Virtually everything that is, is made up of atoms.
Chapter 12, page 361
Balloon and sweeter animation
Sub-Particles in the
Atom
Each element is chemically unique. To understand why they are unique,
you need to know the structure of the atom (the smallest particle of an element)
and the characteristics of its components.
Element = made of one kind of Atom.
Li
Compounds = made of different atoms chemically bonded in
whole number ratios.
H2O
•Mixtures are physical combinations of elements or compounds with variable composition
O2 + H2.
Particles or
Pure substances
Sub-Particles in the Atom
Location
in the Atom
Sub-Particle
Mass
Charge
proton
~1 a.m.u.
1+
in nucleus
neutron
~1 a.m.u.
0
in nucleus
electron
~0 a.m.u.
1-
orbits nucleus
atomic.mass.unit= a.m.u. ~ 1.992 ×10−27 kg or 1/12 the mass of C-12
Size of an atom
• Atoms are incredibly tiny.
• Measured in picometers (10-12 meters)
– Hydrogen atom, 32 pm radius
• Nucleus tiny compared to atom
– Radius of the nucleus near 10-15 m.
– Density near 1014 g/cm3
• IF the atom was the size of a stadium, the nucleus
would be the size of a marble.
California WEB
What holds an atom together?
• Nuclear Tug-Of-War
• • Electrostatic force – like charges repel and un-like
charges attract
• Strong Nuclear Force – holds nucleons (p+ & n0)
• together, very strong nuclear force but over short
distances
– Stable nuclei are SMALL
– Large nuclei tend to be unstable (radioactive)
• • Electrostatic Force
• – Holds electrons on atom
Balloon and sweeter animation
Counting Particles in Atoms
C
Atomic Number = number of protons (p+)
= unique for each element
12
6
C
14
6
Mass Number = A
C
12
6
Atomic Number = Z
Atomic Mass Number = Mass of an atom =
number of protons + neutrons = (p+) + (no); (e- do not have mass)
California WEB
How can I remember how many
protons or electrons there are?
Just remember the A.P.E. rules!
•atomic number
=
•number of protons =
•number of electrons
Now, how do I remember how many
protons there are?
Just remember the M.A.N.!
•mass number
-
•Atomic number
=
•number of neutrons
Neon
Ne
Protons: 10
Electrons: 10
Neutrons: 10
Atomic Number: 10
Atomic Mass: 20
Phosphorus
P
Protons: 15
Electrons: 15
Neutrons: 16
Atomic Number: 15
Atomic Mass: 31
Aluminum
Al
Protons: 13
Electrons: 13
Neutrons: 14
Atomic Number: 13
Atomic Mass: 27
Argon
Ar
Protons: 18
Electrons: 18
Neutrons: 22
Atomic Number: 18
Atomic Mass: 40
Silicon
Si
Protons:
14
Electrons: 14
Neutrons: 14
Atomic Number: 14
Atomic Mass: 28
Symbols
Contain the symbol of the element, the mass
number and the atomic number (top heavy)
# protons
+ # neutrons
mass number
# protons
Mass
number
Atomic
number
X
Symbols
• Find the
– Atomic number
– Mass number
– number of electrons
– number of protons
– number of neutrons
=9
= 19
=9
= 9+
= 10
19
9
F
So let’s practice!
Symbols
Find the
– number of protons = 35
– number of neutrons = 45
– number of electrons = 35
– Atomic number = 35
– Mass number = 80
http://www.chem.purdue.edu/gchelp/liquids/bromine.gif
80
35
Br
Symbols
Find the
– number of protons = 11
– number of neutrons = 12
– number of electrons = 11
– Atomic number = 11
– Mass number = 23
23
11
Na
Sodium atom
Ions
To find net charge on an atom, consider the p+ and the e–.
cation: a (+) ion
anion: a (–) ion
-- more p+ than e–
-- more e– than p+ atoms
-- formed when atoms lose e–
-- formed when gain e–
-
p+
+
++
ion: a charged atom
-
+ + +
n0
e- - - - +3 and -4 = -1
-
+
++
-
p+ + + +
n0
e- - +3 and -2 = +1
Symbols
Find the
– number of protons = 11
– number of neutrons = 12
– number of electrons = 10
– Atomic number = 11
– Mass number = 23
23
11
1+
Na
Sodium ion
Symbols
If an element has an atomic number of 23
and a mass number of 51 what is the
– number of protons
= 23
– number of neutrons = 28
– number of electrons = 23
– Complete symbol
51
23
V
Symbols
If an element has 60 protons and 84
neutrons what is the
– Atomic number
= 60
= 144
– Mass number
– number of electrons = 60
– Complete symbol
144
60
Nd
Symbols
If a neutral atom of an element has 78
electrons and 117 neutrons what is the
– Atomic number = 78
= 195
– Mass number
– number of protons = 78
– Complete symbol
195
78
Pt
Mass Number
• mass number= protons + neutrons
• always a whole number
• NOT on the
Periodic Table!
