How many elements are there in the periodic table

periodic table

Our editors will review what you’ve submitted and determine whether to revise the article.

Our editors will review what you’ve submitted and determine whether to revise the article.

The periodic table is a tabular array of the chemical elements organized by atomic number, from the element with the lowest atomic number, hydrogen, to the element with the highest atomic number, oganesson. The atomic number of an element is the number of protons in the nucleus of an atom of that element. Hydrogen has 1 proton, and oganesson has 118.

The groups of the periodic table are displayed as vertical columns numbered from 1 to 18. The elements in a group have very similar chemical properties, which arise from the number of valence electrons present—that is, the number of electrons in the outermost shell of an atom.

The arrangement of the elements in the periodic table comes from the electronic configuration of the elements. Because of the Pauli exclusion principle, no more than two electrons can fill the same orbital. The first row of the periodic table consists of just two elements, hydrogen and helium. As atoms have more electrons, they have more orbits available to fill, and thus the rows contain more elements farther down in the table.

The periodic table has two rows at the bottom that are usually split out from the main body of the table. These rows contain elements in the lanthanoid and actinoid series, usually from 57 to 71 (lanthanum to lutetium) and 89 to 103 (actinium to lawrencium), respectively. There is no scientific reason for this. It is merely done to make the table more compact.

Read a brief summary of this topic

periodic table, in full periodic table of the elements, in chemistry, the organized array of all the chemical elements in order of increasing atomic number—i.e., the total number of protons in the atomic nucleus. When the chemical elements are thus arranged, there is a recurring pattern called the “periodic law” in their properties, in which elements in the same column (group) have similar properties. The initial discovery, which was made by Dmitry I. Mendeleyev in the mid-19th century, has been of inestimable value in the development of chemistry.

It was not actually recognized until the second decade of the 20th century that the order of elements in the periodic system is that of their atomic numbers, the integers of which are equal to the positive electrical charges of the atomic nuclei expressed in electronic units. In subsequent years great progress was made in explaining the periodic law in terms of the electronic structure of atoms and molecules. This clarification has increased the value of the law, which is used as much today as it was at the beginning of the 20th century, when it expressed the only known relationship among the elements.

History of the periodic law

The early years of the 19th century witnessed a rapid development in analytical chemistry—the art of distinguishing different chemical substances—and the consequent building up of a vast body of knowledge of the chemical and physical properties of both elements and compounds. This rapid expansion of chemical knowledge soon necessitated classification, for on the classification of chemical knowledge are based not only the systematized literature of chemistry but also the laboratory arts by which chemistry is passed on as a living science from one generation of chemists to another. Relationships were discerned more readily among the compounds than among the elements; it thus occurred that the classification of elements lagged many years behind that of compounds. In fact, no general agreement had been reached among chemists as to the classification of elements for nearly half a century after the systems of classification of compounds had become established in general use.

J.W. Döbereiner in 1817 showed that the combining weight, meaning atomic weight, of strontium lies midway between those of calcium and barium, and some years later he showed that other such “ triads” exist (chlorine, bromine, and iodine [halogens] and lithium, sodium, and potassium [alkali metals]). J.-B.-A. Dumas, L. Gmelin, E. Lenssen, Max von Pettenkofer, and J.P. Cooke expanded Döbereiner’s suggestions between 1827 and 1858 by showing that similar relationships extended further than the triads of elements, fluorine being added to the halogens and magnesium to the alkaline-earth metals, while oxygen, sulfur, selenium, and tellurium were classed as one family and nitrogen, phosphorus, arsenic, antimony, and bismuth as another family of elements.

Attempts were later made to show that the atomic weights of the elements could be expressed by an arithmetic function, and in 1862 A.-E.-B. de Chancourtois proposed a classification of the elements based on the new values of atomic weights given by Stanislao Cannizzaro’s system of 1858. De Chancourtois plotted the atomic weights on the surface of a cylinder with a circumference of 16 units, corresponding to the approximate atomic weight of oxygen. The resulting helical curve brought closely related elements onto corresponding points above or below one another on the cylinder, and he suggested in consequence that “the properties of the elements are the properties of numbers,” a remarkable prediction in the light of modern knowledge.

