Do Now: (3 min)
In the gold foil experiment, Rutherford made two
observations:
• Some particles passed straight through the
foil
• Some particles bounced off the foil
What TWO conclusions about the structure of the
atom did Rutherford make based on these
observations?
Don’t forget to get your Do Now checked off by Ms.
Akagi within the first 5 MINUTES of class!
Do Now Discussion
What TWO conclusions about the
structure of the atom did Rutherford make
based on these observations?
1. Since
particles passed through – atoms
are mostly empty space
2. Since
some particles bounced off –
atoms have a solid center called the
nucleus
Atomic Structure and Element
Type
10/21/09
Cornell Notes
From yesterday:

There are 3 subatomic particles that
make up the atom:
◦ Proton
◦ Neutron
◦ Electron

Today, we will be discussing and describing
the importance of each of these particles.
Neutron
 Charge: no
charge/neutral
 Location: Nucleus
 Size/Mass: similar to a proton
(1.67 x 10-27 kg)
 Role: Determines the isotope of an
element (which we’ll discuss on
Monday)
Electron
 Charge: -1
(negative)
 Location: electron cloud/ outside of
nucleus
 Size/Mass: super tiny!
(9.1 x 10-28 kg)
 Role: responsible for how atoms
react and bind with each other
Proton:
 Charge: +1
(positive)
 Location: nucleus
 Size/Mass: similar to neutron
(1.67 x 10-27 kg)
 Role: determines what type of
element an atom is
Atoms are NEUTRAL in charge!
Why?
 In their elemental form, atoms have the
same number of electrons as they do
protons
 Electrons and protons have opposite
charges (positive and negative)
 When equal in numbers, the charges
cancel each other out!
How is one element different from
another element?
Atomic Number: the number of protons in
an atom. Each element has a different
atomic number.
Atomic
Number
Element
Symbol
Element
Name
Example:
Magnesium
atoms has an
atomic
number of
12, so it has
12 protons
and 12
electrons!
Examples:

If an atom has an atomic number of 10, how
many protons does it have?
10!
Atomic number = number of protons

If an atom has an atomic number of 10, how
many electrons does it have?
10!
Atoms have the same number of
protons and electrons (neutrally
charged)
Examples:
Looking at the periodic table,
What element has an atomic number of
13?
Aluminum
 What element has an atomic number of
35?
Bromine

Examples
Looking at Cobalt:
• What is the atomic
number of Cobalt?
27
• How many Protons are in
one cobalt atom?
27
• How many electrons are in
one cobalt atom?
27
Brochure: The Atom
Making sure we have everything about the atom in
one place! (read written instructions carefully!)
Step 1: Fold a piece of paper into three sections
Step 2: Front section is the title page
Step 3: Back center section is on the gold foil
and cathode ray experiments
 Step 4: Three inside sections are on the parts of
the atom
 Step 5: Last section is on atom neutrality and the
atomic number


