The chemical properties of a metal describe how it interacts with other substances, forming new chemical compounds. Metals comprise the vast majority of the periodic table, located on the left side and in the center blocks. This is distinct from physical properties, such as luster, conductivity, or malleability. The defining chemical characteristic of metals is their tendency to participate in reactions by losing electrons, which dictates their overall reactivity.
The Tendency to Lose Electrons
The fundamental chemical behavior of any metal stems from its electronic structure, specifically the ease with which it gives up its outer-shell electrons. Metals typically possess a small number of valence electrons, usually one, two, or three, in their outermost energy shell. The atomic structure of metals means these valence electrons are not held tightly by the nucleus, a condition reflected in their relatively low ionization energy and low electronegativity.
This tendency makes metals highly electropositive, meaning they readily donate electrons during a chemical reaction to achieve a more stable electron configuration. The process of losing electrons is known as oxidation, and when a neutral metal atom undergoes this change, it becomes a positively charged ion, or cation. For instance, a sodium atom loses one electron to form a \(Na^{+}\) cation, while a magnesium atom loses two electrons to form a \(Mg^{2+}\) cation.
Because they are electron donors, metals act as reducing agents in chemical reactions, causing the reduction of the other reacting substance. The more easily a metal atom loses its electrons, the greater its reducing power and the higher its overall chemical reactivity.
How Metals React with Common Substances
The ability of metals to lose electrons is manifested through reactions with substances like oxygen, water, and acids. When exposed to the atmosphere, most metals react with oxygen to form metal oxides, a process commonly referred to as oxidation or corrosion. A familiar example is the formation of rust, which is iron oxide, when iron is exposed to oxygen and moisture.
The reaction with water shows a wide range of behaviors depending on the specific metal. Highly reactive metals, such as the alkali metals like sodium and potassium, react vigorously and exothermically with cold water, producing a metal hydroxide and releasing hydrogen gas. Metals lower on the reactivity scale, such as zinc, may only react with steam, while metals like copper and gold show practically no reaction with water at all.
Metals that are more reactive than hydrogen also readily react with dilute acids, such as hydrochloric acid. In these reactions, the metal displaces hydrogen from the acid, resulting in the formation of a metal salt and the liberation of hydrogen gas. For example, zinc metal reacts with hydrochloric acid to produce zinc chloride and hydrogen gas.
The Nature of Compounds Metals Form
The compounds resulting from metal reactions exhibit distinct chemical properties, particularly concerning their bonding and behavior in water. When a metal reacts with a nonmetal, such as chlorine or oxygen, the complete transfer of electrons results in the formation of an ionic compound, often called a salt. These compounds are characterized by strong electrostatic attractions between the positively charged metal cations and the negatively charged nonmetal anions.
The metal oxides formed during the reaction with oxygen are characterized by their basic chemical nature. Basicity means that when these oxides dissolve in water, they form alkaline solutions, specifically metal hydroxides. For example, sodium oxide reacts with water to yield sodium hydroxide, which is a strong base.
This basicity of metal oxides stands in contrast to the oxides of nonmetals, which are typically acidic. The distinct behavior of metal oxides in water is a defining chemical property separating metals from nonmetals. This characteristic of forming ionic compounds and basic oxides is a direct consequence of the metal’s tendency to lose electrons.