How Many Elements Are There?

An element refers to a substance made of atoms of the same kind. All the atoms in a particular element bear the same atomic number. Elements cannot be broken further into smaller substances using chemical reactions. However, they can only be transformed into other elements by nuclear procedures. The atoms in an element contain the same number of protons, but the number of neutrons varies. When the number of protons in an atom is changed, then the element changes.

Properties of Elements

Every known element has a name and a number, which are listed in the periodic table. The periodic table outlines each element’s electron configuration, the atomic number of the element, and the chemical properties of the element. The atomic number refers to the number of protons found in the atom of an element. Elements can be categorized into three major groups that include metals, nonmetals, and metalloids. The elements found on the left side of the periodic table are typically metals. While the elements on the right side of the periodic table are non-metals. Some elements like hydrogen and sodium are popular while others like dysprosium remain unknown because they are rarely used. Elements like copper, carbon, and silver have been in existence for thousands of years.

Current Number of Elements

The periodic table contains a total of 118 elements. Four of these were included on the list in 2016. These are Nihonium (113), Moskovi (115), Tennessine (117), and Oganesson (118). The first 98 elements listed in the periodic table occur naturally while the rest can only be found in nuclear accelerators and laboratories. Thirty-two of the 98 elements are in their pure form. The rest exist as compounds. Eighty of the natural elements are stable, meaning that they cannot be subjected to radioactive decay. Ten of the 98 elements only exist in trace amounts. Typically, all the elements of the periodic table with a higher atomic number than lead are unstable, thus subject to radioactive decay. Although several of the discovered elements exist naturally, only a few of these exist in their native form. Among the few are noble gases that do not form compounds easily, as well as metals like copper, silver, and gold. Non-metals that fall into this category include nitrogen, oxygen, and carbon. Elements that do not exist in their native form include alkali and alkaline metals as well as rare earth elements.

Rare vs Native Elements

Rare elements are obtained through the radioactive decay of some common elements. For instance, francium results from decayed actinium. A number of the elements listed in the periodic table recently may have been produced through the decay of unknown elements that have been in existence for a long time. Native elements, on the other hand, are naturally occurring elements in an uncombined form. However, only a few native elements are found in compound form.

The Future of the Periodic Table

Six new elements were discovered between 2012 and 2016, filling the gaps that were remaining at the bottom of the periodic table. The year 2019 marked the 150th year since the table was established. As the chemical properties of known elements continue to change, new discoveries of elements continue to occur. Most of the periodic table changes will result from human-made elements made by scientists using high energy accelerators. However, unlike natural elements that can be handled, these synthetic elements are likely to be unstable, thus decaying quickly. Nonetheless, there is a possibility for more exciting discoveries in the atomic world.

How to Read the Periodic Table

Core Concepts:

In this tutorial, you will learn how to read the periodic table. We will take a close look at the groups of the periodic table. In addition, you will learn about the different properties of the periodic table groups, periods, and families. If you enjoy this article, be sure to check out our others!

Related Articles:

Vocabulary

Do you have a better periodic table?

We think our periodic table is one of the best in the world! Visit our interactive periodic table.

The Periodic Table and the Periodic Trends

The periodic table is organized into groups (vertical columns), periods (horizontal rows), and families (groups of elements that are similar). Elements in the same group have the same number of valence electrons. Meanwhile, elements in the same period have the same number of occupied electron shells. In 1869 Russian chemist Dmitri Mendeleev noticed there existed an innate pattern of organization for the chemical elements. From this deduction, he formed the periodic table. It is important to note how the location of elements on this table tells us about their properties. A quick way to understand an element’s chemical and physical properties is to know the periodic trends. These trends tell you where the highest and lowest types of properties are concentrated on the periodic table. For a more in-depth explanation of periodic trends, click here.

