What are Metals and Non-metals in Chemistry?

The periodic table is composed of metals, semi-metals and nonmetal elements. The physical and chemical properties of metals and nonmetals differ from each other. The study of metals and nonmetals will help one to understand the appropriate application of the particular element.

Introduction

The various particles or the elements observed in our day-to-day surroundings are classified into three major categories, namely,

1. Metals which is are solid, rigid and hard material.

2. Non-metals that do not have any characteristic feature of metal.

3. Metalloids are the substances or the elements whose properties lie between metal and non-metals or contain the properties of both metals and non-metals.

These elements are mainly classified based on their physical properties. The word ‘metal’ is coined from Greek word ‘metallon’ which means ‘mine or quarry or a metal’. Metal may be a single element (copper or silver) or an alloy (stainless steel) or a molecular compound (polymeric sulphur nitride).

Many elements in the periodic table are classified as metals such as alkali metals, alkaline metals, transition metals, lanthanide metals, actinide metals etc. Almost 95 of 118 elements in the periodic table are considered to be metals. The metallic nature of an element decrease when moving from the left side to the right side of the periodic table. Metals also differ from each other in any aspects. Some metals are hard and brittle at room temperature while some are liquid at room temperature. The melting point of some metals are very high and in some cases, it is very low. Generally speaking, metals are good conductors of heat and electricity. However, some metals are poor conductors.

Occurrence of Metals and Non-metals

Most of the metals naturally occur in earth’s crust as either metal oxides, metal sulphides and also in sea water as soluble salts. Metals like sodium, magnesium are found as their salts in sea water. Gold is an exception metal found as an element itself. The metals or elements naturally occurring in the earth’s crust are called minerals. The minerals which are tremendously used to extract metals are specifically termed ores.

On the other hand, non-metals are present either in their free state or in the combined state in earth’s crust, atmospheric air, living organisms etc. For example, nitrogen is present in atmospheric air as a free state and as proteins in living organisms in a combined state. Sulphur is present in a free state in the earth’s crust and in a combined state as sulphides and sulphates.

The Distinguishing Physical Properties of Metals and Non-Metals

• Metals have the capacity to be hammered at a high tensile strength and drawn as a thin sheet and as wires i.e. metals are malleable and ductile in nature. E.g. Gold, silver, copper, etc., whereas non-metals do not show these properties.
• A freshly prepared metal or a pure metal is very shiny and can be polished so as to give a reflective surface. This is due to the lustrous appearance of metals. Non-metals do not have the ability of metallic lustre. Exceptionally iodide crystals show the lustrous property.
• Metals are generally hard and rigid while non-metals are soft in nature. The hardness of each metal varies based on the type of metal or element. Exceptionally sodium and gallium are metals that are soft in nature and diamond is an allotrope of a non-metal carbon and is the hardest substance present.
• Metals are present as only solids and liquids while non-metals exist in solids and gaseous states. The exceptional case is, bromine is a non-metal in a liquid state.
• Due to the hard and rigid nature of metals, they have a high density while non-metals are less denser than metals.
• All the metals act as good conductors of heat and electricity as they readily tend to lose electrons i.e. they are highly electropositive in nature, while non-metals are considered to be bad conductors or insulators of heat and electricity as they are highly electronegative or tend to gain electrons. E.g. Most of the electrical wires are made of copper. Few exceptional are lead and mercury. These are the metals that act as bad conductors of heat and graphite, is a non-metal that acts as a good conductor of electricity.
• As metals are highly electropositive in nature, they act as good reducing agents, while non-metals are highly electronegative, and act as great oxidizing agents.
• Metals are considered to be sonorous i.e. on hitting with each other or on any hard object they create sounds, while non-metals are not sonorous in most cases.
• Metals are easily corrodible in nature as they are highly reactive in nature while non-metals are less corrodible.

The Chemical Properties of Metals and Non-Metals

Metals contain few electrons in the valence shell because of which they are highly electropositive, i.e. they lose the valence electrons readily to form cations and tend to gain the nearby noble gas configuration. Similarly, non-metals are electronegative in nature, i.e. they form anions readily by gaining electrons and tend to attain the nearby noble gas configuration.

Some of the chemical properties of metals and nonmetals are given below,

1. Metals can generally act as potential reducing agents while non-metals are capable to act as oxidizing agents.
2. Metals generally form basic oxides while non-metals form acidic oxides.
3. The hydrides formed by metals are unstable while the hydrides formed by non-metals seems to be stable.

Metals and non-metals react with many compounds and form different products. Few are given below:

Metals react with either atmospheric oxygen without any catalyst or heating or they react with oxygen on heating and form the corresponding metal oxides. These metal oxides are considered to be basic in nature as the metal oxides form bases with water. Similarly, non-metals react with oxygen to form acidic oxides as these oxides produce acids with water.

Oxides of aluminium, zinc, iron and tin are considered as amphoteric oxides as they react with both acids and bases.

For Eg: Al₂O₃ is an amphoteric oxide that is insoluble in water but reacts with both acids and bases.

Metals react with water to form respective hydroxides, which are basic in nature and liberate hydrogen gas. In exception, amphoteric metals produce metal oxides on reacting with water.

• Non-metals do not show any sort of chemical reactions with water.
• Metals react with dilute acids like hydrochloric acid (HCl) or sulphuric acid (H₂SO₄) to form salts and liberate hydrogen gas. The intensity of reactivity depends on the metal reacts. Exceptionally, copper, gold, and silver do not react with dil. HCl.
• Metals when reacting with dilute nitric acid (HNO₃) do not evolve hydrogen gas. HNO₃ is a strong oxidizing agent and thus the hydrogen gas liberated is oxidized to water and the nitric acid itself gets reduced as nitric oxide.
• Metals react with common bases such as sodium hydroxide (NaOH) to form salt and further liberate hydrogen gas. Non-metals react with bases to form salts but they do not liberate hydrogen gas.
• Metals react with non-metals such as F, Cl, Br, I, S, etc., and for metal salts.
• The compounds formed between a metal and a non-metal are termed ionic compounds as the metal completely loses an electron and forms cation and the non-metal gains the electron and forms anion. The bond formed between these two ions is termed ionic bond and the compounds are termed ionic compounds.

Practice Problem

Classify the following into metals and nonmetals

Na,Cl,C,K,Fe,Ca,O,P,Mg

Solution:

Metals: Na,K,Fe,Mg,Ca

Non metals: Cl,C,O,P

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for

B.Sc Chemistry

M.Sc Chemistry