Download section_3.2

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
Slide 2
Dalton’s Atomic Theory

Elements are made of tiny particles called
atoms

All atoms of a given element are identical

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
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.
Slide 4
Formulas of Compounds

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
 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
Slide 5
Rules for Writing Formulas

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

When only one atom of a given type is
present, the subscript 1 is not written
Slide 6
Formula Practice
SO3 – 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