Summary
Key terms
Metals: Metals are those which have unbound free electrons, beyond closed shells. In metals, these unbound electrons are given off or donated during compound formation. Metals are all good conductors of heat and electricity.
Non–metals: Non–metals are bad conductors of electricity because unlike metals, they have no free electrons. Non–metals may be solid, liquid or gases at the room temperature. For example, Carbon, Sulphur and Phosphorus are solid non–metals. Bromine is a liquid non–metal, whereas Hydrogen, Nitrogen and Oxygen are gaseous non–metals.
Metalloids: Elements placed in between the metals and non–metals in the periodic table are called metalloids. Metalloids form a bridge between strictly metal elements and strictly
non–metal elements. Metalloids are dull like non–metals but conduct heat and electricity like metals.
Eg: Boron(B), Silicon(Si), Germanium(Ge), Arsenic(As), Antimony(Sb), Tellurium(Te) and Selenium(Se). Of these Si and Ge are called semiconductors.
Eg: Boron(B), Silicon(Si), Germanium(Ge), Arsenic(As), Antimony(Sb), Tellurium(Te) and Selenium(Se). Of these Si and Ge are called semiconductors.
Metallic bond: The "fluid" of electrons holding the positively charged metal ions together in the compound this type of chemical bond known as a Metallic bond.
Metallic lustre: The property of a metal of having a shining surface is called 'metallic lustre' .
Eg: Gold, Silver and Copper.
Eg: Gold, Silver and Copper.
Malleability: Metals having the ability to withstand hammering and can be made into thin sheets known as foils is Malleability. Gold and Silver metals are some of the best malleable metals.
Ductility: The property which allows the metals to be drawn into thin wires is called ductility. Gold is the most ductile metal.
Key concepts
- Metals have loosely bound free electrons which are given off while formation of a compound. In non–metals, there are no free electrons and they borrow electrons during formation of a compound. Some elements placed in between the metals and non–metals in the periodic table are called metalloids. Metalloids have characteristics of both metals and non–metals. They form a bridge between strictly metal elements and strictly non–metal elements.
- Metals have many uses in daily life. Iron metal is used for making utensils such as cooking vessels, water boilers, stoves etc.,. Aluminium and Titanium(light metals) are widely used in making air crafts. Copper is most widely using for making electromagnetic wires because it is a good conductor of electricity. Silver, Gold and Platinum are widely used in making jewellery.
- Metals are highly electropositive elements that have a tendency to lose electrons and form cations. Metallic bonding constitutes the electrostatic attractive forces between the delocalized, called conduction electrons, gathered in an electron cloud, and the positively charged metal ions.
- Due to the strong coulombic forces between positively charged metal ions and electrons, metals are hard solids and have high melting and boiling points. All metals are opaque (we can't see through them). Metals are lustrous (shiny), malleable (can be hammered into sheets) and ductile (can be drawn into wires). They are good conductors of electricity and heat. Metals are sonorous or make a bell like sound when struck. All of these properties of metals are due to free electrons. Metals have 1 to 3 electrons in their outermost shell. Inner shell electrons of transition elements also participate in metallic bond so they are very hard and posses high density.
- Metals corrode easily since they loose electrons easily and get oxidized by atmosphere. Most metals form basic oxides. They have lower electronegativities and can act as good reducing agents. Metals that are highly reactive than hydrogen displace and liberate hydrogen gas with dilute acids. Metals like Cu, Ag, Au, Pt, Hg, do not react with dilute acids since they are less reactive. Reactivity of metals determines which salt is formed when a metal is added to a salt solution. In displacement reactions more reactive metal displaces the less reactive metal in the metal salt.
- The electronegativities and ionization energies of the metalloids are between those of metals and non–metals, so the metalloids exhibit characteristics of both classes. Silicon, for example, possesses a metallic lusture but it is a semiconductor and brittle in nature. The reactivity of metalloids depends on the element with which they are reacting. For example boron acts as a non–metal when reacting with sodium and as a metal when reacting with fluorine. There is a large variation in boiling points, melting points and densities of metalloids due to individual unique properties such as polymerisation, allotropism etc.,. Due to their intermediate conductivity metalloids such as silicon and germanium are used in semiconductor industry.
- Non-metals are the elements with high electronegativity, which form negative ions by gaining electrons. Non-metals are poor conductors of heat and electricity, do not reflect light and have no lustre (no shine). Non-metals are brittle. The oxides of non–metals are covalent and acidic or neutral in nature. The acidic oxides of non–metals dissolve in water to form acids. Non–metals cannot give electrons(oxidizing behaviour) to reduce the hydrogen ions into hydrogen gas so they do not react with water or steam or dilute acids to evolve hydrogen gas. Like metals a more reactive non–metal displaces a less reactive non–metal from its salt solution. Non–metals react with chlorine to form covalent chlorides, which are non–electrolytes (do not conduct electricity) and they form covalent hydrides.
- Hydrogen (H) is the first of the nonmetals. It is the chief component of water which is necessary for life on Earth. Boron (B) commonly used in the form of boric acid, an antiseptic, used to cover superficial wounds and for preserving food grains. Carbon(C) is the most familiar nonmetal in the solid form. Some typical uses of carbon are – in the form of carbon dioxide in coals, as graphite in pencils, as diamonds as jewellery and as cutting tools, all organic compounds contain carbon. Nitrogen (N)exists as a free gas present in the air as the major component. It is important in many industrial compounds such as Ammonia [NH3], Nitric acid [HNO3], Ammonium compounds e.g. NH4Cl,NH4NO3. Oxygen (O) is essential for combustion of fuels to generate energy. It is used as oxidizing agent in many reactions. Phosphorus (P) is used to make H3PO4 acid, which is used to make phosphate fertilizers. An alloy of P called phosphor–bronze is made from P, Cu and Sn which has many applications as it is a stretchable metallic material. Sulfur (S) is used to make H2SO4 acid, which is used in the manufacture of many compounds such as detergents, plastics, explosives, etc. Sulfur is used for vulcanization of rubber.
Overview
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