Chemistry Chapter 10

What are the steps to drawing a Lewis Structure?

- A single bond contains two electrons and is represented by a solid line. - 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.

What describes the "normal" bonding pattern for a neutral atom of each element, assuming that the octet rule is obeyed?

- H forms one covalent bond and is generally not found as a central atom in covalent species. - F always forms a single covalent bond. - C usually forms four covalent bonds.

What defines also Resonance structures?

- An individual resonance structure doesn't accurately represent the structure of the species. - Resonance structures differ only in the arrangement of electrons.

What describes a covalent species that has four electron groups around the central atom?

- The ideal bond angle for a four-electron system is 109.5°. - If all four electron pairs are bonding pairs, the shape of the system is tetrahedral. - A bent shape is observed if there are two bonding pairs and two lone pairs.

What describes how formal charge is assigned to an atom in a Lewis structure?

- The number of shared electrons equals twice the number of bonds in the structure. - The atom is considered to "own" half the shared electrons. - Formal Charge = (valence e⁻) - (unshared e⁻ +1/2shared e⁻)

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 ___° while the other two groups lie above and below this plane

Bipyramidal, 120, 90.

The angle formed by the nuclei of two surrounding atoms with the nucleus of the central atom in a structure is called a(n) _____ angle. The value predicted for such an angle using the VSEPR theory would be 180 degrees, based upon geometry alone. This is referred to as the _____ bond angle. In practice, this value often deviates from the predicted value for various reasons.

Bond, Ideal

In a single, double, or triple bond the shared electrons paired are localized between the bonded atoms. In a resonance hybrid, electrons are ______ or spread out over two or more adjacent atoms. Instead of a double or triple bond between two such atoms, the bond is considered a(n) _______ double or triple bond, with a fractional bond order.

Delocalized, Partial.

What describes the basic principle of VSEPR theory?

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

The formal charge of an atom in a Lewis structure is the charge the atom would have if all bonding electrons were shared _____ between the atoms. The formal charge doesn't necessarily reflect an actual charge on the atom.

Equally.

What defines Resonance Structures?

Lewis structures for the same species are similar but differ in the placement of electrons.

A structure containing a central atom with two electron groups, designeated AX2, has a ______ shape with a bond angle of _____ degree.

Linear, 180.

A Lewis structure will usually require one or more multiple bonds if there is an atom presented that doesn't have a full ______ after all available electrons have already been placed. The multiple bond is formed by exchanging one _____ electron pair for each new bond.

Octet, Lone.

All shared bonding electrons are assigned to the more electronegative atom in order to determine Oxidation number Half the shared bonding electrons are assigned to each atom of the bond in order to calculate Formal Chrnge

Oxidation number. Doesn't change for a particular atom from one resonance form to another. Formal charge. May change for a particular atom from one resonance form to another.

AX₄ AX₃E AX₂E₂

Tetrahedral Trigonal Pyramidal Bent

A structure containing a central atom surrounded by three electron groups will have a _____ planar arrangement in which the ideal bond angle is _____ °.

Trigonal, 120.

The electron-group arrangement around a central atom is defined by the number of ______-electron groups. The Molecular shape is defined by the relative positions of the _______ around the central atom. Two species may have the same electron-group arrangement but have different molecular shapes.

Valence, Atoms

According to VSEPR theory, each group of _____ electrons around a central atom will be located as far away from the others as possible, in order to minimize electron-electron ________.

Valence, Repulsions.

Some elements don't obey the octet rule because they have more than eight valence electrons, i.e., they have a(n) ________ valence shell. This only possible for elements that have available ___ orbitals, i.e., elements from the period ___ of the periodic table onwards.

Expanded, d, 3.

AX₆ AX₅E AX₄E₂

Octahedral Square Pyramidal Square Planar

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

Polar, Greater, Cancel, Nonpolar.

What describes Formal Charge?

- Formal Charges can be used to select the most important resonance structures for a species. - The formal charge of an atom is the change it would have if all bonding electrons were shared equally.

The steps of drawing a Lewis structure in the correct order, starting with the first step on top.

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 doesn't have an octet.

Determine 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.

The molecular shape of a covalent species is determined not only by the number of _______ electron groups that join the atoms, but by the number of ______ electron groups as well, since these electrons also occupy space.

Bonding, Nonbonding.

To classify molecular shapes, a structure is assigned a specific AXmEn designation, where A is the _____atom, X is a(n) ________ atom, and E represents a(n) _______ valence electron group that is usually a lone _____.

Central, Surrounding, Nonbonding, Pair.

A 5-electron group system (shown) has two different types of positions for substituents. The three positions marked "1" form a trigonal plane about the central atom and are called _____ positions while the two positions marked "2" are ____ positions. Lone pairs prefer to occupy the ____ positions.

Equatorial, Axial, Equatorial.

Individual bond dipoles cancel Individual bond dipoles won't cancel A species will be nonpolar overall A species will be polar overall.

For a species that has identical bonds and a symmetrical geometry. For a species with an unsymmetrical geometry. In individual bond dipoles cancel. If individual bond dipoles don't cancel.

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

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

Some covalently bonded species don't obey 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

A molecule that contains covalent bonds and has a(n) ________ arrangement of electron groups will have an overall ______ polarity, which is measured as a dipole ______.

Unsymmetrical, Molecular, Moment.