Lesson Explainer: Metals, Nonmetals, and Metalloids Chemistry • 7th Grade

In this explainer, we will learn how to describe, compare, and explain the physical and chemical properties of metals, nonmetals, and metalloids.

The periodic table of elements has many interesting trends, and one of the most obvious is the transition of metals to metalloids and then to nonmetals as we move from the left-hand side to the right-hand side of the periodic table. The phenomenon is fascinating not only because it is maintained for almost all rows of the periodic table, but also because it can be explained with relatively simple theories about the exchange of valence electrons and intermolecular bonding patterns. The periodic table has been divided into separate metal and nonmetal sections for a relatively long time now. Jöns Jacob Berzelius was a 19th century scientist considered to among the founders of modern chemistry. He classed elements as metals or nonmetals more than one-hundred years ago. His classifications were based on the physical properties of elements.

The following figure uses red and blue colors to show how the periodic table transitions from metal elements to nonmetal elements. The metal elements are represented with the color red, and they can be found on the left-hand side of the periodic table. The nonmetal elements are represented with the color blue, and they can be found on the right-hand side of the periodic table. The metalloid elements are represented with a yellow color, and they can be found in between the left- and right-hand sections of the periodic table. The white cells represent chemical elements with unknown chemical properties.

Hydrogen is the only element that does not conform to the simple and easy-to-understand principle that metals are on the left-hand side of the periodic table and nonmetals are on the right-hand side. Hydrogen is a rather unusual element because it has the valence electron configuration of a metal, but it has nonmetal chemical properties. This has spurred some interesting debates about the position of hydrogen in the periodic table. Some scientists argue that hydrogen should be placed above carbon in the periodic table. Other scientists state that it should be placed above fluorine. Hydrogen is currently placed above group 1 metals, but it could be above a different group in the future.

Metal and nonmetal elements have very different chemical and physical properties because they are made up of atoms that are bonded in very different ways. Metal atoms usually form giant three-dimensional structures that are made up of billions of positively charged ions in a sea of delocalized electrons. Nonmetal atoms usually form much smaller covalently bonded molecules. Metals are not more useful than nonmetals, and nonmetals are not necessarily any more useful than metals. The materials have very different physical and chemical properties, and they are each very well suited for a set of specific industrial and commercial applications.

Metals are known to be hard and to have high melting points and boiling points because they are made up of metal cations in a sea of delocalized electrons. There are strong electrostatic attraction forces between the metal cations and the delocalized electrons. It takes a lot of heat or mechanical energy to break them apart. Tungsten atoms are held together with some of the strongest metallic bonds of any pure metal element. Tungsten metal has the highest melting point of all the metallic elements. It has a melting point of . Tungsten metal is used to make the filaments of most light bulbs, specifically because it can glow white-hot without melting. Mercury atoms are held together with extremely weak metallic bonds. Mercury has the lowest melting point of all the metallic elements. It has a melting point of just . Mercury is used to make thermometers because it has a low melting point and it is a liquid at room temperature.

Most metals are strong, and this makes them suitable for constructing vehicles and for making the structural support components of large buildings and monuments. Hard metals are regularly used to make cars, and they are also used to make larger transport vehicles like cargo ships and even airplanes. There also happens to be an unimaginably high number of large buildings and monuments that contain steel skeletons or some other types of metal support structures.

Metals are known to have a relatively low number of valence electrons and a relatively large atomic radius. Metals usually have a valence shell that is less than half full, and they have an atomic radius that is larger than nonmetals of the same period. Metals tend to have a relatively low electron affinity and ionization energy because they have such a large atomic radius.

