Suggested Reading pgs Pages 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 Indivisible This 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
4 g 32 g 36 g 4 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:
Salt - NaCl is 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