Group vs Period

Groups are the columns of the periodic table, and periods are the rows. There are 18 groups, and there are 7 periods plus the lanthanides and actinides.

Periods on the Periodic Table

So what is a period on the periodic table? Periods are the horizontal rows of the periodic table. There are seven periods total and each element in a period has the same number of atomic orbitals. The top period, which contains hydrogen and helium, has only two orbitals. As you go down the rows, the number of orbitals increases. Below is a table to help visuals the periodic number and the corresponding orbitals.

Groups of the Periodic Table

As previously mentioned, the vertical columns on the periodic table are called “groups”. There is eighteen groups on the periodic table in total, and each periodic table group contains elements with the same number of valence electrons.

The number of valence electrons present dictates the properties of an element. The reason for this is that the valence electrons, which are the electrons in the outermost shell, are the ones taking part in chemical reactions. These electrons are either donating, accepting, or sharing. Moreover, the more filled the valence shell is, the more stable the element.

How many groups are in the periodic table?

There are 18 groups in the periodic table, one per each column of the periodic table. The first column on the left is group 1, and the last column on the right is group 18.

Groups and Valence Electrons

The first group is the least stable as it only has one valence electron. Meanwhile, group eighteen is the most stable as these elements have a full valence shell (eight valence electrons). Below is a table relating the group numbers to the number of valence electrons.

Families of the Periodic Table

On the periodic table, there are families which are groups of elements with similar properties. These families are alkali metals, alkaline earth metals, transition metals, post-transition metals, metalloids, halogens, noble metals, and noble gases. Many of these families belong to a single group on the periodic table. However, not all of the families overlap with periodic table groups. For example, the transition metals contain all elements from group three to group twelve. Below is a periodic table where displaying the location of each family.

The Alkali Metals (Group 1)

The alkali metals consist of all of the elements in group one with the exception of hydrogen. These elements are extremely reactive and for this reason, are usually found in compounds. In addition, they are water-sensitive (they react violently with water), so they must be stored in oil. The most reactive alkali metal is francium and it decreases as you go up the group. This means lithium is the least reactive. Physically, the alkali metal family is silvery, white, and light. They also have low melting and low boiling points.

The Alkaline Earth Metals (Group 2)

The alkaline earth metals are the second most reactive family on the periodic table (following behind the alkali metals). Moreover, they are strong reducing agents which means they donate electrons in chemical reactions. They are also good thermal and electrical conductors. Physically, they have low density, low melting point, and a low boiling point.

Rare Earth Metals: Lanthanides

Lanthanides are a family of rare earth metals that contain one valence electron in the 5d shell. They are highly reactive and a strong reducing agent in reactions. Furthermore, they are a silvery-bright metal and are relatively soft. They also have both high melting points and high boiling points. The rare earths include elements like neodymium and erbium.

Rare Earth Metals: Actinides

Actinides are another family of rare earth metals. Like the lanthanides, these elements are highly reactive. They also have high electropositivity and are radioactive. Additionally, these elements contain paramagnetic, pyromorphic, and allotropic properties. Physically, they are very similar to lanthanides. They are silvery metals that are soft, malleable, and ductile.

The Transition Metals (Groups 3-11)

The transition metals typically form two or more oxidation states. They have low ionization energies and high conductivity. In addition, they have high melting points, high boiling points, and high conductivity. Physically they are both metallic and malleable.

Post Transition Metal

The post transition metals are located in between the transition metals and the metalloids. At standard temperature, they are in a solid state of matter. They tend to have a high density as well as high conductivity. Physically they are malleable and ductile.

The Metalloids

The metalloids display properties of both metals and non-metals. For example, metals are good conductors and non-metals are poor conductors. This means metalloids are semiconductors (only conducts electricity at high temperatures.). Also, they are more brittle than metals but less brittle than non-metals. Physically they can be either shiny or dull and are typically ductile and malleable.