Heat energy is transferred through a solid substance when one particle collides with another particle, and electrical energy is transferred through a solid substance when charge carriers move about and conduct an electric current. Metals have high electrical and thermal conductivity because they contain delocalized electrons. The delocalized electrons can conduct an electric current because they are highly mobile and they can easily move from the negative terminal of an electric circuit to its positive terminal. The delocalized electrons can conduct heat energy because they can easily move through a metallic lattice and collide with other metal cations and electrons. Lots of metals are used for making cookware and radiators because they have such a high thermal conductivity. Some metals are also used to make electrical equipment because they can conduct a large electric current. Copper has been used to make electrical wiring all around the world for more than a century because it is particularly good at conducting electricity, and it is not too expensive.

Metals are described as being malleable because they can be reshaped without breaking. They are described as being ductile because they can be drawn into long wires without cracking. Metals do not generally break or crack when they are struck with a lot of mechanical force because they contain a highly elastic sea of delocalized electrons. The positions of the individual metal ions might change when a metal is beaten and molded, but the sea of delocalized electrons is not significantly disrupted or destroyed. Metals tend to be highly sonorous, and they will make a clearly audible sound when they are beaten with something like a hammer or mallet. Their sea of delocalized electrons is highly flexible, and it can propagate incoming kinetic energy as an outward-moving sound wave.

Pure metal elements are usually described as being lustrous (shiny). The lustrous appearance of a metal can be explained in terms of its delocalized electrons. It is said that the delocalized electrons at the surface of the metal are continuously absorbing and reflecting photons of light energy. The sea of electrons is continuously reflecting photons of light, and this makes the surface of a metal look shiny. Highly lustrous metals like gold and silver are suitable for making decorative jewelry because they are shiny, and they also tend to be malleable. Gold and silver can be reshaped into trinkets and sculptures that have an aesthetically pleasing shape and a shiny surface.

Nonmetal elements are known to have a relatively high number of valence electrons and a relatively small atomic radius. They usually have a valence shell that is more than half full and an atomic radius that is smaller than metals of the same period. Nonmetals usually have a high electron affinity and ionization energy value because they have such a small atomic radius.

Nonmetal elements usually form simple covalently bonded compounds. These structures contain just a few atoms, and they do not generate strong intermolecular forces of attraction. There are relatively weak intermolecular interactions between adjacent covalently bonded molecules, and it does not take too much energy to break them apart. This explains why nonmetal elements are almost always brittle if they do form solids at room temperature, but this is not always guaranteed. Some nonmetal elements can only form a gas at room temperature. Solid and gaseous nonmetal elements usually have a low density because there are weak intermolecular interactions between adjacent nonmetal molecules.

The nonmetal elements do not tend to conduct electricity because they do not usually contain any charge-carrying particles. There are, however, at least a couple of nonmetal carbon allotropes that have surprisingly high electrical conductivity values. Graphite and nanoparticles are carbon allotropes that can conduct a large electric current. These materials contain delocalized electrons that can move from the negative terminal of an electric circuit to its positive terminal. Graphite and nanoparticles are some of the only nonmetal elements that can conduct a large electric current.

Ordinary nonmetal materials have low thermal conductivity because they do not contain delocalized electrons. They are made up of atoms that are unable to rapidly exchange heat energy with each other. Heat energy is transferred very ineffectively through a nonmetal material. It can only be transferred if hot nonmetal atoms vibrate and collide with cold nonmetal atoms.

Graphite is considered to be a very useful nonmetal material because it can be used to make pencil cores. It is ideally suited for making pencil cores because it is nonmalleable and brittle. It will break apart and leave a black residue if it comes into contact with harder substances like paper. Graphite is known to have a low density and to be inductile. The other nonmetal elements have many important industrial applications, and this includes the use of chlorine for purifying water and the use of iodine as a general-purpose disinfectant. There is also the use of charcoal to decolorize sugar or the use of phosphorus to make matches and fertilizer.

