The periodic table organizes all known elements based on their atomic structure and chemical behaviors. Elements are positioned in rows called periods and columns known as groups, creating a system that allows scientists to predict an element’s characteristics based solely on its location. The majority of elements on this chart are classified as metals, which share a distinct set of physical and chemical traits.
Locating Metals on the Periodic Table
The elements classified as metals dominate the periodic table, occupying the entire left side and the center block of the chart. Their territory is clearly demarcated by a distinct dividing line often referred to as the “stair-step” or zigzag line, which runs diagonally from the element Boron down to Astatine. Elements to the left of this line, with the notable exception of hydrogen, are metals. This extensive area includes the first two columns, the large central block spanning columns 3 through 12, and the elements beneath the stair-step line. Metals account for over 90 of the 118 known elements.
Defining Physical and Chemical Properties
The defining characteristics of metals are linked to a unique structure involving their valence electrons. Physically, metals are known for their bright, reflective surface (luster) and their ability to conduct both heat and electricity effectively. This high conductivity is a result of metallic bonding, where the outermost electrons are delocalized and move freely throughout the atomic structure, creating a mobile “sea of electrons.”
Metals also exhibit specific mechanical properties, being both malleable and ductile. Malleability means they can be hammered or rolled into thin sheets without shattering, while ductility allows them to be drawn out into thin wires. The atoms in a metal are arranged in a regular structure, which enables layers of atoms to slide past one another. Chemically, the most distinguishing feature of metals is their tendency to lose valence electrons, usually one, two, or three, to form positively charged ions called cations. This low ionization energy means they are highly electropositive and readily participate in chemical reactions by donating electrons.
Major Groups of Metals
The metallic region of the periodic table is subdivided into distinct groups. The Alkali Metals, found in Group 1, are the most reactive of all metals because they possess only a single valence electron, which they shed easily to achieve a stable electron configuration. These metals, which include sodium and potassium, are soft enough to be cut with a knife and have relatively low melting points. Their high reactivity means they are never found in their elemental form in nature and must be stored under oil to prevent aggressive reactions with air and water.
Alkaline Earth Metals
Next in Group 2 are the Alkaline Earth Metals. They are still reactive but less so than their Group 1 neighbors because they must lose two valence electrons. These metals, such as calcium and magnesium, are generally harder, denser, and have higher melting points than the alkali metals.
Transition and Inner Transition Metals
Moving toward the center of the table, Groups 3 through 12 contain the Transition Metals, including familiar elements like iron, copper, and gold. Transition metals are characterized by higher melting and boiling points and are much harder and stronger than the Group 1 and 2 metals, making them useful for construction and machinery. They can form compounds with vibrant colors and exhibit multiple positive charge states. The two rows often displayed separately at the bottom of the table, the Lanthanides and Actinides, are known as the Inner Transition Metals. The actinides, in particular, are largely radioactive and include elements like uranium and plutonium.
The Contrast: Non-Metals and Metalloids
To the right of the stair-step line are the Non-Metals. They are typically dull in appearance, brittle when solid, and are poor conductors of heat and electricity. Non-metals tend to gain or share electrons in chemical reactions, giving them a high electronegativity. Many exist as gases at room temperature, such as oxygen and nitrogen, or as brittle solids like sulfur.
The elements that directly border the stair-step line are called Metalloids, or semi-metals. They represent a transitional zone on the table and exhibit properties of both metals and non-metals, including silicon and germanium. Metalloids often look metallic with a shiny appearance but are brittle like non-metals. Their electrical conductivity falls between that of metals and non-metals, making them semiconductors, which is why they are used in the electronics and computer chip industries.