Chemistry · Structure 2: Models of bonding and structure. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
A covalent bond is the electrostatic attraction between a shared pair of electrons and the nuclei of the two atoms. Atoms usually share enough electrons to reach eight in the outer shell (the octet rule). Sharing two or three pairs gives a double or triple bond. In a coordination bond both shared electrons come from the same atom, as in NH4+.
Shape is found with VSEPR theory: electron domains (bonds and lone pairs) around the central atom repel and move as far apart as possible. Lone pairs repel more than bonding pairs, so they reduce the bond angle.
Covalent substances are either simple molecules held together by weak intermolecular forces, or giant networks of covalent bonds with very high melting points.
Giving the molecular shape as the electron domain geometry. Count lone pairs when you find the domains, but name the shape from the positions of the atoms only.
Answer: Trigonal pyramidal; polar
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