Unit 9- Chemical Bonds

Question 1

chem bonds

Answer 1

forces that hold the atoms together in substance
- ionic bonding: cation + anion (ionic cpd)(transfer of e-)
- covalent bonding: nonmetal eles (molec cpd)

Question 2

Lewis Electron-Dot Symbol

Answer 2

Symbol of ele surrounded by dots which represent their ve-

• cations: most have no ve- shown
• anions: most hve 8 ve-

Question 3

lattice energy

Answer 3

energy required to sep 1 mol of ionic solid into its gaseous ions

LE= (k|Q1Q2|)/r

Q1 and Q2 = ionic charges
r = distance between ions in the solid
- use Q1Q2 for LE but when all the same, use r

Question 4

covalent bonding

Answer 4

results from atoms sharing an e- pair

Question 5

bond length

Answer 5

the distance between the nuclei of 2 bonded atoms

Question 6

Lewis Structures

Answer 6

show how the ve- are arranged in a molec or polyatomic ion

Question 7

bonding pairs

Answer 7

e- shared between 2 atoms and are rep by lines

Question 8

lone pairs

Answer 8

entirely on one atom and are rep by 2 dots

Question 9

octet rule

Answer 9

atoms share e- until each atom is surrounded by 8 e-
- single bond: share 1 pair e-
- double bond: share 2 pair e-
- triple bond: share e pair e-

Question 10

bond order

Answer 10

the # of e- pairs shared between 2 atoms
- as bond order incs, length of bond decs and strength of bond incs

Question 11

skeleton structure

Answer 11

shows which atoms are bonded to each other

Question 12

central atom

Answer 12

bonded to 2 or more other atoms
- usually farthest left and down on periodic table

Question 13

terminal atom

Answer 13

bonded to 1 other atom
* H and F are always terminal

Question 14

writing Lewis Structure

Answer 14

1. start with the skele structure
2. sum the ve-
3. substract 2e- for each bond in skele structure
4. count the # of e- needed to satisfy octet rule (if # needed > # remain, add 1 bond for each additional 2e- needed )
5. place remaining e- as lone pairs to satisfy octet rule

Question 15

bond polarity

Answer 15

• UNEQUAL sharing leads to a POLAR covalent bond
• EQUAL sharing leads to a NONPOLAR covalent bond

Question 16

dipole movements

Answer 16

measure of the unequal sharing of e-
- zero for nonpolar
- NOT zero fro polar

Question 17

polar covalent bond symbol

Answer 17

δ with a +/- to show charges

Question 18

Electronegativity

Answer 18

measure of the ability of an atom to attract the shared e- in a chem bond
- inc up and right
H= 2.1
C= 2.5
N= 3.0
O= 3.5
F= 4.0
- diff in electroneg shows if polar or not and comparison to other molecule shows length of arrow. longer = more polar

Question 19

Formal charges

Answer 19

a charge assigned to atoms in Lewis structures by assuming the shared e- are divided equally between the bonded atoms

formal charge= # of ve - # of lone pair e - # of bonds

Question 20

comparing Lewis Structures

Answer 20

1. SMALLEST formal charges are FAVORED (more stable)
2. adjacent atoms w/ formal charges of the SAME sign are much LESS favorable
3. neg formal charge on MORE electroneg atoms are FAVORED

Question 21

resonance structures

Answer 21

differ only in the distribution of the ve-
- indicated by double handed arrow

Question 22

avg structure

Answer 22

avg of all resonance structures
- resonance structures contribute equally

Question 23

bond order

Answer 23

avg of the bonds
(ex: 1 double bond and 1 single bond = 3/2 = 1.5)

Question 24

electron deficient molec

Answer 24

central atoms from Group 2A and 3A do not have enough ve- to complete an octet

Question 25

odd e- molec

Answer 25

species with odd # of e-

Question 26

expanded valence shell molec

Answer 26

have more than 8e- about an atom in Lewis structure (extra e- on central atom)
- only 3rd period elements or later
- formula: ZFn (where Z= P, S, Cl, As, Se, Br, Te, I, or Xe and Fn= terminal atom)

Question 27

Oxides of heavier elements

Answer 27

have a central atom from the 3rd or later periods

Question 28

bond energies (bond dissociation energy)(D)

Answer 28

the energy required to break 1 mol of bonds in a gaseous species
- Always endothermic
- deltaH reaction = sum(bond energies of bonds broken) - sum(bond energies of bonds formed)
- lewis structured need to be written
- bond energies (except of diatomics) are avg energies