There are two basic definitions of metal, the astronomical one and the chemical one. Astronomically, "metals" can refer to all elements heavier than hydrogen and helium. In chemistry, metal is used much more specifically. Metals are elements which form ionic bonds by releasing electrons and becoming positively charged ions, and which conduct electricity. All metals are solid at room temperature and standard pressure, and can be found in the left and middle of each row on the periodic table.
- Normally Solid -
The first and most obvious trait of metals is that they are solid under the normal conditions in which we encounter them on Earth. This is not to say that they cannot either melt or boil; however, these typically require the application of several hundred degrees of temperature change.
In contrast, the non-metals are more likely to be liquid or gas at room temperature. The lightest of these, hydrogen and helium, require temperatures hundreds of degrees below zero in order to condense into a liquid and then to freeze. Helium is only solid at about two degrees above absolute zero.
- Form Positive Ions and Ionic Bonds -
Chemically, metals all share a tendency to form positive ions by releasing their outer electrons. Those on the farthest left of the periodic table, like sodium and lithium, always give up one ion, the only one in their outermost shell. Elements in the middle of the periodic table are somewhat more complex, and may sometimes give up varying numbers of electrons. In all cases, however, the reason metals surrender electrons is because they have a small number of electrons in their outer shell, and give them up in order to empty that shell entirely. In contrast, the non-metals absorb electrons in order to fill their outer shell.
The result of these differing processes is that metals always form bonds with non-metals called ionic bonds. Ionic bonds are relatively easy to calculate on the basis of the expected exchange of electrons, which is always balanced. For example, sodium and chlorine form an ionic bond - sodium chloride, better known as table salt - when the sodium metal atom surrenders one electron and gains a +1 positive charge, and the chlorine non-metal atom gains one electron and gains a -1 negative charge.
Metals are commonly found in special solutions called "alloys." These are not the same as chemical bonds. Instead, they are mixtures made up of molten metals, which are then hardened. Steel, for example, is an alloy which consists of iron and trace amounts of one of several strengthening elements, usually carbon but also manganese or chromium.
- Electricity and Conductivity -
Metals are also alike in that they are conductive: that is, a sample made up of metal can conduct an electrical charge from one end to the other. The reason this occurs is because of the ways in which large numbers of metal atoms clump together in solid form. A small number of electrons are essentially able to float freely through the partially filled outer shells of the atoms, so that if an electric charge (which consists of nothing more than a flow of electrons) is applied to one end of a metal sample, those electrons can be quickly passed from one end to the other.
There is considerable variation in the degree to which metals conduct electricity. The best conductors are silver and gold. Copper comes third, but is most commonly used in electrical applications because it is far cheaper to acquire.
- Finding Metals on the Periodic Table -
Most elements in nature are metals - and therefore most of the periodic table is made up of metals. On the right side of the table, however, are non-metallic elements, like the halogens and noble gases. Specifically, boron, silicon, germanium, arsenic, antimony, tellurium, and polonium occupy an in-between zone called the "metalloids," and everything to the right of them is a non-metal.
Along the periodic table, the metals are also divided into several key categories based on shared characteristics. The left-most column consists of the alkali metals, which are usually grey and dangerously reactive, so much so that large clumps will explode if dropped into water.
Other groups share characteristics rather than (necessarily) columns on the periodic table. For example, the base metals react with oxygen quickly, like nickel, lead, zinc, and iron. (Iron also belongs to a separate category, ferrous metals, which are those elements that are magnetic.) Third, precious metals are less reactive, highly conductive, and generally much more valuable, such as gold, palladium, platinum, silver, and iridium. Before the rise of modern chemistry, the categories of "base metal" and "precious metal" were defined much more simply: base metals were common and relatively cheap, while precious metals were rare and highly expensive.