Video Transcript
In this video, we will learn about
the physical properties of metals and nonmetals. We will learn how to identify these
properties and describe them.
Most things around us have unique
characteristics by which we can identify and describe them. This also applies to chemical
elements and compounds. There are 118 known different
chemical elements. Each element is unique. For example, the number of protons
in the nucleus of an atom of an element is different to the number of protons in an
atom of another element. However, many elements share
similar characteristics. Scientists have grouped elements
into three broad categories based on how the elements are similar. These are the metals, the
nonmetals, and the metalloids.
All metal elements are unique, but
all metals share some similar characteristics. In the same way, all nonmetal
elements are unique. But all nonmetal elements are
similar in some ways. And all metalloid elements are
unique and yet are similar in some ways to both metals and nonmetals. Let’s focus on the characteristics
or properties that metal elements all tend to have and the characteristics or
properties that nonmetal elements tend to have.
So, what do we mean when we talk
about properties? “Properties” is a word which means
characteristics or attributes. It is the way we describe
something. In science, we can describe an
element, or any substance, by its physical or chemical properties. A physical property is a property
or characteristic of a substance which can be observed and measured without changing
the chemical identity of that substance. A chemical property is a property
which is observed and measured while a substance undergoes a chemical reaction. Chemical properties are discussed
further in another video.
So let’s dive right in and have a
look at the common physical properties of metals and of nonmetals. All metals are solid at normal room
temperature. There is one exception, and that is
the metal mercury. Mercury is a silver color, and at
room temperature, it is a liquid. Most metals tend to be hard, and
most are shiny when their surfaces are clean. We say they are lustrous. This photograph shows a piece of
metal with a high luster.
Thermal energy, which we feel as
heat, can pass easily through metals. We say metals are good thermal
conductors. That is why we make pots from metal
so heat from the stove can quickly and easily reach the food to cook it. So, a good thermal conductor is a
substance through which thermal energy can pass easily.
Electrical energy, as electrical
current, can easily pass through metals. We say metals are good electrical
conductors. And that is why we use metals in
electrical wires. The metal copper, in particular, is
an excellent electrical conductor.
Another two physical properties of
metals which we can observe and measure is that they are malleable and ductile. “Malleable” means capable of being
extended or shaped by beating with a hammer or by the pressure of rollers. In other words, most metals can be
hammered into flat sheets or rolled into flat sheets using a lot of pressure. “Ductile” means capable of being
drawn or pulled into a wire or thread. For example, copper metal can be
pulled into wires.
Metals tend to have less than four
electrons in their outer shell. This influences how metals
react. Another common property of metal
atoms is that they tend to lose electrons from their outer shell when they react
with other atoms. When they lose electrons, the metal
atoms become positively charged ions.
Now, let’s investigate common
physical properties of nonmetals. Many nonmetals are solids at room
temperature, some are gases, and only one is a liquid. Bromine is a brown-red liquid at
room temperature. Nonmetals are usually not lustrous
or shiny. We say they have no luster. Instead, most nonmetals appear
dull. They do not conduct heat or
electricity well. We say they are poor thermal and
electrical conductors. There are a few exceptions though,
like graphite, for example. That gray-black substance we use in
pencils is graphite. Graphite is one of the forms of the
element carbon. Graphite does conduct heat and
electricity well.
Unlike metals, nonmetals are not
malleable or ductile. They cannot be hammered or rolled
into flat sheets, and they cannot be pulled into long, thin wires. They are brittle. This means that when they are
hammered or any sudden force is applied to them, they break or they shatter. We saw earlier that metal atoms
lose electrons when they react and form positive ions. The opposite tends to happen with
nonmetal atoms, which tend to have more than four electrons in their outer
shell. When nonmetal atoms react with
other atoms, they tend to gain one or more electrons. They become negatively charged
ions.
Do you notice that metals and
nonmetals react oppositely? This is because metal atoms lose
their outer electrons when they react and give them to the nonmetal atoms. So, when metals react with
nonmetals, we end up with positively charged metal ions and negatively charged
nonmetal ions. Now we know the common physical
properties of metals and nonmetals.
