Textbook Ch.7: Covalent Bonding

Question 1

What did Lewis suggest about nonmetal atoms?

Answer 1

Lewis suggested that nonmetal atoms, by sharing electrons to form an electron-pair bond, can acquire a stable noble-gas structure

Question 2

Valence electrons

Answer 2

electrons in the outermost principal energy level

• Shown as dot symbols around the element

Question 3

In Lewis structures of a molecule or polyatomic ion, valence electrons ordinarily ____

Answer 3

occur in pairs

Question 4

Covalent bond

Answer 4

a pair of electrons shared between two atoms

• Shown by a straight line between bonded atoms in a Lewis structure

Question 5

Unshared pair / Lone pair

Answer 5

a pair of electrons owned entirely by one atom

• Shown as a pair of dots on that atom in a Lewis structure

Question 6

Single bonds

Answer 6

a single electron pair shared between two bonded atoms

• 1 line between two atoms on a Lewis structure

Question 7

Double bonds

Answer 7

when bonded atoms share two electron pairs

• 2 lines between two atoms on a Lewis structure

Question 8

Triple bonds

Answer 8

when bonded atoms share three electron pairs

• 3 lines between two atoms on a Lewis structure

Question 9

Octet rule

Answer 9

atoms in covalently bonded species tend to have noble-gas electronic structures

• Nonmetals (except H) achieve a noble-gas structure by sharing an octet of electrons (eight)
• Hydrogen atoms, in molecules or polyatomic ions, are surrounded by a duet of electrons (two)

Question 10

List the steps for writing Lewis Structures

Answer 10

1. Count the number of valence electrons. (the last digit of the group number)
2. Draw a skeleton structure for the species, joining atoms by single bonds
   - The central atom is usually the one written first in the formula, put this in the center. Terminal atoms are often H, O, or a
   halogen
3. Determine the number of valence electrons still available for distribution
4. Determine the number of valence electrons required to fill out an octet for each atom (except H)

Question 11

If after drawing the skeleton of a Lewis structure, the number of electrons available is equal to the number required, you…

Answer 11

distribute the available electrons as unshared pairs, satisfying the octet rule for each atom

Question 12

If after drawing the skeleton of a Lewis structure, the number of electrons available is less than the number required, you…

Answer 12

must modify the skeletal structure by changing single bonds to multiple bonds

Question 13

If after drawing the skeleton of a Lewis structure, the number of electrons available is greater than the number required you…

Answer 13

distribute leftover electrons around the central atom

Question 14

Multiple bond formation is limited to which elements?

Answer 14

C, N, O, and S

Question 15

Which atoms never form double bonds?

Answer 15

hydrogen and halogen atoms

Question 16

Resonance forms

Answer 16

two structures separated by a double-headed arrow when the single Lewis structure does not adequately reflect the properties
of the substance

• Ex: in SO₂, you don’t know which oxygen the sulfur will be double-bonded to, it could be double-bonded to either

Question 17

Resonance forms differ only in:

Answer 17

the distribution of electrons, not n the arrangement of atoms

Question 18

Formal charge

Answer 18

a way to choose the more plausible of two resonance structures. It is the difference between the number of valence electrons in the free atom and the number of valence electrons assigned to the atom in the Lewis structure. The assigned electrons include

• All the unshared electrons owned by that atom
• One half of the bonding electrons shared by that atom

Question 19

Equation of formal charge (Cբ):

Answer 19

Cբ = X-(Y + Z/2)

X= number of valence electrons in the free atom in the Lewis structure

Y=the number of bonding electrons shared by the atom in the Lewis structure

Z=the number of bonding electrons shared by the atom in the Lewis structure

Question 20

Ordinarily, the more likely Lewis structure is the one in which:

Answer 20

• The formal charges are as close to zero as possible

- Any negative formal charge is located on the most strongly electronegative atom

Question 21

What are some molecules that do not follow the octet rule?

