Class 6 - Elements, compounds and mixtures

CLASS - 6

 Elements, compounds and mixtures

Ø  An element is a pure substance which cannot be split further into simpler substances by any physical or chemical method.

Ø  An element is made up of only one kind of atoms.

Ø  Elements can exist in three states:

Solids: Gold(Au), Iron(Fe), Sodium(Na), Carbon(C) etc.

Liquids: Bromine(Br), Mercury(Hg).

Gases: Chlorine(Cl), Hydrogen(H) etc.

Ø  Elements are Classified into : Metals, Non metals, Metalloids and Noble gases.

Ø  Metalloids are neither completely metals nor nonmetals. They bear the characteristics of both.

Ø  Noble gases are a special group of nonmetals that do not react chemically with other elements and exist in gaseous state. Helium(He), Neon(Ne) etc.

Ø  Metals are malleable and ductile where as nonmetals are not.

Ø  Malleability is the ability of a metal to be beaten (hammered) into sheets. Example: Iron, Silver, Gold etc.

Ø  Ductility is the ability of a substance to be drawn into wires. Example : Copper, Aluminium etc.

Ø  Potassium is the reactive metal.

Ø  Mercury is liquid metal.

Ø  Sodium is a soft metal.

Ø  Zinc is brittle and can easily break into pieces.

Ø  Bromine is liquid nonmetal.

Ø  Graphite is a form of Carbon it has luster and good conductor of electricity.

Ø  Diamond is another form of Carbon. It is the hardest substance known.

Ø  Iodine(nonmetal) has luster.

Ø  Boron, silicon, Germanium, Arsenic etc are the metalloids.

Ø  The non-metallic elements Fluorine, Chlorine, Bromine, Iodine are highly reactive and they are called Halogens.

Ø  The Earth’s crust is made up of several elements like Silicon, Oxygen, Iron, Aluminium, Calcium, Sodium, Potassium and Magnesium.

Ø  The most abundant element in the Earth’s crust is Oxygen followed by Silicon.

Ø  The elements are tabulated in the periodic table in order to study their properties in a systematic manner.

Ø  The horizontal rows the periodic table are called ‘Periods’ and the vertical columns are called ‘Groups’.

Ø  Some atoms like Sodium, Calcium or Carbon can exist independently but some cannot.

Ø  An atom of Hydrogen cannot exist independently, but two atoms combine to form a molecule which can exist independently.

Ø  Molecule is the smallest particle of a pure substance that can exist independently.

Ø  A molecule retains all the properties of the substance.

Element	Compound	Mixture
1. Made up of one kind of atoms. 2. Cannot be broken down into simpler substances by physical or chemical methods 3. It has its own set of properties. e.g: Zinc, Iron etc.	1. Made up of two or more kinds of atoms combined chemically in a fixed ratio. 2. Can be broken down into simpler substances by chemical methods. 3. The properties differ from those of its elements. e.g. Zinc sulphide etc.	1. Made up of two or more pure substances mixed mechanically in any ratio. 2. The components of the mixture can separated by physical methods. 3. It has no definite set of properties. e.g. Zinc + Sulphur etc.

Ø A radical is a group of atoms.

Ø Certain elements show more than one valency i.e variable valency. e.g. Copper shows Cu⁺ and Cu²⁺