Elements Compounds and Mixtures If we look around us we see many objects. All these objects occupy space and have mass. This is called Matter.
A substance is a kind of matter that cannot be separated into the other kinds of matter by any physical process. Matter which consists of only one type of constituent particle is called a pure substance.
Numerous attempts were made to find out what this matter is made of. Robert Boyle in 1661 used the term element for the first time.
Elements can be broadly divided into metals, non-metals and metalloids. Metals and non-metals can be differentiated on basis of physical and chemical properties. Physical properties are the properties which are determined by presence of nucleons in nucleus of atom and Chemical Properties are the properties which are determined by presence of valence electrons in the shell.
- Lustre: The ability of substance to shine is called its lustrous behavior.
- Texture: The substance may be hard or soft.
- Malleability: The ability of element to be beaten into thin sheets is known as malleability.
- Ductility: The ability of an element to be drawn into thin wires is known as ductility.
- Density: Density is defined as mass per unit volume.
- Melting and Boiling Point: The packing of constituent atoms and attractive force among them decides the melting point and boiling point of substance.
- Sonorosity: The ability of an element to produce the ringing sound is referred to its sonorosity.
- Electrical and thermal conductivity: The ability of an element to conduct electricity and heat respectively refers to the electrical and thermal conductivity of an element. If a substance is able to conduct then it is called conductor else it is called insulator.
Difference Between Metals and Non-Metals
Hence, on basis of physical properties metals and non-metals can be differentiated as:
|5.||Density||High density||Low density|
|6.||Melting Point||High melting point||Low melting point|
|7.||Boiling Point||High boiling point||Low boiling point|
|9.||Electrical conductivity||Good conductors||Poor conductors|
|10.||Thermal conductivity||Good Conductors||Poor Conductors|
|11.||Example||Sodium, magnesium||Fluorine, neon|
Till date, we have 118 elements. Ninety-two elements are naturally occurring and the rest are man-made. Majority of elements are in solid-state.
These elements may exist as compounds or mixture.
Have you ever seen sodium? Sodium element is stored in kerosene oil so as to avoid contact with oxygen. Similarly chlorine was used in atomic bombs by Hiroshima and Nagasaki. Union of these two elements forms sodium chloride which is an important ingredient of table salt. Hence, substance composed of two or more elements, chemically combined with one another in a fixed proportion is known as compound.
Example: Carbon is an element which is important constituent of organic compounds while oxygen is supporter of combustion. The union of these two elements forms a compound carbon dioxide which is non-supporter of combustion.
Example: Hydrogen is an element which is used as fuel in rockets while oxygen is an element that is supporter of combustion. Union of these two elements forms a compound water which is used to extinguish fire.
The properties of compound are as follows:
- The properties of compound are entirely different from its constituents.
- It has fixed composition.
- It can be decomposed by chemical means like electrolysis.
- A chemical reaction takes place during the formation of a compound.
- Constituent elements cannot be separated by physical processes.
When the elements are mixed in any ratio and each constituent retains its properties is known as mixture.
Example: When iron and sulphur are mixed and bar magnet is brought close to it then it is seen that iron gets attracted to it .Hence we say that the property of iron and sulphur are retained.
The properties of mixture are as follows:
- The properties of mixture are reflected in its constituents.
- It doesn’t have fixed composition.
- The constituents of mixture can be separated by physical means like magnetic separation.
- No chemical reaction takes place during the formation of mixture.
The mixtures may be homogenous or heterogeneous. When we mix salt and water then its particles are not seen. In this type of mixture, there is uniform composition throughout. This is known as homogeneous mixture. Example: mixture of sugar and water.
When we mix sand and water then its particles are distinctly visible. In this kind of mixture, there is non-uniform composition i.e. the heavy particles settle down due to sedimentation. This is known as heterogeneous mixture. Example: mixture of mud and water.
Homogeneous mixture is also known as true solution. The properties of true solution are as follows:
- Solutions are homogeneous mixture, a property they share with pure substance elements & compounds.
- A solution can vary in its composition.
- The particles of a solution are smaller than 1nm (10-9m) in a diameter. So, they cannot be seen with naked eyes.
- The path of a light is not visible in a solution as they have much smaller particles size which cannot scatter a beam of light.
- Solutions can generally be separated by physical process.
- Solutions are usually stable as the solute particles in them do not settle down when left undisturbed. These solute particles even cannot be separated from the mixture by the process of filtration
Heterogeneous mixture is further divided into suspension and colloid.
The heterogeneous mixture in which solute particles do not dissolve but remain suspended throughout the bulk of medium is known as suspension.
The properties of suspension are as follows:
- The particles of suspension are so large that it is distinctly visible.
- The particles of suspension scatter a beam of light passing through it and make a path visible.
- When the particles of suspension are allowed to stand undisturbed for some time, then heavy particles settle down.
- Suspension is either opaque or translucent.
- The particles of suspension can be separated by filtration technique.
Colloid: The heterogeneous mixture in which the size of particles is more than that of true solution but less than that of suspension is known as colloid.
The properties of colloid are as follows:
- The special technique like centrifugation is used to separate its constituent particles.
- Colloidal sols are quite stable i.e. the colloidal particles do not settle down when left undisturbed.
- Colloidal particles are not visible to naked eyes.
- It is heterogeneous in nature.
Hence, we conclude:
Also Read : Atomic Models in Chemistry
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