Chapter 4

Question 1

Drawing Lewis Dot Structures

Answer 1

1) count & use all Valence e- –> rmr they are the ones involved in chem reactions
2) place the atom that can make the most bonds in middle
3) each atom should have 8 atoms –> start by making the surrounding atoms happy first

Question 2

Length & Strength of single, double, & triple bonds

Answer 2

STRENGTH: C-C < C=C < C☰C
LENGTH: C☰C < C=C < C-C

• double & triple bonds involve more attractive forces between 2 atoms then single bonds do. The atoms are closer to each other. As a result, triple bonds are shorter & much stronger than double bonds which are shorter & stronger than single bonds

Question 3

Incomplete Octet

Answer 3

• is when fewer e-s are available than needed to complete the octets of the atoms in an molecule

Question 4

Expanded Octet

Answer 4

• there are more e-s available than needed. This normally results in expanded octets associated with the central atom
  –> An expanded is possible for elements belonging to period 3 or higher in the periodic table (elements that contain d-orbitals)
• Phosphorus can have up to 10e- (5 bonds)
• Sulfur can have up to 12e- (6 bonds)
• Cl, Br, & I can have up to 14e- (7 bonds)

Question 5

The Shape of Molecules: VSEPR

Answer 5

• Valence Shell Electron Pair Repulsion theory
  1) The shape of a molecule depends on the repulsion between the e- pairs in the valence shell around the molecule’s central atom. The e- pairs will stay as far apart as possible

2) e- pairs can be either bond pairs (single, double, or triple) or lone pairs (LP) around the central atom

3) Lone pairs spread out and take up more room then bonded pairs so they will push the bonded atoms closer together

Question 6

Valence Bond Theory

Answer 6

• Covalent bonds occur when 2 half-filled orbitals overlap & 2e- occupy the same region of space

Question 7

Sigma bond

Answer 7

• Sigma Symbol (σ)
• the 1st bond formed between 2 atoms. All single bonds are sigma bonds.
• end-to-end (head on) overlap of orbitals
• stronger than pi bond due to better overlap
• can be made from pure (s, p, d) orbitals or hybrid orbitals (sp^3, sp^2…)

Question 8

Pi bond

Answer 8

• Pi Symbol π
• the 2nd or 3rd bond formed between2 atoms
• occurs in double or triple bonds
• side by side overlap of parallel orbitals –> not as strong as sigma bond due to poorer overlap
• Additional overlap occurs using UNHYBRIDIZED orbitals, not hybrid orbitals. Pi bonds must be made from pure “p” or “d” orbitals –> (we won’t do d)

Question 9

Metals have ________ EN values. Nonmetals have _______ EN values.

Answer 9

low –> tend to lose e-s
high –> tend to gain or share e-s

Question 10

Intramolecular BONDS

Answer 10

• forces of attraction within molecules. They are chemical bonds that hold atoms together
• they keep a molecule intact
• responsible for chemical properties of a compound. –> are formed or broken during chem reactions
• FROM WEAKEST TO STRONGEST: nonpolar covalent, polar covalent, ionic, metallic bonds

Question 11

Intermolecular FORCES

Answer 11

• forces of attraction between molecules
• IMFs hold collections of molecules to one another and are responsible for the physical properties of compounds –> Ex, melting & boiling points, state, density, solubility, viscosity…
• cuz e-s are not involved, IMF are not as strong as intramolecular bonds. The strength of attraction increases as the size and shape of the molecule increases
• FROM WEAKEST TO STRONGEST: LDF, DP-DP, H-bonds

Question 12

Non-polar covalent bonds

Answer 12

• the 2 non-metals have the same or similar attraction (pull) for e-s. As a result, the e-s are shared equally 2 non-metals
• ∆EN <0.5

Question 13

Polar Covalent Bond

Answer 13

• the atom with the stronger pull (higher EN value) bears a partial negative charge as e- density is closer to this atom and the opposite.
• polar bonds have a “dipole moment” or a dipole (–>) cuz the poles have diff partial charges
• ∆EN 0.5-1.7

Question 14

Ionic Bonds

Answer 14

• gain or loss of e-
• ∆EN >1.7
• the positive & negative ions are arranged in crystal lattice
• have high melting points (>300 degrees C) & boiling points due to strong electrostatic attraction
• as a solid, ionic compounds can’t conduct electricity as the charged ions can’t move.
  –> to conduct electricity, 2 conditions must be met
  1) u need to have charges
  2) the charges must be able to move
• however, when dissolved in water or in molten state (the charged ions are free to move) –> the can conduct electricity (electrolytes)

Question 15

Metallic Bonding

Answer 15

• metals have low ionization energy & low electronegativity. The valence e- in metals are only loosely held to the nucleus, so they are relatively free to move from atom to atom
• the fixed positively charged metal ions are surrounded by a sea of moving e-s
• the hardness & melting point of a metal depend largely on how many valence e-s the metal has. The greater the # of valence e-s, the more firmly the metal ions are held in place. –> This increases both the hardness & melting point of the metal
• due to the sea of moving e-s, metals are malleable (hammerer into thin sheets) & ductile (drawn into wire) –> when hit by a hammer, the ions in the metal can slide past each other bcuz it causes little change in their environment. The sea of e-s is always surrounding the ions

Question 16

Metals are:

Answer 16

• excellent conductors of electricity. the ve- are free to move between atoms
• excellent conductors of heat as the freely moving e-s can pass along the KE (heat) easily

Question 17

London Dispersion Forces (LDF)

Answer 17

• weakest IMF but exist between all atoms & molecules
• caused by a random, uneven distribution of e-s within an atom. This results in a slightly negative and slightly positive charge on either side of the atom –> the opposite charges then attract each other, causing a domino effect
• cuz this is all by chance, the attraction coms & goes –> it is temporary & weak.
• the strength of LDFs depends one the size & shape of the molecule or atom.
• SIZE: larger molecules have higher melting/boiling points, they tend to be liquid or solids
• SHAPE: large surface area of interaction leads to stronger attraction

Question 18

Dipole-Dipole

Answer 18

• they exist between polar molecules –> is permanent, and not by chance
• polar molecules will naturally orient themselves so that the positive pole of one molecule will be next to & attract the negative pole of an adjacent molecule
  -will result in higher mp/bp cuz more E will be required to overcome the attractions between the molecules
• stronger than LDF cuz permanent
• the greater the polarity, the stronger the DP-DP attraction

Question 19

Hydrogen Bonding

Answer 19

-special DP-DP forces
- occurs when a H atom is covalently bonded to a highly electronegative element: N, O, F-H
- the H atom is small & carries a significant partial positive charge which is strongly attracted to the partial negative charge on other molecules. On average, H-bonds are 5X stronger than regular DP-DP attractions
- H-bonding significantly increases such physical properties as mp & bp
- make life on earth possible

Question 20

Ion-Dipole Forces

Answer 20

• solubility of ionic compounds in water
• the ionic bonds holding a crystal lattice together are strong. However, when the surface of that lattice is in connect with water, each ion on that surface will attract the oppositely charged end of polar water molecules near them (ion-dipole force)
• the negative oxygen ends of water surround cations
• positive hydrogen ends of water surround an anion
• as the ions move away from the lattice surface, the immediately become surrounded or enclosed in a hydration shell.