Chemistry Regents Review

Dalton's model of the atom

• atoms cannot be created nor destroyed
• mass of reactants = mass or products

Thompson's model of the atom; "Plum pudding"

• cathode ray tubes
• discovery of the electron
• positive and negative charges randomly scattered

Rutherford's model of the atom; "Nuclear model"

• gold foil experiment
• atom is mostly empty space
• positively charged center (nucleus)
• negative charges randomly scattered around nucleus

Bohr's model of the atom; "Planetary model"

• electrons revolve around nucleus, like planets to the sun
• orbitals = circular paths

Modern model; "Wave Mechanical"

• electrons have particle and wavelike properties
• orbital = location of an electron (not a circular path)

Charge, weight, and location of proton

+1, 1 amu, nucleus

Charge, weight, and location of electron

-1, 0 amu, orbitals

Charge, weight, and location of neutron

0, 1 amu, nucleus

Amount of each subatomic particle

number of protons = atomic number

number of electrons = number of protons (IF NOT AN ION)

number of neutrons = (mass number) - (number of protons)

Isotope

same element, different mass number; same number of protons, different number of neutrons

Average atomic mass formula

(% abundance as decimal)(mass) + (% abundance as decimal)(mass)

Principle energy level

orbital

• 1st p.e.l. = maximum 2 electrons
• 2nd p.e.l. = 8 electrons
• 3rd p.e.l. = 18 electrons

Valence electrons

electrons in the outermost principle energy level

The farther away an orbital is from the nucleus…

the more energy the orbital and its electrons have

Ground state

the state where the atoms are in the lowest available principle energy levels

• stable

Excited state

the state when an electron absorbs exactly the right amount of energy, jumping to a higher energy level

• unstable
• releases energy, in the form of bright line spectra, when it returns to ground state
• spectra lines are unique to each element

Pure substances

elements or compounds

• can only be broken down / changed by a chemical reaction

Elements

contains 1 type of atom, cannot be decomposed further

Compounds

contains 2 or more elements chemically combined in fixed proportions

Mixtures

2 or more elements combined without a chemical reaction taking place

• can be homogeneous or heterogeneous

Separation methods of mixtures

distillation, filtration, evaporation, chromatography, desalination (all physical separation)

Filtration: small particles pass through, large particles trapped

• Filtrate - substance that passes through the filter

• Residue - substance trapped on the filter

• Cannot be used to separate homogeneous mixtures, including solutions

Distillation: separation based on differences in boiling points

Chromatography: components of a mixture separate based on differences in the attraction from a transporting medium

Separation methods of compounds

chemical reactions; cannot be separated physically

Molecular formula

shows the actual ratio of atoms (ex. C₆H₁₄)

Empirical formula

shows the ratio of atoms in simplest terms (ex. C₆H₁₄ would turn into C₃H₇)

Structural formula

shows bonding

Charge of an atom

neutral, number of protons = number of electrons

Ions

charged particles

• loss of electrons = positive ion

• gain of electrons = negative ion

Polyatomic ions

ions that contain more than one element

Exothermic reaction

heat is released; heat is a product (ex. breaking a bond = exothermic; “breaking glowstick releases light”)

Endothermic reaction

heat is absorbed; heat is a reactant (ex. forming a bond = endothermic)

Law of Conservation of Mass

during a chemical reaction, matter is neither created nor destroyed, the number and types of atoms on both sides of the chemical equation must be the same

Synthesis

2 or more elements/compounds combine to form 1 product

Decomposition

a single compound is broken down to form 2 or more products

Single Replacement

a single element replaces another element in a compound

Double Replacement

the elements in combining compounds “switch”

An element can only replace an element that is…

less reactive

Naming ionic compounds

keepthe name of the first element, modify ending to -ide unless it is a polyatomic ion

Naming covalent compounds

follow ionic rules, then use a prefix for the amount of the first element (ex. 2 = di)

Gram Formula Mass

(amount of each individual atom) * (its weight); expressed in grams rather than amu

Percentage of Water in a Hydrate

(mass of water) / (mass of the whole compound) * 100

Mole

the number of particles (Avogadro’s number) that have a mass equal to the gram formula mass (ex. 18g of H₂O is 1 mole because H₂O has a gfm of 18g)

Phase changes

Change	Name
solid → liquid	melting / fusion
liquid → gas	vaporization
liquid → solid	freezing / solidification
gas → liquid	condensation
solid → gas	sublimation
gas → solid	deposition

Kinetic Energy

energy of motion

• greater the kinetic energy, the faster the particles are moving

Potential Energy

stored energy; energy of position

During phase change…

kinetic energy - constant

potential energy - changes

• If heating, potential energy ↑

• If cooling, potential energy ↓

There are __ phases present during phase change

2

Heat flows from…

hot → cold, until at equilibrium

Heat equations and their purposes

q = mc∆T	use when there is a change in temperature
q = mH₁	use when melting / freezing is taking place
q = mH₂	use when evaporation / condensation is taking place

H₁ = heat of fusion

H₂ = heat of vaporization

Kinetic Molecular Theory

used to explain the behavior of gases

Assumptions:

• Gas particles are in constant, random straight line motion

• Gas particles collide with each other and the walls of the container (collisions are elastic - no net change in energy)

• Gas particles are separated by great distances (volume of particles is negligible)

• Gas particles do not attract each other

Gas Relationships

Pressure and # of particles	Direct
Pressure and Temperature	Direct
Pressure and Volume	Indirect
Temperature and Velocity	Direct

Combined Gas Law

(P₁V₁) / T₁ = (P₂V₂) / T₂

• Temperature MUST be in Kelvins

• If any variables are constant, cross them out in the formula

Gases behave most ideal in…

high temperature and low pressure

• Most ideal gases - hydrogen, helium

Avogadro’s Law

equal volumes of gases at the same temperature and same pressure have an equal number of particles