Slide 1

Section 3.2Atoms & Compounds

ObjectivesTo 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

Slide 2

Dalton’s Atomic TheoryDalton’s Atomic TheoryElements are made of tiny particles called Elements are made of tiny particles called

atomsatoms

All atoms of a given element are identicalAll atoms of a given element are identical

The atoms of a given element are different The atoms of a given element are different from those of any other elementfrom those of any other element

Atoms of one element can combine with Atoms of one element can combine with atoms of another element to form atoms of another element to form compounds. A given compound always has compounds. A given compound always has the same relative numbers and types of the same relative numbers and types of atoms. This is called the atoms. This is called the law of constant law of constant compositioncomposition

Slide 3

Dalton’s Atomic TheoryDalton’s Atomic TheoryAtoms are indivisible in chemical processes. Atoms are indivisible in chemical processes.

Atoms are not created or destroyed in Atoms are not created or destroyed in chemical reactions. A chemical reaction chemical reactions. A chemical reaction simply changes the way the atoms are simply changes the way the atoms are grouped together.grouped together.

Slide 4

Formulas of CompoundsFormulas of Compounds

A A compoundcompound is a distinct substance that is is a distinct substance that is composed of atoms of two or more elementscomposed of atoms of two or more elements

A compound always contains the same A compound always contains the same relative masses of those elementsrelative masses of those elements

In a In a chemical formulachemical formula, the atoms are , the atoms are indicated by the element symbols and the indicated by the element symbols and the number of each type of atom is indicated by number of each type of atom is indicated by a subscripta subscript

Slide 5

Rules for Writing FormulasRules for Writing Formulas

Each atom is represented by its element Each atom is represented by its element symbolsymbol

The number of each type of atom is indicated The number of each type of atom is indicated by a subscript written to the right of the by a subscript written to the right of the element symbolelement symbol

When only one atom of a given type is When only one atom of a given type is present, the subscript 1 is present, the subscript 1 is notnot written written

Slide 6

Formula PracticeFormula PracticeSO3 – 1 sulfur atom and 3 oxygen atoms

N2O3 -- 2 nitrogen and 3 oxygen

PCl3 -- 1 phosphorus, 3 chlorine

CBr4 -- 1 carbon, 4 bromine

A compound containing two iron atoms and three oxygen atoms Fe2O3

A compound containing three hydrogen atoms, one phosphorus atom and four oxygen atoms H3PO4

A compound containing one hydrogen, one chlorine, and four oxygen atoms HClO4