M2, B3 Bonding And Structure
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What is ionic bonding
A strong electrostatic force of attraction between oppositely charged ions
What is an ion
A charged species
Give the NAME and charge of the ions of the following: Potassium Nitrogen Bromine Calcium Phosphorus
Potassium= k+= potassium Nitrogen= N-3 = Nitride Bromine= Br-= bromide Calcium= Ca2+= calcium Phosphorus= P3-= phosphide
Give the charges and valences of the following complex ions: Nitrate Carbonate Sulfate Ammonium
Nitrate= NO3-, -1 valency Carbonate= CO3 2-, -2 valency Sulfate= SO4 2-, -2 valency Ammonium= NH4 +, +1 valency
Ionic compounds: high or low melting point?
Very high because a lot of energy is needed to overcome the strong electrostatic forces of attraction between oppositely charged ions.
Why are ionic compounds usually soluble in water?
Water is polar so the lattice of the ionic compound is broken down because the opposite charged ions are attracted to water molecules
What is a covalent bond
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
How is the direction of electrostatic attraction different in covalent vs ionic bonds?
Ionic bonds- all directions Covalent bonds- directional (only acts between the two atoms)
What are DATIVE covalent (coordinate) bonds?
When both (2) electrons are donated by only one of the atoms in the bond. E.g- NH3 + H = NH4 +
The shapes of molecules is determined by considering the valence shell electron pair repulsion theory. What does this say we need to consider when determining the shape of molecules? (3)
The number and type of electron pairs around the central atom. Electron pairs repel each other- they end up as far apart as possible. Lone pairs of electrons repel more than bonded pairs.
What is the molecular shape when there are 2 bonded pairs and 0 lone pairs?
Linear — bond angle 180° Examples: BeCl₂, BeF₂, CO₂
What is the molecular shape when there are 3 bonded pairs and 0 lone pairs?
Trigonal planar — bond angle 120° Examples: BF₃
What is the molecular shape when there are 4 bonded pairs and 0 lone pairs?
Tetrahedral — bond angle 109.5° Examples: CH₄, CCl₄, SiCl₄
What is the molecular shape when there are 3 bonded pairs and 1 lone pair?
Pyramidal — bond angle ≈107° Examples: NH₃, PF₃, NCl₃
What is the molecular shape when there are 2 bonded pairs and 2 lone pairs?
Non-linear (bent or V-shaped) — bond angle ≈104.5° Examples: H₂O, OF₂
What is the molecular shape when there are 6 bonded pairs and 0 lone pairs?
Octahedral — bond angle 90° Examples: SF₆
Why is the bond angle in NH₃ smaller than in CH₄?
Because lone pairs repel more strongly than bonding pairs, reducing the angle from 109.5° to 107°. (-2.5)
Why is H₂O’s bond angle smaller than NH₃’s?
H₂O has two lone pairs, which push bonding pairs closer together — decreasing the bond angle to about 104.5°. (-2.5)
Explaining the shape and angle of molecules. What is the general questions to ask when writing an answer? (5)
• How many bond pairs are there? • How many lone pairs are there? • Is there equal repulsion of bonding pairs? • Is there lone pairs that repel more? • So what would the bond angle be?
What is electronegativity?
The ability of an atom to attract electrons to itself in a covalent bond. Electronegativity increases across a period and UP a group, so Flourine is the most electronegative element (all group 8 elements are stable)
Non polar molecules: How are electrons shared, and why is this?
Electrons are shared equally between 2 atoms because the atoms have the same electronegativity. E.g- Cl-Cl H-H O=O I-I C-H
Polar molecules: How are electrons shared, and why is this?
Electrons are shared unequally because one atom has a greater electronegativity than the other one. This pulls the shared electrons closer to one of the atoms, creating a dipole (slight charge).
How does the size of electronegativity difference determine the bond type?
-If the difference is large, the bond is ionic (electronegativity increases across a group, a bond with a group 1 or 2 with a group 6 or 7 will mean a large electronegativity difference). -If the difference is small the bond will be covalent.
Define intermolecular forces of attraction
Forces of attraction that exist BETWEEN molecules. they only occur in simple molecular structures