+
+
+
Neutron
Electrons
eNucleus
+ +
e-
ee-
ee-
+
Nucleus
Carbon-12
Neutrons 6
Protons
6
Electrons 6
Proton
Isotopes
• Atoms of the same element with different
mass numbers.
• Nuclear symbol:
Mass #
12
Atomic #
6
• Hyphen notation: carbon-12
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
C
Isotopes
• Dalton was wrong.
• Atoms of the same element can have different
numbers of neutrons.
• different mass numbers.
• called isotopes.
Isotopes
+
+
+
Neutron
Electrons
Nucleus
+ +
+
Nucleus
Carbon-12
Neutrons 6
Protons
6
Electrons 6
Nucleus
Proton
Proton
+
+
+
+
Neutron
+
Electrons
+
Carbon-14
Neutrons 8
Protons
6
Electrons 6
Nucleus
What is an isotope?
same number of protons, different numbers
of neutrons.
B-10
10B
5
Boron-10
Boron-11
B
B
Protons:
5
Protons:
5
Electrons:
5
Electrons:
5
B-11
Neutrons:
5
Neutrons:
11B
5
Atomic Number: 5
Atomic Number: 5
Atomic Mass:10
Atomic Mass:11
6
What is the average
atomic mass of Carbon?
Carbon- 12
Carbon- 14
C
C
Protons: 6
Protons: 6
Electrons: 6
Electrons: 6
Neutrons: 6
Neutrons: 8
Atomic Number: 6
Atomic Number: 6
Atomic Mass: 12
Atomic Mass:14
37
Cl
Isotopes
17
• Chlorine-37
– atomic #:
17
– mass #:
37
– # of protons:
17
37
– # of electrons:
17
– # of neutrons:
17
20
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Cl
Writing Isotopes
• Put the mass number after the name of the
element
• carbon- 12
• carbon -14
• uranium-235
– Or
Mass #
12
Atomic #
6
California WEB
C
Using a periodic table and what you know about atomic number,
mass, isotopes, and electrons, fill in the chart:
Element
Symbol
Atomic
Number
Mass
#
# of
protons
# of
neutron
# of
electron
8
8
8
39
Potassium
+1
Br
45
30
65
-1
30
Atomic Number = Number of Protons
Number of Protons + Number of Neutrons = Atomic Mass
Atom (no charge) : Protons = Electrons
Ion (cation) : Protons > Electrons
charge
Ion (anion) : Electrons > Protons
Using a periodic table and what you know about atomic number,
mass, isotopes, and electrons, fill in the chart:
ANSWER KEY
Element
Symbol
Atomic
Number
Mass
#
# of
protons
# of
neutron
# of
electron
charge
O
8
16
8
8
8
0
Potassium
K
19
39
19
20
18
+1
Bromine
Br
35
80
35
45
36
-1
Zinc
Zn
30
65
30
35
30
0
Oxygen
Atomic Number = Number of Protons
Number of Protons + Number of Neutrons = Atomic Mass
Atom (no charge) : Protons = Electrons
Ion (cation) : Protons > Electrons
Ion (anion) : Electrons > Protons
Isotopes
• Because of the existence of isotopes, the mass of a
collection of atoms has an average value.
• Average mass = ATOMIC WEIGHT = ATOMIC MASS
• Boron is 20% B-10 and 80% B-11.
– That is, B-11 is 80 percent abundant on earth.
• For boron atomic mass
= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu
Average Atomic Mass
• massed average of all isotopes on the
Periodic Table
• round to 2 decimal places
Avg.
(mass)(%) + (mass)(%)
Atomic =
100
Mass
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Average Atomic Mass
• EX: Calculate the avg. atomic mass of oxygen if its
abundance in nature is 99.76% O-16, 0.04% O-17,
and 0.20% O-18.
Avg.
(16)(99.76) + (17)(0.04) + (18)(0.20)
Atomic =
100
Mass
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
=
16.00
amu
Average Atomic Mass
• EX: Find chlorine’s average atomic mass if approximately 8
of every 10 atoms are chlorine-35 and 2 are chlorine-37.
Avg.
(35)(8) + (37)(2)
Atomic =
10
Mass
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
= 35.40 amu
17
Cl
35.453
• Assume you have only two atoms of chlorine.
• One atom has a mass of 35 amu (Cl-35)
• The other atom has a mass of 36 amu (Cl-36)
• What is the average mass of these two isotopes?
35.5 amu
• Looking at the average atomic mass printed on the periodic
table...approximately what percentage is Cl-35 and Cl-36?
55% Cl-35 and 45% Cl-36 is a good approximation