Download Atomic Theory

The Structure of Atoms
Thanks to those 7
scientists (and many more)
what do we know about
atoms today?!
Structure of atoms
 Atoms can’t be broken into smaller pieces,
BUT they are made of smaller pieces!
 Those smaller pieces all on their own don’t
act like the element the atom is from.
 Atom: the smallest particle of an element
with the chemical properties of that element.
Two areas of an Atom
 Nucleus: made up of:
 Protons
(+ positive), mass number = 1
 Neutrons (0 neutral), mass number = 1
 Make up the mass of the atom
+
0
0
+
 Electrons (- negative)
 Around
the nucleus
 Tiny, mass number = 0
 Lots of space between the nucleus and the
electrons.
-
Subatomic Particles
 Protons, neutrons and electrons
Subatomic Particles
Subatomic
Particle
Charge
Location
Mass
proton
positive (+)
nucleus
1 amu
neutron
neutral (0)
nucleus
1 amu
electron
negative (-)
around nucleus
~1/2000 amu
Defining an Atom
 Nuclei (plural of nucleus) made of protons
and neutrons
 Number of Protons (+) = number of
electrons (-)
 Atoms are neutral!
 # protons tells us what kind of element an
atom is!
Holding it all together
 Nuclear forces hold protons and neutrons
together
 The positive force of the nucleus holds the
electrons near the nucleus.
 Positive and negative attract.
 Mass number = protons + neutrons
 Everything heavy in an atom
 Electrons
aren’t heavy at all!
Atomic Number
(= number of protons)
Element Symbol
Element Name
Average atomic mass
6
C
Carbon
12.011
Protons
Neutrons Mass
number
Electrons Element
-
+
0
0
+
-
Protons
Neutrons Mass
number
Electrons Element
2
2
2
4
Helium
-
+
+
0
-
0
0
+
-
-
+
0
+
-
-
+
0
0
0
+
+
0
-
-
-
+
-
0
0
-
-
+
0
+
+
0
+
0
0
+
+
0
-
-
+
0
0
+
-
-
+
0
0
0
+
+
+
0
0
+
0
0
0
+
+
-
+
-
-
-
-
-
+
0
0
+
-
0
-
+
0
0
0
+
+
+
0
0
+
0
0
0
+
+
+
-
+
-
-
-
-
-
0
+
-
+
0
0
-
+
0
+
+
0
+
0
0
+
+
0
-
-
Protons
Neutrons Mass
number
Electron Element
s
2
2
4
2
Helium
3
3
6
3
Lithium
5
7
5
7
10
14
5
7
Boron
Nitrogen
10
10
20
10
Neon
11
11
22
11
Sodium
8
8
16
8
Oxygen
Which element…?
 Has 20 protons?
Which element…?
 Has 15 protons?
Which element…?
 Has 17 protons?
Which element…?
 Has 53 protons?
Which element…?
 Has 79 protons?
Which element…?
 Has 40 electrons?
Which element…?
 Has 77 electrons?
Which element…?
 Has 50 electrons?
Which element…?
 Has 118 electrons?
Atomic Number
(= number of protons)
Element Symbol
Element Name
Average atomic mass
6
C
Carbon
12.011
Protons: defining an atom
 Atomic number: Atoms of different elements
have different numbers of protons.
Trends in Atomic Numbers
 Atomic numbers increase to the right and
down the Periodic Table of the Elements.
 Check it out.
Isotopes
Average atomic mass
-
-
6
+
C
0
+
0
+
12.01
-
+
+
0
0
-
0
+
0
-
-
 But why is the atomic mass (on the periodic
table) different from the mass number
(protons + neutrons)?
 Carbon atomic mass = 12.011 amu
 Mass number = 12 amu
Isotopes
 Atoms of the same element can have different numbers




