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“Success in life comes not from
holding a good hand, but in
playing a poor hand well.”
~Warren G. Lester
Chemistry
Chemistry is a
branch of science
that investigates
the properties of
matter and the
ways in which
matter interacts,
combines, and
changes.
Chemistry: The Study of Matter
and Its Changes
Chemistry is the study of matter and its changes.
Matter is anything that has mass and has volume.
The universe can be divided into two broad
categories: Matter and Energy
Classification of Matter
Definitions for Components of Matter
Element - the simplest type of substance with unique physical and
chemical properties. An element consists of only one type of atom. It
cannot be broken down into any simpler substances by physical or
chemical means.
Atoms are the smallest particle of an element that retains the
properties of that element.
Elements are represented by chemical symbols.
Examples are H, CO, Co, and Mg.
Note that the first letter is capital,
second is lower case.
Laminated Periodic Tables
Elements and Compounds:
Pure substance = element or compound
– Elements cannot be decomposed to simpler forms by any
amount of chemical transformation or physical means.
– Compounds are composed of two or more elements in
definite proportions, can be broken down by chemical
means.
General features of the atom.
The atom is an electrically neutral, spherical entity composed of a
positively charged central nucleus surrounded by one or more
negatively charged electrons in an electron cloud.
The atomic nucleus consists of protons and neutrons.
Ask me about: Wms Brice stadium and a golf ball.
Subatomic Particles
o
A proton is about 2000 times more massive than an electron
1 u = 1 atomic mass unit = 1 amu = 1.66 x 10 -24 grams
© 2013 Pearson Education, Inc.
Chapter 3
8
Protons Determine the Element
• The atomic number, Z, represents the number of protons,
p+, in the nucleus of an atom.
• The atomic number is usually the biggest number listed in
the box for each element (look at periodic table).
• The atomic number (or number of protons) identifies an
element.
• The modern periodic table orders elements according to
increasing atomic number.
• The charge of a proton is assigned numerical value of +1.
• Mass of a proton is 1.0 amu
• 1 amu = 1.66 x 10 -24 grams
Electrons, e’
• A neutral atom has as many electrons outside its nucleus as
protons within its nucleus , # p+ = # e’
• e’ has about 2000 times less mass than a proton.
• e’ has a relative charge of - 1.
• Atoms can lose and gain one or more electrons to form ions.
• Two types of ions:
• Cation forms when atom loses e’s.
Na ---------> Na +1 + e’
• Anion forms when atom gains e’s.
Cl + e’ ----------> Cl -1
Neutrons,n0
• Neutrons are almost as massive as protons but carry no
electrical charge. Mass of a n0 is 1.0 amu.
• Neutrons are located in the nucleus.
• Cannot determine the # n0 ‘s by looking at the periodic table!
• The sum of neutrons and protons in an atom is called the
mass number, A. It has units of amu. Cannot find mass #
on periodic table !
mass # = # p+ + # n0
Check Your Understanding
What is the atomic number for phosphorus ?
How many protons does a calcium atom have ?
How many electrons does an oxygen atom have ?
If Z = 24, identify the element.
For element Z = 13, determine the number of e’s.
Check Your Understanding
What is the atomic number for phosphorus ?
15
How many protons does a calcium atom have ?
20
How many electrons does an oxygen atom have ?
8
If Z = 24, identify the element.
chromium
For element Z = 13, determine the number of e’s.
13
Isotopes
The number of neutrons in the
atoms of an element can vary
resulting in ISOTOPES.
– Can be naturally occurring or
man-made
An example is carbon. Two
isotopes of carbon are shown.
Top: # p+ = 6
# e’ = 6
# n0 = 6
Bottom: # p+ = 6
# e’ = 6
# n0 = 7
Isotopes
Isotopes are named using the MASS NUMBER:
Carbon-12
Oxygen-16
Atomic Number, Mass Number, and
Atomic Symbol
Figure 2.7
X = Atomic symbol of the element
A = mass number; A = Z + N
Z = atomic number
(the number of protons in the nucleus)
N = number of neutrons in the nucleus
=A-Z
Isotopic Symbols
52
Cr
Determine #p+,# e’, and # n0
24
32
P
Determine #p+,# e’, and # n0
Isotopic Symbols
52
Cr
#p+ = 24
# e’ = 24
# n0 = 28
24
32
P
#p+ = 15 # e’ = 15 # n0 = 17
Isotopic Symbols
What is the name for the isotope that has
92 protons and 143 neutrons ?
Uranium-235 (“Little Boy” atomic bomb)
Highly enriched
Uranium-235
Learning Check
Which of the following represent
isotopes of the same element?
#1
#2
#3
#4
234
234
235
238
91
X
93
X
92
X
92
ID the elements represented above
X
Average Atomic Mass
• Atomic masses listed on the periodic table are weighted
averages of the masses of all the naturally occurring
isotopes for that element.
• Silver has two naturally occurring isotopes. One has a
mass of about 107 amu and the other has a mass of about
109 amu.
• Silver-107 has an abundance in nature of 51.86%.
• Silver-109 has an abundance in nature of 48.14%.
• Silver’s average atomic mass is the weighted average of
these isotopes.
• Look on periodic table, what is silver’s average atomic
mass (also called atomic mass)?
What is the difference?
Average Atomic Mass
Mass Number
• Found on the periodic
table.
• Atomic mass is the
weighted average
mass of an atom
based on the relative
natural abundance of
that element's
isotopes.
• NOT on periodic table
• A count; exact
number
• The total number of
neutrons and protons
in a given isotope.
Most Common Mass Number
--Look at average atomic mass given on periodic table
--Round the value to whole number
Example:
Write the isotopic symbol for the most common isotope of:
Phosphorus-see board
You try:
Write the isotopic symbol for the most common isotope of:
Calcium
Iodine
Zinc
Average Atomic Mass
See Handout
Honors Only
Rutherford’s Gold Foil Experiment
• Rutherford’s experiment
involved firing a stream of
tiny positively charged
particles (alpha particles)
at a thin sheet of gold foil
(2000 atoms thick).
• Nobel Prize in 1908
• https://www.youtube.com/
watch?v=kBgIMRV895w
• Start at 3 min
Honors Only
Give Handout
Handout-Atomic Structure WS