The Atom: From Philosophical Idea to Scientific Theory Section 3.1

Defining the Atom- (see p. 43) The _______philosopher ____________(460 B.C. – 370 B.C.) was among the first to suggest the existence of _________(from the Greek word “atomos”). He believed that “atoms” were __________ and ________________. His ideas did agree with later scientific theory, but did not explain __________ _____________. They were ______________ ___________________but just philosophy.

Foundations of the Atomic Theory Better equipment (technology) for the study of matter became available later in history as _____________________ started being conducted. This lead to the discovery of several ________________________. There was no real explanation for the laws until ____________proposed his atomic theory.

Law of Conservation of Mass __________________________: mass is neither created nor destroyed during ordinary chemical reactions or physical changes

Law of Definite Proportions _____________________________: chemical compounds contain the same elements in exactly the same proportions by mass, regardless of the size of the sample

Law of Multiple Proportions _________________________: if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers

Visual for Law of Multiple Proportions

Dalton John Dalton was a schoolteacher in England around 1800. He proposed an explanation for the three laws previously mentioned. He said that elements were composed of ________and only ______________ __________ of atoms could combine to form ____________________.

Dalton’s Atomic Theory 1) All matter is composed of extremely small particles called __________ 2) Atoms of a __________________ are _________________in size, mass, and other properties; atoms of __________ elements _________in size, mass, and other properties 3) Atoms cannot be _______________, _____________, or ______________

Continued 4) Atoms of different elements combine in ___________________ _______ to form __________________. 5) In chemical reactions, atoms are _____________, ______________, or _________________.

Modern Atomic Theory Dalton’s theory was scientific, but not entirely correct. We now know that atoms are _______ into smaller particles. A given element can have atoms with _________________masses. Dalton’s model is called the “_______ __________” or “____________” model.

Dalton’s idea of the atom A Particle Model of the Atom