chem

Solid

A state of matter with definite shape and volume, where particles vibrate in fixed positions.

Liquid

A state of matter with definite volume but no definite shape, where particles are close together and can slide past each other.

Gas

A state of matter with no definite shape or volume, where particles move freely and spread out.

Physical Change

A change that does not alter the substance's identity, only its form or state.

Chemical Change

A change that produces a new substance by rearranging atoms, usually irreversible.

Pure Substance

Material with a fixed composition that consists of only one type of particle.

Mixture

A combination of two or more substances that can be physically separated.

Homogeneous Mixture

A mixture that has a uniform composition throughout, such as air or salt water.

Heterogeneous Mixture

A mixture where the components are not uniform, like salad dressing or granite.

Filtration

A separation technique that removes solids from liquids.

Distillation

A method to separate liquids based on their boiling points.

Scientific Notation

A way of expressing numbers as a product of a number between 1 and 10 and a power of 10.

Significant Figures

Digits in a number that carry meaningful information about its precision.

Density

A physical property defined as mass per unit volume.

Atomic Number

The number of protons in the nucleus of an atom, defining the element.

Electron

A negatively charged subatomic particle discovered by J.J. Thomson.

Proton

A positively charged subatomic particle found in the nucleus, identified by Rutherford.

Neutron

A neutral subatomic particle discovered by James Chadwick.

Isotope

Atoms of the same element with the same number of protons but different numbers of neutrons.

Cation

A positively charged ion, formed by losing electrons.

Anion

A negatively charged ion, formed by gaining electrons.

Alkali Metals

Group 1 elements that have a 1+ charge and are highly reactive.

Alkaline Earth Metals

Group 2 elements with a 2+ charge.

Halogens

Group 17 elements known for their strong reactivity and 1- charge.

Noble Gases

Group 18 elements that are inert and have a full valence electron shell.

Plum Pudding Model

An early model of atomic structure proposed by J.J. Thomson, suggesting electrons are scattered within a positively charged 'soup'.

Gold Foil Experiment

An experiment conducted by Rutherford that led to the discovery of the nucleus.

Diatomic Molecule

A molecule consisting of two atoms, such as H₂ or O₂.

Molar Mass

The mass of one mole of a substance, expressed in grams per mole.

Empirical Formula

The simplest whole-number ratio of elements in a compound.

Molecular Formula

The actual number of atoms of each element in a molecule.

Balancing Reactions

The process of ensuring the same number of each type of atom appears on both sides of a chemical equation.

Conservation of Mass

The principle stating that matter is not created or destroyed in a chemical reaction.

Synthesis Reaction

A type of reaction where two or more substances combine to form a new compound.

Decomposition Reaction

A reaction where a compound breaks down into simpler substances.

Single Replacement Reaction

A reaction where one element replaces another in a compound.

Double Replacement Reaction

A reaction involving the exchange of ions between two compounds.

Combustion Reaction

A rapid reaction between a hydrocarbon and oxygen that produces carbon dioxide and water.

Avogadro’s Number

6.022 × 10²³, the number of particles in one mole of a substance.

Percent Composition

The percent by mass of each element in a compound.

Phase Change

The transition of a substance from one state of matter to another.

Density Formula

Density = mass ÷ volume.

Accuracy

The degree to which a measurement reflects the true value.

Precision

The degree to which repeated measurements yield the same result.

Captive Zeros

Zeros that occur between non-zero digits and are considered significant.

Leading Zeros

Zeros to the left of the first nonzero digit, which are not significant.

Trailing Zeros

Zeros to the right of a decimal point that are significant only if there is a decimal.

Dimensional Analysis

A mathematical technique utilized to convert between units.

Hydrocarbon

Compounds composed solely of hydrogen and carbon, typically burned in combustion reactions.