Octet rule

• Electrons tend to lose, gain or share electrons in order to acquire a noble gas core electron configuration.

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Ions​

• Cation: an atom that lost electrons and is positively charged.

• 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:

• Formed when one or more electrons are transferred from one atom to another. Atoms are either oxidized (loses electrons) or reduced (gains electrons).

• Under normal conditions ionic compounds are typically solids and have a lattice type structure, as shown bellow.

Physical proprieties ​

• High melting and boiling points

• Low volatility

• Only conduct electricity when molten or in aqueous solution

• Dissolve in polar solvents 

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Common molecules

• Ammonium:

• Hydroxyl:

• ​Nitrate:

• Hydrogen carbonate:

• Carbonate:

• Sulphate:

• Phosphate:

​Bonds

• Definition: Electrostatic attraction between a shared pair of electrons and the positively charged nuclei.​

• Single bond: a bond that has only one pair of shared electrons.

• Double bond: a bond that has two pairs of shared electrons.

• Triple bond: a bond that has three pairs of shared electrons.

• Bond length: Triple<Double<Single

• Bond strength Single<Double<Triple

• Electronegativity: The relative attraction that an atom of an element has for the shared pair of electrons.

• Bond Polarity: Due to the difference in the electronegativity of the atoms in a bond.

• Important: Bond polarity should not be mixed with molecular polarity!!!

• 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​

Lewis (electron dot) structure

• Representation of molecules

​Valence shell electron pair repulsion (VSEPR theory)

• Used to deduce the shape of covalent molecules

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Molecular geometry

• Linear

  • number of domains:​ 2

  • Bond angle: 

  • Shape:

  • examples:

​Valence shell electron pair repulsion (VSEPR theory)

• Used to deduce the shape of covalent molecules

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Molecular geometry

• Linear

  • number of domains:​ 2

  • Bond angle: 

  • Shape:

  • examples:

• Trigonal planar

  • number of domains:​ 3

  • Bond angle:

  • Shape:

  • examples:

• V-shaped (bent)

  • number of domains:​ 3

  • Bond angle:

  • Shape:

  • examples:

• Tetrahedral

  • number of domains: 4​

  • Bond angle:

  • Shape:

  • examples:

• Trigonal pyramidal

  • number of domains:​ 4

  • Bond angle:

  • Shape:

  • examples:

• V-shaped (bent)

  • number of domains:​ 4

  • Bond angle:

  • Shape:

  • examples:

Resonance structures

• 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

• Molecules that have the same molecular formula but different molecular structures

• Examples: Oxygen gas (      ) and ozone (      )

• Carbon allotropes:

  • Graphite​

    • Covalent bonds​

    • layered structure

    • London Forces between layers

• ​

  • Diamond

    • Covalent bonds​

    • tetrahedral structure

• ​

  • Graphene

    • Covalent bonds​

    • 2 dimensional crystal

    • One single layer

• • C 60 Fulerene

    • Molecular structure​

    • Spherical (buckyballs, soccer ball shape) structure

Note: You should be able to compare and contrast the carbon allotropes.

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Coordinate covalent bond

• When a shared pair of electrons comes from a single atom

• Example: 

Silicon dioxide, sio2

• Giant lattice structure of SiO4 arrays

• High melting and boiling point

• As shown bellow each Si atom (Black) bonds with 4 O atoms (Red)

Exceptions to the octet rule

• There are few exceptions to the octet rule

• Examples:

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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

• Dispersion forces of instantaneous induced dipole-induced dipole forces

• 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

• Factors that affect London Forces:

  • Number of electrons:​ more electrons lead to more polarization

  • Shape of the molecule: the bigger the carbon chain, the bigger the boiling point ( this is further explained in Topic 10)

  • 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

• ​Permanent dipole forces

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Hydrogen Bonds

• The attraction between hydrogen and a pair of non-bonding electrons of F, O or N

Lattice that consists of positive ions and surrounded by a "sea" of electrons

Proprieties:

• High electric conductivity

• High thermic conductivity

• High melting and boiling points

• Solid at Standard conditions (Exception: Hg)

Factors that affect the strength:​

• Number of Valence electrons

• Charge of metal ions

• ionic radius of ions

Alloys

• 2 or more metals in the bond (there may be non-metals like carbon)

  • Brass = copper + zinc​

  • Steel = iron + carbon + tungsten and others

  • Dental amalgaman: mercury + zinc + tin

    • Harmful ​