Video Transcript
What are the physical properties
used to classify elements into metals, nonmetals, or metalloids? (A) Reactivity, density, and
mass. (B) Physical state, hardness, and
color. (C) Ability to burn, corrosivity,
and texture. (D) Luster, mass, and
conductivity. (E) Luster, conductivity, and
malleability.
In this question, we need to
identify which of the answer choices is a list of physical properties that are used
to classify the elements on the periodic table as metals, nonmetals, or
metalloids. Let’s first discuss what a physical
property is.
A physical property is a property
of a substance that can be observed without changing the composition of the
substance. For example, if we placed a piece
of solid carbon on a balance, we could measure its mass. Mass is a property that depends on
how much of a substance we have. So, if we had the same amount of
another substance and placed it on the balance, it would have the same mass. We can see that mass is listed as a
property in answer choice (D). Samples of any two elements could
have the same mass, so mass cannot be a property used to classify elements as
metals, nonmetals, or metalloids. Mass is also listed in answer
choice (A), but let’s come back to that later. For now, let’s eliminate answer
choice (D).
When we observe a physical
property, such as mass, color, or density, we do not change what a substance is made
of. Before measuring the mass of the
carbon, it was composed of only carbon atoms. After making the measurement, it
was still composed of only carbon atoms. Now, let’s say we wanted to find
out if carbon can be burned. We could try to ignite the piece of
carbon. In doing so, a chemical reaction
would take place. The carbon would react with oxygen
in the air to form carbon dioxide. The result of observing carbon’s
ability to burn is that carbon is converted into a new substance, carbon dioxide
gas, which has a completely different composition.
Instead of being made of only
carbon atoms, carbon dioxide molecules are composed of both carbon and oxygen. When we burn carbon, we are
observing a chemical property. A chemical property is a property
of a substance that can only be observed by changing the composition of the
substance. Let’s take a look at answer choice
(C). We see “ability to burn” in the
list of properties. Since we now know that this is a
chemical property, not a physical property, we can eliminate answer choice (C).
Now let’s come back to answer
choice (A). Density and mass are physical
properties. But we already know that mass
cannot be used to classify elements as metals, nonmetals, or metalloids. We also know that when a chemical
reaction takes place, a chemical property is being observed. So, if we observe how reactive an
element is, we are observing a chemical property, not a physical property. For all of these reasons, we can
eliminate answer choice (A).
The remaining answer choices only
contain physical properties. So, now we need to determine which
of these are the physical properties used to classify elements as metals, nonmetals,
or metalloids. Most of the 118 known elements are
metals. Less are nonmetals. And even less are metalloids. A metalloid is an element that has
the properties of both metals and nonmetals. Most metals are solids at room
temperature. All metalloids are solids at room
temperature. And nonmetals may be solids,
liquids, or gases at room temperature. Physical state is listed in answer
choice (B). But if most metals, some nonmetals,
and all metalloids are solids at room temperature, then physical state cannot be
used to classify an element as a metal, nonmetal, or metalloid. So, we can eliminate answer choice
(B).
This leaves only answer choice (E),
which must be the correct answer. There are important differences in
the conductivity of the elements. Metals tend to be very
conductive. Metalloids are less conductive. And nonmetals tend to be the least
conductive. So, conductivity is a physical
property that can be used to classify an element as a metal, nonmetal, or
metalloid. Malleability is another property
that is used to classify the elements. An element is malleable if it can
be shaped by being struck with a hammer or if pressure is applied. In general, metals are
malleable. However, metalloids and nonmetals
tend to not be malleable. Finally, most metals are lustrous,
or shiny. But most metalloids and nonmetals
are not lustrous.
In conclusion, the physical
properties that are used to classify elements into metals, nonmetals, or metalloids
are luster, conductivity, and malleability, or answer choice (E).
