chapter 1-3

Atom

smallest unit of an element.

Molecule

2+ atoms bonded together.

Scientific law

summary of observations

Theory

explanation of why/how something happens.

Law of Conservation of Mass

Matter cannot be created or destroyed in a chemical reaction.

Solid

fixed shape & volume.

Liquid

fixed volume

Gas

variable shape & volume.

Crystalline solid

ordered structure (NaCl).

Amorphous solid

no long-range order (glass).

Element

one type of atom.

Compound

2+ atoms chemically bonded.

Mixture

physical combination of substances (homogeneous = uniform

Physical property

observed without composition change (melting point).

Chemical property

involves a change in composition (flammability).

Physical change

no new substance (melting ice).

Chemical change

new substance formed (rusting).

Intensive property

independent of amount (density

Extensive property

depends on amount (mass

SI base units

meter

Density formula

d = m/V.

Temperature conversion

K = °C + 273.15

°C = (°F - 32)/1.8.

Accuracy

closeness to true value.

Precision

reproducibility of measurements.

Random error

unpredictable variation.

Systematic error

consistent bias/error.

Dimensional analysis

Using conversion factors to cancel units and solve problems.

Law of Definite Proportions

A compound always has the same ratio of elements by mass.

Law of Multiple Proportions

When 2 elements form multiple compounds

Dalton's Atomic Theory

(1) Matter = atoms. (2) Atoms of an element are identical. (3) Atoms combine in whole numbers. (4) Atoms rearrange in reactions.

Proton

+1 charge

Neutron

0 charge

Electron

-1 charge

Atomic number

number of protons.

Mass number

number of protons + neutrons.

Isotope

Atoms of the same element with different numbers of neutrons.

Periodic Law

Properties of elements are periodic functions of their atomic numbers.

Cation

positive ion (lost e⁻).

Anion

negative ion (gained e⁻).

Mole

6.022 × 10²³ particles (Avogadro's number).

Molar mass

Mass of 1 mole of a substance (g/mol).

Ionic compound

metal + nonmetal (transfer of electrons).

Molecular compound

nonmetal + nonmetal (sharing electrons).

Empirical formula

simplest ratio.

Molecular formula

actual number of atoms.

Diatomic elements

H₂

Polyatomic ions

NO₃⁻ (nitrate)

Hydrates

Ionic compounds with water molecules (CuSO₄·5H₂O = copper(II) sulfate pentahydrate).

Percent composition formula

% element = (mass of element in 1 mol compound ÷ molar mass) × 100.

Empirical formula from percent composition

Convert % → grams → moles → simplest whole-number ratio.

Molecular formula from empirical formula

Molecular = n × Empirical

Combustion analysis

Burn compound → collect CO₂ and H₂O → use their masses to find C and H content (and O if needed).