Chapter 3 Chemical Foundations: Elements, Atoms, and Ions

3.1 The Elements We will be doing an activity to learn the various elements in the periodic table Assign Elements!

3.2 Atoms and Compounds Objectives: 1. To learn about Dalton’s theory of atoms 2. To understand and illustrate the Law of constant composition 3. To learn how a formula describes a compound’s composition

A. Dalton’s Atomic Theory What was known about the nature of materials: 1. Most natural materials are mixtures of pure substances. 2. Pure substances are either elements or combinations of elements- called compounds. 3. A given compound always contains the same proportions (by mass) of the elements. Law of constant composition- a given compound always has the same composition regardless of where it comes from

Dalton’s Atomic Theory: 1. Elements are made of tiny particles called atoms. 2. All atoms of a given element are identical. 3. The atoms of a given element are different from those of any other element. 4. Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms. 5. Atoms are not created or destroyed in chemical reactions. The atoms will be rearranged differently after a chemical reaction.

B. Formulas of Compounds Tools for Writing Formulas: 1. Each atom present is represented by its element symbol 2. The number of each type of atom is indicated by a subscript written to the right of the element symbol. 3. When only one atom of a given type is present, do not write the #1.

Practice a. A molecule contains four phosphorus atoms and ten oxygen atoms. b. A molecule contains one uranium atom and six fluorine atoms. c. A compound contains one aluminum atom for every three chlorine atoms.