The Halogens (Group 17)

The name halogen means “salt formers” in greek. This is evident in nature as halogens interact with metals to form various salts. On another note, the halogens are a unique group of elements. They are the only periodic family that contains elements in the three states of matter at standard temperature. There are 6 halogens and they are located in group 17. These elements include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). They are highly reactive, highly electronegative, and highly toxic non-metals.

Noble Metals

The noble metals consist of ruthenium (Ru), osmium (Os), rhodium (Rh), iridium (Ir), Pd, platinum (Pt), gold (Au), silver (Ag). Like the noble gases, they are inert due to having a complete valence shell. In addition, noble metals have catalytic tendencies. Also, they are very resistant to corrosion, tarnishing, and oxidation. Finally, like many of the other metals, they are soft and ductile.

Noble Gases (Group 18)

The noble gases, also called aerogens, are inert gases. Some examples include argon, krypton, and neon. They can be found in group eighteen on the periodic table. Likewise, this means they have a complete valence shell. For this reason, they are stable and relatively unreactive. Furthermore, the noble gases have low boiling points and low melting points. Physically they are colorless and have no smell.

See some cool Elements

Summary Table for Family Properties

See a Cool Chemistry Experiment

The periodic table

Periods

The periodic table of the elements contains all of the chemical elements that have been discovered or made; they are arranged, in the order of their atomic numbers, in seven horizontal periods, with the lanthanoids (lanthanum, 57, to lutetium, 71) and the actinoids (actinium, 89, to lawrencium, 103) indicated separately below. The periods are of varying lengths. First there is the hydrogen period, consisting of the two elements hydrogen, 1, and helium, 2. Then there are two periods of eight elements each: the first short period, from lithium, 3, to neon, 10; and the second short period, from sodium, 11, to argon, 18. There follow two periods of 18 elements each: the first long period, from potassium 19, to krypton, 36; and the second long period, from rubidium, 37, to xenon, 54. The first very long period of 32 elements, from cesium, 55, to radon, 86, is condensed into 18 columns by the omission of the lanthanoids (which are indicated separately below), permitting the remaining 18 elements, which are closely similar in their properties to corresponding elements of the first and second long periods, to be placed directly below these elements. The second very long period, from francium, 87, to oganesson, 118, is likewise condensed into 18 columns by the omission of the actinoids.

Groups

Classification of elements into groups

The six noble gases—helium, neon, argon, krypton, xenon, and radon—occur at the ends of the six completed periods and constitute the Group 18 (0) group of the periodic system. It is customary to refer to horizontal series of elements in the table as periods and vertical series as groups. The seven elements lithium to fluorine and the seven corresponding elements sodium to chlorine are placed in the seven groups, 1 (Ia), 2 (IIa), 13 (IIIa), 14 (IVa), 15 (Va), 16 (VIa), and 17 (VIIa), respectively. The 17 elements of the fourth period, from potassium, 19, to bromine, 35, are distinct in their properties and are considered to constitute Groups 1–17 (Ia–VIIa) of the periodic system.

The first group, the alkali metals, thereby includes, in addition to lithium and sodium, the metals from potassium down the table to francium but not the much less similar metals of Group 11 (Ib; copper, etc.). Also the second group, the alkaline-earth metals, is considered to include beryllium, magnesium, calcium, strontium, barium, and radium but not the elements of Group 12 (IIb). The boron group includes those elements in Group 13 (IIIa). The other four groups are as follows: the carbon group, 14 (IVa), consists of carbon, silicon, germanium, tin, lead, and flerovium; the nitrogen group, 15 (Va), includes nitrogen, phosphorus, arsenic, antimony, bismuth, and moscovium; the oxygen group, 16 (VIa), includes oxygen, sulfur, selenium, tellurium, polonium, and livermorium; and the halogen group, 17 (VIIa), includes fluorine, chlorine, bromine, iodine, astatine, and tennessine.

