PHYSICAL AND CHEMICAL PROPERTIES OF METALS - CHEMISTRY - 2025

The properties of metals, both physical and chemical, are key to the construction of countless artifacts and engineering works, as well as decorative ornaments in various cultures and celebrations.

Since time immemorial they have aroused curiosity for their attractive appearance, contrasting the opacity of the rocks. Some of these most valued properties are high resistance to corrosion, low density, great hardness and toughness and elasticity, among others.

Metals are recognizable at first glance by their shiny and usually silver-toned surfaces. Source: George Becker via Pexels.

In chemistry he is more interested in metals from an atomic perspective: the behavior of their ions against organic and inorganic compounds. Likewise, salts can be prepared from metals for very specific uses; for example, copper and gold salts.

However, it was the physical properties that first captivated humanity. In general, they are characterized by being durable, which is especially true in the case of noble metals. Thus, everything that resembled gold or silver was considered valuable; coins, jewels, jewels, chains, statues, plates, etc. were made.

Metals are the most abundant elements in nature. Just take a look at the periodic table to certify that almost all of its elements are metallic. Thanks to them, materials were available to conduct electric current within electronic devices; that is, they are the arteries of technology and the bones of buildings.

Physical properties of metals

The physical properties of metals are those that define and differentiate them as materials. It is not necessary that they undergo any transformation caused by other substances, but by physical actions such as heating them, deforming them, polishing them, or simply looking at them.

Brilliance

The vast majority of metals are shiny, and also have grayish or silver colors. There are some exceptions: mercury is black, copper is reddish, gold is golden, and osmium shows some bluish hues. This brightness is due to the interactions of photons with its surface electronically delocalized by the metallic bond.

Hardness

Metals are hard, except alkaline ones and some others. This means that a metal bar will be able to scratch the surface it touches. In the case of alkali metals, such as rubidium, they are so soft that they can be scraped off with a fingernail; at least before they start to corrode the meat.

Malleability

Metals are usually malleable at different temperatures. When struck, and if they are deformed or crushed without fracturing or crumbling, then the metal is said to be malleable and exhibits malleability. Not all metals are malleable.

Ductility

Metals, in addition to being malleable, can be ductile. When a metal is ductile it is capable of undergoing deformations in the same direction, becoming as if it were a thread or wire. If it is known that a metal can be traded in cable wheels, we can affirm that it is a ductile metal; for example, copper and gold wires.

Synthetic gold crystals. Alchemist-hp (talk) www.pse-mendelejew.de

Thermal and electrical conductivity

Metals are good conductors of both heat and electricity. Among the best conductors of heat we have aluminum and copper; while those that conduct electricity best are silver, copper and gold. Therefore, copper is a metal highly appreciated in the industry for its excellent thermal and electrical conductivity.

Copper wires. Scott ehardt

Sonority

Metals are sound materials. If two metal parts are struck, a characteristic sound will be produced for each metal. Experts and lovers of metals are in fact able to distinguish them by the sound they emit.

High melting and boiling points

Metals can withstand high temperatures before melting. Some metals, such as tungsten and osmium, melt at temperatures of 3422 ºC and 3033 ºC, respectively. However, zinc (419.5ºC) and sodium (97.79ºC) melt at very low temperatures.

Among all, cesium (28.44 ºC) and gallium (29.76 ºC) are those that melt at the lowest temperatures.

From these values ​​an idea can be obtained as to why an electric arc is used in welding processes and intense flashes are caused.

On the other hand, the high melting points themselves indicate that all metals are solid at room temperature (25 ° C); With the exception of mercury, the only metal and one of the few chemical elements that is liquid.

Mercury in liquid form. Bionerd

Alloys

Although not as such a physical property, metals can mix with each other, provided that their atoms manage to adapt to create alloys. These are thus solid mixtures. One pair of metals can be alloyed more easily than another; and some in fact cannot be alloyed at all due to the low affinity between them.

Copper "gets along" with tin, mixing with it to form bronze; or with zinc, to form brass. Alloys offer multiple alternatives when metals alone cannot meet the required characteristics for an application; as when you want to combine the lightness of one metal with the tenacity of another.

