Allotropes, Alloys and Ores of metals and non-metals

Both metals and non-metals show polymorphism or allotropy. This is the occurrence of an element in more than one form but in the same physical state. These forms are called polymorphs or allotropes.

Elements                      Major Allotropic Forms

Carbon                          Diamond and Graphite

Sulphur                          Rhombic sulphur

                                        Monoclinic sulphur

Tin                                  White tin and Red tin

Oxygen                           Dioxygen (Oxygen)

                                        Trioxygen (Ozone)

Phosphorus                   White phosphorus

                                         Red phosphorus

All the allotropes of an element have the same chemical properties even though they have different appearances or crystalline strictures. For instance, diamond (a hard form of carbon) and graphite (a soft form of carbon) can be shown to be the same element by combustion whereby a sample of each allotrope is burnt in excess oxygen. The product in each case is carbon(IV)oxide.

Metals are at times mixed intimately with other metals or non-metals to form alloys. The alloys combine the strength and the properties of the constituent elements.

Examples:

Alloys                       Constituent Elements

Brass                            Copper and Zinc

Bronze                          Copper and Tin

Steel                              Iron and Carbon

Duralumin                    Aluminum, Magnesium,

                                      Manganese and Copper

Sodium Amalgam       Sodium and Mercury

Zinc Amalgam              Zinc and Mercury

It should be noted that an amalgam is an alloy of mercury and another metal.

The form in which a metal occurs naturally is known as the ore. Metals can be removed or extracted from their ores by various means depending on their degree of activity. The activity series is the arrangement of elements in the decreasing order of reactivity or electropositivity or metallicity.

Those metals that are highly or moderately reactive do not occur free in nature but rather they occur in form of compounds in their ores.

The compounds found in ores are usually oxides or sulphides or trio of at on area (IV) of metals. These ores are either concentrated (by floatation) or roasting (heating in air) and then reduced chemically or electrolytically to release or free their metals. Elements in this category include potassium, sodium, calcium, aluminium and iron.

Ores                          Element sought

Haemitite                          Iron

Casseterite                       Tin

Bauxite                        Aluminum

Zinc blend                        Zinc

Galena                             Lead

Malachite                      Copper

However, there are other metals that have low reactivity and so they are usually found free in nature. Such metals include Platinum and Gold.

Metalloid are elements that are neither distinctly metallic nor clearly non-metallic e.g. Silicon, Arsenic, Tellurium, etc. The properties of metalloids are intermediate between those of metals and those of non-metals. For instance, they are semiconductors rather than being good conductors or nonconductors of electricity.

Deliquescent, Hygroscopic and Efflorescent Compounds

These are substances composed of two or more kinds of atoms (elements) joined together in a definite grouping.

The properties of a compound are distinct and different from those of the individual elements that are combined in its make-up.

There are several millions of compounds known. These compounds are derived from the elements e.g. water consists of hydrogen and oxygen atoms in ratio 2 to 1; common salt consists of sodium and chlorine atoms in ratio 1 to 1.

Compounds are usually classified in a number of ways:

Based on the behavior when exposed to the atmosphere, compounds are classified into three: deliquescent, hygroscopic and efflorescent.

Deliquescent compounds are those compounds that absorb moisture from the atmosphere and form the solutions of tjr compounds e.g. sodium hydroxide pellets, anhydrous calcium chloride and iron(III)chloride.

Hygroscopic compounds are those that absorb moisture from the atmosphere and become wet. Their ability to absorb water from air is less than that of deliquescent compounds. Hence the solid ones from pasty substances and not solution while the liquid ones become diluted e.g. sodium trioxonitrate(V), copper(II)oxide and concentrated tetraoxosulphate(VI)acid.

Efflorescent compounds are compounds that give out their water of crystallization to the atmosphere at ordinary temperatures e.g. sodium trioxocarbonate(IV)decahydrate loses nine of its ten moles of water of crystallization on exposure to air.

It should be noted that all deliquescent substances are also hygroscopic but not all hygroscopic substances are deliquescent. Hygroscopy is the ability of a substance to draw water vapour to itself and become wet. Both hygroscopic and deliquescent substances have this ability.

However, if a substance goes beyond being wet and becomes a solution in the course of drawing water to itself, it shows deliquescency.

