Download Atomic theory

Thursday, Oct. 20th: “A” Day
Friday, Oct. 21st: “B” Day
Agenda
Chapter 2 Tests
Begin Chapter 3: “Atoms and Moles”
Sec. 3.1: “Substances are Made of Atoms”
In-Class: Sec 3.1 review, pg. 78: #1-8
Movie: “Atoms: The Building Blocks of Matter”
Homework:
Concept Review: “Substances Are Made of Atoms”
“Happy Mole Day” video
*Quiz over section 3.1 next class*
Ch. 2 Test
Class
3A
4A
2B
4B
Average
Our Understanding of Atoms
Required Many Centuries
As early as 400 B.C.E. the Greek
philosopher Democritus identified invisible
units of matter called “atoms”.
Democritus was unable to provide
scientific data to convince people that
atoms really did exist.
Most people believe that an atom looks
like the picture on the left. The diagram on
the right is a much better model of the atom.
Law of Definite Proportions
The law of definite proportions: a
chemical compound always contains the
same elements in exactly the same
proportions by weight or mass.
Every molecule of a substance is made of
the same number and types of atoms.
Example: NaCl is ALWAYS
39.34% Na and 60.66% Cl
Law of Conservation of Mass
The law of conservation of mass: mass
cannot be created or destroyed in ordinary
chemical and physical changes.
Example: in chemical reactions, the mass
of the reactants is equal to the mass of
the products.
Law of Conservation of Mass
Law of Multiple Proportions
The law of multiple proportions: when
two elements combine to form two or more
compounds, the mass of one element that
combines with a given mass of the other is
in the ratio of small, whole numbers.
Example: Water is H2O, NOT H3O1.5
Law of Multiple Proportions
Example: when carbon and oxygen combine, they
combine in ratios of small, whole numbers
CO (carbon monoxide)
CO2 (carbon dioxide)
Atomic Theory
Atomic theory: all matter is made up of
atoms.
In 1808, John Dalton came up with his
own atomic theory….
5 Principles of Dalton’s Atomic Theory
1. All matter is made of extremely small particles
called atoms, which can’t be subdivided,
created, or destroyed.
2. Atoms of a given element are identical in their
physical and chemical properties.
3. Atoms of different elements differ in their
physical and chemical properties.
4. Atoms of different elements combine in simple,
whole number ratios to form compounds.
5. In chemical reactions, atoms are combined,
separated, or rearranged but never created,
destroyed, or changed.
Problems with Dalton’s Atomic
Theory
 Data obtained since Dalton’s time shows that
the first 2 principles are NOT true in all cases.
 1st principle: all matter is made of extremely
small particles called atoms, which can’t be
subdivided, created, or destroyed.
 The atom CAN be divided into smaller
particles. What are they?
 Scientists have also been able to destroy
and create atoms using technology.
Problems with Dalton’s Atomic
Theory
2nd principle: atoms of a given element are
identical in their physical and chemical
properties.
Isotopes of the same element have
different atomic masses
Problems with Dalton’s Atomic
Theory
4th principle: atoms of different elements
combine in simple, whole number ratios to
form compounds.
Dalton didn’t know that atoms of the
SAME element can also combine with
each other. (O2, N2, S8, H2, Cl2)
The 4th principle principle isn’t wrong,
it’s just missing some information.
Dalton’s Atomic Theory
Dalton’s theory continues to be modified
and expanded as scientists learn more
and more about atoms.
In-Class Assignment
Sec 3.1 review
Pg. 78: #1-8
Concept Review:
“Substances are Made of Atoms”
*Be ready for a quiz over this section
next class period*
Movie: “Atoms, the Building Blocks
of Matter”
Get out a piece of paper and write down
10 things that you learned from the
movie…
This is ALL stuff that we
will cover in Ch. 3
Happy Mole Day!
Mole day is October 23rd and occurs at
precisely 6:02 in the morning and 6:02 in
the evening.
Scientists celebrate mole day because the
mole is the SI base unit for the amount of
a substance.
The number of particles in 1 mole of any
substance is 6.022 X 1023, which is
Avogadro’s number.
We will learn more about the mole in
section 3.4 as we begin counting atoms…