonate to barium carbonate due to reduction in polarizing power
- Due to increase in ionic character of the carbonates, their decomposition temperature increases down the group
What is the trend of hydrolysis of group II salts?
- As the cationic radius increases from beryllium to barium, the charge density and polarizing power of the cations reduces as well
- As the polarizing power decreases down the group, the degree of hydrolysis of group II also decrease
- Be2+ ion with the highest polarizing power has its salts hydrolyzed in water forming acidic solutions
- The high polarizing power of the beryllium ion results into formation of the strong Be–O bond that weakens the O–H bond in the complex
- The solvent water molecules remove a proton from the complex, forming hydronium ions in the solution becomes acidic
- A few magnesium and calcium salts are hydrolyzed in water forming slightly acidic solutions
- Sr and Ba salts are not hydrolyzed in water
Define a complex
A complex is a compound or ion consisting of a Central metal ion or atom bonded to negatively charged ions or neutral molecules with lone pairs of electrons through coordinate bonding
What factors favor complex ion formation?
- small, highly charged cations
- Presence of empty orbitals on the Central metal ion or atom
- Lone pair of electrons on the ligands
Why does the ability to form complexes decrease down the group in group II?
This is because as ionic radius increases down the group, both the charge density and polarizing power decrease, and the ability of the cations to attract lone pairs of electrons from ligands reduces
What is a ligand?
A negatively charged ion or neutral molecule, with at least one lone pair of electrons, which it can donate to empty orbitals of a metal cation or atom
Define diagonal relationship
This is the trend in which elements in adjacent groups and periods of the periodic table at right angles to each other show similar chemical properties.
Give examples of pairs of elements that exhibit diagonal relationship
Lithium and magnesium
Beryllium and aluminum
Boron and silicon
Why does beryllium show anomalous behavior from the rest of the group II elements?
- Beryllium has high ionization energy compared to other group members
- Beryllium ion has a very small ionic radius compared to the rest of the group II cations. This results into high charge density and polarizing power that favors covalent bonding and high lattice energy resulting into low, solubility of beryllium compounds in water.
- Beryllium is much more electronegative compared to the rest of the group II members in this favors covalent bonding.
Why do beryllium and aluminum show diagonal relationship?
- Both have similar electronegativity
- Both have similar polarizing power
- Both have high and similar ionization energy
In which ways do beryllium and aluminum show diagonal relationship?
- Both metals are rendered passive by nitric acid (due to the formation of a protective layer)
- Both metals react with hot, concentrated, sodium hydroxide, liberating, hydrogen gas
- The oxide and hydroxide of both the beryllium and aluminum are amphoteric
- Their chlorides are polymeric, and when anhydrous readily dissolve in organic solvents, and are readily hydrolyzed by water, liberating, hydrogen chloride gas
- Both beryllium carbide and aluminum carbide give methane when reacted with water
- Similar complexes of beryllium and aluminum show similar stabilities
In which properties do lithium and magnesium show diagonal relationship?
- On combustion, both lithium and magnesium form normal oxides
- Both magnesium and lithium and heated combine directly with nitrogen forming metal nitrides
- The carbonates, fluorides and phosphates of both lithium and magnesium are insoluble in water
- Both lithium and magnesium react with carbon forming ionic carbides
- Their hydroxides, nitrates, and carbonates are readily decomposed on heating
How does magnesium react with air?
- At ordinary temperature magnesium is not attacked by dry air.
- It burns with a bright white flame on strong heating, forming a white ash consisting of magnesium oxide and magnesium nitride.
- If to the products, a little water is added, and the mixture warmed ammonia gas is involved.
How does magnesium react with dilute acids?
With dilute hydrochloric, sulphuric acid and nitric acid, magnesium readily liberate, hydrogen gas
How does magnesium react with concentrated acids?
With concentrated sulphuric acid, magnesium liberates sulphur dioxide gas
How does magnesium react with non-metals?
Hot magnesium vigorously reacts with several non-metals, including chlorine, sulphur, nitrogen, and phosphorus, forming a variety of compounds
How can one prepare magnesium oxide?
- Strong heating of magnesium carbonate
- Strong heating of magnesium hydroxide
- Strong heating of magnesium nitrate
How is magnesium hydroxide prepared?
By precipitation, by adding aqueous sodium hydroxide to an aqueous solution of any soluble magnesium salt
True or false
Magnesium hydroxide is only slightly soluble in water
True
True or false
Magnesium hydroxide is acidic and does not react with acids
False
Magnesium hydroxide is basic, and readily reacts with acids forming a salt and water
How is magnesium carbonate prepared?
By adding aqueous sodium hydrogen carbonate to aqueous magnesium sulphate
Why is sodium hydrogen carbonate solution preferred to sodium carbonate solution in the preparation of magnesium carbonate?
Sodium hydrogen carbonate solution is much less hydrolyzed producing much fewer hydroxide ions than sodium carbonate when in solution
How is anhydrous magnesium chloride prepared?
Heating magnesium in a stream of dry chlorine gas, or hydrogen chloride gas
How are magnesium chloride crystals prepared?
Reacting excess magnesium metal, magnesium oxide, magnesium hydroxide, or magnesium carbonate with dilute hydrochloric acid, and filtering off the excess solid to obtain a solution of magnesium chloride, which is concentrated by evaporation and left a cool, forming crystals of the salt
Why can’t anhydrous magnesium chloride be obtained directly by heating hydrated magnesium chloride?
The hydrated salt undergoes hydrolysis on heating to a basic compound
How are magnesium sulphate crystals prepared?
