What is ionic bonding?
-The electrostatic forces of attraction between oppositely charged ions
-This is usually formed by electron transfer between metals and nonmetals
-Structure: giant ionic lattice -» repeating 3D arrangement of oppositely charged ions
-Strength: depends on ionic charge and ionic radius:
-Higher charge and smaller ions = stronger attraction
What are the properties of ionic bonding?
-Properties: High mp/bp, conduct electricity when molten or dissolved as ions can move. Does not conduct electricity when solid as ions are not free to move/are fixed in lattice. Often soluble in water
What is metallic bonding?
-The electrostatic forces of attraction between the positive metal ions and delocalised electrons
-Structure: giant metallic lattice
-Strength: depends on no.of protons, delocalised electrons and size of ion
-More protons + delocalised electrons = stronger bond
-smaller ion = stronger bond
What are the properties of metallic bonding?
-Properties: High mp/bp, good conductor of electricity because delocalised electrons can move through structure, insoluble in water. Malleable because layers can slide over each other
What is covalent bonding?
-The electrostatic forces of attraction between the shared pairs of electrons and the nuclei of the (2) bonded atoms
-This is usually formed by a shared pair of electrons between 2 atoms
-Structure: macromolecular (Diamond, Graphite, Silicon Dioxide) and simple molecular (Iodine, Water, Carbon Dioxide, etc)
-Simple molecular = van der waals, permanent dipoles + Hydrogen Bonding
What are the formula of the following ions?
Ammonium = NH₄⁺
Carbonate = CO₃²⁻
Hydroxide = OH⁻
Nitrate = NO₃⁻
Sulphate = SO₄²⁻
Describe the properties of Iodine (Simple Molecular)
-Weak intermolecular forces (vdw forces) between its molecules
-Strong covalent bonds within the 2 Iodine atoms
-Low mp/bp as breaking weak forces not bonds
Describe the properties of Diamond (Macromolecular)
-Each Carbon atom is covalently bonded to 4 others, leaving no free electrons - hence diamond doesn’t conduct electricity and has a high melting point/boiling point
Describe the properties of Graphite (Macromolecular)
-Each Carbon atom is covalently bonded to 3 others in layers of hexagons.
-The layers are held together by weak Van der Waals forces
-The delocalised electrons between layers can move freely and carry charge
-High mp/bp because Strong covalent bonds between carbon atoms require a large amount of energy to break.
Describe the properties of Silicon Dioxide (Macromolecular)
-Each Silicon atom is covalently bonded to 4 oxygen atoms.
-No delocalised electrons or ions so doesn’t conduct electricity
-Very high mp/bp because a large amount of energy is required to break the strong covalent bonds throughout the giant lattice.
What is coordinate bonding?
A coordinate bond is a shared pair of electrons with both electrons donated from one atom
E.g. NH₃+H⁺→NH₄⁺
Nitrogen atom donates a lone pair of electrons to a hydrogen ion (H⁺) to form a coordinate bond
What is electronegativity?
-The power of an atom to pull a pair of electrons in a covalent bond towards itself
What are the trends in electronegativity?
-Increases across a period (nuclear charge ↑, atomic radius ↓)
-Decreases down a group (Shielding ↑, atomic radius ↑)
-Fluorine is the most electronegative, Francium is the least electronegative
What is a polar bond?
A polar bond is an unequal sharing of electrons due to difference in electronegativity ( δ⁺ and δ⁻ dipoles)
What is a non polar bond?
A non polar bond is equal electronegativity; an equal sharing of electrons
How do you determine if a molecule is polar?
A molecule is polar if:
-It has polar bonds (difference in electronegativity) and
-The molecule is asymmetrical (dipole charges don’t cancel)
How do you determine if a molecule is non polar?
A molecule is non polar if:
-All bonds are non polar or
-It’s symmetrical in shape (dipole charges cancel and surrounding atoms around central atom are identical/the same)
What is a key principle in VSEPR?
-Electrons pairs repel and try to get as far apart as possible
-If there are no lone pairs, the electron pairs repel equally
-If there are lone pairs of electrons, then lone pairs repel more than bonding pairs
-lp/lp repulsion > lp/bp repulsion > bp/bp repulsion
What do the number of bonding pairs and lone pairs around the central atom determine?
1) The molecular shape and
2) The bond angles (because lone pairs push bonds closer together)
Which shape has 2 bonding pairs and 0 lone pairs?
-Linear, bond angle = 180 degrees = symmetrical
-Example = BeCl₂
Which shape has 3 bonding pairs and 0 lone pairs?
-Trigonal Planar, bond angle = 120 degrees = symmetrical
-Example = BCl₃
Which shape has 4 bonding pairs and 0 lone pairs?
-Tetrahedral, bond angle = 109.5 degrees = symmetrical
-Example = CH₄
Which shape has 5 bonding pairs and 0 lone pairs?
-Trigonal Bipramidal, bond angle = 120 & 90 degrees = symmetrical
-Example = PF₅
Which shape has 6 bonding pairs and 0 lone pairs?
-Octahedral, bond angle = 90 degrees = symmetrical
-Example = SF₆