of neutrons.
Because these atoms have the same number of
protons, they are the same element, and acts the same
More or fewer neutrons only changes the mass of the
atom!
Isotopes are atoms of the same element with different
masses because of different numbers of neutrons
Identified by mass number
Naming Isotopes
 Mass number (A): the total number of
protons and neutrons in the nucleus of an
isotope
 Hyphen Notation:
 Element-Mass number
 Hydrogen-3
 Nuclear Symbol
mass _ number
atomic_ number
A
Z
X
Symbol
Nuclear symbols
 Helium-4: 4 is the mass number
 The
total number of protons plus neutrons
 This helium isotope can also be written:
 4He
2
4
is the mass number, 2 is the number of
protons
 Write the nuclear symbol for Carbon-13
 13C
6
Nuclear symbols
 Helium-4: 4 is the mass number
 The
total number of protons plus
neutrons
 This helium isotope can also be written:
4
4
2
He
is the mass number, 2 is the number of
protons (from the periodic table)
Isotope Notation
Mass
number
Atomic
number
• Al-27
• Aluminum-27
27
13
Al
-
+
0
0
+
-
-
0
0
+
-
+
0
+
-
-
0
+
0
+
-
-
+
0
0
+
+
0
-
-
0
+
0
+
-
-
+
0
0
+
+
-
-
-
+
0
-
0
0
-
+
+
0
+
0
0
-
+
+
+
0
-
-
-
+
0
-
0
0
-
+
+
0
+
0
0
-
+
+
+
-
-
-
+
+
-
+
0
0
-
+
0
+
0
0
+
0
-
-
+
0
+
-
-
+
0
0
0
+
+
0
-
-
+
0
+
-
-
+
0
0
0
+
+
-
-
-
+
-
0
0
-
-
+
0
+
+
0
+
0
0
+
+
0
-
-
-
+
-
0
0
-
-
+
0
+
+
0
+
0
0
+
+
-
Practice naming Isotopes
 The notation Sn-117 represents an isotope of
the element ____________.
 Its mass number is ________.
 Since its atomic number is __________,
the atom contains
 _________ protons,
 _________ electrons and
 _________ neutrons.
 Cesium-133 is an isotope whose mass
number is _________.
 Its atomic number is ________.
 The atom contains _______ protons,
 ________ electrons and
 ________ neutrons.
 An isotope contains 27 protons and 39
neutrons. The isotope is an atom of the
element ____________.
 Its atomic number is _________.
 This atom has _______ electrons.
 Its mass number is __________.
Applications of Isotopes
 Over time (a long time!) one isotope can lose
neutrons and turn into another.
Measure the % of C-14 to calculate age
 What objects have been dated using carbon-
14 isotopes?
Shroud of Turin
The Giant Periodic Table Project
6
C
Carbon
12.011
The Giant Periodic Table Project
 Be neat
 Be bold! We need to be able to read this
from anywhere in the room!
 Be creative, but not cluttered.
 Be accurate.
 Atomic mass to TWO digits (Ex: 12.01) is
ideal.
Calculating your grade
 Let’s imagine that
your grade in biology
was based on the
following:
 40% Tests
 30% Labs
 20% Homework
 10% Class work
 Your averages for
each of the
categories are:
 Tests: 79%
 Labs: 88%
 Homework: 65%
 Class work: 90%
Now you try:
 Let’s imagine that
your grade in biology
was based on the
following:
 40% Tests
 30% Labs
 20% Homework
 10% Class work
 Your averages for
each of the
categories are:
 Tests: 90%
 Labs: 70%
 Homework: 85%
 Class work: 95%
Mixtures of Isotopes
 In nature, elements occur as a mixture of
isotopes.
 We use the weighted average of the isotope
masses – average atomic mass
 On the periodic table, the average atomic
mass is below the element name.
 Check it out.
Example: Chlorine
 In nature, chlorine exists as:
 75.77%
chlorine-35
 24.23% chlorine-37
(35  75.77)  (37  24.23)
100
35.453
 In nature, the element lithium has isotopes
in the following natural abundance:
 7.5% lithium-6
 92.5% lithium-7
 Calculate the average atomic mass.
relative number of
atoms
Mass spectrum of copper
100
80
69.09
60
30.91
40
20
0
63
65
mass number
 Copper has two naturally occurring isotopes.
They are present in the following percents:
63
 69.09% Cu
29
63
Cu
 30.91
65
29
Cu

 Calculate
the average atomic mass.
Calculate the average atomic mass of Ne
relative number of
atoms
Mass spectrum of neon
100
91
80
60
40
20
0.3
0
20
21
mass number
9
22
 So what if someone gives us the mass of a
sample of an element?
 How do we figure out how many atoms we
have?
 We use…
 THE MOLE
The mole
 Mole: The SI unit for amount of substance
 Contains as many particles as there are
atoms in 12 grams of carbon-12
 There are 6.022x1023 atoms in 12 grams of
carbon-12
 Avogadro’s Number = 6.023x1023
Molar Mass
 The mole: the amount of a substance that
contains one Avogadro’s number (that is,
6.022x1023) of particles.
 Molar mass is the mass of one mole of a
pure substance (units: g/mol)
Find the molar mass of…
 Oxygen
Find the molar mass of…
 Phosphorus
Find the molar mass of…
 Sodium
Find the molar mass of…
 Gold