The metalloids, we said, have some
properties of both metals and nonmetals. Metalloids are solids at room
temperature. Most metalloids have luster, like
metals, but tend to be brittle, like nonmetals. Metalloids are neither good nor
poor thermal and electrical conductors but are intermediate conductors, or
semiconducting. Metalloids are discussed more in
another video. Now, let’s practice what we have
learnt.
Which of the following images shows
a nonmetal?
We are asked to select the picture
of a nonmetal. All elements can be either a metal,
a metalloid, or a nonmetal. Metals tend to have the same
properties as each other. And nonmetals tend to have their
own set of properties. Metalloids have some properties of
metals and some of nonmetals. Metals tend to be lustrous, which
means shiny, when they have clean surfaces. Nonmetals tend to be dull, although
crystalline nonmetals may have a few surfaces which reflect light. We can see that images (A), (B),
and (C) show very shiny substances. These are metals. We can rule out these answer
options as we want to find the nonmetal. Image (D) shows a substance which
is mostly dull. This must be a nonmetal.
Let’s briefly remind ourselves of
some other properties of metals and nonmetals. Metals are malleable and
ductile. Nonmetals are not; they are
brittle. “Malleable” means they can be
hammered into flat sheets, and “ductile” means they can be pulled into long, thin
wires. “Brittle” means hard but can break
easily. We can see that answer (A) shows a
wire. This confirms (A) is a metal since
it is ductile.
Image (D) is actually a photograph
of a crystalline piece of the nonmetal sulfur. If we were to hammer this piece of
sulfur, it would shatter. Metals are good conductors of
thermal energy, which we feel as heat, and electricity, but most nonmetals are
not. An example of an exception is the
nonmetal graphite, which is a form of carbon. Graphite is a good conductor of
both thermal energy and electricity. Finally, which image shows a
nonmetal? The answer is (D).
The bar chart below shows the
electrical conductivity of five elements. Which element is a nonmetal?
All elements can be grouped into
the metals, the metalloids, and the nonmetals. Metals tend to have similar
physical properties. Nonmetals tend to have their own
set of physical properties. And metalloids have properties of
both the metals and nonmetals. Metals are lustrous, which means
shiny. Nonmetals are dull. Metals can be hammered or
shaped. We say they are malleable. Nonmetals cannot be shaped. When hammered, they break or
shatter. Nonmetals are brittle. Metals conduct heat and electricity
well, while nonmetals do not. There are a few exceptions
though. Graphite, which is a form of
carbon, is an example. Graphite does conduct thermal and
electrical energy well.
The question asks us to identify
which element on the bar graph is a nonmetal. We have the elements lithium,
vanadium, chlorine, silver, and manganese. Notice that the 𝑦-axis shows the
electrical conductivity of these elements. A simple definition of electrical
conductivity is the degree to which a material conducts electricity or electrical
current. So, electrical conductivity is a
measure of the ease with which electrical current can pass through a substance or
material. We can see that the electrical
conductivity values for lithium, vanadium, silver, and manganese are very high. So these elements conduct
electricity well and must therefore be metals. Therefore, we can rule these out as
answer options.
Chlorine, however, has a much lower
electrical conductivity. So chlorine is a poor conductor of
electricity and so must be a nonmetal. To conclude, which element is a
nonmetal? The answer is chlorine.
Now let’s summarize what we have
learnt in this video. We learnt about the physical
properties of metals and nonmetals. We learnt that metals tend to be
lustrous, while nonmetals tend to be dull. Metals can be hammered, rolled, and
shaped and pulled into wires. They are malleable and ductile. Nonmetals cannot be shaped. They are brittle and break when a
strong force is applied to them.
Metals are good thermal and
electrical conductors, while nonmetals, in general, are not. There are exceptions though. We saw that graphite, a form of
carbon, is an example of a nonmetal which does conduct both thermal energy and
electricity well.
We also learnt that metals tend to
lose outer electrons when they react with other atoms and form positively charged
ions. Nonmetals tend to gain electrons
and form negatively charged ions. Finally, we also learnt that
metalloids display properties of both metals and nonmetals.
