Chapter 2: Atoms and Elements

Vocabulary flashcards covering key terms, people, laws, and concepts from Chapter Two: Atoms and Elements (Lesson One).

Brownian Motion

The random motion of microscopic particles suspended in a fluid caused by collisions with invisible molecules; evidence for atoms and molecules (Einstein and Perrin).

Atom

The fundamental, originally indivisible unit of matter; later understood as the building block of elements.

Molecule

A group of two or more atoms bonded together; smallest unit of a compound.

Democritus

Ancient Greek philosopher who proposed that matter consists of indivisible atoms moving through empty space; summarized as 'Nothing exists except atoms and empty space.'

Leucippus

Early philosopher who introduced atomism; atoms differ in shape and size and move through empty space.

Aristotle

Ancient philosopher who argued against atomism, proposing that matter is made of four elements and is infinitely divisible.

Plato

Ancient philosopher who, like Aristotle, did not embrace atomism; supported the idea of four elemental components for matter.

Four Elements

Water, Fire, Earth, and Air; proposed as the basic components of matter by classical thinkers.

John Dalton

English chemist who revived atomic theory and argued that matter is composed of atoms with simple, common properties and combine in simple whole-number ratios.

Dalton's Atomic Theory

Atoms are the tiny, indestructible particles of elements; atoms of a given element are identical; atoms combine in simple whole-number ratios to form compounds; atoms cannot change into other elements; in reactions, atoms are rearranged.

Law of Conservation of Mass

In chemical reactions, matter is neither created nor destroyed; the mass of the reactants equals the mass of the products.

Antoine Lavoisier

French chemist who formulated the Law of Conservation of Mass; helped establish modern chemistry.

Joseph Proust

French chemist who formulated the Law of Definite Proportions.

Law of Definite Proportions

A given compound always contains its elements in fixed, definite mass ratios (also called the Law of Constant Composition).

Water composition (H2O)

In water, the mass ratio of hydrogen to oxygen is 1:8 (e.g., 2 g H and 16 g O in 18 g of water).

Ammonia composition (NH3)

Mass ratio N:H is 14:3 (approximately 4.67:1).

Law of Multiple Proportions

When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in small whole-number ratios.

Carbon Monoxide and Carbon Dioxide

Two compounds of carbon and oxygen; the masses of oxygen that combine with 1 g of carbon form small whole-number ratios (e.g., CO and CO2 show different O:C ratios).

Constant Composition

Another name for the Law of Definite Proportions.

Indestructible particles

Another way to describe atoms in Dalton's theory as the basic, indivisible units of matter.

Empty space

The void through which atoms move in atomistic theories (as proposed by Democritus and Leucippus).

Simple, whole-number ratios

In compounds, atoms combine in simple whole-number ratios to form substances, a key idea underlying several classical laws.