Classifying the Periodic Table
Discovery Education Science © Discovery Communications, LLC
Since ancient times, scientists knew that some materials existed
in pure forms. They couldn’t be broken down into smaller parts.
Gold and mercury were two of those substances. As
technology improved, scientists could experiment
on materials and see how they behaved. Scientists
recognized a group of substances, or elements, that
made up of our earth.
In the 1800s, many different scientists were
interested in experimenting. They discovered the
relationship between elements. In 1862, a French
scientist, A.E.Beguyer de Chancourtois, organized
known elements by their atomic weight. Soon
different scientists organized the over 56 known
elements into a chart. The chart displayed a symbol
for the element’s scientific name and its atomic
weight. The chart was called the Periodic Table. There are over
114 elements organized on the Periodic Table today. Scientists
keep discovering more.
Relationships and patterns are easy to notice when you look at
the table. The elements can be classified by physical properties
into three groups. Describing elements by their look, their feel,
or how they behave under certain circumstances, like being
heated or allowing an electric charge to flow
through, can help us group them.
Metals
Metals make up the largest group on the table,
almost 75%. Some metals are familiar to everyone,
especially Fe (iron), Au (gold) and Ag (silver).
Metals have a certain look to them. They are solid at
room temperature except for Hg (mercury), which is
a liquid. They have a shiny luster or appearance.
Metals can also be bent or change shape without
breaking. Also, metals can be beaten into flat sheets
without breaking. This is called malleability.
Another characteristic of all metals is the ability to conduct heat
or electricity.
Au or gold is naturally found as flakes or
nuggets like this one.
Scientists continue to find new elements
for the Periodic Table.
Discovery Education Science © Discovery Communications, LLC
All metals have free electrons. That means the electrons float
freely between the atoms and are not stuck. Since energy is
Classifying the Periodic Table
transferred by moving electrons, it is easy to see
that free electrons would be able to transfer
energy more easily. This property is called
conductivity. Not all metals have the same ability
to conduct. It depends on how far their electrons
can move before bumping into something else.
Copper (Cu) has a weak bond with its electrons.
The electrons move easily around copper atoms,
so copper is a great conductor of both heat and
electricity.
Nonmetals
Nonmetals are the opposite of metals. They are grouped in the
upper right corner of the Periodic Table. Elements like O
(oxygen) and H (hydrogen) are members of nonmetals. They
can be a solid or a gas at room temperature. They have an
appearance that is dull or without luster. Nonmetals are very
poor conductors of heat or electric energy.
But what about water? Water is made from two nonmetal
elements (two hydrogen atoms and an oxygen atom), and yet it
is a good conductor of electricity, right? It is not the water
molecules that conduct the electricity, but the metals that are
dissolved in the water, like Na (sodium) or Cl (chloride).
Nonmetal solids are also brittle, like S (sulphur)
or C (carbon). If they are pounded, they break
easily. They can’t they be flattened into a sheet or
pulled into thin strips like metals.
Metalloids
There are always things that don’t quite fit in.
Metalloids are the elements that don’t belong in
either the metals or nonmetals groups. There are
seven known metalloids, B (boron), Si (silicon),
Ge (germanium), As (arsenic), Sb (antimony), Te
(tellurium), and Po (polonium).
These elements share some characteristics of both metals and
Copper wire carries electricity through all of
our
houses.
In this form, crystalline silicon has a shiny
lustre.
Discovery Education Science © Discovery Communications, LLC
Classifying the Periodic Table
non-metals. Silicon has a shiny luster, but it is brittle and
conducts electricity poorly. Some metalloids change their
characteristics when they react with different elements. Boron
acts like a metal when it reacts with fluorine and yet, behaves as
a non-metal when reacting with sodium. These elements can be
very useful when we need to use something that has properties
of a metal but not as strong. The computer industry makes great
use of the element silicon. Silicon conducts some electric
current, but does not get hot. It is very useful in computer chips
and transistors.
The known elements can be sorted and classified in many
different ways, but using physical properties to classify the
elements on the Periodic Table is a good way to understand how
we can make use of their different properties.
Comprehension Questions
1. What metals can you find in your home? Why do you think that
metal was used?
2. Why is it important for copper wires to be coated in plastic?
