Unit 3

Question 1

What is Valence Shell Electron - Pair Repulsion Theory (VSEPR)?

Answer 1

Describes the orientation of electron groups around the central atom.

• States that electrons are arranged as far apart as possible around the central atom
• States that the specific shape of a molecule is determined by the number of atoms attached to the central atom.

Question 2

Explain a linear molecular shape

Answer 2

Linear
- 2 electron groups

• 2 bonded pairs
• 0 lone pairs

Question 3

Explain a trigonal planar molecular shape

Answer 3

Trigonal planar
- 3 electron groups

• 3 bonded pairs
• 0 lone pairs

Question 4

Explain a bent molecular shape

Answer 4

Bent
(two ways to write)

120 Degrees
- 3 electron groups
- 2 bonded pairs
- 1 lone pair
or
109 Degrees
- 4 electron groups
- 2 bonded pairs
- 2 lone pairs

Question 5

Explain a tetrahedral molecular shape

Answer 5

Tetrahedral
- 4 electron groups

• 4 bonded pairs
• 0 lone pairs

Question 6

Explain a trigonal pyramidal molecular shape

Answer 6

Trigonal pyramidal
- 4 electron groups

• 3 bonded pairs
• 1 lone pairs

Question 7

How do you predict the molecular shape of a compound?

Answer 7

1. Draw the Lewis structure
2. Count the number of bonded pairs and lone pairs for the central atom
3. Using the info you know about each shape, determine the correct shape

Question 8

How do you determine the polarity of a molecule?

Answer 8

The molecule is polar if there are different terminal atoms or if there are lone pairs around the central atom. Otherwise, the molecule is nonpolar!

Question 9

What’s the difference between intramolecular and intermolecular forces?

Answer 9

An “intramolecular force” is the force that holds atoms together within a molecule (covalent bond), while an “intermolecular force” is the force that exists between separate molecules.
- Intramolecular forces are all stronger than intermolecular forces.

Question 10

Explain Ionic Bonds.

Answer 10

• Strong bonds between ions.

Question 11

Explain Dipole-Dipole forces.

Answer 11

• Medium strong forces between polar molecules.
• Molecules orient themselves so that their negative side aligns with the positive side of another molecule.

Question 12

Explain Hydrogen Bonds.

Answer 12

• Strong forces between all molecules.
• Molecule has N, O, or F attached to a hydrogen atom; H atom forms hydrogen bond with the N, O, or F on another molecule.

Question 13

Explain Dispersion Forces.

Answer 13

• Weak forces between all molecules.
• Electrons in a neutral atom or molecule “flow” to one side of the atom/molecule and create a temporary negative charge.

Question 14

Explain the melting points of intermolecular forces.

Answer 14

Melting points of compounds are related to the strength of intermolecular forces between molecules or compounds.
- They are lower due to weak forces such as dispersion forces
- They are higher due to stronger forces such are hydrogen bonding.

Question 15

What is a Chemical change/reaction?

Answer 15

A chemical change occurs when a substance is converted into one or more new substances with different formulas and different properties.
- It may be observed by the formation of bubbles, a change in color, the production of a solid, or heat.

Question 16

What symbols are used in chemical equations?

Answer 16

• An arrow separates reactants from the products
• Reactants are written on the left side of the arrow, products are written on the right side of the arrow
• Multiple reactants or products are separated by a plus sign
• The delta sign indicates heat is used to start the reaction
• Physical states of compounda are denoted in parentheses: solid (s), liquid (l), gas (g), aqueous (aq) or dissolved in water

Question 17

How do you identify a balanced chemical equation?

Answer 17

In a balanced chemical equation, no atoms are lost or gained. Also, the number of atoms on the reactant side is equal to the number of atoms on the product side for each element.

Question 18

T/F: When balancing an equation its okay to change the subscripts.

Answer 18

False!

Question 19

Explain a Combustion Reaction.

Answer 19

In a combustion reaction, a carbon-containing compound burns in oxygen gas to form carbon dioxide and water.
- Energy is released as a product in the form of heat.
Fuel + O2 → H2O and CO2
If I tell you “fuel” = CH4

Question 20

What are the types of Chemical Reactions? Which should I remember?

Answer 20

• Combination Reaction
• Decomposition Reaction
• Single Replacement Reaction
• Double Replacement Reaction
• Combustion Reaction (remember this one!)

Question 21

Explain an Oxidation-Reduction Reaction.

Answer 21

It provides us with energy from food, provides electrical energy in batteries, and occurs when iron rusts.

In an oxidation-reduction reaction, electrons are transferred from one substance to another.

Question 22

What’s the difference between Oxidation and Reduction?

Answer 22

Oxidation: (loss of electrons)
- always involves a loss of electrons
- may also be seen as an addition of oxygen
- may also be seen as the loss of hydrogen atoms

Reduction: (gain of electrons)
- always involves a gain of electrons
- may also be seen as the loss of oxygen
- may also be seen at the gain of hydrogen

OIL RIG:
Oxidation Is Loss
Reductions Is Gain

Question 23

How do you identify if an equation is an oxidation or reduction?

Answer 23

If the charge goes up its oxidized, if the charge goes down its reduced.

Question 24

T/F: Oxidation and Reduction processes always travel in
pairs. When one reactant is oxidized, another reactant has to be reduced.

Answer 24

True

Question 25

Explain Avogadro’s Number (The Mole).

Answer 25

Small particles such as atoms, molecules, and ions are counted using the mole.
1 mole = 6.02 x 10^23 items

Question 26

What is the molar mass?

Answer 26

The quantity called molar mass is the quantity in grams that equals the atomic mass of that element.

For example, 1 mole of sodium has a mass of 22.99 grams.

Question 27

Explain the law of conservation of mass.

Answer 27

It indicated that in an ordinary chemical reaction, matter cannot be created or destroyed, no change in total mass occurs, and the mass of products is equal to the mass of reactants.

Question 28

What is a mole-mole factor/ratio?

Answer 28

A ratio of the moles for any two substances in a equation.

Question 29

What is a Limiting Reactant?

Answer 29

A limiting reactant in a chemical reaction is the substance that is used up first. It limits the amount of product that can form.
- The reactant that does not completely react and is leftover
at the end of the reaction is called the excess reactant.

Question 30

What is a Actual, Theoretical, and Percent Yield?

Answer 30

When the reaction does not go to completion, or some of the reactant or product is lost, the amount of product produced may be less.
* Theoretical yield is the maximum amount of product, which is calculated using the balanced equation.
* Actual yield is the amount of product actually obtained.
* Percent yield is the ratio of actual yield to theoretical yield.

Question 31

How do you balance equations?

Answer 31

1. Write an equation using the correct formulas for the reactants and products.
2. Count the atoms of each element in the reactants and products. (make a chart)
3. Use coefficients to balance each element.
4. Check the final equation to confirm it is balanced.

Question 32

How do you calculate the molar mass of a compound?

Answer 32

Add each element’s molar mass together.