1. Slide 1 Section 3.2 Atoms & Compounds Objectives  To learn about Dalton’s Theory of atoms  To understand and illustrate the Law of constant composition  To learn how a formula describes a compound’s composition

2. Slide 2 Dalton’s Atomic Theory Elements are made of tiny particles called atoms Elements are made of tiny particles called atoms All atoms of a given element are identical All atoms of a given element are identical The atoms of a given element are different from those of any other element The atoms of a given element are different from those of any other element Atoms of one element can combine with atoms of another element to form compounds. A given compound always has the same relative numbers and types of atoms. This is called the law of constant composition Atoms of one element can combine with atoms of another element to form compounds. A given compound always has the same relative numbers and types of atoms. This is called the law of constant composition

3. Slide 3 Dalton’s Atomic Theory Atoms are indivisible in chemical processes. Atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together. Atoms are indivisible in chemical processes. Atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together.

4. Slide 4 Formulas of Compounds A compound is a distinct substance that is composed of atoms of two or more elements A compound is a distinct substance that is composed of atoms of two or more elements A compound always contains the same relative masses of those elements A compound always contains the same relative masses of those elements In a chemical formula, the atoms are indicated by the element symbols and the number of each type of atom is indicated by a subscript In a chemical formula, the atoms are indicated by the element symbols and the number of each type of atom is indicated by a subscript

5. Slide 5 Rules for Writing Formulas Each atom is represented by its element symbol Each atom is represented by its element symbol The number of each type of atom is indicated by a subscript written to the right of the element symbol The number of each type of atom is indicated by a subscript written to the right of the element symbol When only one atom of a given type is present, the subscript 1 is not written When only one atom of a given type is present, the subscript 1 is not written

6. Slide 6 Formula Practice SO 3 – 1 sulfur atom and 3 oxygen atoms N 2 O 3 -- 2 nitrogen and 3 oxygen PCl 3 -- 1 phosphorus, 3 chlorine CBr 4 -- 1 carbon, 4 bromine A compound containing two iron atoms and three oxygen atoms Fe 2 O 3 A compound containing three hydrogen atoms, one phosphorus atom and four oxygen atoms H 3 PO 4 A compound containing one hydrogen, one chlorine, and four oxygen atoms HClO 4