Themes

Metals, non-metals and metalloids: characteristics and differences

The metals, metalloids and non – metals are the three divisions that can be classified all chemical elements of the periodic table. The elements that belong to each of these divisions share a set of physical and chemical characteristics or properties, which differentiate them from other elements.

The lower image shows a periodic table showing the locations of the metallic, non-metallic and metalloid elements. Note that metalloids only have seven elements, while the vast majority correspond to metallic elements. On the other hand, non-metals, with the exception of hydrogen, are positioned at the extreme right of the table.

Positions of the metallic (yellow), nonmetallic (blue) and metalloid (green) elements in the Periodic Table. Source: DePiep / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Metals (sodium, potassium, copper, gold, etc.) possess characteristics, in principle, very different from those of non-metals (chlorine, carbon, sulfur, oxygen, etc.). However, metalloids (boron, silicon, germanium, arsenic, etc.) consist of a slight fusion of both worlds, building the border between metals and non-metals.

Thus, metalloids have both metal and non-metal characteristics. Among these chemical divisions we have dozens of anomalies, for example, the liquid state of mercury, which are due to the structure of its atoms.

Metals

No metals

Metalloids or semi-metals

Physical characteristics

Shiny, silver, ductile, dense, porous, opaque.
Variable physical states, most of them gaseous.

Mix of characteristics between metals and non-metals.

Chemical characteristics

They give up electrons easily.
They gain electrons easily, except gases.

Amphoteric, bad oxidizing agents and bad reducing agents. Low thermal conductivity.

Examples

Gold, copper, silver, gallium, cesium, mercury.

Sulfur, carbon, phosphorus, nitrogen, hydrogen.

Characteristics of metals

Physical

Metals are generally solid with silver sheen, malleable, ductile, dense, hard, and opaque. However, some such as gold, copper, mercury, cesium and osmium, have distinctive colors, the first two being the most prominent. We also have brittle metals, such as manganese and bismuth; or soft, like sodium, which can even be sliced ​​with a knife.

Metals are excellent conductors of heat and electricity, have high melting and boiling points , and form compacted crystalline structures. On the other hand, these elements have the extraordinary ability to mix with each other to produce solid solutions called alloys.

Although they tend to be solid, there are metals that are liquid at moderate temperatures, such as mercury, gallium, and cesium.

Chemical

Metals are species that give up electrons easily. Therefore, it is normal from them that cations originate, oxidizing in innumerable chemical reactions.

Its low ionization energies, these are the energies necessary to remove an electron from its voluminous atoms in the gas phase, as well as its low electronegativities, are related to its natural tendency to oxidize.

For example, sodium oxide, Na 2 O, dissolves in water to produce OH  ions , the product of the resulting NaOH:

Na 2 O (s) + H 2 O (l) → 2NaOH (aq)

Likewise, metal oxides react with acids to form salts and water:

NiO (s) + H 2 SO 4 (aq) → NiSO 4 (aq) + H 2 O (l)

The oxidation numbers of metals are usually positive, and generally have values ​​ranging from +1 (Na + ) to +3 (Al 3+ , Ga 3+ , Fe 3+ ); however, titanium and zirconium have oxidation numbers of +4, Ti 4+, and Zr 4+ , respectively. Some can be very positive (Mn 7+ , Os 8+ and Ir 9+ ).

Characteristics of non-metals

Physical

Nonmetals have more variable physical states, although most are gaseous. Among the solids we have sulfur, carbon (coal or diamond), phosphorus, selenium and iodine. Bromine is the only nonmetal that exists as a reddish-brown liquid. Meanwhile, fluorine, chlorine, nitrogen, oxygen, hydrogen, helium, argon, etc., are gaseous elements.

Nonmetals are, under normal conditions, poor conductors of heat and electricity. They are not very dense and their solids are generally brittle.

Unlike metals and their silver colors, nonmetals tend to be colorless and dim, but there are yellow (sulfur), green (chlorine), purple (iodine), red, and white (phosphor).

Chemical

Nonmetals are species that gain electrons easily, except for noble gases due to their lack of reactivity. Therefore, they tend to form anions, and combine with metal cations to form a conglomerate of salts and ceramic compounds (halides, chlorides, iodides, sulfides, phosphides, nitrides, etc.).

Metals, when combined with each other, give rise to alloys, linked internally by the metallic bond. Nonmetals, on the other hand, originate covalent compounds (molecules) through the formation of covalent bonds; that is, they exhibit a relatively equal sharing of bond electrons.

Nonmetals usually produce acidic compounds, which when dissolved in water release H 3 O + ions . For example, CO 2 , an acidic oxide, reacts with water to form carbonic acid, H 2 CO 3 :

CO 2 (g) + H 2 O (l) → H 2 CO 3 (aq)

Nonmetals have high electronegativities, with fluorine being the most electronegative element of all. Likewise, they are characterized by their high ionization energies, since it is difficult to remove electrons from their small gaseous atoms.

Their ease of gaining or accepting electrons make them good oxidizing agents. However, they can also lose electrons, showing both positive oxidation numbers (S 4+ , N 5+ , O 2+ , H + ) and negative (F  , O 2- , H  ).

Characteristics of metalloids or semimetals

Metalloids exhibit a mixture of the physical and chemical characteristics of metals and non-metals. All are slightly dense white and silver solids, semiconductors, brittle, capable of alloying with some metals, and that melt or boil at very high temperatures. Physically, metalloids look like metals, but chemically they behave like non-metals.

The metalloid or nonmetal elements are antimony, polonium, tellurium, arsenic, germanium, silicon and boron.

Its compounds tend to be amphoteric, so they react with acids and bases. Also, metalloids are not good oxidizing agents, nor are they good reducing agents. Its thermal conductivities are not very high, except for that of silicon. And with respect to their electrical conductivities, those of arsenic and antimony are quite similar to those of other metals.

They can form salts and ionic compounds, as well as molecules or covalent compounds, which are characterized by being volatile or polymeric. In vague words: metalloids make up the most unusual and extraordinary chemical compounds or materials, such as superacids, silica, ceramics, glass, semiconductors, and alloys.

There are those who consider metalloids as part of post-transitional metals, and others who claim that they should be treated as non-metallic elements.

Related Articles

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button