AP Chem Unit 2

who discovers atoms are not indivisible, they have electrons

JJ thompson

cathode rays can be deflected using

electric and magnetic fields

cathode

carries a negative electrical charge

electron

a negatvely charged, low mass particle present in all atoms

Properties of Electrical Charge

• positive and negative attract

• same charges repel each other

• positive and negative charges of the same magnitude sum to zero when combined

radioactivity

emmission of small energetic particles from the core of certain unstable atoms

types of radioactivity

alpha particles, beta particles, gamma rays

Rutherford's Gold Foil Experiment

• Shot alpha particles at gold foil, some pass through, some don't

• proves the nuclear theory of an atom

Nuclear theory (not completely true)

• most of the atom's mass and all its positive charge are contained in a small core called the nucleus

• most of the volume of the atom is empty space, where negative electrons are dispersed

• there are as many negatively charged electrons outside the nucleus as there are positively charge particles (protons) within the nucleus

  • So the atom  is neutral

atomic number

number of protons

• identifies the element

isotopes

diff. number of neutrons

ions

particles that have gained or lost electrons

atomic mass

average mass of all the isotopes atomic mass = (%)(amu)+(%2)(amu2)+(%3)(amu3)...

Mass spectrometry

measuring the mass of atoms and molecules

• identify and measure the amount of different compounds in a sample by converting them into ions and separating them based on their mass-to-charge ratio 

Chemical formula

indicates the elements in the compound and the relative number of atoms/ions for each

Empirical formula

gives the relative number of atoms of each element in a compound

Molecular formula

give the actual number of atoms of each element in a molecule of a compound.

Formula unit

the smallest electrically neutral collection of ions, not a molecule

Hydrates

contain a specific number of water molecules associated with each formula unit

anhydrous

without water

hyrdrous

with water

Naming molecular compounds:

• prefix + name of first element + prefix+base name of 2nd element + ide

mass percent composition

the element's percentage of the compound's total mass

Obtaining the Empirical formula from Experimental data

1. write or calculat ehte given masses of each element

2. convert mass to moles using the molar masses

3. write a pseudoformula for the compound using number of moles from each element as subscripts

4. divide all the subscripts by the smallest subscript

5. multiply them all by some number to make them whole numbers (if already whole, multiply by 1)

Determining the molecular formula for compounds:

1. find the empirical formula

2. calculat ethe molar mass

3. calculat ehte empirical formula mass

4. divide molar mass by empirical mass, that number is n

5. multiply each subscript ni the empirical formula by n

Combustion analysis

converting C and H, or C, H and O into some amount of water and carbon dioxide

Organic compounds

composed of C and H and some other elements

Hydrocarbons

only contain C and H 

naming hydrocabrons

base name (determined by # of C atoms)+ suffix (detemined by presence of multiple bonds)

Balancing equations

add coefficients to the reactants and products to make the number of each type of atom the same on both sides

Writing combustion equation: 

1. write out the CxHy --> CO2 + H2O

2. balance the equation

Stoichiometry

• numerical realtionships between chemical amounts in a balanced chemical equation are called reaction stoichiometry

• use the chemical or empirical formulas as conversion factors

Limiting reactant:

the one you will run out of first

Theoretical yield:

the maximum amount of product that can be made in a chemical reaction based on the amount of limiting reactant

actual yield:

The amount of product actually produced in a chemical reactant

• obtained from a lab

• always less than or equal to the theoretical yield

Percent Yield:

the percentage of the theoretical yield that was actually attained. (ratio of the actual yield to the theoretical yield)

Reactant in excess

any reactant that occurs in a quantity greater than is required to completely react with the limiting reactant

calculating limiting reactant 

1. Balance the chemical equation

2. convert mass of each reactant into moles, least amount of moles is the limiting reactant

Calculate theoretical yield:

1. convert moles of limiting reactant to mole of product

2. convert moles of product to grams, this is the maximum amount of product that can be formed

Calculate percent yield

1. divide actual yield by theoretical yield

2. multiply by 100

Calculate reactant in excess

1. identify the limiting reactant

2. calculate the amount of excess reactant consumed (using moles of limiting reactant)

3. calculate the amount of excess reactant remaining by subtracting consumed from original (initial amount of excess reactant - step 2)

Solution

mixture of two substances, homogenous

solute

minority component

solvent

majority component

aqueous solution

water is the solvent

dilute solution

small amount of solute relative to the solvent

concentrated solution

large amount of solute relative to the solvent

synthesis or combination reactions

two or more substances react to form one product

decomposition reactions

one substance breaks down into 2 or more substances

displacement reaction/single replacement reaction

a free elemnt replaces a less active element in a compound

double replacement reaction

involves the exchange of positive ions between two compounds

• usually results in the production of a precipitate (solid) or water

combustion reactions

• most often involve the reaction of oxygen gas and as compound containing C and H or C, H, Oto from H2O and CO2