Electrons shared between two atoms in a covalent bond.
The number of electron pairs involved in a covalent bond. In terms of
Molecular Orbital theory
, it is the
bonding electron pairs minus the number of antibonding electron pairs. Greater
bond order means greater bond strength and shorter bond length.
The phenomenon in which carbon, usually tetravalent, can form a trivalent
species with a positive charge. Such a carbon atom is extremely unstable due to
its lack of an octet, but its reactivity makes it a source of a great deal of
fascinating chemistry that will be discussed in later sections.
Interaction between atoms held together by the sharing of electrons.
A method of keeping track of the movements of pairs of electrons during
chemical reactions. Uses double-headed arrows to denote movement of
electrons from source to destination.
The phenomenon in which electrons in some molecules are not fixed to specific
atoms or bonds but are spread out over several atoms or bonds. Delocalization
is an energetically favorable process: by distributing charge over a greater
volume, the net energy of the molecule is lowered, resulting in resonance
The presence, in a bond or molecule, of a positive end and a negative end.
The measure of the polarity of a molecule. Higher dipole moments are accorded
polar molecules. Not all molecules with dipolar bonds have dipole moments: the
moment is dependent on both orientation and magnitude of dipolar forces; it is
possible for the dipolar forces of a molecule to cancel each other out,
resulting in a molecule with no significant dipole moment.
The relative tendency for an atom to attract electrons to itself. Measured
on an arbitrary scale of 4.0, with fluorine being the most electronegative
element. Electronegativity increases from left to right across the periodic
table and decreases as you move down a group.
An accounting scheme that estimates the charge on an atom. The formal
charge is calculated by subtracting the number of lone electrons and half
the number of bonded electrons from the group number.
Lewis Dot structure
A common way to represent molecules, it uses lines to depict bonded electron
pairs and dots to represent lone pairs. Inner-shell electrons are
Electrons in the valence shell of an atom that don't participate in
A collection of atoms held together by covalent bonds.
The cardinal rule of bonding. The octet rule states that atoms gain
when they have a full complement of 8 electrons in their valence
Polar covalent bond
A covalent bond between atoms of differing electronegativities such that
one atom has a partial positive charge and the other has a partial
The weighted average of several resonance structures that gives a composite
view of the electronic structure of a molecule.
Because resonance allows for delocalization, in which the overall energy of
a molecule is lowered since its electrons occupy a greater volume, molecules
that experience resonance are more stable than those that do not. These
molecules are termed resonance stabilized.
One of several Lewis structures that can be drawn for a given atomic
connectivity. Each resonance structure contributes an aspect of the
The number of bonds an atom typically forms. Carbon is tetravalent,
nitrogen is trivalent, oxygen is divalent, and hydrogen/halogens are
The electrons in the outermost energy shell of an atom. The configuration of
these electrons determine the chemical properties of the element.
The highest energy shell in an atom. All interactions between atoms take
place through the electrons of the valence shell.