As of 2014, there are 118 elements known to science. The most recently discovered element, ununpentium, was confirmed in 2013.
All of the known elements are arranged in a grid called the periodic table. Each element is organized in the periodic table by its atomic number from hydrogen in the top left corner to ununoctium in the lower right corner. Each row of the table is called a period.
The columns on the periodic table are referred to as groups. Elements within a specific group generally share similar chemical properties and are classified in the following manner.
- The elements in the group on the far left are alkali metals. These elements are highly reactive to water, producing alkaline solutions and hydrogen gas.
- Elements in the second group are alkaline metals.
- Groups 3-12 consist of three different categories of elements. On the main part of the table are transition metals. Transition metals are distinguished by their high densities.
- Additional elements listed below the main body of the periodic table are lanthanides and actinides.
- Groups 13-16 also contain three different element types. These are post-transition metals, metalloids and non-metals.
- Group 17 contains elements known as halogens. Halogens are found naturally as solid, liquids and gases. Each molecule of a halogen contains two atoms, making them diatomic.
- Elements in the far right group of the periodic table are the noble gases. Unlike halogens, noble gases are monotomic, meaning molecules contain only one atom.