Chemistry: The Central Science Chapter 8

Ionic Bonds

electrostatic Forces that exist between ions of opposite charge

Covalent Bonds

result from sharing of electrons by two atoms

-electrons may not be shared equally between two atoms

Metallic Bonds

bind together atoms in metals

Lewis Symbols

electrondot symbols that represent the valence electrons of an atom

Octet rule

the tendencies of atoms to gain, lose, or share the valence electrons often follow this rule. Which can be viewed as an attempt by atoms to achieve a noble-gas configuration.

Lattice energy

measures the magnitude of attraction, it is the energy needed to separate an ionic lattice into gaseous ions.

*Lattice energy increases with increasing charge on the ions and with decreasing distance between the ions (closer the ions, the stronger the charge)

Born-Haber

cycle is a useful thermochemical cycle in which we use Hess's law to calculate the lattice energy as the sum of several steps in the formation of an ionic compound.

Lewis Structures

indicate how many valence electrons are involved in forming bonds and how many remain as unshared electron pairs.

Single bond

the sharing of one pair of electrons

Double / triple bonds

the sharing of two or three pairs of electrons between two atoms (4 or 6 electrons) (Double / triple bonds are examples of multiple bonding between atoms)

Bond polarity

helps describe unequal sharing of electrons in a bond. (Covalent Bonds)

Nonpolar covalent bond

the electrons in the bond are shared equally by the two atoms

Polar covalent bond

one of the atoms exerts a greater attraction for the electrons than the other.

Electronegativity

is a numerical measure of the ability of an atom to compete with other atoms for the electrons shared between them. (Fluorine=most electronegative element) (Electronegativity values range from .7 for Cs and 4.0 for F)

Electronegativity trend

electronegativity generally increases from left to right in a row, and decreases going down a column in the periodic table

Polar molecule

one whose centers of positive and negative charge do not coincide

Formal charge

for each atom it is the charge that the atom would have if all atoms had the same electronegativity.

(determined after Lewis structure is drawn)

Exceptions to the octet rule

1. a molecule has an odd number of electrons

2. it is not possible to complete an octet around an atom without forcing an unfavorable distribution of electrons

3. a large atom is surrounded by so many small electonegative atoms that it must have more than an octet of electrons around it. (octet is expanded with d orbitals)

Bond enthalpy

measures the strength of a covalent bond, it is the molar enthalpy change upon breaking a particular bond

(strengths of covalent bonds increase with the number of electron pairs shared between two atoms)

Bond length

between two bonded atoms is the distance between two nuclei. The average bond length between two atoms decreases as the number of bonds between the atoms increases.