Consider significant figures when necessary.
What is Chemistry?
- Chemistry is the study of matter and its interactions
- Matter is anything that takes up space and has volume/is made up of atoms.
- Atoms - basic building block/one individual unit → Helium atom
- Molecules - Multiple atoms bonded together → O2 Molecule
- Element - Categorization of the type of atom → Helium
- Compound - Multiple elements bonded together → H2O compound
- Physical Properties - the way that something appears → Color of an object
- Physical Change - An alteration of appearance → Melting
- Chemical Properties - Properties that can only be changed chemically → Boiling point.
- Chemical Change - A change of composition → Rust
- Mixture - Two different substances combined - but not chemically bonded
Significant Figures Rules
- Basics
- Any digit from 1-9 is always significant.
- Zeroes between non-zero digits are always significant - (1000 → 1) vs (1001 → 4).
- Trailing zeroes in numbers with no decimal point are not significant. (24000 → 2)
- Trailing zeroes in numbers with a decimal point are significant. (1.2345000 → 8)
- Leading zeroes are not significant. (0.000000001 → 1)
- Counting numbers have infinite significant figures.
- If you have a number that ends in a 0 but needs a certain number of significant figures, use scientific
notion or a decimal point after the number without anything afterward (90. has 2 significant figures).
- Addition/Subtraction
- Line up the decimal points and round to the number with the decimal points that are farthest to the left.
- Multiplication/Division
- Round to the number with the least amount of significant figures.
Units of Measurement
- Metric Prefixes
- Kilo - K - 1000
- Deci - D - 0.1
- Centi - C - 0.01
- Mili - M - 0.001
- Micro - υ - 0.000001
- Nano - n - 0.000000001
Atomic Numbers
- Atomic # - # of protons
- Mass - Mass of the atoms (# in isotope name)
- # Protons → = to atomic number
- # Electrons → = to protons
- # Neutrons → Mass - protons
Avg Atomic Mass
- Multiply the weight of the atom with its percentage in the sample
- Add the sums & divide by 100
Moles
- 1 mol = 6.02 * 10^23 atoms
- 1 atom = certain weight | 1 mol amt of atoms = same weight in grams
- Elements stay in the same ratio no matter what
- i.e. if there are 12 molecules of NH3, there will be 12 N atoms and 36 H atoms
- if a set of elems is in parentheses, that means there’s more than one
- i.e. Ca(NO3)2 means there’s 1 Ca atom and 2 NO3 ions → (2 nitrogen atoms and 6 oxygen
atoms)
Dalton
- Each element is composed of extremely small particles called atoms
- Atoms can be broken down into smaller parts
- All atoms of a given element are identical, but the atoms of one element are different from the atoms of all other
elements
- There are different isotopes of a single element - silicon has multiple different kinds of atoms, but they’re
all silicon because they have the same number of protons
- Atoms of one element cannot be changed into atoms of a different element by chemical reactions; atoms are
neither created nor destroyed in chemical reactions.
- The rest of the wood burns into carbon dioxide at a certain temperature, creating a different substance
- Compounds are formed when atoms of more than one element combine; a given compound always has the same
relative number and kind of atoms.
- The formatting of the elements matter - a compound can have the same exact ratio and number of
elements but the arrangement of the elements determines the properties of the compound.
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