Gen Chemistry Notes: Matter, Atoms, Molecules, and Measurements

Vocabulary flashcards covering key terms from the notes on matter, atoms, molecules, mixtures, and basic measurement concepts.

Matter

Anything that has mass and occupies space.

Mass

A measure of the amount of matter in an object; typically measured in grams.

Element

A pure substance consisting of only one type of atom; defined by its atomic number.

Atom

The basic unit of an element; composed of protons and neutrons in the nucleus and electrons surrounding it.

Atomic number

The number of protons in the nucleus; identifies the element.

Atomic mass

The average mass of an atom, in atomic mass units (amu).

Proton

Positively charged subatomic particle in the nucleus; mass ~1 amu.

Neutron

Electrically neutral subatomic particle in the nucleus; mass ~1 amu.

Electron

Negatively charged subatomic particle surrounding the nucleus; very small mass.

Nucleus

The center of an atom containing protons and neutrons.

Electron cloud

Region around the nucleus where electrons are likely to be found.

Molecule

Two or more atoms held together by chemical bonds.

Compound

A substance formed when two or more elements join chemically in fixed proportions; all compounds are molecules.

Pure substance

A substance with a fixed composition, either an element or a compound.

Homoatomic

A molecule composed of the same element (e.g., O2).

Heteroatomic

A molecule composed of different elements (e.g., H2O).

Macroscopic

Scale visible to the naked eye.

Microscopic

Scale visible under a light microscope; not visible to the naked eye.

Submicroscopic

Scale requiring advanced tools to observe; atoms and molecules beyond light microscopy.

TEM (Transmission Electron Microscope)

A microscope used to observe submicroscopic structures, including atoms.

Physical properties

Characteristics observed without changing composition (e.g., color, density, melting point).

Chemical properties

How a substance changes or reacts to form new substances (e.g., flammability).

Mixtures

A combination of two or more substances physically mixed; can be separated by physical methods.

Homogeneous mixture

A uniform mixture with the same composition throughout (solutions).

Heterogeneous mixture

A mixture with a non-uniform composition; different parts are visible.

Separation of mixtures

Physical methods (filtration, distillation, etc.) to separate components.

Meter (m)

Unit of length in the metric system.

Liter (L)

Unit of volume; 1 L = 1000 mL.

Gram (g)

Unit of mass; common unit for small masses.

Celsius (°C)

Temperature scale where water freezes at 0°C and boils at 100°C; C = K − 273.

Fahrenheit (°F)

Temperature scale where water freezes at 32°F and boils at 212°F.

Kelvin (K)

Absolute temperature scale; 0 K is absolute zero; C = K − 273.

Boiling point of water

100°C (212°F) at standard pressure.

Freezing point of water

0°C (32°F).

Kelvin to Celsius conversion

To convert K to °C, subtract 273; C = K − 273.

Significant figures

Digits that carry meaning about measurement precision; uncertain digits are not known.

Multiplication/division sig figs rule

Result should have as many significant figures as the least precise factor.

Addition/subtraction sig figs rule

Result should be rounded to the least precise decimal place among the terms.

Density

Mass per unit volume; density = mass/volume.

Volume

Amount of space a substance occupies; commonly measured in liters or cubic meters.