4.1 Ionic Bonding And Structure
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Ionic bond
Electrostatic attraction between oppositely charged ions
What type of elements can an ionic bond be formed between?
Elements with electronegativity difference of 1.8 or greater
Where are the electrons transferred from?
The transfer is from one or more electrons from the valence shell of one atom to the other’s valence shell
Octet rule
Atoms are more stable with electron configuration of a noble gas
Why is ammonium chloride an exception to the usual metal-non metal ionic bond?
NH4Cl is an exception because it has both ionic bonding between ions and covalent bonding between atoms
Lattice structure
Regular crystalline arrangement made of alternating cations and anions. Ratio is 1:1
What does “ionic bonding is non-directional” mean?
It means the force of attraction occurs in all directions around ions
Are all ionic compounds molecules?
No. Eg. NaCl is always referred to as a compound not a molecule
Polyatomic ions and bonding
Those that consist of more than one type of atom. Usually their atoms are bonded by covalent bonds but between them and another ion is an ionic bond
Formula for hydroxide, carbonate and ammonium ions
OH- HCO3- NH4+
Ion formulae for nitrate and nitrite
Nitrate: NO3- Nitrite: NO2-
Ion formulae for chlorate, perchlorate, chlorite and hyperchlorite
Chlorate: ClO3- Perchlorate: ClO4- Chlorite: ClO2- Hyperchlorite: ClO-
Ion formulae for sulfate, sulfite and phosphate
Sulfate: SO4 2- Sulfite: SO3 2- Phosphate: PO4 3-
How many ions does Fe2(SO4)3 have?
5 ions
Why do compounds with ionic bonds have high melting and boiling points?
As the attraction/ bond between ions is very strong, large amounts of energy are required to overcome them. Hence the MP and BP is high and they are usually solids under STP
In Na2O and MgO, which will have higher melting point and why?
MgO will have higher melting point as the greater the charge and the smaller its atomic radius, the higher attraction will be.
Volatility
How easily a substance evaporates
Why do ionic compounds have low volatility?
As they require a lot of energy to overcome strong forces of attraction, they don’t evaporate so easily hence low volatility
What are the 2 steps in solubility?
• Dissolves: Breaks down lattice structure 2. Hydrates: Separated ions get surrounded by water molecules
What does solubility depend on?
The forces of attraction between water and ions
Why are water molecules polar?
Because of difference in electronegativity in H+ and O2-. This leads to partial opposite charges
How does polarity help water as a solvent?
Partial charges of water are attracted to opposite charges of ions and allows water to separate compounds
Why are hexane and propane limited solvents?
They are non-polar and so they have difficulty in disrupting lattice structure
What does electrical conductivity depend on?
The presence of mobile ions