1 ALL MATTER IN THE UNIVERSE IS MADE OF VERY SMALL PARTICLES

Metals in our lives

Metals are the most widely spread elements on Earth. Out of the 118 known elements in the periodic table, there are only 25 semimetals and non-metals. The remaining elements are metals. It is assumed that newly discovered or artificially made elements will be also metals. In the nature metals are mostly found in the form of oxides, sulphides and salts. Heavy metals are also found in the nature as pure metals. Metals are a typical electropositive element which means that they easily break off electrons and they act as cations in compounds.

Metals are solids with regularly arranged lattice. Mercury is an exception, as it remains liquid in the normal temperature and normal (atmospheric) pressure. Metals have a metallic sheen – apart from red-brown copper and golden gold, which are exceptions. All metals are electricity conductive, malleable, and ductile – it is possible to make very thin plates out of them.

Density of metals

Density ( physical quantity which is equal to a proportion of physical object´s weight and its volume)of metals varies and depends on the inner setting. Density value of alloys is always in the range between the densities of pure metals and depends on the ratio of metals present in the alloy. Examples of pure metals densities are shown in Table 1. Densities of alloys and their compositions are shown in Table 2.

**Table 1:** Density of metals
Pure metal	density
iron	7.800
copper	8.960
tin	7.260
aluminium	2.700

**Table 2:** Density and composition of alloys
alloy	composition	density
brass	copper (70%) + tin (30%)	8.400
stainless steel	iron + chromium	8.000
duralumin	aluminium (96%) + copper (4%)	2.800

Alloy of metals

Alloy of metals is a compound of metals made by smelting of a metal with another metals, or other elements or compounds. According to the number of components, alloys are divided into binary – they contain two components, ternary – they contain three components and quaternary – they contain a four-component alloy. The first historically significant alloy of metals was bronze. Its properties were discovered already in the prehistoric times. The discovery of bronze meant an immense technological progress in the making of tools, weapons, and adornments. In contrast to pure metals – copper and tin, which bronze is made from, it has higher hardness. To prove its significance for man – one whole era of human history was named after it – the Bronze Age. Alloys of metals are made because of their properties that pure metals simply do not have. Intentional adding of elements to metals is called alloying. Alloying of steel by chromium can serve as an example. Steel made this way is resistant to rusting and it is used for production of exhaust pipes, cutlery and dishes.

Magnetic properties of metals

Magnetic properties of metals are given by moving electrons present in atoms of metals. Moving electrons create elementary magnetic fields around themselves. These elementary magnetic fields get together and define the final magnetic field of atoms and therefore magnetic properties of a substance.Atoms of diamagnetic substancesare arranged in a way that single elementary magnetic fields of electrons are disrupted. Diamagnetic substances weaken the magnetic field, which they are put into. Gold, silver, copper and bismuth are examples of metals that fall into diamagnetic metals.

Paramagnetic substances have elementary magnetic fields arranged in a way that substances which are put into it, intensify the magnetic field only slightly. On the surface, they act as very weak magnets. By outer magnetic field, atoms cannot be arranged in a way that a substance would intensify the magnetic field in a more significant way. Aluminium, tin and chromium are examples of metals that fall into diamagnetic metals. In order to distinguish paramagnetic and diamagnetic substances, we use a measuring method which is based on a measurement made by magnetic induction using a coil or a method which measures the force caused by a magnetic field or a method which is based on the change of materials´ properties in the presence of a magnetic field.

Ferromagnetic substances have atoms arranged in a similar way as paramagnetic substances. In contrast to paramagnetic substances, atoms of ferromagnetic substances are arranged into small domains that are positively magnetised. Substances significantly intensify the magnetic field they are put into and they are strongly pulled in by the field. This force is strong enough to be sensed by us. Iron, cobalt, nickel and their alloys belong among ferromagnetic substances. Magnetic properties of metals and alloys of metals are used when producing electromagnets, relays, inductive hobs and dishes. In the past, they were also used when making audio tapes

Reactivity series

Products made of metals are affected not only by air, changes of temperature but also by various aqueous solutions. Chemists were looking into properties of pure metals and came to a conclusion that resistance to a liquid environment depends on the ability to form cations, either easily or less easily. According to this finding, they arranged metals into The Reactivity Series (Fig. 1), where metals are arranged in order of their reactivity, from the most reactive – they make cations the easiest – to the least reactive. Metals that form cations more reluctantly – copper, mercury, silver and gold are called noble metals. They are written in italics in The Reactivity Series. Metals described as non-noble metals, that form cations easily, are stated on the right side. The more right-sided the metal is, the more readily they react.

Picture 2: The Reactivity Series

Gaseous hydrogen results from the reaction of a non-noble metal with an acid as well as the salt of the particular metal and an acid. Gaseous hydrogen is released in the form of bubbles (Reactive schemes 1, 2, 3). A noble metal does not react with an acid at all (Reactive scheme 4). The test to prove the presence of hydrogen can be done by collecting it into a test tube turned upside-down and placing it over the lit burner. Hydrogen makes the “pop” sound.

Reaction scheme 4: Reaction of hydrochloric acid with zinc

Zn + 2HCl → ZnCl₂ + H₂

Reaction scheme 5: Reaction of hydrochloric acid with iron

Fe + 2HCl → FeCl₂ + H₂

Reaction scheme 6: Reaction of hydrochloric acid with aluminium

2Al + 6HCl → 2Al → Cl₃ + 3H₂

Reaction scheme 7: Reaction of hydrochloric acid with copper

Cu + HCl → unresponsive

Corrosion

Resistance of metals to corrosion does not depend on the nobility of a metal. On the surface of aluminium, a thin layer of aluminium oxide forms spontaneously. In contrast to iron, the layer is more complex and protects the metal. We call it passivation of metal. If aluminium is used for chemical reactions, the layer must be removed. The removal of aluminium oxide from the surface can be done mechanically by using emery paper. Products made of copper or a green layer – patina that passivates the surface of copper, covers their alloys. A layer of zinc oxide that protects it against weak aqueous solutions covers the surface of zinc.

Rusting, that is corrosion, of iron is caused by humid air or aqueous solutions and their reaction with iron. An uneven porous layer forms on the surface of iron – rust, which contains primarily iron oxide of rusty colour. The layer of the oxide does not protect the metal, it peels off causing the corrosion spreads further. That is why it is necessary to protect all the iron objects that are exposed to air moist and aqueous solutions (for example rain) by water repulsive coating or to cover them with a layer of resistant metal. Electroforming and hot-dip galvanizing are used the most commonly