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Starter 9/24

What is a Theory?


Give me three examples of theories.
What is an Opinion?

Give me three examples of opinions.
What’s the difference between opinions and
theories?
 How can you differentiate between the two?
 Why should you be able to differentiate
between opinion and theory?

Ch. 3: Atoms
3.1 Foundations
History

Democritus
 named the most basic
particle
 atom- means “indivisible

Aristotle
 didn’t believe in atoms
 thought matter was
continuous
History
 by


1700s, all chemists agreed:
on the existence of atoms
that atoms combined to make
compounds
 Still
did not agree on whether
elements combined in the same ratio
when making a compound
Law of Conservation of Mass
 mass
is neither created or destroyed
during regular chemical or physical
changes
Law of Definite Proportions
 any
amount of a compound contains
the same element in the same
proportions by mass
No matter
where the
copper
carbonate is
used, it still
has the same
composition
Law of Multiple Proportions
applies when 2 or more elements combine
to make more than one type of compound
 the mass ratios of the second element
simplify to small whole numbers

Law of Multiple Proportions
Dalton’s Atomic Theory
1.
2.
3.
4.
5.
All mass is made of atoms
Atoms of same element have the same
size, mass, and properties
Atoms can’t be subdivided, created or
destroyed
Atoms of different element combine in
whole number ratios to make compounds
In chemical reactions, atoms are
combined, separated, and rearranged.
Modern Atomic Theory

Some parts of Dalton’s theory were wrong:



atoms are divisible into smaller particles
(subatomic particles)
atoms of the same element can have different
masses (isotopes)
Most important parts of atomic theory:


all matter is made of atoms
atoms of different elements have different
properties
Starter 12/9
 What
are some technological advances
that have changed your life for the
better?

Any that made your life worse?
 Can
you think of any technological
advancements that were accidents?

i.e. someone stumbled onto a huge
discovery quite by accident.
Ch. 3: Atoms
3.2 Structure of Atom
Structure of Atom

Nucleus:



contains protons
and neutrons
takes up very little
space
Electron Cloud:


contains electrons
takes up most of
space
Subatomic Particles
 includes



all particles inside atom
proton
electron
neutron
 charge
on protons and electrons are
equal but opposite
 to make an atom neutral, need equal
numbers of protons and electrons
Subatomic Particles
number of protons identifies the atom as a
certain element
 protons and neutrons are about same size
 electrons are much smaller
 nuclear force- when particles in the nucleus
get very close, they have a strong attraction




proton + proton
proton + neutron
neutron + neutron
Atomic Radius




size of atom
measured from center of nucleus to outside of
electron cloud
expressed in picometers (1012 pm = 1 m)
usually 40-270 pm
Example
 An
atom has a radius of 140 pm.
How large is that in meters?
1m
12
10
140 pm  12
 140 10  1.4 10 m
10 pm