Matter Quiz
Atomic Theory Notes
Warm - Up
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What are some pieces of evidence for
a chemical change?
What is the difference between a
physical change and a chemical change?
Compare the Kelvin and Celsius
temperature scales.
What is the difference between
homogeneous and heterogeneous
mixtures?
Objective
• Today I will be able to:
– Demonstrate knowledge of matter and energy by
taking a quiz
– Identify the parts of the atom and their isotopes
– Calculate atomic masses of isotopes given a set of
data
Homework
• Atomic Structure Practice
Agenda
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Warm – Up
Matter Quiz
Review STEM fair Experimental Design
Atomic Theory Notes
Atomic Theory Practice
Exit Ticket
Atomic Theory Notes
Modern Atomic Theory
• Atom – smallest part of
matter that represents a
particular element
• Composed of electrons,
protons, and neutrons
• Protons and neutrons
(nucleons) form the
nucleus of an atom
• Mostly empty space
Subatomic Particles
Name
Symbol
Charge
Proton
p+
+1
Neutron
n
0
Electron
e-
-1
Subatomic Particles
Name
Mass (g)
Mass (amu)
Location
Proton
1.673 x 10-24
1
Nucleus
Neutron
1.673 x 10-24
1
Nucleus
Electron
9.109 x 10-28
(considered
to be zero)
.0005
Outside
Nucleus
Do particles smaller than protons and
neutrons exist?
• Quarks – subunits of protons and neutrons
– Never observed directly or found in isolation
– 6 “flavors” or different types
– Most common are:
• “Up” quark = +2/3
• “Down” quark = -1/3
– “Up” and “down” quarks are the most stable
– “Up” and “down” quarks have the smallest mass
are the lowest energy
Quarks
• Protons are made of two “up” quarks and one
“down” quark
• Neutrons are made of one “up” quark and
two “down” quarks
• Quarks are held together by “gluons”
How do electrons form?
• Mesons – particles made of quarks
• Short-lived particle - produced by high energy
interactions of matter
• Mesons decay to form electrons
What information can we get from the
periodic table?
Atomic Number
• number of protons in the nucleus
– You cannot change the number of protons!!!
– Determines the identity of an element
– Also the number of electrons in a neutral atom
Atomic Number
• What is the atomic number of carbon?
–6
• How many protons and electrons would there
be in a neutral atom of carbon?
– 6 protons and 6 neutrons
• How many protons and neutrons would there
be in a neutral atom of oxygen?
– 8 protons and 8 neutrons
Atomic Mass
• Measured in atomic mass units
• The number or protons and neutrons in an
atom
How did we arrive at measuring
atomic mass in atomic mass units?
• Based on the Carbon-12 scale
• By international agreement, a carbon atom
contains 6 protons and 6 neutrons, or 12 amu
• Therefore, 1 amu is 1/12 of a carbon atom
• Since the mass in grams of protons and
neutrons are about the same, they both have
an atomic mass unit of 1
Why aren’t electrons accounted for in
the calculation of the atomic mass?
• Electrons are small!
• It takes almost 2,000 electrons to equal the
mass of one proton or neutron
• Electrons are assumed to have a mass of 0
amu
If each proton and neutron has a mass
of one amu, then why aren’t the
atomic masses on the periodic table
whole numbers?
• Isotopes of elements
– atoms with the same number of protons but
different numbers of neutrons
Isotopes
• Some isotopes are found more common than
others
• We can determine which isotope is more
common by looking at the atomic mass
• Atomic Mass is calculated weighted averages
How do we calculate a weighted
average?
Category
Score
Exams (50%)
80%
Labs (25 %)
75%
Classwork (15 %)
95%
STEM fair (10 %)
87%
(.50 x 80) + (.25 x 75) + (.15 x 95) + (.10 x 87) =
81. 7 % = 82 %
Atomic Mass is calculated using the
same method of weighted averages
Carbon Isotope
C – 14
1%
C - 12
99%
(.01 x 14) + (.99 x 12) =
12.02 amu
Ions
• When an atom gains or loses an electron, an
Ion is formed
– Cation – atom loses an electron and makes a
positive ion
– Example: Lithium (Li) loses one electron
• It becomes Li+
– Anion – atom gains an e- and makes a negative
ion
• Example: Sulfer (S) gains two electrons
– It becomes S-2
Ions
• Examples
• What is the chemical symbol for the ion with:
• 13 protons and 10 electrons
- Al+3
• 7 protons and 10 electrons
- N-3
• How many protons and electrons are present
in a(n):
• S-2 ion
- 16 p+ and 18 e• Li+1 ion
- 3 p+ and 2 e-
Be careful with terminology!
• Atomic Mass – average mass of the naturally
occurring isotopes of an element
– Seen on the periodic table
• Mass Number – number of protons and
neutrons in an atom’s nucleus
– Seen in symbolic representations
Symbolic Representations of Elements
• An atom with 7 protons and 7 neutrons has a
mass number of 14 and is usually written as…
N
14
7
• How many protons, neutrons, and electrons?
27
13
+3
Al
13 p+, 14 n, and 10 e79
34
-2
Se
34 p+, 45 n, and 36 e-
Exit Ticket
• Draw the symbolic representation of the K1+
ion