Glossary
Compound
A pure substance formed when two or more different elements are chemically bonded together in a fixed ratio.
Example:
Carbon dioxide (CO2) is a compound because it's made of carbon and oxygen atoms chemically joined in a 1:2 ratio.
Element
A pure substance consisting of only one type of atom, which cannot be broken down into simpler substances by chemical means.
Example:
Gold (Au) is an element; you can't chemically break it down into anything simpler.
Empirical Formula
The simplest whole-number ratio of atoms in a compound, derived from experimental data like percent composition.
Example:
While hydrogen peroxide's molecular formula is H2O2, its empirical formula is HO, representing the simplest ratio of hydrogen to oxygen atoms.
Formula Unit
The lowest whole-number ratio of ions in an ionic compound, representing the empirical formula of the compound.
Example:
For calcium chloride, CaCl2, one formula unit consists of one calcium ion and two chloride ions.
Gas
A state of matter with no fixed shape or volume, expanding to fill its container, with particles widely spread out and in constant, random motion.
Example:
The helium inside a balloon is a gas that will expand to fill the entire room if the balloon pops.
Law of Definite Proportions
States that a chemical compound always contains the same elements in the same proportions by mass, regardless of the source or sample size.
Example:
Every sample of pure water, whether from a tap or a glacier, will always have hydrogen and oxygen in the same 1:8 mass ratio, illustrating the Law of Definite Proportions.
Liquid
A state of matter with a fixed volume but no fixed shape, adapting to its container while particles can flow past each other.
Example:
When you pour water into a glass, the liquid takes the shape of the glass but its volume remains constant.
Matter
Anything that has mass and takes up space.
Example:
The air you breathe, the water you drink, and the desk you study on are all forms of matter.
Mixture
Matter composed of two or more substances that are physically combined but not chemically bonded, and can often be separated by physical means.
Example:
Saltwater is a mixture where salt and water are combined but retain their individual chemical identities.
Pure Substance
Matter composed of a single type of atom or molecule, having a consistent and uniform composition throughout.
Example:
Distilled water is a pure substance because it consists only of H2O molecules, with no dissolved impurities.
Solid
A state of matter characterized by a fixed shape and volume, with particles densely packed and vibrating in place.
Example:
An ice cube is a solid that maintains its rigid shape even when moved from one container to another.