Download 3.1 The Element A. Abundances of Eleme B. Names and Symbols

3.1 The Element
A. Abundances of Eleme
B. Names and Symbols for the
Elements
3.2 Atoms and Compounds
A. Dalton's Atomic Theory
B. Formulas of Compounds
3.3 Atomic Structure
A. The Structure of the Atom
• Thomson's Experiment
• The Plum Pudding Model
• Rutherford's Experiment
B. Introduction to the Modern
Concept of Atomic Structure
C. Isotopes
3.4 Using the Periodic Table
A. Introduction to the Periodic Table
B. Natural States of the Elements
3.5 Ions and Their Compounds
A. Ions
• Cations and Anions
• Ion Charges and the Periodic
Table
B. Compounds That Contain Ions
T
he chemical elements are essential to each of us in our daily lives. The most
important element is carbon, which is found in virtually all of the molecules that
make up the living cell. Although certain elements are present in our bodies in tiny
amounts, these elements can have profound effects on our health and behavior. As we
will see in this chapter, lithium can be a miracle treatment for someone with manicdepressive disease, and our cobalt levels can have a remarkable impact on behavior.
Many elements in our bodies serve no useful purpose, but they are found in the food we
eat, the water we drink, and the air we breathe. As a result, the human body typically
contains significant amounts of elements such as aluminum, barium, strontium,
uranium, and gold, which are usually deposited in the bones or liver.
Many elements have great economic significance. For example, about 1 billion tons of
iron and 60 million tons of aluminum are produced in the world each year and are used
mainly in structural materials. Iron is also important in another way that we seldom
think about. The earth's core, 4000 miles in diameter, consists mostly of molten iron. The
center of the earth's core, with a diameter of about 1500 miles, may consist of solid iron.
As we will see as we progress in our study of chemistry, most of the chemical elements
have an important impact on our lives.
Prereading Questions
1. What elements do you think are most abundant in the human body?
2. Do you know any chemical formulas for compounds? For example,
3.
what is the chemical formula for water? What is the chemical formula
for table salt? Do you know any other formulas?
Have you heard the terms electrons, protons, neutrons, or nucleus! What
do you know about these?
What does the term periodic mean? How do you think this applies to
the term periodic table?
Name at least one element that normally exists as a solid and at least
one element that normally exists as a gas.
The Elements
Key Term
Element symbols
Objectives
I To learn about the relative abundances of the elements
> To learn the names of some elements
1 To learn the symbols of some elements
The Greeks were the first to try to explain why chemical changes occur. By
about 400 B.C. they had proposed that all matter was composed of four fundamental substances: fire, earth, water, and air.
The next 2000 years of chemical history were dominated by alchemy. Some
alchemists were mystics and fakes who were obsessed with the idea of turning
cheap metals into gold. However, many alchemists were sincere scientists, and
this period saw important events: the elements mercury, sulfur, and antimony
were discovered, and alchemists learned how to prepare acids.
As we saw in Chapter 2, all of the earth's materials (and those of other parts
of the universe) can be broken down chemically into about 100 different elements. At first it might seem amazing that the millions of known substances
are composed of so few fundamental elements. Fortunately for those trying to
understand and systematize it, nature often uses a relatively small number of
fundamental units to assemble even extremely complex materials. For example,
hemistry Explorers
Robert Boyle (1627-1691)
The first scientist to recognize the importance
of careful measurements was Ireland's Robert
Boyle. He is best known for his pioneering work
on the properties of gases, but Boyle's most
important contribution to science was probably
his insistence that science should be firmly
grounded in experiments. For example,
Boyle held no preconceived notions
about how many elements there might
be. His definition of the term element
was based on experiments: A substance
was an element unless it could be
broken down into
two or more simpler substances. For
example, air could
not be an element, as
the Greeks believed,
because it could be
broken down into many
substances. As Boyle's experimental definition of an element became generally accepted, the list of known elements grew
and the Greek system of four elements died.
proteins, a group of substances that serve the human body in almost uncountable ways, are all made by linking together a few fundamental units to form
huge molecules. A nonchemical example is the English language, in which
hundreds of thousands of words are constructed from only 26 letters. Compounds
are made by combining atoms of the various elements, just as words are constructed from the 26 letters of the alphabet.
Words
bed
Compounds
chief
CO2
a, b,>,c,
c,
d, e, f,
h, i
'
H, O, N, C
'f >
fad
NH,
""bag
H2O
Did You Know?
N2O
Just as you had to learn the letters of the alphabet before you could learn to
read and write, you need to learn the names and symbols of the chemical elements before you can read and write chemistry.
The number of elements
changes regularly as new
elements are made in
particle accelerators.
A. Abundances of Elements
At present, about 115 different elements are known, 88 of which occur naturally. (The rest have been made in laboratories.) The elements vary greatly in
abundance. In fact, only nine elements account for most of the compounds
found in the earth's crust. In Table 3.1, the elements are listed in order of abundance (mass percent) in the earth's crust, oceans, and atmosphere.
Table 3.1 Distribution (Mass Percent) of the 18 Most Abundant
Elements in the Earth's Crust, Oceans, and Atmosphere
Element
Mass Percent
Element
Mass Percent
oxygen
49.2
titanium
0.58
silicon
25.7
chlorine
0.19
aluminum
7.50
phosphorus
0.11
iron
4.71
manganese
0.09
calcium
3.39
carbon
0.08
sodium
2.63
sulfur
0.06
potassium
2.40
barium
0.04
magnesium
1.93
nitrogen
0.03
hydrogen
0.87
fluorine
0.03
all others
0.49
•ft. Active Reading Question
1. What element is nearly half of the earth's crust, oceans, and atmosphere?
2. What percent of the mass of the crust, ocean, and atmosphere do the top nine
elements make?
3.1 The Elements
53
Oxygen, in addition to accounting for about 20 percent of the earth's atmosphere (where it occurs as O2 molecules), is also found in virtually all rocks, sand,
and soil on the earth's crust. In these materials, oxygen is not present as O2 molecules but exists in compounds that usually contain silicon and aluminum atoms.
The list of elements found in living matter is very different from that for the
earth's crust, as shown in Table 3.2. Oxygen, carbon, hydrogen, and nitrogen
form the basis for all biologically important molecules. Some elements found
in the body (called trace elements) are crucial for life, even though they are
present in relatively small amounts (Table 3.3). For example, chromium helps
the body use sugars to provide energy.
Table 3.2 Top Ten Elements
in the Human Body
Table 3.3 Trace Elements
in the Human Body
Element
Mass Percent
oxygen
65.0
arsenic
carbon
18.0
chromium
hydrogen
10.0
cobalt
nitrogen
3.0
copper
calcium
1.4
fluorine
phosphorus
1.0
iodine
magnesium
0.50
manganese
potassium
0.34
molybdenum
sulfur
0.26
nickel
sodium
0.14
selenium
Trace Elements
silicon
vanadium
One more general comment is important at this point. As we have seen,
elements are fundamental to understanding chemistry. However, students may
be confused by the many different ways that chemists use the term element
illustrated below.
54
Word
Meaning
Element
Microscopic form
Single atom of that element
Element
Macroscopic form
Sample of that element large enough to
weigh on a balance
Element
Generic form
When we say the human body contains the element sodium or lithium,
we do not mean that free elemental sodium or lithium is present. Rather
we mean that atoms of these elements are present in some form.
Chapter 3 Chemical Foundations: Elements, Atoms, and Ions
B. Names and Symbols for the Elements
The names of the chemical elements have come from many sources. Sometimes
the names come from descriptions of the element's properties, sometimes the
name reflects the place where the element was discovered, and sometimes the
name honors a famous scientist.
Sources of Names of Chemical Elements
Greek, Latin, or
German words
describing a property
of the element
Place where the
element was
discovered
Latin
Greek
gold
aurum (shining down)
lead
plumbum (heavy)
americium —» America
germanium —»
californium
California
polonium —» Poland
chlorine
color
iodine
color
*—'^ i
Germany
bromine
stench
_Jj^t^^^^
^itiBpB»
francium —> France
Famous scientists
Albert Einstein
einsteinium
Alfred Nobel
nobdium
Marie Curie
curium
We often use abbreviations to simplify the written word. For example, it is
much easier to put MA on an envelope than to write out Massachusetts, and
we often write USA instead of United States of America. Likewise, chemists
have invented a set of abbreviations or element symbols for the chemical elements. These symbols usually consist of the first letter or the first two letters
of the element names. The first letter is always capitalized, and the second is
not. For example,
fluorine
oxygen
carbon
F
0
C
neon
silicon
Ne
Si
Sometimes, however, the two letters used are not the first two letters in the
name. For example,
zinc
chlorine
Zn
Cl
cadmium
platinum
Cd
Pi
Information
In the symbol for an
element, only the first letter
is capitalized.
3.1 The Elements
55
Chemistry in Your World
Trace Elements: Small but Crucial
We all know that certain chemical elements, such as calcium, carbon, nitrogen, and iron, are essential
for humans to live. Many other elements, present in tiny amounts, are also essential for life.
proper calcium levels in the bones, and copper is
involved in the production of red blood cells.
In the Body
In Our Personal Environment
Exposure to trace elements in water, food, and air
also affects our health. Exposure to aluminum in
baked goods and cheese, as well as from cookware
and utensils, is of concern to scientists.
In Behavior
Chromium assists in the metabolism of sugars,
cobalt is present in vitamin Bi 2 , iodine is necessary for the proper functioning of the thyroid
gland, manganese plays a role in maintaining
Lithium has helped some people with bipolar
I disorder, a disease in which a person's behavior
| varies between inappropriate highs and the
o blackest of depressions.
e
Studies on inmates at a prison in Illinois have
shown that trace elements in the hair of prisoners
are related to behaviors. There is an inverse relationship between the levels of cobalt in the hair
and the degree of violence in the prisoners.
The symbols for some other elements are based on the original Latin or Greek
name.
Current Name
Original Name
Symbol
gold
aurum
Au
lead
plumbum
Pb
natrium
sodium
Na
Fe
iron
ferrum
A list of the most common elements and their symbols is given in Table 3.4.
You can also see the elements represented on a table in the inside back cover
of this text. We will explain the form of this table (which is called the periodic
table) in later chapters.
Active Reading Question
1. Give three examples of elements whose symbols are the first two letters of the
name of the element.
2. Give three examples of elements with symbols in which the first letter is not the
first letter of the name of the element.
56
Chapter 3 Chemical Foundations: Elements, Atoms, and Ions
Table 3.4 The Names and Symbols of the Most Common Elements*
Element
Symbol
Element
Symbol
aluminum
Al
lithium
Li
arsenic
As
mercury (hydrargyrum)
Hg
barium
Ba
neon
Ne
boron
B
nitrogen
N
bromine
Br
oxygen
O
calcium
Ca
platinum
Pt
carbon
C
potassium (kalium)
K
chromium
Cr
silicon
Si
cobalt
Co
silver (argentium)
Ag
copper (cuprum)
Cu
sodium (natrium)
Na
gold (aurum)
Au
sulfur
S
Pb
zinc
Zn
lead (plumbum)
*Where appropriate, the original name is shown in parentheses so that you can see
the sources of some of the symbols.
Section 3.
leview Questions
1. Give four different chemical meanings for the
word element and an example of each.
2. How many of the top ten elements in the
human body are also top ten elements in the
earth's crust, ocean, and atmosphere? What are
these elements?
3. Make a list of elements that you think were
named after a place.
4. Give the symbol for each of the given
elements.
a. iron
b. zinc
c. hydrogen
d. lithium
e. copper
f. neon
5. Give the name for each of the given symbols.
a. Ba
b. Cl
c. Si
d. F
e. N
f. Br
6. The graph below shows the mass percentages
of the five most abundant elements in the
human body. Use this graph to answer the following questions.
1.6%
Oxygen
Carbon
Hydrogen
Nitrogen
Calcium
Phosphorus
Others
a. What is the fourth most abundant element
by mass in the human body?
b. Which element is almost twice as abundant
by mass as hydrogen in the human body?
c. What percentage of the human body is not
made up of oxygen, carbon, or hydrogen?
3.1 The Elements
3.2
Key Term
Law of constant
composition
Dalton's atomic theory
Atoms and Compounds
Objectives
I
To learn about Dalton's theory of atoms
I
To understand and illustrate the law of constant composition
} To learn how a formula describes a compound's composition
Atoms
Compound
Chemical formula
A. Dalton's Atomic Theory
As scientists of the eighteenth century studied the nature of materials, several
things became clear:
1. Most natural materials are mixtures of pure substances.
2. Pure substances are either elements or combinations of elements called
compounds.
3. A given compound always contains the same proportions (by mass) of
the elements. For example, water always contains 8 g of oxygen for
every 1 g of hydrogen, and carbon dioxide always contains 2.7 g of
oxygen for every 1 g of carbon. This principle became known as the law
of constant composition. It means that a given compound always has the
same composition, regardless of where it comes from.
John Dalton, an English scientist and teacher, was aware of these observations. In the early 1800s, he offered an explanation for them that became
known as Dalton's atomic theory. The main ideas of this theory (model) can be
stated as follows:
Dalton's Atomic Theory
1. Elements are made of tiny particles called atoms.
2. All atoms of a given element are identical.
3. The atoms of a given element are different from those of any other
element.
4. Atoms of one element can combine with atoms of other elements to
form compounds. A given compound always has the same relative
numbers and types of atoms.
5. Atoms are indivisible in chemical processes. That is, atoms are not
created or destroyed in chemical reactions. A chemical reaction simply
changes the way the atoms are grouped together.
Dalton's model successfully explained important observations such as the
law of constant composition. This law makes sense because if a compound
always contains the same relative numbers of atoms, it will always contain the
same proportions by mass of the various elements.
58
Chapter 3 Chemical Foundations: Elements, Atoms, and Ions
mistry Explorers
John Dalton (1766-1844)
Dalton was an English scientist who made his
living as a teacher in Manchester. Although
Dalton is best known for his atomic theory, he
made contributions in many other areas,
including meteorology (he recorded daily
weather conditions for 46 years, producing a
total of 200,000 data entries). A rather shy man,
Dalton was color-blind to red (a special handicap for a chemist) and suffered from lead poisoning contracted from drinking substances that
had been drawn through lead pipes.
Like most new ideas, Dalton's model was not accepted immediately. However,
Dalton was convinced that he was right and used his model to predict how a given
pair of elements might combine to form more than one compound. Dalton
pictured compounds as collections of atoms. For example, nitrogen and oxygen
might form a compound containing one atom of nitrogen and one atom of
oxygen (written NO), a compound containing two atoms of nitrogen and one
atom of oxygen (written N 2 O), or a compound containing one atom of nitrogen
and two atoms of oxygen (written NO 2 ).
NO
NO,
N,O
When the existence of these substances was verified, it was a triumph for Dalton's
model. Because Dalton was able to predict correctly the formation of multiple
compounds between two elements, his atomic theory became widely accepted.
j==^_-i^L Active Reading Question
How does Dalton's model explain the law of constant composition?
B. Formulas of Compounds
A compound is a distinct substance that is composed of the atoms of two or more
elements and always contains exactly the same relative masses of those elements.
In light of Dalton's atomic theory, this statement simply means that a compound
always contains the same relative numbers of atoms of each element. For example,
water always contains two hydrogen atoms for each oxygen atom.
Reading Tip
Here, relative refers to
ratios.
3.2 Atoms and Compounds
59