Matter is anything that has mass and occupies space. Everything around us (air, water, wood, stone) is matter; light, heat, sound and thoughts are not. Matter is made of particles that are extremely small, have spaces between them, are always moving, and attract each other.
Diffusion: particles of different substances mix on their own (smell of perfume, ink in water). It is fastest in gases, slowest in solids, and increases with temperature.
Brownian motion: random zig-zag motion of tiny particles in a fluid, caused by bumping of fast-moving molecules (Robert Brown).
States of matter
Property
Solid
Liquid
Gas
Shape
Fixed
Takes the shape of the container
No fixed shape
Volume
Fixed
Fixed
Not fixed
Compressibility
Negligible
Very small
High
Particle spacing
Very close
Close
Far apart
Attraction
Strongest
Medium
Very weak
Flow
No
Yes
Yes
Examples
Ice, wood, iron
Water, milk, oil
Air, oxygen, steam
Plasma (ionised gas, the fourth state: Sun, stars, lightning, neon signs) and Bose-Einstein condensate (very near absolute zero) are other states.
LPG is liquefied under pressure; CNG is compressed natural gas; dry ice is solid carbon dioxide (sublimes, no liquid stage).
Melting point of ice = 0 C (273 K); boiling point of water = 100 C (373 K).
Latent heat is the heat absorbed at constant temperature during a change of state.
Evaporation happens at all temperatures, only at the surface, and causes cooling. It rises with higher temperature, larger surface, lower humidity and more wind. Boiling happens at one fixed temperature, throughout the liquid.
Pressure raises the boiling point. A pressure cooker cooks quickly; at high altitude water boils at a lower temperature.
Physical and chemical change
Physical change
Chemical change
No new substance is formed; usually reversible
A new substance forms; usually irreversible
Melting ice, dissolving salt, folding paper
Rusting, burning, cooking, curdling of milk, souring, photosynthesis, digestion
Signs of a chemical change: change of colour, gas released, heat or light, precipitate, change of smell.
Pure substances and mixtures
Type
Meaning
Examples
Element
One kind of atom; cannot be broken further
Iron, oxygen, gold, mercury, carbon
Compound
Two or more elements chemically combined in a fixed ratio
Water, salt, sugar, CO2
Mixture
Two or more substances physically mixed; no fixed ratio; properties of components remain
Air, sea water, soil, alloys
Homogeneous mixture: uniform throughout (a solution): salt in water, air, brass, vinegar. Heterogeneous mixture: not uniform: sand and water, oil and water.
Alloys are homogeneous mixtures of metals, e.g. brass (copper and zinc), bronze (copper and tin), steel (iron and carbon), solder (tin and lead), stainless steel (iron, chromium, nickel).
Element examples:gold, silver, copper, mercury (liquid metal), bromine (liquid non-metal); liquid at room temperature: mercury, bromine (also gallium and caesium on warm days).
Solute is dissolved; solvent dissolves it. Water is the universal solvent.
Tyndall effect: scattering of a light beam by colloidal particles (a sunbeam through a dusty room, headlights in fog).
Concentrationmass percent = (mass of solute / mass of solution) x 100.
Saturated solution: cannot dissolve more solute at that temperature. Solubility generally increases with temperature for solids; gases dissolve less in warm water.
Methods of separation
Method
Used for
Example
Handpicking
Large impurities
Stones from rice
Winnowing
Light and heavy particles using wind
Grain from husk
Threshing
Grain from stalks
Wheat
Sieving
Different sizes
Flour from bran
Sedimentation and decantation
Insoluble heavier solid in liquid
Muddy water
Filtration
Insoluble solid from liquid
Tea leaves, water purification
Evaporation
Soluble solid from solution
Salt from sea water
Crystallisation
Pure crystals from solution
Sugar, alum, copper sulphate
Magnetic separation
Magnetic from non-magnetic
Iron filings from sand
Sublimation
A sublimable solid from a mixture
Ammonium chloride from salt
Centrifugation
Tiny suspended particles
Cream from milk, blood cells
Separating funnel
Two immiscible liquids
Oil and water
Simple distillation
Liquid from a dissolved solid
Pure water from salt water
Fractional distillation
Liquids with close boiling points
Air gases, petroleum, alcohol and water
Chromatography
Dyes and pigments
Ink colours, plant pigments
Loading (adding alum)
Fine suspended clay
Water purification
Purification of drinking water: sedimentation, filtration, chlorination (kills germs), boiling and UV or RO.
Prepared for exam revision from the NCERT Science textbooks for Classes 6 to 10 and standard sources. Space missions, awards and records change, so check official sources for recent facts. Found a mistake? Tell us.