Chemical _ And _ Chemical Changes.pptx

CHEMICA AND CHEMICAL CHANGES FOR CLASS 7th CBSE
BY MAHALAXMI

1. CHEMICALS and CHEMICALCHANGE Water, Common Salt, Sodium bicarbonate Elements Pure Substances Compunds Gold, oxygen, Carbon Aluminium, Hydrogen, Chemical Substances: All substances are made up of matter. Anything that has weight and occupies space is called matter . Atom is the smallest unit of matter. The word Atom is derived from the Greek word Atomos meaning indivisible. Two or more atoms that are chemically bound together are called molecule.

2. Element 1. An element is a substance that cannot be decomposed into simpler substances by chemical means. 2. Element is made up of only one kind of atom. 3. eg :  Iron, gold, hydrogen and oxygen are some of the elements. Compound 1. A compound is a substances in which two or more elements are combined together chemically indefinite proportion, they are called Compound. 2. eg : Water:-Two atoms of hydrogen and one atom of oxygen makes water {H 2 O}.

3. There are 118 known elements, 92 are found in nature, and 26 are mam-made. All elements have a name and a symbol to represent them The symbol consists of one or two letters taken from the common or Latin/Greek name of the element CHEMICAL SYMBOLS

4. Name of the Elements Symbols Hydrogen H Carbon C Nitrogen N Oxygen O Sodium Na(Natrium) Magnesium Mg Aluminium Al Chlorine Cl Calcium Ca Argon Ar Gold Au( Aurum ) Sulphur S Iron Fe( Fermum )

5. Types of Changes Changes are of two types: 1)Chemical Change 2)Physical Change Chemical Change A  chemical change  occurs when a new substance is formed through a  chemical reaction  like when fruit ripens or rots. When something undergoes a " chemical reaction " and a new substance is formed as a result, we call this  chemical change. Physical Change A change in which a substance undergoes a change in its physical properties is called a Physical change A physical change is generally reversible . In such a change no new substance is formed

6. Rusting Fe + O 2 + H 2 O Fe 2 O 3 Iron (Iron Oxide) Rust (oxygen in Air) Water Chemical change Some characteristics of chemical changes are : 1.A new substance is formed. 2.It is a permanent change. 3.The composition of new substance changes. 4.It is irreversible. 5.Heat or light evolved or absorbed during change.

7. Copper sulphate + Iron Iron sulphate + copper CuSO 4 Fe FeSO 4 Cu