Although hydrogen is included in Group 1 (Ia), it is not closely similar to either the alkali metals or the halogens in its chemical properties. It is, however, assigned the oxidation number +1 in compounds such as hydrogen fluoride, HF, and −1 in compounds such as lithium hydride, LiH; and it may hence be considered as being similar to a Group 1 (Ia) element and to a Group 17 (VIIa) element, respectively, in compounds of these two types, taking the place first of Li and then of F in lithium fluoride, LiF. Hydrogen is, in fact, the most individualistic of the elements: no other element resembles it in the way that sodium resembles lithium, chlorine resembles fluorine, and neon resembles helium. It is a unique element, the only element that cannot conveniently be considered a member of a group.

A number of the elements of each long period are called the transition metals. These are usually taken to be scandium, 21, to zinc, 30 (the iron-group transition metals); yttrium, 39, to cadmium, 48 (the palladium-group transition metals); and hafnium, 72, to mercury, 80 (the platinum-group transition metals). By this definition, the transition metals include Groups 3 to 12 (IIIb to VIIIb, and Ib and IIb).

Periodic trends in properties

The periodicity in properties of the elements arranged in order of atomic number is strikingly shown by the consideration of the physical state of the elementary substances and such related properties as the melting point, density, and hardness. The elements of Group 18 (0) are gases that are difficult to condense. The alkali metals, in Group 1 (Ia), are soft metallic solids with low melting points. The alkaline-earth metals, in Group 2 (IIa), are harder and have higher melting points than the adjacent alkali metals. The hardness and melting point continue to increase through Groups 13 (IIIa) and 14 (IVa) and then decrease through Groups 15 (Va), 16 (VIa), and 17 (VIIa). The elements of the long periods show a gradual increase in hardness and melting point from the beginning alkali metals to near the centre of the period and then at Group 16 (VIa) an irregular decrease to the halogens and noble gases.

The valence of the elements (that is, the number of bonds formed with a standard element) is closely correlated with position in the periodic table, the elements in the main groups having maximum positive valence, or oxidation number, equal to the group number and maximum negative valence equal to the difference between eight and the group number.

The general chemical properties described as metallic or base forming, metalloid or amphoteric, and nonmetallic or acid forming are correlated with the periodic table in a simple way: the most metallic elements are to the left and to the bottom of the periodic table and the most nonmetallic elements are to the right and to the top (ignoring the noble gases). The metalloids are adjacent to a diagonal line from boron to polonium. A closely related property is electronegativity, the tendency of atoms to retain their electrons and to attract additional electrons. The degree of electronegativity of an element is shown by ionization potential, electron affinity, oxidation-reduction potential, the energy of formation of chemical bonds, and other properties. It is shown to depend upon the element’s position in the periodic table in the same way that nonmetallic character does, fluorine being the most electronegative element and cesium (or francium) the least electronegative (most electropositive) element.

The sizes of atoms of elements vary regularly throughout the periodic system. Thus, the effective bonding radius (or one-half the distance between adjacent atoms) in the elementary substances in their crystalline or molecular forms decreases through the first short period from 1.52 Å for lithium to 0.73 Å for fluorine; at the beginning of the second period, the bonding radius rises abruptly to 1.86 Å for sodium and gradually decreases to 0.99 Å for chlorine. The behaviour through the long periods is more complex: the bonding radius decreases gradually from 2.31 Å for potassium to a minimum of 1.25 Å for cobalt and nickel, then rises slightly, and finally falls to 1.14 Å for bromine. The sizes of atoms are of importance in the determination of coordination number (that is, the number of groups attached to the central atom in a compound) and hence in the composition of compounds. The increase in atomic size from the upper right corner of the periodic table to the lower left corner is reflected in the formulas of the oxygen acids of the elements in their highest states of oxidation. The smallest atoms group only three oxygen atoms about themselves; the next larger atoms, which coordinate a tetrahedron of four oxygen atoms, are in a diagonal belt; and the still larger atoms, which form octahedral oxygen complexes (stannic acid, antimonic acid, telluric acid, paraperiodic acid), lie below and to the left of this belt. Only the chemical and physical properties of the elements are determined by the extranuclear electronic structure; these properties show the periodicity described in the periodic law. The properties of the atomic nuclei themselves, such as the magnitude of the packing fraction and the power of entering into nuclear reactions, are, although dependent upon the atomic number, not dependent in the same periodic way.

