Elements of Life: Group 2 ( Structure types & Bonding - S Block ) Flashcards
What block are group 2 elements
S block
Why are group 2 elements in the s block
Outer electrons are in an s subshell
What happens to atomic radius as you go down Group 2
Increases
Why does atomic radius increase as you go down the group
- More electrons
- More electron shells
( no. filled electron shells increases )
What happens to 1st ionisation as you go down group 2
Decreases
Why does 1st ionisation decrease as you go down group 2
- More shells
- Distance between nucleus + outer shell increases
- More shielding ( from larger no. of inner electrons
= attraction between nucleus and outer electrons decreases
(atomic radius increases
no. filled electron shells shielding outer shell increases)
What happens to reactivity as you go down group 2
Increases
Why does reactivity increase as you go down group 2
- More shells
- Distance between nucleus + outer shell increases
- More shielding ( from larger no. of inner electrons
= attraction between nucleus and outer electrons decreases
(atomic radius increases
no. filled electron shells shielding outer shell increases)
What happens in group 2 reactions
Group 2 atoms lose outer their 2 outer electrons to form 2+ ions
What is required for group 2 atoms to lose their 2 outer electrons to form 2+ ions
Absorption of an amount of energy equal to the sun of the 1st and 2nd ionisation energies
Show the rule for ionisation energies of group 2 atoms in terms of equations
Mg (g) —> Mg 2+ (g) + 2e-
Requires:
1st + 2nd IEs
=738+1451
= 2189 kJmol -1
What are typical melting points of group 2 atom generally like
High
Why do group 2 atoms have high melting points
- Giant metallic structure
2. Strong electrostatic attraction between the lattice of positive ions and the sea of delocalised electrons
What happens to group 2 melting points as you go down the group
Decrease
Why does group 2 melting point decrease as you go down the group
- Atoms get bigger
- Distance between sea of electrons and positive nuclei increases
- Electrostatic attraction between positive ions and sea of delocalised electrons get weaker
What atom is the exception in group 2 melting point trend and why
Magnesium = lowest melting point = different lattice arrangement to other group 2 metals
What do group 2 metals burn in air to form
Oxides
Give equation of oxidation of group 2 metals using Mg as example
2Mg(s) + O2(g) —> 2Mg(2+)O(2-)
What are group 2 metal oxides also know as
Bases
What do bases dissolved in water form to give ( and why )
Alkalis
O2- ion has a strong affinity (attraction) for H+ ions
Give equation of group 2 oxides dissolved in water to give an alkali using Mg as example
Mg(2+)O(2-) (s) + H2O (l) —>
Mg(2+) (OH-)2 (s)
What do group 2 metals reacting with water form
Hydrogen gas and alkaline solutions
Give equation for group 2 metal reacting with water
X = any group 2 metal
X(s) + 2 H2O (l) —>
X(OH)2 (s) +H2 (g)
What is special about the reaction of Mg with water
It is slow
Reacts fast with steam = magnesium oxide and hydrogen gas produced
What do group 2 metal hydroxides dissolved in water form
Alkaline solutions
Give the equation of group 2 metal hydroxides dissolved in water
X = any group 2 metal
X2+(OH-)2 (s) —>
X2+ (aq) + 2 OH- (aq)
What happens to group 2 hydroxides solubility as you go down the group
Increase
Why does solubility of group 2 hydroxides increase as you go down the group
X = any group 2 metal
As size of X 2+ ion increases attraction for OH- ions decreases
What’s is the rule about about solubility and precipitate
Least soluble = precipitate
Most soluble = no precipitate
What happens to strength of alkaline solution of group 2 metals as you go down the group
Increases
How would you describe strongest alkali (I.e Barium)
Gives the highest concentration of OH- ions
What happens to the solubility of group 2 sulphates as you go down the group
( similar trends for carbonates & chromates )
Decreases
Describe magnesium sulphate (MgSO4)
Soluble = clear solution
Describe barium sulphate ( BaSO4 )
Insoluble = white precipitate
What is the insolubility of barium sulphate used to test for
Sulphate ions ( SO4 2- (aq) ) in an aqueous solution
Sulphate ions present = white precipitate of BaSO4 (s)
Definition of thermal decomposition
Substance breaks down into simpler substances when heated
What decomposes on heating
Metal carbonates = metal oxide + carbon dioxide
Give equation of thermal decomposition of group 2 metal carbonates
X= any group 2 metal
heat
XCO3 (s) ——> XO (s) + CO2 (g)
What happens to thermal stability of group 2 carbonates as you go down the group
Increases
Why does thermal stability of group 2 carbonates increases as you go down the group
- Size of ions increases
- Polarising power decreases
- Higher temp needed to decompose carbonate ion
High charge density =???
High polarising power
High polarising power =???
High charge density
What happens to polarising power ( charge density ) as you go down the group and why
Decreases because metal ions increase in size
Why do metal ions with a high charge density ( high polarising power ) decompose easier on heating
They distort the electron cloud of the carbonate ion
Can group 1 carbonates decompose on heating
No because have low polarising power
What is the name of group 2 metals
Alkaline earth metals