Chemical properties

Chemical properties are those inherent to their atoms and how they interact with molecules outside their environment to stop being metals, to become other compounds (oxides, sulfides, salts, organometallic complexes, etc.). It is then about their reactivity and their structures.

Structures and links

Metals, unlike non-metallic elements, are not grouped as molecules, MM, but as a network of M atoms held together by their outer electrons.

In this sense, the metallic atoms remain strongly united by a “sea of ​​electrons” that bathe them, and they go everywhere; that is, they are delocalized, they are not fixed in any covalent bond, but they make up the metallic bond. This network is very orderly and repetitive, so we have metallic crystals.

Metallic crystals, of different sizes and full of imperfections, and their metallic bond, are responsible for the observed and measured physical properties for metals. The fact that they are colorful, bright, good conductors, and sound is all due to their structure and their electronic delocalization.

There are crystals where the atoms are more compacted than others. Therefore, metals can be as dense as lead, osmium, or iridium; or as light as lithium, even capable of floating on water before reacting.

Corrosion

Metals are susceptible to corroding; although several of them can exceptionally resist it under normal conditions (noble metals). Corrosion is a progressive oxidation of the metal surface, which ends up crumbling, causing stains and holes that spoil its shiny surface, as well as other undesirable colors.

Metals such as titanium and iridium have a high resistance to corrosion, since the layer of their formed oxides does not react with humidity, nor do they allow oxygen to penetrate the interior of the metal. And of the easiest metals to corrode we have iron, whose rust is quite recognizable by its brown color.

Reducing agents

Some metals are excellent reducing agents. This means that they give up their electrons to other electron-hungry species. The result of this reaction is that they end up becoming cations, M ^{n +}, where n is the oxidation state of the metal; that is, its positive charge, which can be polyvalent (greater than 1+).

For example, alkali metals are used to reduce some oxides or chlorides. When this happens with sodium, Na, it loses its only valence electron (because it belongs to group 1) to become a sodium ion or cation, Na ⁺ (monovalent).

Similarly with calcium, Ca (group 2), which loses two electrons instead of just one and remains as a divalent cation Ca ²⁺.

Metals can be used as reducing agents because they are electropositive elements; they are more likely to give up their electrons than to gain them from other species.

Reactivity

Having said that electrons tend to lose electrons, it is to be expected that in all their reactions (or most) they end up transforming into cations. Now, these cations apparently interact with anions to generate a wide range of compounds.

For example, alkali and alkaline earth metals react directly (and explosively) with water to form hydroxides, M (OH) _n, formed by M ^{n +} and OH ^- ions, or by M-OH bonds.

When metals react with oxygen at high temperatures (such as those reached by a flame), they transform into M ₂ O _n oxides (Na ₂ O, CaO, MgO, Al ₂ O ₃, etc.). This is because we have oxygen in the air; but also nitrogen, and some metals can form a mixture of oxides and nitrides, M ₃ N _n (TiN, AlN, GaN, Be ₃ N ₂, Ag ₃ N, etc.).

Metals can be attacked by strong acids and bases. In the first case salts are obtained, and in the second again hydroxides or basic complexes.

The oxide layer that covers some metals prevents acids from attacking the metal. For example, hydrochloric acid cannot dissolve all metals to form their respective water-soluble metal chlorides.

References

1. Whitten, Davis, Peck & Stanley. (2008). Chemistry (8th ed.). CENGAGE Learning.
2. Shiver & Atkins. (2008). Inorganic chemistry. (Fourth edition). Mc Graw Hill.
3. Home Science Tools. (2019). Metals Science Lesson. Recovered from: learning-center.homesciencetools.com
4. The Rosen Publishing Group. (2019). Metals. Recovered from: pkphysicalscience.com
5. Toppr. (sf). Chemical Properties of Metals and Nonmetals. Recovered from: toppr.com
6. Wikipedia. (2019). Metal. Recovered from: en.wikipedia.org