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Physical and Chemical Changes: Most Important Questions for quick revision. Class 7 Chemistry 

Matter and its Composition : Most Important Questions for quick revision. Class 7 Chemistry 

Selina Concise ICSE Solutions for Class 7 Chemistry  Chapter 4 Atoms, Molecules and Radicals Points to Remember : 1. Atoms of the most elements are composed of still smaller particles known as fundamental particles or subatomic particles. They are  protons ,  electrons  and  neutrons . 2. Protons are the positively charged particles present in an atom. 3. Electrons are the negatively charged particles present in an atom and its mass is 1/1837 the mass of one hydrogen atom. 4. Neutrons are particles with no electrical charge. Its mass is equal to one atomic mass unit. 5. The central part of an atom is called nucleus, which contains both protons and neutrons. 6. Shells or orbits around the nucleus. 7. Atomic number  refers to the number of protons present in an atom. It is denoted by the alphabet Z. 8. Mass number — Mass number is the sum of number of protons and neutrons present in the nucleus of an atom. Mass number (A) = Number of protons + Number of neutr...

Selina Concise ICSE Solutions for Class 7 Chemistry  Chapter 3 Elements, Compounds and Mixtures Points to Remember : 1. Every substance is made up of very tiny particles, called molecules. Molecules are formed from even smaller particles called atoms. 2. Element—  (a) Element is the simplest pure substance. It cannot be divided further into simpler substances by any chemical method, e.g. oxygen, hydrogen, sulphur, etc. (b) At present 116 elements are known, of which 92 are natural elements. 3. Based on their properties, elements are classified into : metals, non-metals, metalloids, noble gases. 4. Metals are ductile, malleable, good conductors of heat and electricity, high melting and boiling points. Metals are sonorous, e.g., Iron, Gold, Silver, etc. 5. Non-metals are solids and brittle in nature, bad conductor of heat and electricity (exception Graphite) low melting and boiling points, e.g. sulphur, carbon, hydrogen, etc. 6. Metalloids—  These elements show properties ...