Suggested Reading pgs.. 67 - 71 Pages 66-70

Chapter 3, Section 1 - Atoms

STM (scanning tunneling microscope) image of a single zigzag chain of cesium atoms (red) on a gallium-arsenide surface (blue)

450 B.C. Greek - Democritus “All matter is composed of tiny, indivisible particles”Atomos means IndivisibleThis idea is not related to a measurable property … it can’t be experimentally tested

Early Models of the Atom

The transformation of a substance into one or more new substance. With new chemical and physical properties.

Reactants Products

Chemical Reaction

States that mass is neither created nor destroyed during ordinary chemical reactions or physical changes.

Law of Conservation of Mass

Law of Conservation of Mass

4 g 32 g

36 g4 H

2 O

4 H

2 O

total mass stays the same atoms can only rearrange

A chemical contains the same elements in exactly the same proportions by mass, regardless of the size of the sample, or the source of the compound.

Law of Definite Proportions:

Law of Definite Proportions:

Salt - NaClis always 39.34% Sodium and 60.66% Chlorine

When elements combine, they do so in small whole number ratios. (non-metals)

Law of Multiple Proportions:

The smallest unit of an element that retains the chemical identity of that element.

There are about 110 different kinds of atoms that combine to form all matter.

Atom

Dalton’s Atomic Theory – Early 1800’s

All matter is composed of atoms. Atoms of a given element are

identical, but are different from atoms of other elements.

Atoms cannot be subdivided, created, or destroyed.

Dalton’s Atomic Theory – Early 1800’s

Atoms of different elements combine in simple whole-number ratios to form chemical compounds.

In chemical reactions, atoms are combined, separated, or rearranged.

Dalton’s Atomic Theory – Early 1800’s

Revisions to Dalton’s Atomic Theory

Atoms are divisible into smaller particles called subatomic particles.

A given element can have atoms with different masses, called isotopes.

Scanning Tunneling Microscope

STM – provides “close” to a 3-D picture of atoms – that’s the best we can see, even today.

STM picture of Nickel atoms