Classification of elements
Today, some 117 chemical elements are known but only 103 out of them are
well characterized in terms of their properties. The systematic classification of these 103 elements reveals that 90 elements are solids, 2 are liquids and 11 are gases. Further, 79 of them are metals, 17 are non-metals and 7 are metalloids. Metals differ from non-metals in many respects. In fact, metals and non-metals are two extremes as regards their properties.
Metals occupy the bulk of the periodic table, while non-metallic elements can
only be found on the right-hand-side of the Periodic Table . A diagonal line, drawn from boron (B) to polonium (Po), separates the metals from the nonmetals. Most elements on this line are metalloids, sometimes called semiconductors. This is because these elements exhibit electrical properties intermediate to both, conductors and insulators. Elements to the lower left of this division - line are called metals, while elements to the upper right of the division - line are called non-metals.
On the basis of their general physical and chemical properties, every element in
the periodic table can be termed either a metal or a nonmetal. (A few elements with intermediate properties are referred to as metalloids).
Physical properties of metals
Metals show following general physical properties.
1) Physical state - Metals are solids at room temperature e.g. sodium, aluminium , potassium, magnesium. There are exception to this. Mercury and gallium are metals but they are in liquid state at room temperature.
2) Luster – Metals have a shining surface called luster when freshly prepared. They have a quality of reflecting light from their surface and they can be polished e.g. metals like gold, silver, copper show this property.

Chemical properties of metals
Metals show following general chemical properties.
1) Electron configuration – Metals usually have 1 to 3 electrons in the outermost shell of their atom. For example, sodium, magnesium and aluminium have 1, 2 and 3 electrons respectively in the outermost shell of their atom.
2) Valency - Metal atoms can lose 1 to 3 electrons in their outermost shell and show valencies1 to 3.
3) Electrochemical nature - Metal atoms have tendency to lose electrons and form cations. . This tendency is called the electropositive nature. Metals generally have moderate to high electropositive nature. For example, Na, Mg and Al have high electropositive character while Zn, Cd , Sn and Pb have moderate electropositive nature.
4) Electronegativity - Metals generally have low electronegativity i.e. tendency to attract electrons in the state of molecule. Foe example, metals like Ca, Mg, Al, Zn have low electronegativity.
5) Formation of oxides – Metals form oxides which are generally ionic and basic
in nature. If this basic oxide dissolves in water, it forms an alkali. For example, oxides of Na, K and Ca viz. Na2O, K2O and CaO are highly basic in nature and when dissolved in water, they form alkalies NaOH, KOH and Ca(OH)2. The oxides react with acids to form salts. Oxides of metals like Pb, Zn, Al and Sn viz. PbO2, ZnO, Al2O3 and SnO2 are moderately basic and they react with acids as well as alkalies to form salt. So such oxides are called amphoteric oxides. The oxides Sb2O3 and Cr2O3 are exceptions and they are acidic in nature.
6) Reducing agent - All metals act as reducing agents. Strongly electropositive metals like Mg, Al and Cr act as strong reducing agents while moderately electropositive elements like Zn, Cd and Sn act as moderate reducing agents.
7) Reaction with water - Strongly electropositive metals like Na and K react even with cold water to produce their hydroxides and they evolve hydrogen gas. The heat evolved is not sufficient for the hydrogen to catch fire. Metals like Mg do not react with cold water . They react only with hot water to form hydroxide evolving hydrogen. The elements less electropositive than Na, K and Mg like Al, Fe and Zn do not react with cold or hot water. These hot metals react only with steam to form their oxides and hydrogen .However, metals like Cu, Ag and Au which are below hydrogen in the activity series do not react with water at all.
8) Reaction with acids - Highly reactive metals like Na, Mg and K react with dilute mineral acids like HCl or H2SO4 to form salt and hydrogen gas. These reactions are displacement reactions. If nitric acid is used, the hydrogen evolved gets oxidized towater and hence no hydrogen gas is evolved. Metals like Cu, Ag and Au which are below hydrogen in the reactivity series do not react with dilute mineral acids and do not evolve H2 .
9) Reaction with non-metals - Metals like Mg, Ca, Al etc. react with non-metals like H, S, Cl, Br and I under different conditions of temperature to form their respective salts. However, all metals are not equally reactive so they require different conditions to react with non-metals.

