CHAPTER 11 - CHEMICAL ELEMENTS
Chemistry is the branch of physical science that deals with the
composition and structure of matter and the reactions that
occur which change one substance into another.
An early form of chemistry called alchemy flourished from
about 500 AD to 1600 AD. Its main goals were to find ways to
change base metals into gold and to discover an "elixir of life"
that would prevent aging.
Modern chemistry began in the 1700's with the work of
Lavoisier. It uses logic in an attempt to explain changes in
matter and avoids superstition, mysticism, and secrecy.
There are 5 major divisions of chemistry.
1. Physical chemistry - applies the theories of physics to the
study of chemical systems.
2. Analytical chemistry - the study of determining what
substances and how much of each are present in a material.
3. Organic chemistry - the study of compounds that contain
carbon.
4. Inorganic chemistry - the study of all other chemical
compounds.
5. Biochemistry - the study of chemical compounds and
chemical reactions that occur in living things.
Classification of Matter
Figure 11.1
A Chemical Classification of Matter
Copyright © Houghton Mifflin Company
11-2
Matter is anything that has mass.
Any form of energy has no mass and is not matter.
A pure substance is a type of matter in which all samples have
the same composition and the same properties.
Only elements and compounds are considered pure substances.
An element is a substance in which all of the atoms have the
same number of protons.
Example
Hydrogen - H, Oxygen - O, Sodium - Na, Chlorine - Cl
A compound is a substance composed of two or more elements
chemically bound in a definite fixed ratio by mass.
Example
Water - H2O, Sodium Chloride NaCl
A compound can be broken down into its component elements
by chemical means. An element cannot be broken down by
chemical means. Only a nuclear reaction can change an
element into a different element.
A mixture is a type of matter composed of two or more
substances that are physically mixed, not chemically bonded.
Different samples of a mixture may have different
compositions and properties.
A heterogeneous mixture is one that is not uniform. Different
substances can be observed.
Examples
Pizza, Italian salad dressing, Chocolate chip ice cream
A homogeneous mixture is composed of two or more
substances that are mixed so thoroughly that they cannot be
distinguished. A solution is a type of homogeneous mixture.
Examples
Coffee, Air, Brass
In a solution, the substance present in the larger amount is
called the solvent. The substance that has been dissolved is
called the solute. When water is the solvent, the solution is said
to be aqueous.
When a solution contains all of the solute it can hold, it is said
to be saturated. If more solute can be dissolved in it it is
unsaturated. If the solution contains more solute than it
normally could dissolve at that temperature, it is said to be
supersaturated.
Solubility of a solute is the amount of a solute that can be
dissolved in a specified mass or volume of solvent at a specific
temperature. In the case of liquid solvents and solid solutes,
solubility increases as the temperature increases. In the case of
liquid solvents and gaseous solutes, the solubility decreases as
the temperature increases.
Figure 11.5
The Effect of
Temperature on
Solubilities of
Salts in Water
Molecules and Allotropes
A molecule is an electrically neutral particle composed of two
or more atoms chemically bonded. If all the atoms are from the
same element, it is a molecule of an element (H2, N2, O2, O3). If
the atoms are from two or more different elements, it is a
molecule of a compound.
Figure 11.11
Representations of Molecules
Copyright © Houghton Mifflin Company
11-5
Allotropes of an element exist when atoms of the element form
different types of bonds and different physical structures. An
example is carbon with diamonds, graphite and fullerenes
(Bucky balls).
The Periodic Table
The periodic table is an organizational chart of the elements.
They are arranged in order of increasing atomic number,
horizontal rows called periods and vertical columns called
groups.
The properties of the elements are relatively constant within a
group but vary across a period in a repeating fashion.
The periodic law states:
The properties of elements are periodic functions of their
atomic numbers.
Dmitri Mendeleev developed the first useful periodic table. Its
modern form is still in use today.
Figure 11.16
Names of Specific Portions of the Periodic
Table
The elements are grouped in several ways.
In one, the representative elements are those in groups 1A
through 8A. These elements contain 1 to 8 electrons in the
outer shell and contain the specially named groups alkali
metals (group 1A), alkaline earth metals(group 2A),
Halogens(group 7A), and the Noble gasses(group 8A).
