Chem 101 Exam 3 Definitions

lines are used to indicate

bond in the plane of the paper

solid wedges are used to indicate

bonds coming out of the paper, towards the viewer

hatched wedges are used to indicate

bond going back into the paper, away from the viewer

perspective formula

drawn chemical formula used to represent the three-dimensional aspect of of a molecule on paper

• lines

• solid wedges

• hatched wedges

VSEPR

theory used to explain and to predict molecular structure, based on the number and location of lone pairs and the number of electron pairs in bonds around a central atom

VSEPR theory

makes the assumption that a molecule adopts a geometry that moves around the electron pairs as far apart as possible in order to minimize electrostatic repulsion

• intended to give only an initial guess at a molecular structure

• applied to any resonance form

steric number

number of electron groups around the central atom

electron geometry

the arrangement of electron pairs (bonding and lone pairs) around a central atom

molecular geometry

the arrangement of bonded atoms around a central atom

dipole

pair of equal and opposite charges separated by a distance

dipole moment

quantitative measure of the degree of charge separation in a molecule

polar molecules

molecules which possess a dipole moment and would have a definite orientation in an electric field

predicted non-polar if

• all the terminal atoms are identical

• there are no long pairs on the central atom

valence bond theory

theory that explains covalent bonding in terms of overlapped atomic orbitals

• a covalent bond is formed when two atoms, that both have singly occupied orbits, approach one another close enough for the orbitals to overlap

• the electrons with opposite spins pair in the region of overlap

• the electrons are attracted to the nuclei of both atoms and thus bond the atoms together

hybrid orbital

modification of the valence bond theory that is used to describe bonds that are obtained by taking combinations of the atomic orbitals of a single atom

hybridization

accounts for the bond angles in certain molecules that are incompatible with the angles predicted by the simple overlap of s, p, and d orbitals

hybrid theory

bond angles and bond strengths are best understood using this

sp³ hybridization

obtained by taking one 2s orbital with three 2p orbitals to give a total of four sp³ hybridized orbitals

sp² hybridization

obtained by taking one 2s orbital with two 2p orbitals to give a total of three sp² hybridized orbitals.

• one 2p orbital remains non-hybridized

sp hybridization orbitals

obtained by taking one 2s orbital and one 2p orbital to give a total of two sp hybridized orbitals.

• two 2p orbitals remain non-hybridized

pressure of a gas

is the result of molecular collisions

barometer

a device used to measure the pressure of the gases in the atmosphere

manometer

a device used to measure the pressure of gases other than those in the atmosphere

Boyle’s Law

at constant temperature and number of moles, the volume and the pressure of a gas have an inverse relationship. As one increases, the other decreases

Charles’ Law

at constant pressure and number of moles, the volume and the temperature of a gas have a direct relationship

• specifically stated, as the temperature of a gas increases, the volume increases

Avogadro’s Law

at constant pressure and temperature, the volume and the number of moles of a gas are directly proportional

• in other words, as the number of moles of a gas increases, the volume increases

The combined Gas Law

when the number of moles of gas is held constant. Boyle’sLaw and Charles’ Law can be combined to yield an equation

the Ideal Gas Law

Boyle’s Law, Charles’ Law, and Avogadro’s Law can be combined to form a single master equation which described the behavior of gases

R

gas constant, which has a numerical value dependent upon the unit of pressure

Standard Temperature and Pressure (STP)

The conditions of 0 degrees C (273.15 K) and 1 atm (760 mmHg) are referred to as STP