Physical properties of non-metals
Non- metals show properties opposite to that of metals. Non-metals show following general physical properties
1) Physical state – Non-metals can exist in solid or liquid or gaseous state at room temperature. . For example, carbon, sulphur, phosphorus, iodine are in solid state, bromine is in liquid state while oxygen, nitrogen, chlorine are in gaseous state at room temperature.
2) Luster – Non-metals do not have luster. They do not reflect light from their surface. ( exception – diamond and iodine ) Non-metals have dull appearance. For example, sulphur, phosphorus and carbon show this property

3) Malleability - Non-metals are non-malleable. If solids, they are brittle i.e. they break or shatter on hammering. For example, coal, sulphur, phosphorus are brittle.
4) Ductility – Non-metals can not be drawn into thin wires. So they are not ductile.
5) Hardness – Non-metals are usually not hard. They are soft. For example, coal, sulphur and phosphorus are soft. Diamond is exception to this. It is the hardest substance known.
6) Conduction - Non- metals are usually poor conductors of heat and electricity.
However, carbon in the form of gas carbon and graphite is exception to this. These forms of carbon are good conductors of electricity.
7) Density – Non- metals which are gases have low density. Solid non-metals have low to moderate density. They are medium light. For example, sulphur, phosphorus and boron have densities 1.82, 2.07 and 2.34 respectively. . However, diamond has high density which is about 3.5.
8) Melting and boiling point – Non-metals usually have low melting and boiling points. For example, phosphorus, sulphur, and iodine have melting points 440, 1150 and 1140 C respectively and boiling points 2800 , 4450 and 1840C respectively. . However, carbon, silicon and boron possess very high melting and boiling points.
9) Tensile strength – Non-metals have low tensile strength i.e. they have no tenacity.
Chemical properties of non - metals
Non – metals show following general chemical properties
1) Electron configuration – Non -metals usually have 4 to 8 electrons in their outermost shell. For example, C, N, O, F and Ne have 4, 5, 6, 7 and 8 electrons in their outermost shell.
2) Valency - Non - metals can gain or share 1 to 4 electrons in their outermost shell and show valencies 1 to 4 . Sometimes, they show valency 5 to 7. For example, P shows valency 5 in P2O5 , S shows valency 6 in SO3 and Cl shows valency 7 in HClO4,
3) Electrochemical nature - Non – metal atoms have tendency to gain electrons and form anions or share electrons with other non-metals to form covalent bonds. Non – metals generally have moderate to high electronegative nature. For example, Cl, O and N have high electronegative nature while Si, P, S and I have moderate

4) Electronegativity - Non - metals generally have high electronegativity i.e. tendency to attract electrons in the state of molecule. Foe example, non - metals like F, Cl, O and N have high electronegativity.
5) Formation of oxides – Non- metals form oxides which are generally covalent and acidic in nature. If this acidic oxide dissolves in water, it forms an oxyacid. For example, oxides of Cl, P and S viz. Cl2O7 , P2O5 and SO3 are highly acidic in nature and when dissolved in water, they form acids like HClO4,.H3PO4 and H2SO4 . These oxides react with alkalies to form salts. Oxides of non- metals like C, H and N i.e. CO, H2O and NO are neutral.
6) Oxidizing agent - All non - metals ( except carbon ) act as oxidizing agents.
Strongly electronegative elements such as F, Cl and O act as strong oxidizing
agents while moderately electronegative elements like sulphur, bromine and iodine act as moderate oxidizing agents. Carbon sometimes acts as a reducing agent.
7) Reaction with water - Non-metals do not react with water . Whether the water is in the form of cold water, hot water or steam, all non-metals remain unresponsive to water. The reason for this is that non-metals are electronegative and are unable to break the bond between H and O in water.
8) Reaction with acids : Most non-metals do not react with non-oxidizing acids. They are not capable of replacing hydrogen from the acids and forming a salt. For example, C, S or P do not react with dilute and concentrated HCl or dilute H2SO4 to give off hydrogen. Concentrated nitric acid, dilute nitric acid and concentrated sulphuric acid act as oxidizing agents and react with non – metals to form their oxides or acids. Nonmetals like N, O, Si, halogens and noble gases are exception to this and they do not react with these acids. Usually solid non-metals react with these oxidizing acids.
9) Reaction with metals - Metals like Mg, Ca, Al etc. react with non-metals like
H, S, Cl, Br and I on heating to form their respective salts. However, all non - metals are not equally reactive so they require different conditions like high temperature toreact with metals.
10) Reaction with non-metals – Non-metals can react with each other. For example,carbon can react with non-metals like H, O, Cl at different temperatures to form the corresponding compounds like CH4 , CO2 and CCl4. Non – metals react with each other under different conditions.

Reactivity series of metals
A series of metallic elements arranged in the increasing or decreasing order
of their reactivity is called a reactivity series of metals.
Although most metals are usually electropositive in nature and lose electrons
in a chemical reaction they do not react with the same vigour or speed. Metals display different reactions towards different substances. The greater the ease with which an element loses its electrons and acquires a positive charge, the greater is its reactivity. Further, the greater the number of shells and lesser the number of valence electrons, the greater is the reactivity of the metal. The activity series of metals, arranges all metals in order of their decreasing chemical activity. As we go down the activity series from potassium to gold the ease with which a metal loses electrons and forms positive ions in solutions, decreases.
The most active metal, potassium, is at the top of the list and the least reactive
metal, gold, is at the bottom of the list. Although hydrogen is a non-metal it is included in the activity series due to the fact that it behaves like a metal in most chemical reactions i.e., the hydrogen ion has a positive charge [H+] like other

Following points become evident from the activity series of metals.
1) The higher the metal in the series, the more reactive it is i.e., its reaction is fast and more exothermic.
2) This also implies that the reverse reaction becomes more difficult i.e., the more reactive a metal, the more difficult it is to extract it from its ore. The metal is also more susceptible to corrosion with oxygen and water.
3) The reactivity series can be established by observation of the reaction of metals with water, oxygen or acids.
4) Within the general reactivity or activity series, there are some periodic table trends:
a) Down Group 1(I) the "Alkali Metals", the activity increases Cs > Rb > K > Na > Li.
b) Down Group 2(II) the activity increases e.g., Ca > Mg.
c) In the same period, the Group 1 metal is more reactive than the group II metal andthe group II metal is more reactive than the Group III metal and all three are morereactive than the "Transition Metals". e.g., Na > Mg > Al (in Period 3) and K > Ca > Ga > Fe/Cu / Zn etc. (in Period 4)

Reactivity series of non – metals
A series of non - metallic elements arranged in the increasing or decreasing
order of their reactivity is called a reactivity series of non - metals.

Activity series can be devised for non-metals as well. Since non-metallic elements tend to accept electrons in redox reactions, the non-metal activity series is arranged so that the most powerful oxidizing agents are considered most active (whereas in the metal series, the most powerful reducing agents are the most active).

