Chemistry Notes

Chemistry is the study of all substances and the changes that they can undergo
Chemistry is called the central science b/c it overlaps so many sciences
The scientific method is a way of answering questions about the world we live in
Steps of the method: observation => question => hypothesis => experiment => conclusion
The variable is the factor being tested

An experimental control responds in a predictable way to the experiment
Mass (kg), length (m), time (s), quantity (mole), temp. (K), electric current (ampere), luminous intensity
(candela), area (m2), volume (m3), force (Newton), pressure (pascal), energy (joule), power (watt),
voltage (volt), frequency (hertz, Hz), electric charge (coulomb, C), NON-SI: volume (liter), pressure
(atm, measured in mm Hg), temp. (Celsius), energy (calorie, cal)

Measurements are uncertain for two reasons: measuring instruments aren’t flawless and measuring always
involves some estimation
A correct answer is an accepted value for a measurement
The certain digits and estimated digit or a measurement are together called the significant digits
A measurement can be compared with its accepted value by calc. its percent error: (measured value –
accepted value) / accepted value

Density is calc. by dividing mass by volume
Speed = distance / time, pop. Density = pop. / area
Converting between units is called dimensional analysisFour step problem solving strategy: analyze, plan, solve, evaluate
Energy is the capacity to do work or produce heat
Potential, kinetic, and radiant energy
0 K and -273 C is absolute zero
Physical changes don’t alter the identity of the substance, while chemical changes do
Law of conservation of matter/energy

An element is a substance that cannot be separated into simpler substances by a chemical change,
a pure substance
Two or more elements combine to form a compound
A mixture is a blend of two or more pure substancesHeterogeneous mixture has visibly different parts, while a homogeneous mixture doesn’t
Ionic bond: pos. charged ion attracted to a neg. charged ion
Ionic compound composed entirely of ions
Pos. charged ions called cations, neg. charged called anions
Octet rule- atoms tend to gain, lose, or share electrons in order to
acquire a full set of valence electrons
(Gilbert) Lewis Dot Diagrams are an easy way to represent valence
electrons making them popular

To name a monatomic anion, replace the suffix with –ide
All ionic compounds are electrically neutral
Monatomic/polyatomic ions- only one atom/more than one atom
Binary ionic compounds contain ions of only two elementsEmpirical formula is same as chemical formula

A covalent bond is formed by a shared pair of electrons between two atoms
A substance of molecules is a molecular substance
A molecular formula tells how many atoms are in a single molecule of a
compound
A structural formula specifies which atoms are bonded to each other in a
molecule

When one atom is significantly more electronegative than another, a covalent
bond
between them is said to be polar- the atom with greater electronegativity gains
a slight negative charge because it has a slight excess of electron density
When in a bond, when both atoms exert an equal pull on the electrons in the
bond, the bond is noonpolar
Chemists name a compound according to the atoms and bonds that compose it
Ionic compounds that absorb water into their solid structures form hydrates
Anhydrous substances are water-free

Electronegativity difference: <0.4>0.5, < 1.9 is polar covalent, and >2.0 is ionic
1+: hydrogen, sodium, potassium, ammonium (NH4+), lithium, silver, copper
2+: magnesium, iron, cobalt, nickel, calcium, zinc, copper
3+: aluminum, iron, cobalt, nickel
1-: fluoride, chloride, bromide, iodide, hydroxide (OH-), hypochlorite (ClO-),
nitrate (NO3-), bicarbonate (HCO3-), acetate (C2H3O2-)
2-: oxide, sulfide, sulfate (SO4 2-), carbonate (CO3 2-),
3-: nitride, phosphide, phosphate (PO4 3-)
To make an acid, take the base element, find cation/anion number, put that
on the end of an H, and at the (H + number) to the front of the compound
in question to make the acid
Mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca
OH- (hydroxide), NO3 – (nitrate), CO3 -2 (carbonate), SO4 -2 (sulfate),
PO4 -3 (phosphate) Two elements- ide ending
Whenever there’s 1 less oxygen than expected, change suffix (-ate -> ite)Transition metals need roman numerals, nonmetals need prefixes

A line spectrum contains only certain colors or wavelengths
The number of protons in an atom is its atomic number
When an atom loses or gains one or more electrons, it acquires a net electrical charge and is
called an ion
Atoms with the same number of protons but different numbers of neutrons are called isotopes
The strong nuclear force holds together the contents of the nucleusNuclear reactions change the composition of an atom’s nucleus