Chemistry LearnSmart Chapter 10 - CH 125

Statements describing how to draw a Lewis Structure.

- An electron is added to the total count for each negative charge on the species. - A Lewis structure includes all the valence electrons in the species - A single bond contains two electrons and is represented by a solid line. .

Statements correctly describing how to determine molecular shape using the VSEPR model.

-Count only the bonding electrons around the central atom. -The total number of shared and unshared electron pairs around the central atom gives the electron-group arrangement. -Use the molecular formula to draw the Lewis Structure.

Describe the effect of molecular polarity on the behavior of a molecular compound.

-The physical properties of a molecular compound are directly related to molecular polarity. -A polar compound will experience stronger intermolecular forces than nonpolar compound.

Describe the bonding and geometry in the anion SeCl5⁻

-The species is square pyramidal (AX5E) -There are six electron groups around the central Se atom. There are six electrons surrounding the central Se atom in this structure. -There is one lone pair associated with the Se atom.

Steps involved in drawing a Lewis Structure

1. Count the valence electrons from all atoms, add or subtract electrons according to the charge. Place the atoms relative to each other. 2. Place a bond between every pair of atoms, using two valence electrons for each bond. 3. Distribute the remaining electrons in pairs to give each atom an octet(except for hydrogen). 4. Form multiple bonds if all electrons have been used and any atom does not have an octet.

Place the steps for determining the shape of a covalently bonded species in the correct order.

1. Use the molecular formula to draw a Lewis Structure. 2. Count all electron groups and assign an electron-group arrangement. 3. Determine the molecular shape by counting bonding groups and nonbonding groups separately.

Certain molecules are electron deficient, having fewer than_________ electrons around the central atom, which nonetheless has a formal charge of zero. Elements that commonly form electron deficient gaseous compounds are beryllium and

8; boron. *aluminum, beryllium, and boron are often electron deficient in molecules.

AX₂E₂

Bent (V-shaped)

Statement correctly describing the basic principle of VSEPR theory

Each group of valence electrons around a central atom is located as far from the others as possible.

AX6

Octahedral

Consider the molecule CCl4-. Each C-Cl bond in this molecule is ____________ because the electronegativity difference between C and Cl is greater than 0.4. Since CCl4 is tetrahedral in shape and symmetrical, the individual bond dipoles cancel and the molecule is nonpolar overall.

Polar; greater; cancel; nonpolar

AX4E2

Square Planar

AX5E

Square Pyramidal

AX₄

Tetrahedral

The Lewis Structure for the cyanide ion is shown. The formal charge on the C atom is equal to ______ and the formal charge on the N atom is equal to ________.

There is a triple bond, the formal charge is calculated using: Valence Electrons - # of Bonds - # of Electrons in Lone Pair Carbon: 4 - 3 - 2 = -1 Carbon is in group 4A so it has 4 valence electrons. Carbon has 3 electrons in 3 bonds, so we substitute "3" for numbers of bonds, and it has a lone pair which is 2 electrons. Nitrogen: 5 - 3 - 2 = 0 Nitrogen is in group 5A so it has 5 valence electrons. Nitrogen has 3 electrons in 3 bonds and one lone pair which is 2 electrons. Remember, that each atom only owns one electron in the bond.

AX₃

Trigonal Planar

AX₂E

Trigonal Planar Bent

AX₃E

Trigonal Pyramidal

True or false: When using VSEPR theory to determine molecular shape, a triple bond counts as a single electron domain even though it consists of 3 shared electron pairs.

True. The three shared pairs remain near each other and act as a single electron group.

Resonance structures are Lewis structures that have the same relative placement of _____ but a different arrangement of ______.

atoms; electrons

The arrangement of 5 electron groups around a central atom is trigonal______. This system has two different bond angles. Three groups lie in a trigonal plane around the central atom with bond angles of _______ degrees while the other two groups lie above and below this plane at an angle of ________ degrees to the trigonal plane.

bipyramidal; 120; 90 *the groups in the equatorial plane are at 120 degrees to each other. *the axial bonds are at a 90 degree angle to the equatorial bond.

A

central atom in structure

Some elements do not obey the octet rule because they have more than eight valence electrons i.e., they have a(n)_________ valence shell. This is only possible for elements that have available_________ orbitals i.e. elements from period____________ of the periodic table onward.

expanded; d; 3

Individual bond dipoles will cancel

for a species that has identical bonds and a symmetrical geometry.

Individual bond dipoles will not cancel

for a species with an unsymmetrical geometry

Formal charge is calculated by assigning each atom ________ the bonding electrons that it shares. Oxidation number is determined by assigning all the shared electrons of a particular bond to the atom with the ______ electronegativity.

half; higher

A species will be nonpolar overall

if individual bond dipoles cancel

A species will be polar overall

if individual bond dipoles do not cancel.

A resonance structure with more charges will be _____ stable than a resonance structure with fewer charges. For two resonance forms with the same formal charges, the resonance structure that has the negative formal charge on the more _________ atom will be more stable.

less; electronegative

A structure containing a central atom with two electron groups, designated AX₂, has a _______ shape with a bond angle of _______ degrees.

linear; 180

E

nonbonding valence electron group

m

number of bonding electron groups

n

number of nonbonding electron groups

X

surrounding atom

A bond angle is the angle formed by the nuclei of _______ surrounding atoms with the nucleus of a central atom. The bond angle predicted from the molecular shape is a(n) _______ bond angle. If the bonding electron groups around the central atom are not_________, the real bond angle will deviate from the predicted bond value.

two; ideal; identical

Some covalently bonded species do not obay the octet rule because they have an odd number of electrons. A species containing one or more _____ electrons is called a free radical. Most odd-electron molecules have a central atom from an odd-numbered group, either Group _____ or Group _____.

unpaired; 5A; 7A

that contains covalent bonds and has a(n) _______ arrangement of electron groups will have an overall _____ polarity, which is measure as a dipole ______.

unsymmetrical; molecular; moment

The formal charge assigned to an atom is calculated by subtracting the number of electrons the atom "owns" from the total number of _______ electrons. The number of electrons "owned" by a specific atom is defined as being the sum of the ________ valence electrons and half the ___________ valence electrons.

valence; unshared; shared