Chapter 8 (Chemistry).

Dipolar molecule/dipole.

* Some regions of a polar molecule are slightly negative and some are slightly positive. A molecule that has two poles is called a dipolar molecule/dipole. When polar molecules are placed in an electric field, they all line up with the same orientation in relation to the charged plates.

Two properties of molecular compounds.

- Low melting and boiling points. - Exist as gases or liquids at room temperature.

Double and Triple Covalent Bonds.

A chemical bond formed when atoms share two pairs of electrons is called a double bond. A chemical bond formed when atoms share three pairs of electrons is called a triple bond.

Nonpolar covalent bond.

A covalent bond between atoms in which the electrons are shared equally.

Polar covalent bond.

A covalent bond between atoms in which the electrons are shared unequally.

Covalent Bond.

A covalent bond is a bond formed when two atoms share electrons.

Molecular formula.

A molecular formula shows the types and numbers of atoms present in a molecule. A molecular formula does now show the arrangement of the atoms in a molecule.

Diatomic molecule.

A molecule consisting of two atoms.

Molecule.

A neutral group of atoms joined together by covalent bonds.

Single Covalent Bonds.

A shared pair of electrons is represented by a single dash.

Octet Rule.

Atoms require the electron configurations of noble gases.

Bond Dissociation Energy.

Bond dissociation energy is the energy required to break the bond between two covalently bonded atoms. Molecules with high bond dissociation energies are relatively unreactive.

Why does the chlorine atom in hydrogen chloride acquire a slightly negative charge?

Chlorine has a higher electronegativity than hydrogen, and, therefore, attracts the bonding electrons slightly away from hydrogen.

Molecular Compounds.

Compounds that are formed when two or more atoms combine to form molecules.

Bond Polarity.

Covalent bonds differ in the way electrons are shared by the bonded atoms, depending on the kind and number of atoms joined together. Nonpolar bond (equally shared) Polar bond (unequally shared)

Dipole interactions.

Dipole interactions occur when polar molecules are attracted to one another.

Dispersion forces.

Dispersion forces (weakest of all molecular interactions) are caused by the motion of electrons. Dispersion forces generally increase in strength as the number of electrons in a molecule increases. The strongest of the intermolecular forces are hydrogen bonds.

Note.

If the electronegativity difference (usually called DEN) is less than 0.5, then the bond is nonpolar covalent. If the DEN is between 0.5 and 1.6, the bond is considered polar covalent If the DEN is greater than 2.0, then the bond is ionic. http://www.tutor-homework.com/Chemistry_Help/electronegativity_table/electronegativity.html

How do intermolecular attractions compare with ionic and covalent bonds?

Intermolecular attractions are weaker than either ionic or covalent bonds.

Coordinate Covalent Bonds.

It is a covalent bond in which one atom contributes both bonding electrons.

Unshared pair.

Lone pair, nonbonding pair.

What is the arrangement of atoms within a molecule called?

Molecular Structure.

Polar molecule.

One end of the molecule is slightly negative and the other end is slightly positive.

Hybrid Orbitals.

Orbital hybridization occurs when several atomic orbitals mix to form the same total number of equivalent hybrid orbitals.

Structural Formula.

Represents the covalent bonds by dashes and shows the arrangement of covalently bonded atoms.

Note:

The effect of polar bonds on the polarity of an entire molecule depends on the shape of the molecule and the orientation of the polar bonds.

What determines the physical properties of a compound?

The physical properties depend on the type of bonding in the compound.

va der Waals forces.

The two weakest attractions between molecules.

VSEPR Theory.

The valence-shell electron-pair repulsion theory states that because electron pairs repel, molecular shape adjusts so the valence-electron pairs are as far apart as possible.

Resonance structures.

They are structures that occur when it is possible to write two or more valid electron dot formulas that have the same number of electron pairs of a molecule or ion.

What happens to polar molecules between a pair of oppositely charged metal plates.

When polar molecules are placed between oppositely charged plates, they tend to become oriented with respect to the positive and negative plates.

Molecular orbital.

When two atoms combine, their atomic orbitals overlap to produce orbitals that apply to the entire molecule.

Types of models/formulas.

a. ball and stick model. b. molecular formula. c. perspective drawing. d. space-filling molecular model. e. structural formula.