Exam 1: Bonding and Structure

Question 1

Octet rule

Answer 1

main group elements bond in such a way that each atom has eight electrons (a completed valence)

EXCEPTIONS:
- hydrogen (2 electrons)
- boron (6 electrons)
- aluminum (6 electrons)
- expanded octets (go above a total of 8 electrons)

Question 2

chemical bonds

Answer 2

atoms form bonds to lower their potential energies by allowing unpaired electrons to become paired

Question 3

ionization energies

Answer 3

metals have low ionization energies and want to form cations

Question 4

electron affinity

Answer 4

nonmetals have negative (favorable) electron affinities and want to form anions (-)

Question 5

ionic bonds

Answer 5

electrons are TRANSFERRED from one entity to the other (based off ionization energies and electron affinities)

Question 6

covalent bonds

Answer 6

electrons are SHARED between atoms (no charges formed); two types

Question 7

polar covalent

Answer 7

electrons are not shared equally with the electron density residing towards the more electronegative atom

Question 8

non polar covalent

Answer 8

electrons are essentially shared equally between the atoms

Question 9

lewis structure

Answer 9

• empirically based method of drawing molecular structures
• valence electrons are represented as dots around the atom
• bonds are represented as lines between atoms

STEPS:
1) determine number of valence electrons
2) draw chemical symbol
3) place one dot on each side of chemical symbol
4) any remaining electrons are paired until no electrons remain

Question 10

expanded octets

Answer 10

• 10 or 12 electrons are possible
• only occurs in period 3 elements or higher
• all thanks to d-orbitals (close enough energy in the outer shell and can accept some electrons)

Question 11

molecular compounds lewis structure (steps)

Answer 11

1) count the total number of electrons available
2) draw skeletal structure (central atom - lowest electronegativity + peripheral atoms + bonds)
3) fill octets of peripheral atoms by adding lone pair electrons
4) add any remaining electrons to the central atom as lone pair electrons
5) calculate any formal charges
6) adjust structure to minimize formal charges

Question 12

how many electrons is a single bond?

Answer 12

2 electrons

Question 13

how many electrons is a double bond?

Answer 13

4 electrons

Question 14

how many electrons is a triple bond?

Answer 14

6 electrons

Question 15

formal charges

Answer 15

• an electron counting system used to determine the best lewis structure
• takes into account the different types of electrons involved with an atom (valence electrons, lone pair electrons, bonding electrons)

FC = # valence - lone pair - 1/2(bonding)

Question 16

valence shell electron pair repulsion theory (VSPER)

Answer 16

• extension of Lewis Theory
• based on the idea that electron groups (lone pairs, single bond, multiple bonds, single electrons) repel one another
• achieve MAXIMUM SEPARATION
• having one central atom geometry depends on (1. # of electron groups, and 2. how many of the groups are bonding groups vs lone pairs)

Question 17

AXE Nomenclature

Answer 17

-A = central atom
-X = peripheral atom
-E = lone pair electrons

• lone pair electrons can affect shape (molecular geometry)

Question 18

AX2

Answer 18

TWO ELECTRON GROUP
- electron geometry = AX2
- molecular geometry = AX2
- shape = linear
- bonding angle = 180

Question 19

AX3

Answer 19

THREE ELECTRON GROUP
- electron geometry = AX3
- molecular geometry = AX3
- shape = trigonal planar
- bonding angle = 120

Question 20

AX2E

Answer 20

THREE ELECTRON GROUP
- electron geometry = AX3
- molecular geometry = AX2E
- shape = bent (changes shape from electron geometry)
- bonding angle = < 120

Question 21

AX4

Answer 21

FOUR ELECTRON GROUP
- electron geometry = AX4
- molecular geometry = AX4
- shape = tetrahedral
- bonding angle = 109.5

Question 22

AX3E

Answer 22

FOUR ELECTRON GROUP
- electron geometry = AX4
- molecular geometry = AX3E (changes shape from electron geometry)
- shape = trigonal pyramidal
- bonding angle = < 109.5

Question 23

AX2E2

Answer 23

FOUR ELECTRON GROUP
- electron geometry = AX4
- molecular geometry = AX2E2 (changes shape from electron geometry)
- shape = bent
- bonding angle = < 109.5

Question 24

AX5

Answer 24

FIVE ELECTRON GROUP
- electron geometry = AX5
- molecular geometry = AX5
- shape = trigonal bipyramidal
- bonding angle = 180, 120, 90

Question 25

AX4E

Answer 25

FIVE ELECTRON GROUP
- electron geometry = AX5
- molecular geometry = AX4E (changes shape from electron geometry)
- shape = see-saw
- bonding angle = 180, 90

Question 26

AX3E2

Answer 26

FIVE ELECTRON GROUP
- electron geometry = AX5
- molecular geometry = AX3E2 (changes shape from electron geometry)
- shape = T-shaped
- bonding angle = 180, 90

Question 27

AX2E3

Answer 27

FIVE ELECTRON GROUP
- electron geometry = AX5
- molecular geometry = AX2E3 (changes shape from electron geometry)
- shape = linear
- bonding angle = 180

Question 28

AX6

Answer 28

SIX ELECTRON GROUP
- electron geometry = AX6
- molecular geometry = AX6
- shape = octahedral
- bonding angle = 180, 90

Question 29

AX5E

Answer 29

SIX ELECTRON GROUP
- electron geometry = AX6
- molecular geometry = AX5E (changes shape from electron geometry)
- shape = square pyramidal
- bonding angle = 180, 90

Question 30

AX4E2

Answer 30

SIX ELECTRON GROUP
- electron geometry = AX6
- molecular geometry = AX4E2 (changes shape from electron geometry)
- shape = square planar
- bonding angle = 180, 90