Please enable JavaScript.
Coggle requires JavaScript to display documents.
Pure Substances, Elements, Uses of Elements and Compounds on the basis of…
Pure Substances
Definite composition & consistent properties throughout.
Uniform composition throughout - homogeneous.
Fixed melting and boiling points.
Characteristic color, odor and taste.
Cannot be broken down by physical means.
Divided into elements and compounds.
Elements
Non-metals
They are dull (iodine and carbon in the form of diamond shine)
Less in no. compared to metals.
Soft solids (Sulphur, iodine) or gases (bromine is liquid)
Are not ductile or malleable
Mostly brittle.
Bad conductors of heat and electricity (except carbon)
Low melting and boiling points except diamond and graphite.
Non-sonorous.
Symbols of elements
Abbreviations used to denote chemical elements.
Berzelius first used alphabets to represent elements.
Each element is denoted usually by the first letter of its English or Latin name written in capital.
But when two elements have the same first letter, the symbol has two letters. Eg. Carbon - C, Calcium - Ca, Cobalt - Co
When two elements have the same first two letters, one of their Latin names is taken. Cobalt - Co, Copper - Cu (cuprum)
Also represents atom of specific element.
Metalloids
Neither metals nor non-metals
Show some properties of both.
Solids.
Boron, silicon, arsenic, antimony, germanium, tellurium and polonium.
Common elements
Universe - hydrogen and helium
Earth's crust - oxygen, silicon, aluminium, iron
Atmosphere - Nitrogen
Human body - carbon, hydrogen, oxygen make up the compounds in all cells.
Noble/Inert gases
Gaseous elements that do not react chemically with other elements.
Found in air in traces.
Helium, neon, argon, krypton, xenon and radon (6)
Metals
Most elements are metals.
Properties
Usually lustrous and hard (Sodium is soft)
They are solids (Mercury is liquid)
They are ductile (can be stretched into thin wires)
They are malleable i.e. can be beaten into thin sheets (zinc is brittle)
They are good conductors of heat and electricity (tungsten is not)
High melting and boiling points.
Sonorous substances.
Made up of 1 kind of atoms.
Pure substance that cannot be broken down into anything simpler by any means.
118 elements discovered so far. 92 naturally occurring elements and 18 artificially created ones.
They make up all other substances.
Periodic table is a systematic arrangement of elements in a tabular form for their convenient study. It has horizontal rows called periods (1,2,3,4) and vertical columns called groups (IA, IIA...Zero)
Uses of Elements and Compounds on the basis of their properties
Gold, platinum and silver are lustrous and can remain in free state. They do not tarnish in air and so are used to make jewelry and ornaments.
Copper and aluminium are good conductors of heat and electricity and are malleable and ductile. So they are used for utensils, wires etc.
When copper is mixed with metals like zinc or tin, brass and bronze are formed which are durable and strong. They are used to make statues, utensils, door knobs, handles, machine parts, taps, electrical fittings etc.
Iron is one of the most useful metals of all. It is strong and easily available, and so is used for heavy tools and machines.
Diamond is the hardest natural substance. Pure ones are used as gems while impure ones to cut glass.
Graphite - pencil lead, lubricants.
Water - universal solvent. Carries dissolved substances in blood and sap in plants. Medicinal solutions and many other uses.
Plastic - non-conductor used as insulator.
Sand is a compound used to make glass.
Argon and neon are filled in electric bulbs because of their inert nature and they do not react with the tungsten filament and prevents it from destruction.
Diamond, graphite and coal are forms of coal.
Compounds
Made up of 1 kind of molecules.
Pure substances formed by chemical combination of 2 or more elements in a definite proportion by mass.
Can be broken down into simpler substances.
Molecule is the smallest unit of a compound which contains atoms of two or more elements in a fixed ratio.
Homogeneous
Physical and chemical properties differ from those of its constituent elements.
Elements cannot be separated by simple physical means.
Energy is absorbed or evolved when compounds are formed.
Atoms and Molecules
Molecules of Elements - Types
Monoatomic - they consist of one atom. (helium, potassium, sodium, calcium
Diatomic - two atoms (elementary gases made up of 1 element only - hydrogen, oxygen, nitrogen, chlorine)
Triatomic - three atoms (ozone)
Polyatomic - 3+ atoms (phosphorous, sulphur)
Atoms are the smallest indivisible units of an element which exhibit all the properties of that element and may or may not have independent existence.
They were discovered by John Dalton
Molecules are the smallest unit of an element or compound which exhibit all properties of that element or compound and have independent existence. They are divisible into atoms.
Molecules of compounds are formed when atoms of 2 or more elements are combined.