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Section 1-2
SECTION SUMMARY
The Periodic Table
Guide for
Reading
How was the periodic
table developed?
What information does
each square of the
periodic table present?
How does the overall
organization of the
periodic table relate to
the physical and
chemical properties of
elements?
How are valence
electrons related to the
periodic table?
Matter has physical and chemical properties. A physical property
can be observed without changing a substance into something else. A
chemical property is observed when a substance interacts with
another substance.
In the 1860s, the Russian scientist Dmitri Mendeleev discovereda
hidden pattern in the properties. of the elements. Mendeleev noticed
that patterns appeared when the elements were arranged in order
of increasing atomic mass. The atomic mass of an element is the
average mass of one atom of the element.
Mendeleev published the first periodic table. In the periodic table, the
properties of the elements repeat in each row, or period, of the table.
The table has been updated as scientists began to identify the particles
that make up atoms.
The modern periodic table contains over 100 squares, one for each
element, arranged in order of atomic number. Each square of the
periodic table includes the element's atomic number, symbol,
name, and atomic mass. The symbol for an element usually contains
either one or two letters.
An element's properties can be predicted from its location in the
periodic table. The elements in a column are called a group, or family.
The groups are numbered from Group 1 through Group 18. The family
name of a group is typically the name of the first element in the column.
Elements in each group have similar characteristics.
Each horizontal row of the table is called a period. The elements in a
period are not alike in properties. From left to right, the elements in a
period change properties in a predictable pattern. There are seven
periods of elements. Periods have different numbers of elements.
The elements on the left side of the table are metals. These usually give
up their valence electrons in a chemical reaction. The nonmetals are on
the far right of the table. They usually gain or share valence electrons in
a chemical reaction. Between the metals and the nonmetals are the
metalloids, elements that have some properties of metals and some
properties of nonmetals.
The periodic table works because it's based on the structure of
atoms, especially the valence electrons. The number of valence
electrons that an element has increases from left to right across a
period.
UNDERSTANDING VALENCE ELECTRONS
The models below show various atoms in which the center black circle represents the nucleus and
the rings represent energy levels. Electrons are shown only on the outermost energy level of each
model. Use the Periodic Table of Elements to provide the missing information in the chart.
MODEL
Element
# OF
VALENCE
ELECTRONS
PERIOD
#
GROUP
#
METAL,
METALLOID,
NONMETAL,
OR NOBLE
GAS
MODEL
Element
# OF
VALENCE
ELECTRONS
PERIOD
#
GROUP
#
METAL,
METALLOID,
NONMETAL,
OR NOBLE
GAS
Interpreting Data and Drawing Conclusions
1. Which of the eight elements in the table is least likely to form an ion? Why?
2. Which of the eight elements in the table is most likely to form positive ions? Why?
3. Which of the eight elements in the table is most likely to form negative ions? Why?
4. Explain why all eight of the elements in the table are located on the same horizontal row of the
Periodic Table of Elements.