Chemistry - Chapter 8

Key Concepts and Glossary Terms for Chapter 8

What information does a molecular formula provide?

**shows how many atoms of each element a substance contains.**

What representative units define molecular compounds and ionic compounds?

**The representative unit of a molecular compound is a molecule. For an ionic compound, the smallest representative unit is a formula unit.**

**covalent bond**

**a bond formed by the sharing of electrons between atoms**

molecule

**a neutral group of atoms joined by covalent bonds**

**diatomic molecule**

**a molecule consisting of two atoms**

**molecular compound**

**a compound that is composed of molecules**

**molecular formula**

**a chemical formula of a molecular compound that shows the kinds and numbers of atoms present in a molecule of a compound**

**What is the result of electron sharing in covalent bonds?**

**electron sharing usually occurs so that atoms attain the electron configurations of noble gases.**

**How are coordinate covalent bonds different from other covalent bonds?**

**the shared electron pair comes from one of the bonding atoms.**

**What are some exceptions to the octet rule?**

It cannot be satisfied in molecules whose total number of valence electrons is an odd number. There are also molecules in which an atom has less, or more, than a complete octet of valence electrons.

**How is the strength of a covalent bond related to its bond dissociation energy?**

**A large bond dissociation energy corresponds to a strong covalent bond.**

**How are resonance structures used?**

**Chemists use resonance structures to envision the bonding in molecules that cannot be adequately described by a single structural formula.** 

single covalent bond

a bond formed when two atoms share a pair of electrons

structural formula

a chemical formula that shows the arrangement of atoms in a molecule or a polyatomic ion; each dash between a pair of atoms indicates a pair of shared electrons

unshared pair

**a pair of valence electrons that is not shared between atoms**

double covalent bond

a bond in which two atoms share two pairs of electrons

triple covalent bond

a covalent bond in which three pairs of electrons are shared by two atoms

coordinate covalent bond

a covalent bond in which one atom contributes both bonding electrons

polyatomic ion

a tightly bound group of atoms that behaves as a unit and has a positive or negative charge

bond dissociation energy

the energy required to break the bond between two covalently bonded atoms; this value is usually expressed in kJ per mol of substance

resonance structure:

one of the two or more equally valid electron dot structures of a molecule or polyatomic ion

How are atomic and molecular orbitals related?

Just as an atomic orbital belongs to a particular atom, a molecular orbital belongs to a molecule as a whole.

What do scientists use the VSEPR theory for?

In order to explain the three-dimensional shape of molecules, scientists use the valence-shell electron-pair repulsion theory.

In what ways is orbital hybridization useful in describing molecules?

it provides information about both molecular bonding and molecular shape.

molecular orbital

an orbital that applies to the entire molecule

bonding orbital

a molecular orbital that can be occupied by two electrons of a covalent bond

sigma bond (σ bond)

a bond formed when two atomic orbitals combine to form a molecular orbital that is symmetrical around the axis connecting the two atomic nuclei

pi bond (π bond)

a covalent bond in which the bonding electrons are most likely to be found in sausage-shaped regions above and below the bond axis of the bonded atoms

tetrahedral angle

a bond angle of 109.5° that results when a central atom forms four bonds directed toward the center of a regular tetrahedron

VSEPR theory

valence-shell electron-pair repulsion theory; because electron pairs repel, molecules adjust their shapes so that valence electron pairs are as far apart as possible

hybridization

the mixing of several atomic orbitals to form the same total number of equivalent hybrid orbitals

How do electronegativity values determine the charge distribution in a polar bond?

When different atoms bond, the more electronegative atom attracts electrons more strongly and acquires a slightly negative charge.

How do the strengths of intermolecular attractions compare with ionic and covalent bonds?

Intermolecular attractions are weaker than either an ionic or a covalent bond.

Why are the properties of covalent compounds so diverse?

The diversity of physical properties among covalent compounds is mainly because of widely varying intermolecular attractions.

nonpolar covalent bond

a covalent bond in which the electrons are shared equally by the two atoms

polar covalent bond (polar bond)

a covalent bond between atoms in which the electrons are shared unequally

polar molecule

a molecule in which one side of the molecule is slightly negative and the opposite side is slightly positive

dipole

a molecule that has two poles, or regions with opposite charges

van der Waals forces

the two weakest intermolecular attractions—dispersion interactions and dipole forces

dipole interactions

intermolecular forces resulting from the attraction of oppositely charged regions of polar molecules

dispersion forces

attractions between molecules caused by the electron motion on one molecule affecting the electron motion on the other through electrical forces; these are the weakest interactions between molecules

hydrogen bonds

attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom

network solid

a solid in which all of the atoms are covalently bonded to each other