Scientists believe that about 25 of the known elements are essential to life. These four elements are found in the basic structure of all biochemical molecules. For example, glucose is a carbohydrate and its molecular formula is C 6 H 12 O 6 — each molecule of glucose is made up of 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms. The other elements found can be divided into two main groups — major elements and trace elements. The human body functions as a result of a large number of chemical reactions involving compounds of all of these elements.
Although many of the elements are required in only very small amounts, they do play a very important role in keeping the body working effectively:. Too little of any given essential element can result in ill health and, if left untreated, could result in death:. Scientific knowledge is never absolute or certain. As scientists discover more about essential elements needed in the diet, old beliefs may have to change in light of new evidence. For example, in Figure 2.
Third, the periodic table is arranged in columns of elements that react similarly. These columns are called groups. The group number is found at the top of the column.
Molecules and compounds
Groups 1—12 contain only metals, Groups 13—16 contain both metals and nonmetals, and Groups 17 and 18 contain only nonmetals. One exception is hydrogen.
Although technically a nonmetal, hydrogen has properties of both metals and nonmetals and is often placed in Group 1. The two long rows that are at the bottom of the periodic table are exceptions. The elements in each of these rows behave similarly, so are considered groups. These two groups are arranged in rows rather than columns. Metals are elements that conduct heat and electricity. Metals are usually malleable , they can be bent or molded without breaking, and lustrous , or shiny.
Most metals are silvery in color Fig. Most metals are solid at room temperature. One exception is mercury Hg , which is a liquid at room temperature Fig. The elements in Group 1, including lithium Li , sodium Na, Fig. These metallic Group 1 elements have similar reactive properties. In Fig 2. When solid, non-metals tend to be brittle, such as sulfur, which flakes apart rather than bending like a metal would Fig.
The elements in Group 17, including fluorine F 2 , chlorine Cl 2 , Fig. The nonmetals in Group 17 are all diatomic two atoms in their elemental form and have similar reactive properties. There are other organizational features of the periodic table. Most periods have the first element of the period in Group 1 and the last element in Group An exception is the first period.
Sometimes hydrogen H is placed in Group 17, above fluorine F , because it has similar properties to the nonmetals in that group; for example, in its elemental state hydrogen exists as a diatomic gas, H2. Sometimes hydrogen is placed in both Groups 1 and Groups of elements have similar properties. The properties of some groups are so unique or important that the groups are referred to by special names.
The elements in this group are called the noble gases. Noble gases seldom react with other elements. Noble gases have many uses, for example, they are used in neon signs Fig 2. Group 1 is often referred to as the alkali metals, Group 2 as the alkaline earth metals, and Group 17 as the halogens. The two groups that are pulled out on the bottom of the periodic table in rows are called the lanthanide rare earth series top row and the actinide series bottom row.
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3.1: Types of Chemical Compounds and their Formulas
Main menu About this Site Table of Contents. Atoms, Molecules, and Compounds. NGSS Performance Expectations: HS-PS Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms. The content and activity in this topic will work towards building an understanding of the structure of atoms and how elements are organized on the periodic table.
Chemical Structures The properties of elements and compounds are determined by their structures.
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Determine how charged matter interacts. Other Organizational Features of the Periodic Table There are other organizational features of the periodic table.
Further Investigations. Table of Contents: Atoms, Molecules, and Compounds. Activity: Electrostatic Forces. Special Features:. Representative Image:. Further Investigations: What is an Invertebrate?
Question Set: What is a Mammal? Further Investigations: What is a Mammal? Share and Connect. We invite you to share your thoughts, ask for help or read what other educators have to say by joining our community. Partner Organizations. Professional Development. Purchase a membership! Atomic Number. Atomic Symbol. Number of Protons.
Covalent Molecules and Compounds
Number of Electrons. Number of Neutrons. Atomic Structure. Physical Properties.