Periodicity Flashcards
What happens to the oxidation states of the period 3 elements in their oxides as we go across the period left to right
It increases
What type of bonding is present in metal oxides
ionic bonding
Explain why metal oxides have a high melting point
The strong electrostatic forces between the oppositely charged ions need a large amount of energy to break.
Which period 3 metal forms an oxide with some covalent character
Aluminium oxide
Explain why aluminium oxide has some covalent character
Aluminium forms a very small ion with a large positive charge. This high electron density distorts the electron cloud of the oxygen ion and leads to some covalent character in the bond.
What property can be used to predict whether an ionic compound exhibits any covalent character?
Electronegativity - the bigger difference between this, the greater the ionic character of the bond.
Describe the bonding in silicon oxide
Giant covalent / macromolecular
Explain why silicon oxide has a high melting point
It is a macromolecular structure. The strong covalent bonds extend throughout the whole structure and require a lot of energy to break.
Describe the bonding in phosphorous oxide and sulphur oxide
Simple covalent molecule with strong covalent bonds within the molecule and weak intermolecular forces
Explain why phosphorous oxide and sulphur oxide have low boiling and melting points
Simple covalent molecule with strong covalent bonds within the molecule and weak intermolecular forces. These weak intermolecular forces do not require much energy to overcome.
Which two oxides of period 3 elements are insoluble?
Aluminium and silicon
Explain why magnesium and sodium oxides dissolve in water to give alkaline solutions
The oxide ions are strong bases as they readily attract protons so they react with water to give hydroxide ions. This forms an alkaline solution.
Explain why magnesium oxide forms a weaker alkaline solution than sodium oxide
Magnesium oxide is less soluble so there are less oxide ions available to react with the water to produce hydroxide ions.
Explain why aluminium oxide is insoluble
The bonding in aluminium oxide is very strong and is strengthened by the covalent character so the ions will not separate in water.
Explain why silicon dioxide is insoluble in water
Silicon dioxide is a giant macromolecule. These types of structure do not dissolve in water.
What ions are formed when phosphorous oxide dissolves in water?
H+ and H2PO4(-)
What ions are formed when sulphur dioxide dissolves in water?
H+ and HSO3(-)
What ions are formed when sulphur trioxide dissolves in water?
H+ and HSO4(-)
equation illustrates acidic nature SiO2
2NaOH + SiO2 –> Na2SiO3 + H20
Exceptions to increase in ionisation E across period
There is a small drop between Mg + Al. Mg has its outer electrons in the 3s sub shell, whereas Al is starting to fill the 3p subshell. Al’s electron is slightly easier to remove because the 3p electrons are higher in energy.
There is a small drop between phosphorous and sulphur. Sulphur’s outer electron is being paired up with an another electron in the same 3p orbital.
When the second electron is added to an orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove.
Colour flames in period 3 oxides
Sodium burns with a yellow flame to produce a white solid
Mg, Al, Si and P burn with a white flame to give white solid smoke
S burns with a blue flame to form an acidic choking gas.
What reacts with water to give an acid
non metal simple molecular compounds
Why is aluminium hydroxide insoluble
Very positive Hsol
LE much larger than hydration enthalpy
