Atoms, Isotopes, and Bohr!
What makes up an atom?
1. An atom is made up of subatomic
particles (protons, neutrons, and
electrons.) Protons and neutrons are
made up of Quarks.
2. An element is made up the same
type of atom.
Parts of the Atom
Neutron
What do you
notice about the
size of each type
of particle?
Proton
Electron
What does an atom really look like?
An atom has a very dense center called a nucleus where the protons
and neutrons are located. The electron cloud is the space around the
nucleus. The dots show where an electron is likely to be.
Charge
Mass (amu)
Location
Proton
+1
1 (very large!)
nucleus
Neutron
0
1 (very large!)
nucleus
Electron
-1
.0005 (very very small!)
outside nucleus
Parts of the Atom
What holds an atom together?
Because protons have a positive charge and electrons have a
negative charge, they are attracted to each other because of the
electromagnetic force (opposite charges attract, like charges repel.)
Atom Diagrams
1. We diagram an atom with electrons
moving in electron shells around the
nucleus.
2. The farther away the electron is from
the nucleus, the more energy the
electron has.
3. Electrons in energy levels are
grouped in pairs.
Let’s Review
1. What does the atomic
number tell you?
1. How do you find the
number of neutrons?
Bohr Model Electron Shells
Bohr Model Practice
So let’s try it….
How to draw a Lithium atom
First, look at the Periodic Table
Second, determine the number
of protons (Look @ the atomic
number)
Then determine the number of
neutrons (Atomic mass – atomic
number)
Then determine the number of
electrons (Look @ the atomic
number)
3
Li
Lithium
7
So let’s try it….
Protons = 3
3
+
+
Li
+
-
-
Lithium
7
Electrons = 3
2 in the 1st shell, 1 in the 2nd shell
Neutrons = 4
(7-3=4)
Isotopes
-
An isotope is an atom that has the same number of protons, but a
different number of neutrons.
Isotopes (continued)
-
You can think of isotopes like atoms having a twin or triplet. It is the
same element, just a different version of it.
-
The element doesn’t change because they have the same atomic
number
How can you tell one isotope
from another?
-
Although isotopes share most of the
same physical and chemical properties,
Isotopes of the same element have
different mass numbers.
-
Atomic Mass = protons + neutrons
-
Protons and Neutrons have a mass of
about 1 atomic mass unit (amu)
-
Electrons have such a small mass they
are considered to be 0 amu
Charge
Mass (amu)
Location
Proton
+1
1 (very large!)
nucleus
Neutron
0
1 (very large!)
nucleus
Electron
-1
.0005 (very very small!)
outside nucleus
Parts of the Atom
What’s the difference? Why are they different?
Atomic Mass
-
The total mass of one atom of an
element
-
Because elements have isotopes, the
atomic mass listed on the periodic
table is a weighted average of all the
naturally occurring isotopes of an
element.
Atomic Mass and Isotopes
There is a lot more Hydrogen-1 than Hydrogen-2 so Hydrogen-1
is weighted more heavily when calculating the atomic mass of
hydrogen.
Mass: ______ Mass: ______ Mass: ______