# The Structure of Atoms

Document Sample

```					 The Structure of Atoms

Thanks to those 7
scientists (and many more)
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

 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   Charge         Location         Mass
Particle
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)   6
Element Symbol
C
Element Name
Carbon
Average atomic mass     12.011
Protons   Neutrons Mass     Electrons Element
number
-

+
0       0
+

-
Protons   Neutrons Mass     Electrons Element
number

2         2       4         2        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     Electron Element
number   s

2         2       4         2       Helium
3         3       6         3       Lithium
5         5       10        5       Boron
7         7       14        7       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)   6
Element Symbol
C
Element Name
Carbon
Average atomic mass     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
0
0
0
+
+
12.01                           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   Symbol
A
Z   X
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
2   He
4  is the mass number, 2 is the number of
protons (from the periodic table)
Isotope Notation

Mass
27
number

Atomic
number
13   Al
• Al-27
• Aluminum-27
-

+
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.

 Let’s imagine that      Your averages for
was based on the         categories are:
following:
 Tests: 79%
 40% Tests
 30% Labs
 Labs: 88%

 20% Homework            Homework: 65%
 10% Class work          Class work: 90%
Now you try:

 Let’s imagine that      Your averages for
was based on the         categories are:
following:
 Tests: 90%
 40% Tests
 30% Labs
 Labs: 70%

 20% Homework            Homework: 85%
 10% Class work          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.
Mass spectrum of copper
relative number of

100
80        69.09
atoms

60
40                              30.91
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

65
 30.91    Cu
29


 Calculate    the average atomic mass.
Calculate the average atomic mass of Ne

Mass spectrum of neon
relative number of

100      91
80
atoms

60
40
20                           9
0.3
0
20          21       22
mass number
 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
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

```
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
 views: 19 posted: 11/7/2012 language: simple pages: 78