E-Lecture - Important Points
- A chemical bond is the attractive force that binds atoms together to form a molecule (or a crystal lattice), an ionic or metallic crystal lattice.
- An ionic bond is the electrostatic attraction between oppositely charged ions (cations and anions).
- A covalent bond is formed by a shared pair of electrons.
- A covalent bond in which one pair of electrons is shared is known as a single bond; for example, H2 written as H – H.
- Atoms can also share more than one pair of electrons to form a multiple bond.
- The sharing of three pairs of electrons forms a triple bond - for example, N2, written as N≡N.
- A dative or coordinate covalent bond is a bond in which one of the atoms supplies both of the shared electrons to the covalent bond.
- In a covalent bond between atoms of different electronegativity, electrons are displaced toward the atom with the higher electronegativity. In terms of electronegativity differences chemical bonds vary over the range: non-polar to polar covalent to ionic.
- Inter-molecular forces are forces of attraction between covalently bonded molecules. These include: London forces, dipole-dipole forces, and hydrogen bonding.
- London forces are forces of attractions between non-polar molecules.
- Dipole-dipole forces are the attractions between dipoles of polar molecules.
- Hydrogen bonding is the attraction of covalently bonded hydrogen to lone pairs on N, O, or F atoms in other molecules or in the same molecule (if the molecule is large enough)
- Molecular geometry is determined by the spatial orientations of the atomic orbitals involved in bonding.
- The VB method often requires that bonding atomic orbitals be hybridized in order to rationalize known structures of molecules. A hybridized orbital is some combination of s, p and d orbitals, such as sp, sp2, sp3.
- The geometric distribution of hybridized orbitals in the valence bond method is the same as the electron set geometry proposed by VSEPR theory.
- Hybrid orbitals overlap in the usual way (end-to-end) and form σ bonds. Unhybridized p orbitals overlap in a side-by-side manner and give rise to π bonds. A double bond consists of one σ bond and one σ bond; a triple bond, one σ bond and two π bonds.
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