Reacting, either excess magnesium metal, magnesium oxide, magnesium hydroxide, or magnesium carbonate with dilute sulphuric acid, and filtering of the excess solid to obtain a solution of magnesium sulphate which is concentrated by evaporation and left to cool to form crystals of the salt
How does calcium react with air?
- When exposed to air at room, temperature, calcium forms in succession, its oxide, hydroxide, and carbonate
- When heated in air it burns with a brick red flame, forming a white solid, consisting of a mixture of calcium oxide and calcium nitride
- Ammonia, gas is liberated when to the mixture warm water is added
How does calcium react with water?
It readily reacts, liberating, hydrogen gas, and forming calcium hydroxide, which is only slightly soluble in water. Therefore, a white suspension is seen in the water.
How does calcium react with hydrogen gas?
When heated in a stream of dry hydrogen gas it produces a colorless salt-like solid called calcium hydride
Calcium hydride, liberates, hydrogen gas when reacted with cold water
How is calcium oxide/quicklime prepared?
Strongly heating calcium carbonate to about 1300K
How does calcium oxide react with cold water?
If cold water is added to the oxide it produces a hissing sound, and the material swells cracks and crumbles into a white powder in an exothermic reaction, forming calcium hydroxide/slaked slime
How is calcium hydroxide prepared?
Action of excess water on calcium oxide
True or false calcium hydroxide is only slightly soluble in water
True
Forms a colorless solution of calcium hydroxide solution
What is the action of carbon dioxide gas on calcium hydroxide solution (lime water)?
- limewater turns milky due to the formation of insoluble calcium carbonate
- However, if excess carbon dioxide is used the insoluble calcium carbonate, dissolves, forming a colourless solution consisting of calcium hydrogen carbonate, which is which is soluble in water
How does calcium hydroxide react with acids?
Calcium hydroxide is strongly basic and reacts with acids forming a salt and water
How is calcium carbonate prepared?
- Calcium carbonate is prepared as a white precipitate by mixing hot solutions of calcium chloride and sodium carbonate
- The precipitate is filtered, washed with hot distilled water and dried in a steam oven
True or false
Calcium carbonate is soluble in water
False
It is practically insoluble
What happens to calcium carbonate on heating?
Decomposes on heating, forming calcium oxide, and carbon dioxide (reversible reaction)
How does calcium carbonate react with acids?
- With dilute nitric acid or dilute hydrochloric acid, Calcium carbonate reacts readily liberating carbon dioxide gas.
- With dilute sulphuric acid, the reaction stops after a short period of time due to formation of a coating of insoluble calcium sulphate on the calcium carbonate, preventing it from further acid attack
How is calcium sulphate prepared?
Prepared as a white precipitate, by mixing moderately concentrated hot solutions of calcium chloride and sodium sulphate
True or false
Calcium sulphate is soluble in water
False
Calcium sulphate is only sparingly soluble in water
True or false
Calcium sulphate is soluble in water
False
Calcium sulphate is only sparingly soluble in water
How can calcium chloride be prepared?
- Reacting excess calcium carbonate with dilute hydrochloric acid and then filtering off the excess solid to obtain a solution of calcium chloride which is concentrated by evaporation and left to cool to form crystals of the salt
- Anhydrous calcium chloride can be obtained by heating the hydrated salt to dryness
What is the result of calcium carbide reacting with cold water?
It rapidly reacts with cold water forming calcium hydroxide and ethyne gas
What is the result of magnesium ions reacting with sodium hydroxide solution?
White precipitate insoluble in excess alkali
What is the result of magnesium ions reacting with ammonia solution?
White precipitate insoluble in excess ammonia
- however this precipitate does not form in presence of ammonia chloride which suppresses ionization of ammonia solution leading to insufficient hydroxide ions to reach the solubility product of magnesium hydroxide
What is the result of magnesium ions reacting with aqueous sodium carbonate/ aqueous ammonium carbonate?
White precipitate formed
What is the result of magnesium ions reacting with sodium phosphate/ disodium hydrogen phosphate?
- To test the solution, solid ammonium chloride is added followed by little sodium phosphate or disodium hydrogen phosphate solution
- A white precipitate forms slowly, insoluble in ammonia but soluble in acids
What is the result of calcium ions reacting with sodium hydroxide solution?
White precipitate insoluble in excess alkali
What is the result of calcium ions reacting with ammonia solution?
No observable change in dilute conditions/ slight white precipitate
What is the result of calcium ions reacting with aqueous sodium carbonate?
White precipitate formed
What is the result of calcium ions reacting with dilute sulphuric acid?
White precipitate forms slowly
What is the result of calcium ions reacting with ammonium oxaloate solution?
White precipitate insoluble in hot ethanoic acid but soluble in mineral acids
What is the result of calcium ions reacting with sodium phosphate/ sodium hydrogen phosphate solution solution?
White precipitate forms
What is the result of barium ions reacting with sodium hydroxide solution?
White precipitate insoluble in excess alkali
What is the result of barium ions reacting with ammonia solution?
No observable change ( if all solutions are prepared in distilled water)
What is the result of barium ions reacting with aqueous sodium carbonate?
White precipitate formed
What is the result of barium ions reacting with dilute sulphuric acid?
A heavy white precipitate forms instantly
What is the result of barium ions reacting with ammonium oxaloate solution?
White precipitate soluble in hot ethanoic acid in dilute mineral acids but not in sulphuric acid
What is the result of barium ions reacting with sodium phosphate/ sodium hydrogen phosphate solution solution?
White precipitate forms
What is the result of barium ions reacting with potass chromate solution?
A yellow precipitate formed, soluble in mineral acids but not dilute sulphuric acid forming an orange solution but insoluble in aqueous sodium hydroxide
