Chemical Bonding and Structure
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What type of state are Ionic Substances in-room Temperature?
Solids
Why is the Melting and Boiling Point of Magnesium Oxide higher than Sodium Chloride?
The electrostatic attractions between 2+ and 2- ions in the Magnesium Oxide are stronger than those between the 1+ and 1- Higher Temp is required to provide sufficient energy to separate the ions in Magnesium Oxide The force of the ions between ions is proportional to the product of the charges (whilst all other things being equal)
How Volatile are Ionic Compounds?
Low Volatility (refers to how readily a substance evaporates) THIS IS BECAUSE THE ELECTROSTATIC FORCES OF ATTRACTION BETWEEN THE IONS ARE STRONG
How Soluble are Ionic Compounds in Water?
Often Soluble in Water Water is a polar solvent, and energy is released when the ions are hydrated by being surrounded by water molecules This energy pays back the energy required to break apart the ionic lattice
How Soluble are Ionic Compounds in Non-Polar Solvents?
Not usually Soluble (hexane) A great Deal of Energy is required to break apart the ionic lattice This is not paid back by the energy released when the non-polar solvent forms interactions with the ions
Electronegativity?
measure of the attraction of an atom in a molecule for the electron pair in the covalent bond of which it is a part
What is the rule of Electronegativity?
In a covalent bond between two different atoms, the atoms do not attract the electron pair in the bond equally This is because of the size of the individual atoms and their nuclear charge
What does it mean if an Element is more electronegative than the other in an ionic compound?
Let’s take a cheeky lil example: HF, Fluorine is more electronegative than hydrogen Thus, F attracts the electrons in the H-F bond more strongly than hydrogen atom does.
Do Noble Gases have electronegativity values?
No, since they don’t form compounds
How does electronegativity compare between Non-Metals and Metals?
Non-Metals have higher electronegativities than metals
What is a Coordinate Covalent Bond?
A Coordinate Covalent bond is a type of covalent bond in which both electrons come from the same atom.
Carbon Monoxide in Covalent Bonding?
Pg 131
Resonance Structures?
Pg 133
How can we predict the shapes of molecules?
VESPR THEORY
VESPR Abbreviation?
Pairs of electrons (electron domains) in the valence (outer) shell of an atom repel each other and will therefore take up positions in space to minimise these repulsions - to be as far apart in space as possible.
What does the shape of a molecule depend on?
Number of Electron Pairs
What is the difference between the black triangle bond symbol and the dashes triangle bond symbol?
Page 138
What is the order of Repulsion Strength for pairs of electrons?
Lone Pair - Lone Pair –> Lone Pair - Bonding Pair –> Bonding Pair - Bonding Pair
Why are the Lone Pair Lone Pair repulsion strengths stronger?
Lone Pairs are held closer to the central nucleus than bonding pairs Lone Pairs are closer to the bonding pairs of the electrons than the bonding pairs are to each other And repel them more strongly Repulsion due to lone pairs causes other bond angles to become smaller
Examples of Molecules that use lone pairs?
NH3 (1 pair) H20 (2 Pairs)
How to distinguish between Polar and Non-Polar Molecules?
If it’s a Hydrocarbon its Non-Polar If the molecule has symmetry, it’s non-polar Polar Molecules have an electronegativity of more than 0.5 Just because a symmetrical molecule is nonpolar doesn’t mean its polar –> Depends on the electronegativity difference If Hydrogen is attached to N, O or F it’s polar
S-O-F rule?
Although S-C is 0 EM C-O is 1 EM Therefore, it’s polar
Why are Molecules of Symmetry non-polar?
The symmetry of the molecules causes the individual dipole moments of the bonds to cancel out.
What is meant by Basic Shape?
The arrangement of the electron pairs around the central atom