Topic 4: Chemical Bonding and Structure
4.1 Ionic Bonding and Structure
Octet rule
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Electrons tend to lose, gain or share electrons in order to acquire a noble gas core electron configuration.
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Ions​
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Cation: an atom that lost electrons and is positively charged.
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Anion: an atom that gained electrons and is negatively charged.
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Definition: The electrostatic attraction between oppositely charged ions.
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Conditions:
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Formed when one or more electrons are transferred from one atom to another. Atoms are either oxidized (loses electrons) or reduced (gains electrons).
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Under normal conditions ionic compounds are typically solids and have a lattice type structure, as shown bellow.
Physical proprieties ​
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High melting and boiling points
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Low volatility
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Only conduct electricity when molten or in aqueous solution
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Dissolve in polar solvents
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Common molecules
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Ammonium:

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Hydroxyl:

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​Nitrate:

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Hydrogen carbonate:

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Carbonate:

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Sulphate:

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Phosphate:

4.2 Covalent Bonding
​Bonds
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Definition: Electrostatic attraction between a shared pair of electrons and the positively charged nuclei.​
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Single bond: a bond that has only one pair of shared electrons.
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Double bond: a bond that has two pairs of shared electrons.
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Triple bond: a bond that has three pairs of shared electrons.
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Bond length: Triple<Double<Single
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Bond strength Single<Double<Triple
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Electronegativity: The relative attraction that an atom of an element has for the shared pair of electrons.
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Bond Polarity: Due to the difference in the electronegativity of the atoms in a bond.
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Important: Bond polarity should not be mixed with molecular polarity!!!
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Microwave:​ Water molecules absorb microwave radiation and constantly change their orientation to align with the waves, thus heating the food.
Bond polarity/character in relation to electronegativity​


4.3 Covalent Structures
Lewis (electron dot) structure
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Representation of molecules
​Valence shell electron pair repulsion (VSEPR theory)
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Used to deduce the shape of covalent molecules
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Molecular geometry
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Linear
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number of domains:​ 2
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Bond angle:
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Shape:
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examples:
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​Valence shell electron pair repulsion (VSEPR theory)
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Used to deduce the shape of covalent molecules
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Molecular geometry
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Linear
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number of domains:​ 2
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Bond angle:
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Shape:
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examples:
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Trigonal planar
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number of domains:​ 3
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Bond angle:
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Shape:
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examples:
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V-shaped (bent)
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number of domains:​ 3
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Bond angle:
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Shape:
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examples:
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Tetrahedral
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number of domains: 4​
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Bond angle:
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Shape:
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examples:
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Trigonal pyramidal
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number of domains:​ 4
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Bond angle:
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Shape:
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examples:
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V-shaped (bent)
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number of domains:​ 4
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Bond angle:
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Shape:
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examples:
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Resonance structures
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A molecule that has the same atom arrangement but different electron arrangement.
Note: Molecules may have the same V-shaped (bent) shape however may have different number of domains!
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Molecular polarity
Using vectors and the atom structure we have:​


Allotropes
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Molecules that have the same molecular formula but different molecular structures
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Examples: Oxygen gas ( ) and ozone ( )


- Carbon allotropes:
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Graphite​
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Covalent bonds​
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layered structure
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London Forces between layers
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Diamond
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Covalent bonds​
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tetrahedral structure
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Graphene
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Covalent bonds​
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2 dimensional crystal
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One single layer
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C 60 Fulerene
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Molecular structure​
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Spherical (buckyballs, soccer ball shape) structure
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Note: You should be able to compare and contrast the carbon allotropes.
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Coordinate covalent bond
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When a shared pair of electrons comes from a single atom
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Example:
Silicon dioxide, sio2
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Giant lattice structure of SiO4 arrays
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High melting and boiling point
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As shown bellow each Si atom (Black) bonds with 4 O atoms (Red)
Exceptions to the octet rule
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There are few exceptions to the octet rule
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Examples:
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4.4 Covalent Structures
van der Waals forces= London forces +Dipole-Dipole forces
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Order of strength
​London Forces< Dipole-Dipole Forces<Hydrogen Bonds
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London Forces
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Dispersion forces of instantaneous induced dipole-induced dipole forces
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Even though the molecules are non-polar, one part of the molecule at a given instant of time has a slightly bigger electron density than the other part
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Factors that affect London Forces:
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Number of electrons:​ more electrons lead to more polarization
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Shape of the molecule: the bigger the carbon chain, the bigger the boiling point ( this is further explained in Topic 10)
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size (volume) of the electron cloud: the bigger the size, the smaller the attraction, therefore the bigger the polarization.​
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Dipole-Dipole forces
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​Permanent dipole forces
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Hydrogen Bonds
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The attraction between hydrogen and a pair of non-bonding electrons of F, O or N
4.5 Metallic Bonding
Lattice that consists of positive ions and surrounded by a "sea" of electrons
Proprieties:
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High electric conductivity
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High thermic conductivity
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High melting and boiling points
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Solid at Standard conditions (Exception: Hg)
Factors that affect the strength:​
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Number of Valence electrons
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Charge of metal ions
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ionic radius of ions
Alloys
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2 or more metals in the bond (there may be non-metals like carbon)
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Brass = copper + zinc​
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Steel = iron + carbon + tungsten and others
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Dental amalgaman: mercury + zinc + tin
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Harmful ​
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