Chemistry Exam 2 Flashcards
Valence Shell Electron Repulsion Theory
-Model used to predict 3D molecule shapes
-based on how electrons repel one another (move as far apart as possible)
Steric Number
-# of electron groups around an atom
-# of atoms attached + # of lone pairs
Molecular Shape vs Electron Geometry
-Electron geometry is the shape of the atom including lone pairs
-molecular shape does not include lone pairs
Molecular Shapes (5 Types)
-tetrahedral
-pyramidal
-bent
-trigonal planar
-linear
Electron Geometry (3 types) & Bond Angles
-linear (180 degrees)
-trigonal planar (120 degrees)
-tetrahedral (109.2 degrees)
VSEPR Steps
- Draw lewis structure
- Find steric #
- Predict maximum angle
Intermolecular Forces
-forces that hold neighboring molecules together
-determined by molecular shape
Bond Type Strengths
- Covalent bonds are stronger than Ionic
- Ionic are stronger than Hydrogen bonds
- Hydrogen bonds are stronger than Van der Waals
Water Dipole Movement
Has a net dipole movement (evenly positive and negative)
Dipole-dipole Interactions in Hydrogen Bonding
-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
Hydrogen Bonding in Water
-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)
Num. of Bonds Differ in Ice and Liquid Water
Both have H-bonds, but liquid water has fewer than half as many as ice
Water as a Solvent
-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)
Hydrocarbon Polarity
Anything that’s 100% hydrocarbon is non-polar (as you add oxygen, it becomes more polar)
Van der Waals Interactions (London Dispersion Forces)
-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
What happens when a droplet of oil is added to water?
What about Olive oil?
The oil will float on water and remain a droplet
(Olive oil will spread out on the surface because it’s slightly polar)
What is a Chemical Reaction?
A chemical change happens when one or more substances are destroyed and one or more new substances are created
Reactants
Substances that are destroyed by the chemical change (bonds break)
Products
Substances created by the chemical change (new bonds form)
Aqueous Solution
Means the substance is dissolved in water
Evidence (Signs) of a Chemical Reaction
- Evolution of light or heat
- Temp change (incr or decr)
- Formation of gas (bubbling or odor) other than boiling
- Color change (due to formation of new substance)
- Formation of precipitate (a new solid forms) from reaction of 2 aqueous solutions
Coefficients vs Subscripts
-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)
Conservation of Mass Law
During a chem reaction, atoms are neither created nor destroyed
5 Basic Types of Chem Reactions
- Single Replacement (Displacement) (Redox)
- Double Replacement
- Synthesis (Combination)
- Decomposition
- Combustion
Single Replacement
-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!)
Double Replacement
-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
Soluble Compounds
Compounds that break down when put in water (ex NaCl)
Solubility Rules
Use the Solubility Chart to determine if products in double replacement will be a precipitate
Synthesis Reaction
-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
Decomposition Reactions
-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)
Combustion Reactions
-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
Avagadro’s Number
-1 mole is equal to 6.02 x 10^23
Molar Mass
= 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)
Molar Mass of Molecules and Compounds (Gram Formula Mass)
-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
Calculations with Molar Mass
moles = given mass (grams) / gram-formula mass
Empirical Formula
Expresses smallest whole # ratio of atoms present
*Ionic formulas are always empirical
*This is the one where you divide the subscripts!
Molecular Formula
States the actual # of each kind of atom found in one molecule of the compound
*a multiple of the subscripts in the empirical formula
