Group 2 - The alkaline earth metals Flashcards
What are all group 2 metals used as
reducing agents
State and explain the trend in atomic radius as you go down group 2
The atomic radius increases down the group.
As you go down there are more electron shells, so the outer electrons are more shielded.
The nuclear attraction decreases as you go down the group, so the electrons are held less tightly
Why is the atomic radius of Barium (56) bigger than that of Magnesium (12)
Barium has more electron shells than magnesium so the outer electrons are more shielded. The nuclear attraction decreases, so the electrons are held less tightly in barium.
Why is there a large increase in ionisation energies on the removal of the third electron
The 3rd electron is removed from a new energy level which is closer to the nucleus and shielded by fewer inner shells.
Why does the first ionisation energy decrease as you go down group 2
The atomic radius increases down the group. There is more shielding of the outer electrons. The nuclear attraction decreases as you go down the group, so less energy is needed to remove the outer electron in barium.
Explain why the first ionisation energy of magnesium is more endothermic than that of calcium
The atomic radius of Mg is smaller than Ca.
There is less shielding of the outer electrons in Mg.
The nuclear attraction increases, so more energy is needed to remove the outer electron in Mg.
Describe the structure of metals.
The positive metal ions are arranged in a regular lattice and are held together by the strong electrostatic forces of attraction between the metal ions and the sea of delocalised electrons. Metals have a giant metallic lattice.
Explain why the melting point decreases as you go down group 2.
The ions become bigger as you go down the group from Be2+ to Ba2+.
They have the same number of delocalised electrons because each atom gives 2 electrons to the sea of electrons.
The attraction between the positive ions and the delocalised electrons gets weaker from Be to Ba, so less energy is needed to break the metallic bonds in Barium.
Why is the melting point of Barium lower than that of Magnesium
Barium ions are bigger than magnesium ions.
Barium and magnesium have the same number of delocalised electrons because the give 2 electrons per atom to the sea of electrons.
The attraction between the positive ions and delocalised electrons is weaker in barium than in magnesium so less energy is needed to break the metallic bonds in barium.
Why does the melting point increase across the period from sodium to magnesium.
Magnesium ions are smaller than sodium ions and have a greater charge.
Magnesium has more delocalised electrons than sodium because each magnesium atom gives 2 electrons to the sea of electrons but each sodium atom only gives one.
The attraction between the positive ions and delocalised electrons is stronger in magnesium than in sodium, so more energy is needed to break the metallic bonds in magnesium.
Explain what happens to reactivity and why as you go down group 2
The atomic radius increases as you go down the group.
There is more shielding of the outer electrons.
The nuclear attraction decreases as you go down the group, so the electrons are held less tightly and are more easily lost.
How do group 2 metals react with oxygen
They react vigorously to form an ionic oxide.
This is a redox reaction as the metal is oxidised and oxygen is reduced
How do group 2 metals react with water
All group 2 element EXCEPT BERYLLIUM react with water to form hydroxides and hydrogen gas.
This is also a redox reaction
At what rate does Mg react with H2O
very slowly
How does Mg react with steam
Very quickly to give magnesium oxide and hydrogen
How does Ba react with water
vigorously
what does the hydroxide formed in the reaction between G2 metals and water form and why
The hydroxide forms an alkaline solution with pH of 10-12 due to the presence of OH- ions.
why do Mg(OH)2 and Ca(OH)2 form weakly alkaline solutions
They are only slightly soluble
When Mg is added to water at room temp, little apparent reaction occurs. Give 2 reasons.
The oxide layer on its surface prevents any further reaction.
The reaction has a high activation energy
Why should water not be used to put out a fire in which magnesium metal is burning
Mg reacts with water to produce H2
There is a risk of explosion as hydrogen is highly flammable
Why does the reaction between barium and excess dilute sulfuric acid stop after a very short time.
** This also happens to BaO, Ca and CaO
The surface of barium gets coated with insoluble sulphate which prevents the acid getting to the surface of barium.
What happens to the solubilities of the hydroxides of G2 metals as you go down the group.
The solubility increases and therefore the solutions of the hydroxides become more alkaline as you go down the gorup.
Solubility of Mg(OH)2
only slightly soluble in water so has low OH- conc
Use of Mg(OH)2
Used as an antacid in treating indigestions as it is only slightly soluble forming a weakly alkaline solution so can be used to reduce the acidity of the stomach acid