The metalloid elements are located in between the metal and nonmetal elements in the periodic table. This is fitting because metalloid elements have some properties of metals and some properties of nonmetals. They tend to have a metallic appearance and an electronegativity value that is in between the high electronegativity of nonmetals and the low electronegativity of metals. They also tend to have a thermal conductivity that is in between the high thermal conductivity of metal elements and the low thermal conductivity of nonmetal elements. The following figure is a cutout of a simplified periodic table. It shows the metalloid elements alongside adjacent metal and nonmetal elements. The figure shows that there are currently six known metalloid elements.

Good examples of metalloids are elements like boron and silicon that form rather lustrous and flaky substances that look somewhat like the transition metal elements, except they seem softer and almost pliable. Silicon and boron have properties that are similar to some transition metal elements because they are solid at room temperature and they both have very high melting points and boiling points. They also have some properties that are similar to those of nonmetal elements. They are brittle, and it does not take too much energy to break them up into small pieces.

The metalloids have a higher electrical conductivity than nonmetals and a lower electrical conductivity than pure metal elements. They tend to be called intrinsic semiconductors because they can conduct a large electric current at high temperatures and a less substantial electric current at low temperatures. Most metalloid elements can be used to make transistors because they are semiconductor materials.

The metalloids have been used so much in modern day electronic devices that some technological hubs have been designated names like Silicon Valley. Some people have even started to name the late 20th century and early 21st century period as the silicon age because silicon has been described as the dominant material of modern civilization. Silicon has been used more and more during the late 20th century, and it is now used to make electronic circuits for almost all modern-day computers. Germanium can also be used to make microchips, but it tends to be used much less frequently than silicon. Antimony has several technological applications, and it is one of the preferred materials for making battery components.

The metalloid elements have several important nontechnological applications. Many metalloid compounds are used to catalyze chemical reactions. Boron trifluoride is a relatively small molecule that has the chemical formula. It is used to catalyze the polymerization reactions of unsaturated polyethers. It is also used to catalyze some isomerization and acylation reactions. The closely related boron trichloride () compound is similarly used to catalyze different types of organic synthesis reactions because it cleaves carbon–oxygen bonds () in ether molecules. Some metalloid substances are also used to make polymer and ceramic substances.

Metalloid elements can be mixed with metals to make alloys that have desirable physical or chemical properties. Tellurium is regularly alloyed with steel to increase its machinability, and arsenic is mixed with platinum or copper to make it more resistant to different forms of corrosion.

The metallic and nonmetallic character of any chemical element can be defined with ionization-energy and electron-affinity parameters. Scientists can use these or other closely related parameters to show that elements tend to become less metallic across any one row of the periodic table. The leftmost elements tend to be significantly more metallic than the elements to their right. The group 1 elements are supposed to have the highest metallic character, and the group 17 elements are supposed to have the lowest metallic character.

Ionization-energy and electron-affinity parameters can similarly be used to show that elements tend to have a high metallic character if they are close to the bottom of the periodic table and a low metallic character if they are close to the top of the periodic table. This statement could be reworded to state that metallic character tends to increase down any one group of the periodic table. Elements at the bottom of a group tend to have the larger atomic radii and the smaller ionization energies. Metallic character increases down a group even if it starts with a metal element. It increases down the group of alkali metals, and it also increases down the group of alkaline earth metals. Nonmetallic character decreases down a group even if it starts with a nonmetal. Iodine can be considered to have a lower nonmetallic character than fluorine because it has the lower electron affinity and first ionization energy.

Cesium is generally considered to be the element with the highest metallic character because it is a group 1 element that is located at the bottom of the periodic table. Fluorine is generally considered to be the element with the highest nonmetallic character because it is a group 17 element that is located at the top of the periodic table.

The following table compares metalloids with both metal and nonmetal elements. It recapitulates several points that have been made throughout this explainer, and it condenses a lot of text down to a relatively small number of important bullet points. The table can be used to prove the overarching point of this explainer. It can be used to prove that there are some elements that cannot be classed as either metals or nonmetals. Some elements must be classed as metalloids because they have the properties of both metal and nonmetal substances.