Organization of the Elements

Introduction to the Periodic Table

People have known about elements like carbon and gold since ancient time. The elements couldn’t be changed using any chemical method. Each element has a unique number of protons. If you examine samples of iron and silver, you can’t tell how many protons the atoms have. However, you can tell the elements apart because they have different properties. You might notice there are more similarities between iron and silver than between iron and oxygen. Could there be a way to organize the elements so you could tell at a glance which ones had similar properties?

What Is the Periodic Table?

Dmitri Mendeleev was the first scientist to create a periodic table of the elements similar to the one we use today. You can see Mendeleev’s original table (1869). This table showed that when the elements were ordered by increasing atomic weight, a pattern appeared where properties of the elements repeated periodically. This periodic table is a chart that groups the elements according to their similar properties.

Why was the Periodic Table Created?

Why do you think Mendeleev made a periodic table? Many elements remained to be discovered in Mendeleev’s time. The periodic table helped predict the properties of new elements.

Mendeleev’s Table

Compare the modern periodic table with Mendeleev’s table. What do you notice? Mendeleev’s table didn’t have very many elements, did it? He had question marks and spaces between elements, where he predicted undiscovered elements would fit.

Discovering Elements

Remember changing the number of protons changes the atomic number, which is the number of the element. When you look at the modern periodic table, do you see any skipped atomic numbers that would be undiscovered elements? New elements today aren’t discovered. They are made. You can still use the periodic table to predict the properties of these new elements.

Periodic Properties and Trends

The periodic table helps predict some properties of the elements compared to each other. Atom size decreases as you move from left to right across the table and increases as you move down a column. The energy required to remove an electron from an atom increases as you move from left to right and decreases as you move down a column. The ability to form a chemical bond increases as you move from left to right and decreases as you move down a column.

Today’s Table

The most important difference between Mendeleev’s table and today’s table is the modern table is organized by increasing atomic number, not increasing atomic weight. Why was the table changed? In 1914, Henry Moseley learned you could experimentally determine the atomic numbers of elements. Before that, atomic numbers were just the order of elements based on increasing atomic weight. Once atomic numbers had significance, the periodic table was reorganized.

Introduction | Periods & Groups | More about Groups | Review Questions | Quiz

Periods and Groups

Elements in the periodic table are arranged in periods (rows) and groups (columns). Atomic number increases as you move across a row or period.

Periods

Rows of elements are called periods. The period number of an element signifies the highest unexcited energy level for an electron in that element. The number of elements in a period increases as you move down the periodic table because there are more sublevels per level as the energy level of the atom increases.

Groups

Columns of elements help define element groups. Elements within a group share several common properties. Groups are elements have the same outer electron arrangement. The outer electrons are called valence electrons. Because they have the same number of valence electrons, elements in a group share similar chemical properties. The Roman numerals listed above each group are the usual number of valence electrons. For example, a group VA element will have 5 valence electrons.

Representative vs. Transition Elements

There are two sets of groups. The group A elements are called the representative elements. The group B elements are the nonrepresentative elements.

What Is on the Element Key?

Each square on the periodic table gives information about an element. On many printed periodic tables you can find an element’s symbol, atomic number, and atomic weight.

Introduction | Periods & Groups | More about Groups | Review Questions | Quiz

Classifying Elements

Elements are classified according to their properties. The major categories of elements are the metals, nonmetals, and metalloids.

Metals

You see metals every day. Aluminum foil is a metal. Gold and silver are metals. If someone asks you whether an element is a metal, metalloid, or non-metal and you don’t know the answer, guess that it’s a metal.

What are Properties of Metals?

Metals share some common properties. They are lustrous (shiny), malleable (can be hammered), and are good conductors of heat and electricity. These properties result from the ability to easily move the electrons in the outer shells of metal atoms.

