Essential Terms

Question 1

Cis-trans isomers (geometric isomers)

Answer 1

Stereoisomers that differ in their cis-trans arrangement on a double bond or on a ring. The dis isomer has a similar group on the same side, and the trans isomer has similar groups on the opposite sides.

Question 2

Constitutional isomers (structural isomers)

Answer 2

Isomers who’s atoms are connected differently; they differ in their bonding sequence.

Question 3

Covalent bonding

Answer 3

Bonding that occurs by the sharing of electrons in the region between two nuclei

Question 4

Single bond

Answer 4

A covalent bond that involves the sharing of one pair of electrons.

Question 5

Double bond

Answer 5

A covalent bond that involves the sharing of two pairs of electrons.

Question 6

Triple bond

Answer 6

A covalent bond that involves the sharing of three pairs of electrons.

Question 7

Degenerate orbitals

Answer 7

Orbitals with identical energies.

Question 8

Delocalized charge

Answer 8

A charge that is spread out over two or more atoms. We usually draw resonance forms to show how the charge can appear on each of the atoms sharing the charge.

Question 9

Dipole moment

Answer 9

A measure of the polarity of a bond or molecule, proportional to the product of the charge separation times the bond length.

Question 10

Electron density

Answer 10

The relative probably of finding an electron in a certain region of space.

Question 11

Electronegativity

Answer 11

A measure of an element’s ability to attract electrons. Elements with higher electronegativities attract electrons more strongly.

Question 12

Electrostatic potential map (EPM)

Answer 12

A computer calculated molecular representation that uses colors to show the charge distribution in a molecule. In most cases, the EPM uses red for high electron density; purple for low electron density.

Question 13

Empirical formula

Answer 13

The ratios of atoms in a compound

Question 14

Formal charges

Answer 14

A method for keeping track of charges, showing what charge would be on an atom in a particular Lewis structure.

Question 15

Hund’s rule

Answer 15

When there are two or more unoccupied orbitals of the same energy, the lowest energy configuration places the electrons in different orbitals with parallel spins rather than in the same orbital with opposite spins.

Question 16

Hybrid atomic orbitals

Answer 16

A directional orbital formed from a combination of ‘s’ and ‘p’ orbitals on the same atom.

Question 17

Ionic bonding

Answer 17

Bonding that occurs by the attraction of oppositely charged ions. Ionic bonding usually results in the formation of a large, three-dimensional crystal lattice.

Question 18

Isotopes

Answer 18

Atoms with the same number of protons but different number of neutrons; atoms of the same element but with different atomic masses.

Question 19

Linear Combination of Atomic Orbitals (LCAO)

Answer 19

Wave functions can add to each other to produce the wave functions of new orbitals. The number of new orbitals generated equals the original number of orbitals.

Question 20

Molecular orbital (MO)

Answer 20

An orbital formed by the overlap of atomic orbitals on different atoms. MOs can be either bonding or antibonding, but only the binding MOs are filled in the most stable molecules.

A bonding MO places a large amount of electron density in the bonding region between the nuclei. The energy of an electron in a bonding MO is lower than it is in an atomic orbital.

An anti bonding MO places most of the electron density outside the bonding region. The energy of an electron in an anti bonding MO is higher than it is in an atomic orbital.

Question 21

Node

Answer 21

Region of space with no electron density

Question 22

Nodal plane

Answer 22

A flat (planar) region of space with zero electron density

Question 23

Stereoisomers

Answer 23

Isomers that differ only in how their atoms are oriented in space.