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Glossary of Chapter 1 - Carbon Compounds and Chemical Bonds

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Structural theory
a fundamental theory in chemistry that was developed in the mid-1800s;
two premises underlie the theory:
1) atoms in organic compounds can form a certain, fixed number of bonds, this is known as valency
2) carbon atoms can use one or more of its valences to form bonds to other carbon atoms
Valence
a measure of the number of bonds an atom can form with other atoms in the compound (i.e., carbon is tetravalent, boron is trivalent, etc.)
Isomerism
a property that is shared by many organic compound, molecules with the same molecular formula but different structural formulas
Structural formulas
a formula that shows how the atoms of a molecule are attached to each other
Connectivity
a generic term used to describe the structural arrangement of a compound
Constitutional isomers
different molecules that have the same molecular formula but differ in their connectivity, or the sequence in which their atoms are bonded together
Ionic bond
also called an electrovalent bond; a bond that is formed by the transfer of one or more electrons from one atom to another to form ions; the bond is formed because of the electric attractive force between the positive and negative ions
Covalent bond
a bond that results when atoms share electrons
Electronegativity
a measure of the ability of an atom to attract electrons
Describe the period trend associated with eletronegativity.
Electronegativity increases from left to right across periods and from bottom to top in groups.
Formal charge
a bookkeeping method used to keep track of electrical charges in a molecule; calculated by taking the difference between the number of valence electrons in the free atom and the number of valence electrons in the bonded atom
Resonance theory
a theory that states that whenever a molecule or ion can be represented by two or more Lewis structures that differ only in the positions of the electrons, two things will be true:
1) none of the resonance structures will be a correct representation of the actual molecule
Resonance structures (contributors)
Lewis structures that differ only in the positions of the electrons;
not structures for the actual molecule or ion, they only exist on paper;
allow us to describe molecules and ions for which a single Lewis structure is inadequate
State the main rules for writing resonance structures.
1) resonance structrues exist only on paper
2) in writing resonance structures, we are only allowed to move electrons
3) all structures must be proper Lewis structures
4) the energy of the actual molecule is lower than the energy that might be estimated for any contributing structure
5) equivalent resonance structures make equal contributions to the hybrid
6) the more stable a structure is (by itself), the greater is its contribution to the hybrid
Orbital
a region of space where the probability of finding an electron is large
Wave functions (psi)
a mathematical expression derived from quantum mechanics corresponding to an energy state for an electron, i.e., for an orbital. The square of psi gives the probability of finding the electron in a particular place in space
Aufbau principle
orbitals are filled so that those of lowest energy are filled first
Pauli exclusion principle
a maximum of two electrons may be placed in each orbital, but only when the spins of the electrons are paired
Hund's rule
this rule requires that degenerate orbitals be filled with one electron each before a second can be added to any of them
Heisenberg uncertainty principle
we cannot know simultaneously the position and momentum of an electron
Orbital hybridization
a mathematical approach that involves the combining of individual wave functions for s and p orbitals to obtain wave functions of new orbitals
Sigma bond
a general term applied to those bonds in which orbital overlap gives a bond that is circularly symmetrical in cross section when viewed along the bond axis;
all purely single bonds are sigma bonds
Alkenes
hydrocarbons whose molecules contain a carbon-carbon double bond
Alkanes
hydrocarbons whose molecules contain a carbon-carbon single bond
Alkynes
hydrocarbons whose molecules contain a carbon-carbon triple bond
Pi bond
a bond formed when electrons occupy a bonding pi molecular orbital (i.e., the lower energy molecular orbital that results from overlap of parallel p orbitals on adjacent atoms)
Stereoisomers
isomers that differ only in the arrangement of their atoms in space
cis-
Latin for "on this side"
trans-
Latin for "across"

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