Deliquescent and hygroscopic compounds are used as drying agents for gases in the laboratory. For instance, concentrated tetra of soul phage(VI)acid is the usual drying agent for acidic gases e.g. sulphur(IV)oxide, calcium oxide is commonly used as the drying agent for the alkaline gas, ammonia. Also, desiccants in desiccators are deliquescent or hygroscopic substances e.g. silica gel, calcium oxide, fused calcium chloride and phosphorus(V)oxide.

Physical and chemical properties of metals and non-metals

There are distinct substances that cannot be spit-up into simpler substances. Such substances consist of only one kind of atom. There are over one hundred elements known to date. Each of the elements is usually symbolized by a capital letter or a capital letter followed by a small letter derived from the English or Latin or Greek name of the element concerned e.g. Hydrogen (H), Sodium (Na), Copper (Cu), Uranium (U), Antimony (SB), Neon (Be), etc.

The elements can be categorized in several ways.

- Based on natural radioactivity, elements are classified into two: radioactive and non-radioactive elements.

Radioactive elements are those that undergo a spontaneous decay or degradation followed by the emission of one or more of the radiations (Alpha, Betta, Gamma).

Such elements include Radium (Ra), Uranium (U), Francium (Fr), Polonium (Po) and Thorium (Th).

Non-radioactive elements do not degrade or emit any radiations. They have stable nuclei and would therefore not undergo radioactive decay e.g. Sodium (Na), Calcium (Ca), etc.

- Based on properties, elements are classified into three: metal, non-metals, and metalloids.

Metals are elements that are ionized by electron loss e.g. Potassium, Sodium, Calcium, lead, etc.

They possess the following physical properties:

i. Ductility and malleability. Hence they are useful in making wire cables and fabrication in construction works.

ii. Good conductor of heat and electricity due to the presence of free mobile electrons in their lattice. They are therefore useful in making cooking pots, boilers and electric cables.

iii. Hard solids with high melting points/boiling points except sodium, which is soft, and mercury, which is a liquid metal.

iv. Lustrous (with silvery colour) hence useful in jewelry and in metallic paints because of its reflectivity.

v. Some of them make a sound note, when struck (sonorous) e.g. copper, iron, and aluminum. Such metals are therefore useful in making musical instruments.

vi. None of the metals are soluble in any ordinary solvent without a chemical change.

The general chemical properties of metal are:

i. Electropositive i.e. loss electron(s) to become ionized hence reducing agents.

ii. Most of the metal s combine with oxygen to form basic oxides e.g. CuO, MgO and CaO. However some metallic oxides are amphoteric e.g. ZnO, PbO. Such oxides react as both acid and base.

iii. Combine with chlorine to form electrovalent chloride e.g. NaCl.

iv. Form metallic hydrides that are ionic.

v. Replace the hydrogen in an acid if more than electropositive than hydrogen.

Non-metals are elements that ionize by electron gain e.g. hydrogen, oxygen, chlorine, bromine, carbon, etc.

Non-metals are therefore oxidizing agents (except a few of them) since they undergo reduction in their ionization process

The general physical properties of non-metals are:

i. Brittle i.e cannot be hammered into sheets (non-mallaeble) or drawn into wires (non-ductile).

ii. Non-conductors of heat and electricity because they do not possess free mobile electrons. However, graphite (a form/allotrope of Carbon) is a good conductor of electricity because it contains free mobile electrons in its lattice.

iii. Mainly gases (e.g. hydrogen, oxygen, nitrogen, chlorine) though some of them exist as solids or liquids. For instance, bromine is a liquid at room temperature, iodine is a soft violet solid, sulphur is a yellow solid, graphite and diamond are solids. While graphite is soft, diamond is the hardest known natural substance.

iv. Most of the non-metals are dull and cannot be polished but diamond (an allotropic firm of carbon) can be polished (lustrous) and can therefore used in jewelry.

v. Non-sonorous.

vi. Have low density though some of them are heavy e.g. diamond.

vi. Some non-metals dissolve slightly in water without reaction (e.g. oxygen) though some of them dissolve with water (e.g. chlorine, bromine).

Some of the general chemical properties of non-metals are:

i. They are mainly oxidizing agents.

ii. Form acidic oxides mainly e.g. carbon(IV)oxide, sulphur(IV)oxide, nitrogen(IV)oxide. The acidic oxides are known as acid anhydrides (compounds that dissolve in water to produce an acidic solution or a solution whose pH is less than 7).

iii. Non-metals combine with other non-metals to form covalent compounds e.g. ammonia, carbon(IV)oxide, hydrogen chloride.