Science High School Reviewer | Grade 4 Science | Physical Science | Properties of Matter | Lesson 26: Classifying Matter

What are elements?
People once thought that all matter was
made up of earth, air, fire, and water. We now
know that all matter is made of elements
(EL•uh•muhnts). An element is a substance that
is made up of only one type of matter.
Scientists call elements “the building blocks
of matter.” That is because an element cannot
be broken down into a simpler form. Hydrogen
and oxygen are elements. So are gold and silver.
Atoms
Elements are made up of atoms (AT•uhmz).
An atom is the smallest part of an element. You
can think of atoms as tiny particles—so tiny that
you cannot see them!
All atoms in an element are alike. For instance,
all the atoms in copper are copper atoms. They
have different properties from the atoms of any
other element.
Neon is a gas. In a
tube, neon glows if
electricity is added.

Metals and Nonmetals
How do we classify elements? One way is to
decide if they are metal (MET•uhl) or nonmetal.
A metal is shiny. It can be bent or hammered
into a shape. Some metals are iron, aluminum
(uh•LEW•muh•nuhm), and copper.
Metals let heat and electricity pass through them
easily. A metal pan over a flame or a heated burner
gets hot very quickly.
Metalloids (MET•uh•loydz), such as silicon,
have some but not all of the properties of metals.
Oxygen and nitrogen are nonmetals. They have
none of the properties of metals. They are gases.
Symbols for Elements
Scientists use symbols to stand for each element.
Often, a symbol is the first letter of the element’s
name. For example, C is the symbol for carbon.
Some elements take their symbols from their
Latin names. The Latin word for gold
is aurum (AW•ruhm). Gold’s symbol
is Au. The first letter in a chemical
symbol is always capitalized.

How are the
elements organized?
Nearly 150 years ago, a Russian
scientist named Mendeleev
(men•duh•LAY•uhf) made a table of
the elements. He based his table on
the known properties of elements. It
is the periodic (peer•ee•OD•ik) table.
Atomic Number
As new elements were found,
they were added to the table. The
modern table is shown above.
The three main groups are metals,
metalloids, and nonmetals. You can
see that the elements are arranged
by their atomic numbers. The
atomic number is related to the
mass of each element.
Columns and Rows
So far, scientists have named 112
elements. The periodic table shows
how they are similar and how they
are different. Elements in the same
column have similar properties.
For example, all the elements in
column 17 combine easily with
other elements. They often form new
substances. The elements in column
18 hardly ever react.
The rows of the table are called
periods. They also group similar
elements. Iron, cobalt, and nickel
are magnetic. They are next to each
other in the table.
Periodic Table of the Elements
State at room temperature:
Solid Liquid Gas

How do scientists use
the periodic table?
When Mendeleev arranged the
elements in a table, he saw a pattern.
Elements with similar properties
were grouped near one another.
Scientists use these patterns to
predict how an element behaves.
Hydrogen (H), for instance, reacts
easily with other substances. The
elements that share its column in
the periodic table also react easily.
Elements that share the same row
often have similar properties, too.
Iron (Fe) is magnetic. Can you find
it in the table? The two elements
next to iron are magnetic too.
Turn back to the periodic table
on the previous page. You can see
that some parts of the table are
not filled in all the way. Why not?
Scientists have not yet found all
the elements they have predicted!