Chemistry Exam 2

Question 1

Valence Shell Electron Repulsion Theory

Answer 1

-Model used to predict 3D molecule shapes
-based on how electrons repel one another (move as far apart as possible)

Question 2

Steric Number

Answer 2

-# of electron groups around an atom
-# of atoms attached + # of lone pairs

Question 3

Molecular Shape vs Electron Geometry

Answer 3

-Electron geometry is the shape of the atom including lone pairs
-molecular shape does not include lone pairs

Question 4

Molecular Shapes (5 Types)

Answer 4

-tetrahedral
-pyramidal
-bent
-trigonal planar
-linear

Question 5

Electron Geometry (3 types) & Bond Angles

Answer 5

-linear (180 degrees)
-trigonal planar (120 degrees)
-tetrahedral (109.2 degrees)

Question 6

VSEPR Steps

Answer 6

1. Draw lewis structure
2. Find steric #
3. Predict maximum angle

Question 7

Intermolecular Forces

Answer 7

-forces that hold neighboring molecules together
-determined by molecular shape

Question 8

Bond Type Strengths

Answer 8

1. Covalent bonds are stronger than Ionic
2. Ionic are stronger than Hydrogen bonds
3. Hydrogen bonds are stronger than Van der Waals

Question 9

Water Dipole Movement

Answer 9

Has a net dipole movement (evenly positive and negative)

Question 10

Dipole-dipole Interactions in Hydrogen Bonding

Answer 10

-Dipoles interact with each other electrostatically
-Partial “sharing” of a hydrogen between 2 electronegative atoms (N or O) called donor and acceptor
-Strongest when 3 atoms (donor, H, and acceptor) are in a straight line (aka molecules in a straight line) bent ones are weaker

Question 11

Hydrogen Bonding in Water

Answer 11

-Each oxygen atom has 2 hydrogens it can donate to other water molecules and 2 lone pairs (can accept hydrogen bonds from other H20 molecules)
-1 molecule can interact with 4 others at once max (usually in ice, about 3 in water)

Question 12

Num. of Bonds Differ in Ice and Liquid Water

Answer 12

Both have H-bonds, but liquid water has fewer than half as many as ice

Question 13

Water as a Solvent

Answer 13

-Good solvent for charged + polar substances that can form H bonds (amino acids, carbs, salts)
-Poor solvent for nonpolar substances (nonpolar gases, phenyl groups, aliphatic chains)

Question 14

Hydrocarbon Polarity

Answer 14

Anything that’s 100% hydrocarbon is non-polar (as you add oxygen, it becomes more polar)

Question 15

Van der Waals Interactions (London Dispersion Forces)

Answer 15

-When electrons become unevenly distributed it creates a temporary dipole that can attract other atoms w/ opposite temporary charges
-Present in polar and non-polar molecules

Question 16

What happens when a droplet of oil is added to water?
What about Olive oil?

Answer 16

The oil will float on water and remain a droplet
(Olive oil will spread out on the surface because it’s slightly polar)

Question 17

What is a Chemical Reaction?

Answer 17

A chemical change happens when one or more substances are destroyed and one or more new substances are created

Question 18

Reactants

Answer 18

Substances that are destroyed by the chemical change (bonds break)

Question 19

Products

Answer 19

Substances created by the chemical change (new bonds form)

Question 20

Aqueous Solution

Answer 20

Means the substance is dissolved in water

Question 21

Evidence (Signs) of a Chemical Reaction

Answer 21

1. Evolution of light or heat
2. Temp change (incr or decr)
3. Formation of gas (bubbling or odor) other than boiling
4. Color change (due to formation of new substance)
5. Formation of precipitate (a new solid forms) from reaction of 2 aqueous solutions

Question 22

Coefficients vs Subscripts

Answer 22

-Coefficients indicate the # of molecules (ex 2H2O = 2 H2O molecules) AND used to balance equations
-Subscripts indicate the number of atoms in a certain element within a molecule (ex H2O has 2 hydrogens but 1 oxygen)

Question 23

Conservation of Mass Law

Answer 23

During a chem reaction, atoms are neither created nor destroyed

Question 24

5 Basic Types of Chem Reactions

Answer 24

1. Single Replacement (Displacement) (Redox)
2. Double Replacement
3. Synthesis (Combination)
4. Decomposition
5. Combustion

Question 25

Single Replacement

Answer 25

-A single uncombined element replaces another element in an ionic compound -2 reactants and 2 products -Not all of these reactions always occur -Look at Activity Series chart (higher "activity" metals tend to replace lower ones!)

Question 26

Double Replacement

Answer 26

-Parts of 2 aqueous ionic compounds switch places to form 2 new compounds -2 reactants and 2 products The reaction occurs when: 1. Solid precipitate forms 2. Gas is produced 3. Or Water is produced

Question 27

Soluble Compounds

Answer 27

Compounds that break down when put in water (ex NaCl)

Question 28

Solubility Rules

Answer 28

Use the Solubility Chart to determine if products in double replacement will be a precipitate

Question 29

Synthesis Reaction

Answer 29

-2 or more simple substances (the reactants) combine to form a more complex structure (the product) Types -Element A + Element B --> Compound -Element + Compound A --> Comp B -Comp A + Comp B --> Comp C

Question 30

Decomposition Reactions

Answer 30

-A more complex substance (the reactant) breaks into 2 or more simple parts (products) *Synthesis and decomp are opposites -Decomp of a compound produces 2 or more elements and/or compounds *products are always simpler than reactants -Gasses are often produced in decomp (O2, H2, N2, CO2)

Question 31

Combustion Reactions

Answer 31

-All involve oxygen (O2) as a reactant, combining with another substance -All comb. reactions are exothermic *Complete comb. of a hydrocarbon ALWAYS produces CO2 + H2O *Incomplete com. can produce CO2 and soot -Any synthesis reaction that involves O2 as a reactant is also considered comb. *Comb of a metal ALWAYS produces a metal oxide

Question 32

Avagadro's Number

Answer 32

-1 mole is equal to 6.02 x 10^23

Question 33

Molar Mass

Answer 33

= The mass of 1 mole of particles (in grams) -Use the ave atomic mass rounded to the nearest whole # (ex 1 mole of C atoms = 12g)

Question 34

Molar Mass of Molecules and Compounds (Gram Formula Mass)

Answer 34

-Also called "molecular mass" -Add up atomic masses of atoms in the formula -Ex 1 mole CaCl2 = 1 mole Ca x 40 g/mol + 2 moles Cl x 35.5 g/mol = 111 g/mol

Question 35

Calculations with Molar Mass

Answer 35

moles = given mass (grams) / gram-formula mass

Question 36

Empirical Formula

Answer 36

Expresses smallest whole # ratio of atoms present *Ionic formulas are always empirical *This is the one where you divide the subscripts!

Question 37

Molecular Formula

Answer 37

States the actual # of each kind of atom found in one molecule of the compound *a multiple of the subscripts in the empirical formula