Answer 21

• NO
• NO₂
• Species in which the central atom is surrounded by more than 4 pairs of valence electrons

Question 22

Bond angles

Answer 22

the angles between bonds. Must be considered when dealing with molecules with three or more atoms

Question 23

Valence-shell-electron-pair repulsion (VSEPR) model

Answer 23

a model in which the valence electron pairs surrounding an atom repel one another. Consequently the orbitals containing those electron pairs are oriented to be as far apart as possible

Question 24

Electron-pair geometry

Answer 24

helps in determining the arrangement of various electron groups

Question 25

Molecular geometry

Answer 25

helps in determining the entire atom and its configuration, it's 3D

Question 26

When describing the species type in molecular geometry, what does X represent?

Answer 26

number of terminal (bonded) atoms

Question 27

When describing the species type in molecular geometry, what does E represent?

Answer 27

the number of unshared pairs

Question 28

Polar

Answer 28

as a result of an asymmetrical distribution of electrons, the bond or molecule contains a positive and negative pole and is therefore a dipole

Question 29

Nonpolar

Answer 29

a symmetrical distribution of electrons which leads to a bond or molecule with no positive or negative poles

Question 30

Nonpolar bonds

Answer 30

formed whenever atoms joined are identical, H₂, F₂, etc

Question 31

Polar bonds

Answer 31

bonds in which the electron density is unsymmetrical

Question 32

The extent of polarity is related to the difference in ____

Answer 32

electronegativity - If it is large, the bond is strongly polar - If small, the bond is slightly polar

Question 33

How do polar molecules align themselves in the presence of an electric field?

Answer 33

- Positive pole aligns with the negative charge | - Negative pole aligns with positive charge

Question 34

How do nonpolar molecules behave in the presence of an electric field?

Answer 34

they show no preferred orientation

Question 35

Dipole moment

Answer 35

a measure of the extent to which molecule tend to orient themselves in an electric field - Polar molecules have dipole moment - Nonpolar molecules have no dipole moment

Question 36

When working with a diatomic molecule, how do you find the polarity?

Answer 36

Polarity of the molecule = polarity of the bond

Question 37

If the molecule has more than two atoms, how do you find the polarity?

Answer 37

Use bond polarity AND molecular geometry (if bonds are symmetrically distributed around central atom or not) If the polar A--X bonds in a molecule AXE are arranged symmetrically around the central atom, A, the molecule is nonpolar

Question 38

Atomic model / valence bond model

Answer 38

a covalent bond consists of a pair of electrons of opposed spin within an orbital Ex: an H atom forms a covalent bond by accepting electrons from another atom to complete it's orbit

Question 39

For an atom to form a covalent bond, it MUST have...

Answer 39

an unpaired electron - The number of bonds formed by an atom should be determined by the number of unpaired electrons - Noble-gas atoms DO NOT form covalent bon

Question 40

Hybrid orbital

Answer 40

Used to modify simple valence bond theory. It involves mixing atomic orbitals to form new hybrid orbitals suitable for pairing electrons

Question 41

What kind of electron pairs can be located in hybrid orbitals?

Answer 41

unshared as well as shared electron pairs

Question 42

The number of hybrid orbitals formed is always equal to:

Answer 42

the number of atomic orbitals mixed

Question 43

How are the geometries of hybrid orbitals predicted?

Answer 43

by the VSEPR theory

Question 44

What happens to multiple bonds in hybrid orbitals?

Answer 44

The extra electron pairs in a multiple bond (one pair in a double bond, two pairs in a triple bond) are not located in hybrid orbitals

Question 45

Sigma (σ) bonding orbital

Answer 45

consists of a single lobe in which the electron density is concentrated in the region directly between two bonded atoms

Question 46

Sigma (σ) bond

Answer 46

consists of an electron pair occupying a sigma bonding orbital - All sigma bonds are single bonds

Question 47

Pi (π) bonding orbitals

Answer 47

consist of two lobes one above the bonding axis, one below it. Along the bonding axis, the electron density is 0

Question 48

Pi (π) bond

Answer 48

electron pair occupying the pi orbital - One of the electron pairs in a multiple bond is a sigma bond, the others are pi bonds