Topic 4/14: Bonding Flashcards
Define volatility.
The tendency of a substance to vaporize
Define ionic bond.
- Electrostatic attraction between oppositely charged ions
- Only occurs between metals (positive charge) and non-metals (negative charge)
- Forms a neutral lattice
Outline physical properties of ionic compounds
- Low volatility (low tendency to vaporize)
- High melting temperatures
- Conduct electricity in molten state (freely moving ions)
- Soluble in polar substances
Define covalent bond.
- Electrostatic attraction between a shared pair of electrons and the positively charged nucleus
- Generally occur between non-metals
- Atoms with similar EN are likely to form a covalent bond (same affinity for electrons, no tendency to donate electrons)
Outline the strengths of electron repulsion.
Lone pair - lone pair > lone pair - bonding pair > bonding pair - bonding pair
Describe properties of diamond.
- Each carbon atom is joined to four other carbon atoms ➜ Giant covalent structure
- Tetrahedral structure held by strong covalent bonds
- High MP
- No delocalized electrons ➜ Low conductivity
- 109 angle
Describe properties of C60 fullerene.
- Sphere made of atoms arranged in a hexagon
- Covalent bonding and London dispersion forces
- Each carbon atom attached to three others
- Delocalized electrons ➜ Good conductivity
- 109~120 angles
Define sigma bonds.
Formed by the head-on overlap of orbitals
Define pi bonds.
Formed by the sideway overlap of adjacent p-orbitals
Formal charge equation
FC = V - (1/2B + L)
- V=Valence electron
- B=bonding electrons
- L=lone pair electrons
Define hybridization.
- A hybrid orbital results because of the mixing of different types of atomic orbitals on the same atom
- Four electron domains: sp3
- Three electron domains: sp2
- Two electron domains: sp
Outline characteristics of a polar molecule.
- Asymmetrical
- Polarities of polar bonds cannot cancel each other
Outline characteristics of non-polar molecules.
- Symmetrical
- Polarities of polar bonds can cancel each other
Define metallic bonding.
Electrostatic attraction between a lattice of positive ions and the delocalized sea of electrons
Outline the characteristics of metals.
- Malleable (layers of metals can slide over each other without breaking bonds)
- Ductile
- Good conductors of heat and electricity (delocalized electrons)
- Low EN values: lose electrons easily to form positive ions
Describe characteristics of alloys.
- Contain more than one metal
- Stronger due to disturbance of the regular network of positive ions
- Atoms of different sizes ➜ Difficult for layers of positive ions to slide over each other
Define cations.
Atoms that lose electrons and have a positive net charge (Positive ions)
Define anions.
Atoms that gain electrons and therefore have a negative net charge (negative ions)
Define bond length.
- Distance between two bonded nuclei
- Decreases as the number of electron pairs increases because there is a greater attractive force between the two nuclei
Define bond strength.
- The energy required to break the bond, described in terms of bond enthalpy
- Increases as the number of electron pairs increases, as more energy is required to break them
Define covalent compounds.
Formed when two or more non-metal atoms bond by sharing valence electrons
Define octet rule.
The tendency of atoms to gain a valence shell with a total of 8 electrons
Which atom is the central atom in a Lewis structure?
The atom with the lowest EN, furthest away from fluorine
Which atoms are exceptions to the octet rule?
- Boron
- Beryllium
- Elements in period 3 and below may expand octets by using d-orbitals in their valence shell
Name molecules with 2 electron domains.
2 BP, 0 LP ➜ Linear, 180 angle
Name molecules with 3 electron domains.
- 3 BP, 0 LP ➜ Trigonal planar, 120 angle
- 2 BP, 1 LP ➜ Bent, 117 angle
Name molecules with 4 electron domains.
- 4 BP, 0 LP ➜ Tetrahedral, 109.5 angle
- 3 BP, 1 LP ➜ Trigonal pyramidal, 107 angle
- 2 BP, 2 LP ➜ Bent, 104.5 angle
Name molecules with 5 electron domains.
- 5 BP, 0 LP ➜ Trigonal bipyramidal, 90 and 120 angles
- 4 BP, 1 LP ➜ See-saw, 90 and 117 angles
- 3 BP, 2 LP ➜ T-shaped, 90 angle
Name molecules with 6 electron domains.
- 6 BP, 0 LP ➜ Octahedral, 90 angle
- 5 BP, 1 LP ➜ Square pyramidal, 90 angle
- 4 BP, 2 LP ➜ Square planar, 90 angle
Describe simple covalent structures.
- A few atoms held by strong covalent bonds
- Weak intermolecular forces ➜ Low BP, liquid or gaseous state
- No free electrons/overall charge ➜ non-conductive
Describe giant covalent structures.
- Contain a lot of non-metal atoms joined by covalent bonds
- Arranged into giant regular lattices
- Involves many bonds ➜ Strong structures
- Strong covalent bonds ➜ High MP
Describe properties of graphite.
- Hexagonal layer structure
- Strong covalent bonds between carbon atoms in each layer
- Weak Van Der Waals forces between the layers ➜ Layers slide over easily
- Delocalized electrons between layers ➜ Good conductivity
- 120 angle
What is the difference between intermolecular forces and intramolecular forces?
- Intermolecular: forces between molecules
- Intramolecular: force between atoms (ionic and covalent)
Describe the three intermolecular forces.
London Dispersion
- Weakest
- Temporary dipoles
Dipole-Dipole
- Dipole: molecule with both positive and negative regions
- Positive side of a polar molecule attracts negative side of another polar molecule
- Strength depends on distance and orientation
Hydrogen bonds
- Strongest
- Attraction between partial positive hydrogen on one molecule and partial negative atom on another molecule
- NOF: nitrogen, oxygen, fluorine
Describe properties of metals.
- Good conductors of heat and electricity
- Highest conductivity when aqueous or melted
- Malleable
- Ductile
- Low EN ➜ lose electrons easily to form positive ions
