The Rutherford gold foil experiment discovered the atomic nucleus. In this experiment, Rutherford beamed particles at a gold foil and observed some particles bouncing back at large angles, indicating a small, dense nucleus at the center of the atom. Dalton's atomic theory proposed that atoms of different elements can combine in simple whole number ratios to form compounds. Isotopes are atoms that have the same number of protons but different numbers of neutrons, giving them the same atomic number but different atomic mass numbers. The periodic table arranges elements into groups based on repeating properties and allows easy comparison of elemental properties.

1. Atomic Structure
Note-taking Guide
•Chapter 4

2. •4.1 Defining the Atom
• An
atom is the smallest particle of an
element that retains its identity in a
chemical reaction.
• It is difficult to directly observe an atom
because it is so small.

3. •Democritus Atomic Philosophy
• He
believed atoms were indivisible and
indestructible.
• He was the first to suggest the existence
of atoms but he lacked experiments to
prove it.

4. •Dalton’s Atomic Theory
• By
using
experimental
connections,
Dalton
transformed
previous ideas
about atoms into
a scientific theory.

5. •Dalton’s Atomic Theory
1. All elements are composed of tiny
indivisible particles called atoms.
• 2. Atoms of the same element are identical.
The atoms of any one element are different
from those of any other element.
• 3. Atoms of different elements can physically
mix together or can chemically combine in
simple whole-number ratios to form
compounds.
• 4. Chemical reactions occur when atoms are
separated, joined, or rearranged. Atoms of
one element, however, are never changed
into atoms of another element as a result of a
chemical reaction.
•

6. •Sizing up the Atom
• Individual
atoms are
difficult to see
because they are so
small.
• Despite their small
size, atoms are
observable with
instruments such as
scanning tunneling
microscopes.

8. •4.2 Structure of the Nuclear Atom
There are three kinds of subatomic particles in
an atom.
• Proton, neutron and electron.
• Protons are positive.
• Electrons are negative.
• Neutrons have no charge.
• The cathode ray experiment showed that
electrons were negative because they were
repelled by a negative plate and attracted
by a positive plate.
•

11. •The Atomic Nucleus
Rutherford developed an experiment called the
Gold- Foil experiment.
• He beamed particles at gold foil.
• Some of the particles passed through easily and
some were deflected back.
• Some bounced off at large angles.
• The nucleus was discovered and that’s what was
causing the bounce back of the particles.
• It was also discovered that atoms are mostly
empty space.
•

13. •Vocabulary Cards
• Atom
• Proton,
neutron,
electron (same
card)
• Cathode Ray
Experiment
• Rutherford GoldFoil Experiment

14. •SUM IT UP
Which
experiment
discovered
the atomic
nucleus?

15. •4.3 Distinguishing Among Atoms
• Elements
are different because they
contain different amounts of protons.
• The atomic number of an element is
the number of protons.
• The atomic mass number is the number
of protons plus the number of neutrons.

16. •Math Monkey Moment
How many protons, neutrons and electrons are in each
atom?
Protons
Be
Na
Ca
Neutron Electron
s
s

17. •Isotopes
• Isotopes
are atoms that have the same
number of protons but different
numbers of neutrons.
• They have the same atomic number
but different atomic mass numbers.
• To distinguish isotopes from each other,
writing elements in shorthand notation is
necessary.

18. •Let’s Practice!
Write the shorthand notations for:
Oxygen
Sulfur
Silver
Bromine
Lead

19. •Math Monkey Moment
How many protons, neutrons and electrons are in each
atom?
Protons
C-14
Ca-44
Li-7
Neutron Electron
s
s

20. •Vocabulary Cards
• Isotope

21. •SUM IT UP
How is an
isotope
different from
a regular
atom?

22. •Atomic Mass
In nature, most elements occur as a mixture
of two or more isotopes.
• Each isotope of an element has a fixed mass
and a natural percent abundance.
• The atomic mass of an element is the
weighted average mass of the atoms in a
naturally occurring sample of the element.
• To calculate the atomic mass of an element,
multiply the mass of an element by the
percent natural abundance and then add
the products.
•

23. •Math Monkey Moment
Do practice problems
21 and 22 on page
116.
Do practice problems
23 and 24 on page
117.

24. #21 boron-11
#22 Silicon-28 must be the most
abundant. The other two must be
present in very small amounts.
Silicon-28 has the closest mass to the
average atomic mass on the periodic
table.
#23 63.6 amu
#24 79.91 amu

25. •Periodic Table-Preview
•A
periodic table arranges elements into
groups based on a set of repeating
properties.
• It allows you to compare the properties
of one element with another easily.
• Each horizontal row is called a period.
• Each vertical column is called a group.

26. •Vocabulary Cards
• Atomic
Mass
• Atomic Number
• Periodic Table
• Table group
• Table period

27. •Science Swag
Research any
element from the
periodic table.
Write a one page
paper about the
element. Things
you could include
are:
Discovery/history
Uses for it now
Future uses

28. •ANY QUESTIONS?

29. •POST IT UP
How can you tell which
isotope is the most abundant
in nature?
I S!
TH
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IN
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DH
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