Question 1

Exceptions to the Octet Rule

Accepted Answer

Hydrogen can only have two valence electrons. Lithium and beryllium, which bond to attain to and four valence electrons, respectively. Boron, which bonds to attain six. Elements beyond the second row can expand their octets to include more than eight electrons by incorporating d orbitals.

Question 2

Ionic Bonding

Accepted Answer

An electron(s) from an atom with a smaller ionization energy is transferred to an atom with a greater electron affinity, and the resulting ions are held together by electrostatic forces.

Question 3

Ionic Compounds

Accepted Answer

High melting and boiling points due to the strong electrostatic forces between ions. Can conduct electricity in the liquid and aqueous states, though not in the solid state. Ionic solids form crystal lattices consisting of arrays of positive and negative ions in which the attractive forces between ions of opposite charge are maximized, while the repulsive forces between ions of like charge are minimalized.

Question 4

Covalent Compounds

Accepted Answer

Contain discrete molecular units with weak intermolecular forces. Consequently, they are low-melting solids and do not conduct electricity in the liquid or aqueous state.

Question 5

Bond Order

Accepted Answer

Number of shared electron pairs between two atoms.

Question 6

Bond Length

Accepted Answer

The average distance between the two nuclei of the atoms involved in the bond. As the number of shared electron pairs increases, the two atoms are pulled closer together, leading to a decrease in bond length. Thus, for a given pair of atoms, a triple bond is shorter than a double bond, which is shorter than a single bond.

Question 7

Bond Energy

Accepted Answer

Energy required to separate two bonded atoms. For a given pair of atoms, the bond energy increases as the number of shared electron pairs increases.

Question 8

Formal Charge

Accepted Answer

The of electrons officially assigned to an atom in a Lewis structure does not always = the of valence electrons of the free atom. THsi difference between these 2 numbers is the formal charge. FC = V-1/2Nbonding - Nnonbonding ``` V = number of valence electrons in atom. Nbonding = number of bonding electrons Nnonbonding = number of nonbonding electrons ``` The formal charge of an ion or molecule is equal to the sum of the formal charges off all the atoms.

Question 9

Resonance Major Contributor

Accepted Answer

A Lewis structure with small or no formal charges is preferred over a Lewis structure with large formal charges. A Lewis structure in which negative formal charges are placed on more electronegative atoms is more stable than one in which the formal charges are placed on less electronegative atoms.

Question 10

Dipole Momenet

Accepted Answer

A vector quantity, defined as the product of the charge magnitude and the distance between the two partial charges. Measured in Debye units.

Question 11

Coordinate Covalent Bond

Accepted Answer

The shared electron pair comes from the lone pair of one of the atoms in the molecule. Once such a bond forms, it is indistinguishable from any other covalent bond. Distinguishing such a bond is useful only in keeping track of the valance electrons and formal charges. Coordinate bonds are typically found in Lewis acid-base compounds. A Lewis Acid is a compound that can accept an electron pair to form a covalent bond. A Lewis base is a compound that can donate an electron pair to form a covalent bond.

Question 12

VSEPR Theory

Accepted Answer

The valence shell electron-pair repulsion theory uses Lewis structures to predict the molecular geometry of covalently bonded molecules. It states that the 3-D arrangement of atoms surrounding a central atom is determined by the repulsions between the bonding and the nonbonding electron pairs in the valence shell of the central atom. These electron pairs arrange themselves as far apart as possible, thereby minimizing repulsion.

Question 13

VSEPR Theory: Steps

Accepted Answer

The following steps are used to predict geometrical structure of a molecule. 1) Draw Lewis structure of molecule. 2) Count the total number of bonding and nonbonding electron pairs in the valence shell of the central atom. 3) Arrange the electron pairs around the central atom so that they are as far apart from each other as possible. For example, the compound AX2 has the Lewis structure X:A:X. A has two bonding electron pairs in its valence shell. To make these electron pairs as far apart as possible, their geometric structure should be linear. X-A-X Study page 353 for other shapes.

Question 14

Valence Electron Arrangements

Accepted Answer

Linear 2 Regions of Electron Density Ex) BeCl2 180 Degree Angle Between Electron Pairs Trigonal Planar 3 BH3 120 Degrees Tetrahedral 4 CH4 109.5 Degrees Trigonal Bipyramidal 5 PCl5 90, 120, 180 Degrees Octahedral 6 SF6 90, 180 Degrees

Question 15

Polarity of Molecules

Accepted Answer

Polarity of a molecule depends on the polarity of the constituent bonds and on the shape of the molecule. A molecule with nonpolar bonds is always nonpolar, a molecule with polar bonds may be polar or nonpolar depending on the orientation of the bond dipoles. A molecule of two atoms bound by a polar bond must have a net dipole moment and therefore be polar. The two equal and opposite partial charges are localized at the ends of the molecule on the two atoms. A molecule consisting of more than two atoms bound with polar bonds may be either polar or nonpolar, since the overall dipole moment of a molecule is the vector sum of the individual bond dipole moments. If the molecule has a particular shape such that the bond dipole moments cancel each other, then the result is a nonpolar molecule. For example, CCl4 has a tetrahedral shape. The four bond dipoles point to the verticies of the tetrahedron and cancel each other, resulting in a nonpolar molecule. However, if the orientation of the bond dipoles are such that they do not cancel out, the molecules will have a net dipole moment and be polar. For example, H2O has two polar O-H bonds. Its shape is angular. The two dipoles add together to give a net dipole moment to the molecule, making it polar.

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