What are the Metals?

Most elements are metals. There are so many metals, they are divided into groups: alkali metals, alkaline earth metals, and transition metals. The transition metals can be divided into smaller groups, such as the lanthanides and actinides.

Group 1: Alkali Metals

The alkali metals are located in Group IA (first column) of the periodic table. Sodium and potassium are examples of these elements. Alkali metals form salts and many other compounds. These elements are less dense than other metals, form ions with a +1 charge, and have the largest atom sizes of elements in their periods. The alkali metals are highly reactive.

The alkaline earths are located in Group IIA (second column) of the periodic table. Calcium and magnesium are examples of alkaline earths. These metals form many compounds. They have ions with a +2 charge. Their atoms are smaller than those of the alkali metals.

The transition elements are located in groups IB to VIIIB. Iron and gold are examples of transition metals. These elements are very hard, with high melting points and boiling points. The transition metals are good electrical conductors and are very malleable. They form positively charged ions.

The transition metals include most of the elements, so they can be categorized into smaller groups. The lanthanides and actinides are classes of transition elements. Another way to group transition metals is into triads, which are metals with very similar properties, usually found together.

Metal Triads

The iron triad consists of iron, cobalt, and nickel. Just under iron, cobalt, and nickel is the palladium triad of ruthenium, rhodium, and palladium, while under them is the platinum triad of osmium, iridium, and platinum.

Lanthanides

When you look at the periodic table, you’ll see there is a block of two rows of elements below the main body of the chart. The top row has atomic numbers following lanthanum. These elements are called the lanthanides. The lanthanides are silvery metals that tarnish easily. They are relatively soft metals, with high melting and boiling points. The lanthanides react to form many different compounds. These elements are used in lamps, magnets, lasers, and to improve the properties of other metals.

Actinides

The actinides are in the row below the lanthanides. Their atomic numbers follow actinium. All of the actinides are radioactive, with positively charged ions. They are reactive metals that form compounds with most nonmetals. The actinides are used in medicines and nuclear devices.

Groups 13-15: Not all Metals

Groups 13-15 include some metals, some metalloids, and some nonmetals. Why are these groups mixed? The transition from metal to nonmetal is gradual. Even though these elements aren’t similar enough to have groups contained within single columns, they share some common properties. You can predict how many electrons are needed to complete an electron shell. The metals in these groups are called basic metals.

Nonmetals & Metalloids

Elements that don’t have the properties of metals are called nonmetals. Some elements have some, but not all of the properties of the metals. These elements are called metalloids.

The nonmetals are poor conductors of heat and electricity. Solid nonmetals are brittle and lack metallic luster. Most nonmetals gain electrons easily. The nonmetals are located on the upper right side of the periodic table, separated from metals by a line that cuts diagonally through the periodic table. The nonmetals can be divided into classes of elements that have similar properties. The halogens and the noble gases are two groups of nonmetals.

Group 17: Halogens

Group 18: Noble Gases

The noble gases are located in Group VIII of the periodic table. Helium and neon are examples of noble gases. These elements are used to make lighted signs, refrigerants, and lasers. The noble gases are not reactive. This is because they have little tendency to gain or lose electrons.

Hydrogen

Hydrogen has a single positive charge, like the alkali metals, but at room temperature, it is a gas that doesn’t act like a metal. Therefore, hydrogen usually is labeled as a nonmetal.

Elements that have some properties of metals and some properties of nonmetals are called metalloids. Silicon and germanium are examples of metalloids. The boiling points, melting points, and densities of the metalloids vary. The metalloids make good semiconductors. The metalloids are located along the diagonal line between the metals and nonmetals in the periodic table.

Common Trends in Mixed Groups

Remember that even in mixed groups of elements, the trends in the periodic table still hold true. Atom size, ease of removing electrons, and ability to form bonds can be predicted as you move across and down the table.

Introduction | Periods & Groups | More about Groups | Review Questions | Quiz

Test your comprehension of this periodic table lesson by seeing if you can answer the following questions: