Earliest classification of elements was on the basis of their appearance and physical or chemical properties. That time few elements were known therefore it was quite easy to classify those elements on the basis of their properties. According to that concept, elements can be classified as metals and non-metals. Both of these types of elements differ in their appearance, reactivity, conductivity and chemical properties. For example, metals have a lustre surface with electropositive nature. They have 1, 2, or 3 electrons in their valence therefore, metals tend to lose electrons to form cations. That is the reason; they are a good conductor of heat and electricity.
Metals are hard, malleable and ductile in nature. Because of the formation of cation, they form ionic compounds with non-metals. On the contrary, non-metals are brittle solids or liquids and gases. They are electronegative in nature as they tend to accept electrons and form anions. These anions can form ionic compounds with metals such as sodium chloride. Today in the long form of the periodic table, non-metals are placed at the right side of the table from 13th to 18th group. Let’s discuss the position of different non-metals in the periodic table with their characteristics.
All the elements on the left side and the middle of the periodic table, except hydrogen, are metallic elements or metals. Also, majority of the elements in the periodic table are metals. All s block elements , all d block elements, and f- block elements are metals. Some of the p block elements are also metals. Therefore, roughly, three-quarters of the elements are metals. The non-metals are separated from metals by a diagonal step-like line that runs from Boron(B) to Astatine (At).
Hydrogen is a non-metal, though it is present on the far left side, with the metals. Some non-metals are gases, some are liquids and the rest are solids at room temperature. Non-metals generally differ from metals in appearance and in other physical properties. Some elements, lying along the line separating metals and non-metals have properties that fall between those of metals and non-metals. These are called semi-metals or metalloids.
The groups starting from group 14 to group 18 are non-metals, with a few metals and metalloids. Group : 14 or IV A
Group IV A of the long form of the periodic table consists of five elements, Carbon (C), Silicon (Si), Germanium (Ge), Tin (Sn) and Lead (Pb). Carbon is an essential constituent of all organic matter while silicon is the main constituent of inorganic matter. In this group, Carbon and silicon are non metals.
Group: 15 or V A
Group V A of the periodic table consists of five elements, Nitrogen (N), Phosphorus (P) , Arsenic (As), Antimony (Sb) , and Bismuth (Bi). In this group, the first two elements, nitrogen and phosphorus are non metals while the next two, As and Sb are metalloids and the last element is a metal.
Group: 16 or VI A
Group VI A of the periodic table consists of five elements, Oxygen (O), Sulfur (S), Selenium (Se) , Tellurium (Te) and Polonium (Po). These elements are collectively called chalcogens, or the ore containing elements. The first four elements are non-metals in this group.
Group: 17 or VII A
Group VII A of the periodic table consists of five elements - Fluorine(F), chlorine (Cl), Bromine(Br), Iodine (I) and Astatine (At). The first four elements are collectively called Halogens. All the elements in this group are non-metals.
Group: 18 or VIII A
Zero group of the periodic table consists of six elements, namely, Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr) and Xenon (Xe). These elements are also called inert gases or noble gases. They are all non-metals.
Some of the characteristics that distinguish a non-metal from a metal are:
- Non-metals vary greatly in their appearance.
- They are not lustrous and are generally poor conductors of heat and electricity.
- The melting points of non-metals are generally lower than those of metals. However, diamond, an allotropic form of carbon, has a high melting point of 3570 degree Celsius.
- Seven non-metals under ordinary conditions, exist as diatomic molecules. These are H2, N2, O2, F2, Cl2, Br2 and I2. The first five are gases, while Bromine is a liquid and Iodine is a volatile solid.
- Non-metals react with metals and gain electrons to form anions or negative ions.
- The oxides of non-metals are acidic, except CO, N2O and NO, which are neutral.
- Non-metals are not malleable and ductile, like the metals.
- Non-metals form negative ions, and so, can combine with metals to form ionic compounds. But, non-metals can also form covalent compounds, unlike their metal counterparts.
- Non metallic character decreases down the group and increases along the period.
- Certain properties are very much applicable to non-metals only.
For example, the property of catenation, by which elements form a side linkage, thereby forming a link with each other, and form long chains are very much the property of non-metals. This is seen predominantly in the carbon group.
Most of the elements on the far right of the periodic table, the 'p' block elements, are non-metals.
Some of the examples are as follows.
List of Non Metals
- Carbon is a non-metal, present in the 4A or 14th group. Carbon forms a large range of covalently bonded compounds. It is solid and has many allotropic forms.
- Hydrogen, is a non-metal, present on the left side of the periodic table. It is the first element of the periodic table and is a gas. Oxygen, a very important constituent of the atmosphere, is a gas and is a non-metal.
The table below shows the list of important non-metals, and its state.
Metals are present on the far left of the periodic table, while non-metals are present in the opposite direction. Some of the marked differences between a non-metal and a metal are:
|Shiny surface, has characteristic luster.
||Not lustrous at all. Most of them are dull elements.
|Good conductor of electricity.
||Poor conductor of electricity, due to the lack of metallic bond.
|Metals are solids, except mercury, the only liquid metal.
||Non-metals are solids, liquids and gases.
|Metals in reaction with non-metals, lose electron(s) to form a positive ion or cation.
||Non-metals gain electron(s) from the metals, to form negative ion or anion.
|Metals only form ionic compounds.
||Non-metals form ionic, covalent and coordinate bonds too.|
Non Metals on the Periodic Table can be classified into different families as follows:
- They belong to 14th group of the periodic table.
- In this group, carbon is the only non-metal.
- This is otherwise called as pnictogens.
- They belong to 15th group of the periodic table.
- In this group, nitrogen and phosphorous are non-metals.
- This is other wise called as chalcogens.
- They belong to 16th group of the periodic table.
- In this group, oxygen, sulfur, and selenium are non-metals.
- This is otherwise called as halogens.
- They belong to 17th group of the periodic table.
- In this group, all the elements are non-metals.
- They are: F, Cl, Br, I, At (radioactive).
- This is otherwise called as inert gases, rare gases, noble gases etc.
- They belong to the last group [18th group] of the periodic table.
- In this group, all the elements are non-metals.
- They are: He, Ne, Ar, Kr, Xe, Rn (radioactive).