Unit 2: Bonding & Lewis Structures Flashcards

Question

Octet Exceptions Expanded Valence

Answer 1

A

the attraction between positive and negative ions, or two nonmetal atoms.

Answer 2

A

are due to the electrostatic attractions between oppositely charged ions.

solids with mp > 400C;
soluble in polar solvent;
conductive,
high ΔEn

Answer 3

A

molecules are formed by the sharing of electrons between atoms

covalent – gases, liquids, solids rt, mp usually <300 C;
many insoluble in polar solvent,
nonconductive,
low ΔEn diff

Answer 4

A

Chemical symbol of element surrounded by dots representing valence electrons

Lewis symbol: inner electrons/nucleus as symbol; valence as dots

Primary contribution = valence electrons

G.N. Lewis – express valence electrons

Answer 5

A

Atoms often gain, lose or share electrons to achieve the same number of electrons as the noble gas closest to them in the periodic table.

Noble gases have very stable electron arrangements, because all noble gases except He have eight valence electrons, many atoms undergoing reactions end up with eight valence electrons. This observation led to octet rule.

Octet Rule: Atoms tend to gain, lose or share electrons until they are surrounded by 8 valence electrons

Answer 6

A

Ionic substances generally result from the interaction of metals on the left side of the periodic table with nonmetals on the right side

For Example:

One element oxidized, another reduced – electron transfers

Ex: NaCl

2Na (s) + Cl2 (g) à 2 NaCl (s)

Answer 7

A

A chemical bond formed by sharing a pair of electrons is a covalent bond.

Represented by a line between atoms in a Lewis structure: X-X

Ionic compound – strong intermolecular, weak intramolecular

Covalent – weak intermolecular, strong intramolecular

Covalent bond formation follows energy curve w/ minimum distance at bond distance

Answer 8

A

if a polyatomic ion is formed, the charge is included as in ionic compounds

NH4+

Answer 9

A

Obey octet rule
Differentiate bonding and nonbonding electrons

Determine bonding electrons:

S = N - A

S = shared

N = needed

A = available

For F₂ as an example
- A = 2 F = 2x7 available;
- N = 2 F = 2x 8 needed
- S = 16 - 14 = 2 shared
- n2 electrons = 1 bond

Answer 10

A

a means devised for keeping track of electrons being gained or lost by a substance.

Track electronic charges

Single atom ions = actual charge

Polyatomics spread over ion; assign # to each atom

General rules but no absolutes

Answer 11

A

The oxidation number of an element in its free (uncombined) state is zero
The oxidation number of a monatomic (one-atom) ion is the same as the charge on the ion.
The sum of all oxidation numbers in a neutral compound is zero.
The sum of all oxidation numbers in a polyatomic (many-atom) ion is equal to the charge on the ion.

Answer 12

A

The oxidation number of fluorine is always –1.
The oxidation number of oxygen in a compound is usually –2, except in peroxides (- 1), superoxides (- ½), or combined with fluorine (+1 or +2)
The oxidation state of hydrogen in a compound is usually +1, except as a binary compound with a metal (-1)

Answer 13

A

Periodic position contributes to oxidation state:
a. Group IA = 1+
b. Group IIA = 2+
c. Group IIIA = 3+ (some exceptions)
d. Group VA = 3- w/ metal, H, NH4+; apply 3 & 4 to element to the right of group V
e. Group VIA = 2- w/ metal, H, NH4+; apply 3 & 4 to element to O or halogen in lower n
f. Group VIIA = 1- in binary compounds; apply 3 & 4 when combined w/ O or halogen in lower n

If En are equal, negative to element closest to F

Answer 14

A

Resonance – situations where a single Lewis structure does not present the actual configuration for a molecule, and it is capable of representation by multiple valid Lewis structures.

Resonance structure – different electron arrangement

Resonance hybrid – real molecule

Ex: CO32-

Answer 15

A

Formal Charge – the charge an atom would have if each bonding electron pair in the molecule were shared equally between its two atoms.

Rules for assigning formal charge for main group elements

FC on an atom is = group number – [number bonds + number unshared electrons].
If # bonds = group number, F.C. = 0
a. in molecule, sum charge = 0
b. in polyatomic, sum charge = charge on ion

Answer 16

A

Keep in mind for formal charges:

a. most likely formula charges minimize charge – closest to 0
b. put negative charges mostly on more electronegative atom
c. If adjacent atoms have same sign (+ or -) usually incorrect

EX: NOCl

Answer 17

A

Some instances octet rule fails: must modify S = N - A formula for these:

A. covalent compounds of Be – use 4 for N

B. group 3A elements – use N = 6

C. Some compounds w/ unpaired electrons NO and NO2

D. Expanded Valence – > 8 electrons; usually S and P