Group 2 - The Alcohol Earth Metals Flashcards
(41 cards)
What are group 2 metals and where are they found and which are the most common?
They are all metals with a shiny silvery white appearance and their compounds are all found in the Earths crust and are widely distributed in rock structures. Calcium and magnesium are the most common
What does the name alkaline earth metals come from?
Their metal oxides
What is the electron configuration of group 2 elements?
They have two electrons in their outer s sub-shell and moving down the group each element has an extra shell of electrons
What is the bonding in group 2 elements?
They have metallic bonding where each metal atom transfers two electrons to create the sea of delocalised electrons
What is the trend in atomic radius of the group 2 elements and why?
The atomic radii increase moving down group 2. Each successive element has an extra shell of electrons and a larger nuclear charge. The additional shell of electrons shield the outer 2s electrons from the nuclear charge. The outer electrons are attracted less strongly and move further away from the nucleus. The atomic radius increases
What is the trend in first ionisation energies moving down group 2?
They decrease down group 2 as extra electron shells are added successfully shielding the outer 2s electrons from the nuclear charge making it easier to remove and electron
What is the first ionisation energy?
The energy needed to remove one mole of electrons from one mole of atoms in the gaseous state
What is the general trend in melting points for group 2 elements?
They generally decrease
What does the melting point of a metal depend on?
The strength of the bonds formed when the elements atoms join together to make giant structures with metallic bonding
What is the melting point an indication for and why?
The energy that must be transferred to the metal for it to melt because when metals melt they gain sufficient kinetic energy to break free from their fixed positions in the surrounding sea of delocalised electrons
Why does the melting point decrease down group 2?
Because moving down group 2 there are more electron shells sheilding the metal ion nucleus from the delocalised electrons reducing the attraction. It becomes easier to break the metallic bonds and the melting point is lower
Why is the melting point of magnesium lower than predicted in the trend?
Because the strength of the metallic bond depends not only on the charges and radii of the metal ions but also on the pattern in which the metal ions pack together
Magnesium and Beryllium have hexagonal close packed structures
Calcium strontium and barium have cubic structures. These are not as close packed as hexagonal.
What does magnesium’s low melting point make it useful as?
A reducing agent in the extraction of titanium metal
What’s tintaniums similarity to steel and what makes it advantageous to steel?
- they both have high tensile strength
- titanium density is half of steel
- it does not corrode because it forms a layer of protective oxide on its surface when exposed to air
What ores are titanium extracted from and why cant this be done by reduction by carbon?
- the ores are: titanium rule, TiO2 and ilmenite FeTiO3
* reduction with carbon produces titanium carbide which makes the metal brittle and useless
Desribe what happens in the extraction of titanium
• titanium (IV) oxide is converted to titanium (IV) chloride, TiCl4, by heating with carbon in a stream of chlorine gas:
TiO2 +2Cl2 + 2C -> TiCl4 + 2CO
•Titanium (IV) chloride is then reduced using magnesium metal as the reducing agent.
TiCl4 + 2Mg -> Ti + 2MgCl2
• This is called the Kroll process. Magnesium is oxidised from oxidation state 0 to +2 in magnesium chloride
• Titanium (IV) chloride and liquid magnesium are heated to about 1200 °c in an inert atmosphere of helium or argon gas
How long does the Kroll process take and why is it a batch process?
- It takes 36-50 hours plus 4 days to cool
* it’s a batch process because the furnace does not operate continuously
Why are group 2 metals good reducing agents?
Because they have two electrons in their outer shells which are readily transferred to other elements and compounds
What is the general equation, the full redox equation and the half equations for the reduction of water to hydrogen? Where M represents a group 2 metal
M + 2H20 -> M(OH)2 +H2
M + 2H2O -> M2+ + 2OH- + H2
M -> M2 + 2e-
2H2O + 2e- -> 2OH- + H2
What does the ease that the metal can transfer electrons depend on?
It depends on the first and second ionisation energies. They decrease going down the group so as you go down the group it becomes easier to transfer two electrons.
Therefore the energy needed to oxidise group 2 metals is less as you go down the group
What happens when magnesium reacts with cold water and steam
- cold water: magnesium reacts very slowly to form magnesium hydroxide and hydrogen has. It takes several days to produce noticeable amounts of hydrogen gas because the magnesium hydroxide formed is almost insoluble and formes a layer on the magnesium metal
- if steam is passed over heated magnesium an exothermic reaction occurs and the magnesium hydroxide initially formed is decomposed into magnesium oxide and hydrogen gas
How does calcium react with water?
It has lower ionisation energies so it reacts more easily. Calcium reacts with cold water to form calcium hydroxide and hydrogen gas. The resulting solution is commonly called limewqter and is used to test for carbon dioxide gas
How do strontium and barium react with waterM
With increasing vigour to produce a metal hydroxide and hydrogen
What is a solute?
A substance that is present in a solution
