IRN-PS 4 Periodic Table of Elements
The Periodic Table of Elements

In the late 1800s, a Russian scientist by the name of Dmitri Medeleev began to look at the properties of known elements in order to organize them. The result was the periodic table of elements. Let’s investigate the organization of the periodic table of elements and how scientists use it today.

The periodic table of elements is a tool that we can use to organize information about the elements. It is made up of horizontal rows called periods and vertical columns called groups or families. Each box in the table contains information about the structure of an element. The elements in each box are arranged according to their atomic numbers and properties. An atom’s identity is directly related to its atomic number, or the number of protons in its nucleus. As you read from left to right along a period, the elements are arranged in increasing order of atomic number.

The elements become increasingly nonmetallic as you move from left to right across the table. A stair-step line on the right side of the table helps us locate the three classifications or groups of elements: metals, nonmetals, and metalloids.

Metals are those elements located to the left of the stair-step line. They tend to lose electrons in chemical reactions to form positive ions – any element that gains or losses electrons becomes an ion.

Metalloids border the stair-step line and have some properties of both metals and nonmetals.

Nonmetals are located to the right of the stair-step line. They tend to gain electrons in chemical reactions to form negative ions.

The vertical columns on the periodic table contain elements that have the same number of electrons in their outermost energy level. Electrons can be found in zones or areas around the nucleus called energy levels. Electrons located in energy levels closest to the nucleus contain lower amounts of energy than those located in energy levels farther from the nucleus. This similar arrangement of electrons causes the elements in a vertical group to have similar chemical and physical properties such as boiling points and reactivity. Vertical groups are often called families because they are “related” by their similar properties. This similarity of properties in the vertical groups causes a repetitive or repeating pattern of physical and chemical properties as you move across the periods on the table.

We can obtain a lot of information about the elements and their atoms by using the periodic table of elements. First of all, by counting the number of boxes that make up the periods and groups, we find that there are more than 110 known elements. Of these, only 92 are found naturally on the Earth. The remaining elements, called synthetic elements, are artificially produced in laboratory settings.

Many periodic tables also tell us an atom’s atomic number, atomic mass, phase of matter at room temperature, number of outer level (valence) electrons, and chemical symbol. Chemical symbols usually come from the ancient or modern name of the element and consist of one, two, or three letters. The first letter is always capitalized. All others letters are lower case.

The elements on the periodic table can combine in many ways to produce compounds that make up all other substances on Earth. Compounds are formed when the atoms of elements react chemically. The number of electrons in the outermost energy levels of an atom determines the chemical properties and reactivity of an element. When a metallic element reacts, or bonds with a nonmetallic element, their atoms gain and lose electrons forming ionic bonds. When two nonmetals react, or bond, the atoms usually share electrons forming covalent (molecular) bonds. Through the gaining, losing, and sharing of electrons, atoms become chemically stable. Atoms react to form chemically stable substances that are held together by chemical bonds and are represented by chemical formulas.

A chemical formula is a type of abbreviation or shorthand used to represent what elements are present in a compound and how many atoms of each element bond to form the compound. It is written using the chemical symbols for the bonded elements and subscript numbers. Subscript numbers always follow and are written below a chemical symbol. For example, the compound we know as water is made up of two atoms of hydrogen bonded to one atom of oxygen. The chemical formula for water (H2O) uses the chemical symbols for hydrogen (H) and oxygen (O) and the subscript number (2). This chemical formula means that there are two atoms of hydrogen and one atom of oxygen bonded together in every molecule of the compound water.

We have learned that the losing and gaining of electrons make an atom an ion. It is interesting to note that atoms can undergo other types of changes. When an atom gains or loses neutrons from its nucleus, it becomes an isotope. An isotope remains the same element because the number of protons stays the same. Most elements have several isotopes that occur naturally. Isotopes continue to have the same physical and chemical properties as the original element. In contrast, if an atom gains or loses a proton, its atomic number changes and it becomes a completely different element.