In this classification method, the elements in groups 3B
through 12B are called the transition elements and contain
metals like copper, silver and gold. They are between groups
2A and 3A.
The inner transition elements are the two rows called the
Lanthanides and Actinides and are placed in a separate area at
the bottom of the chart. Uranium and plutonium belong in this
classification.
Another way to classify elements is into the categories of metals
and nonmetals. Elements on the left side of the chart including
all of the transition elements and inner transition elements are
metals. The elements in the upper right hand corner and far
right on the table are called nonmetals. The elements that form
a zigzag line between the metals and nonmetals are called
metalloids.
Properties of Metals
Good conductors of heat and electricity
Malleable - can be beaten into thin sheets
Ductile - can be stretched into wire
Possess metallic luster
Solid at room temperature(except Hg)
Have 1 to 3 valence electrons
Lose electrons to form positive ions
Properties of Nonmetals
Poor conductors of heat and electricity
Brittle if solid
Nonductile
No metallic luster
Solid, liquid, or gas at room temperature
Have 4 to 8 valence electrons
Gain electrons or share electrons
Elements near the bottom of the chart have stronger metallic
characteristics. Elements to the right on the chart have
stronger nonmetal characteristics.
The electrons in an atom are arranged in major energy levels
called shells. On the periodic table each period corresponds to
the beginning of a shell.
The shells are further subdivided into sub shells which are
composed of orbitals each with one or two electrons with
different spins.
Figure 11.18
Shell Distribution of Electrons in Periods
1, 2, and 3
Copyright © Houghton Mifflin Company
11-8
The outermost shell in an atom is called the valence shell and
the electrons in it are called the valence electrons. These are
the electrons involved in forming chemical bonds. All of the
elements in a group have the same number of valence electrons
and form compounds in a similar fashion.
Atomic size is also a periodic property. As you go across a
period atomic size decreases. Since the number of positive
charges in the nucleus is increasing, the force pulling the
electrons in toward the nucleus increases and results in a
smaller orbit radius.
As you go down the periodic table, atomic size increases since
you are adding one shell for each period you add.
Figure 11.20
The Relative Sizes of Atoms of Representative
Elements
Ionization energy (energy required to remove an electron) is
also periodic. It increases as you go across a period. More
protons in the nucleus hold the electrons with greater
attractive force.
As you go down the periodic table, ionization energy decreases.
As you add shells that are further from the nucleus, the
attractive force becomes weaker.
Naming Compounds
Spotlight
Naming
Compounds
Binary compound formulas are written with the metallic ion
first followed by the negative ion.
To name a binary compound, write the name of the positive ion
and the name of the negative ion. Replace the end of the
negative ion name with the suffix ide.
Example
NaCl - Sodium Chloride
Al2O3 - Aluminum Oxide
When two nonmetals combine to form a compound, they very
often can combine in at least two ratios to form two different
compounds. Generally the Greek numeric prefixes are used to
distinguish the compounds.
Example
NO - Nitrogen Monoxide
NO2 - Nitrogen Dioxide
N2O5 - Dinitrogen Pentoxide
An ion is an atom or a group of chemically combined atoms
that have an electric charge because they have gained or lost
one or more electrons. When more atoms than one combine to
form an ion it is called a polyatomic ion.
Example
Acetate
Hydroxide
Carbonate
Phosphate
Ammonium
C2H3O2OHCO3-2
PO4-3
NH4+
When writing a compound name with a polyatomic ion, just
write the name of the positive ion and then the name of the
negative ion.
Example
Na2CO3
NH4Cl
Sodium Carbonate
Ammonium Chloride
Some compounds have special names that do not follow these
rules. Examples are water, ammonia, methane, Sulfuric Acid,
and others. For these you must recognize the formula and
remember the common name.
Study
P 306 Key terms
P 306 Matching Questions
P 307 Multiple Choice Questions
P 307 Fill in the Blank Questions
P 308 Questions 4, 5, 6, 7, 9, 13, 16, 17, 18, 19, 20, 21, 22, 25,
26, 27, 28, 31, 32
P 309 Exercises 1, 7, 9, 15, 17, 27, 29