Applications of reactivity series
1) One can understand the relative strength of reducing and oxidizing agent from the position of the elements in the series. For example, the elements like K, Na, Zn etc. which are placed high in the series can easily lose electrons and act as good reducing agents. The elements which are below hydrogen in this series like Cu, Ag, Au can not lose electrons easily. So they can not act as reducing agents. Instead, their cations act as good oxidizing agents.
2) Looking at the reactivity series, one can understand the spontaneity of the
reaction. One metal can displace another metal from its salt solution. This can
happen only if the first element is in the higher position in the series as compared to the second element which is displaced from its salt solution. For example, Zn can displace Fe from FeSO4 solution but Cu can not displace Fe from FeSO4 solution because Zn is above Fe while Cu is below Fe in the reactivity series. Similarly, for the anions – Cl can displace Br from its salt solution ( KBr) but I can not displace Br
from its salt solution ( KBr).
3) One can make a choice of suitable electrodes for setting up of an electrolytic
or electrochemical cell. One can choose an electrode with +ve electrode potential ( higher in position in the reactivity series ) and an electrode with –ve electrode potential ( lower in position in the reactivity series ) , combine them and set up the cell. For example a combination of Zn half cell and Cu half cell sets up a Daniel cell.
4) If one knows the standard electrode potential of two electrodes, then he can
find out the standard E.M.F. of the cell. For example, the standard oxidation potential of Zn half cell is + 0.76 V and that of Cu half cell is – 0.34 V. So the E.M.F. of Daniel cell is (0.76 ) – ( - 0.34 ) = 1.10 V.
5) If a solution contains two or more cations , one can predict which cation will
be discharged first at the cathode during electrolysis. For example, if the solution contains equal concentration of Na+ and H+ ions , then according to rule, the ion which is lower in position in the reactivity series is discharged first at the cathode. So, in this case, H+ will be discharged in preference to Na+ ions in electrolysis.
6) If a solution contains two or more anions , one can predict which anion will
be discharged first at the anode during electrolysis. For example, if a solution
contains equal concentration of Cl - and OH – ions, then as per rule, the ion which does not contain oxygen is discharged first in preference to the ion which contains oxygen. So,in this case, Cl – will be discharged in preference to OH – ions in electrolysis.

Noble metals
In a chemical language, noble means inactive.
The metals which are inactive are called noble metals.
The noble metals are - ruthenium, rhodium, palladium, silver, osmium, iridium,
platinum, gold , mercury and rhenium
Properties of noble metals
1) Noble metals are resistant to corrosion and oxidation in moist air.
2) Noble metals are not affected by air, water, acids, heat etc.
3) Ordinarily, they do not take part in chemical reactions . Hence they are called noble metals.
4) They tend to be precious, often due to their rarity in the Earth's crust.
Noble metals should not be confused with precious metals (although many
noble metals are precious). Usually, rhodium, palladium, silver. platinum, gold and indium are known as the precious metals. Chemically, the precious metals are less reactive than most elements. Precious metals have luster , they are softer or more ductile and they have higher melting points than many metals. They are very expensive. Gold, silver, and platinum are both noble and precious metals.
Uses of noble metals
1) Some of the precious metals like Ag, Au and Pt are used for making coins, ornaments and jewelry. They are considered as bullion metals.
2) Ruthenium is used in strengthening alloys of Pd and Pt.
3) Rhodium is used in electroplating platinum and white gold to provide them with reflective surfaces.
4) Palladium is used in jewelry, dentistry, blood sugar testing strips, watch making, spark plugs for aircrafts and surgical instruments.
5) Indium has many industrial uses because of its hardness , high resistance to corrosion and high melting point. It is widely used in spark plugs, electrodes and catalysis.
6) Silver is used in medicines due to its antibacterial properties.
7) Platinum is used as a catalyst and in making electrodes.
Purity of gold
The purity of gold is expressed in carats, often abbreviated as ‘ct’ of ‘K’ in the
USA and some other countries. Pure gold has a purity of 24 carats.
As a measure of purity, one carat is 24 times the purity by mass of gold :
X = 24 Mg / Mm
Where X is the carat rating of the material, Mg is the mass of pure gold or platinum in the material and Mm is the total mass of the material.