Hard crystalline shiny rock consisting of of carbonates of Calcium ( Ca CO3)and magnesium (MgCO3). Taj Mahal in India is almost entirely marble.
Majority of the elements
in the Periodic Table are metals.
Fig. Periodic Table The periodic Table shows all the elements. Out of that except the red, blue and the halogens in between all the others are metals.
Go to Periodic Table .
They all have the following general properties.
- Usually high dense except alkali metals.
- A clean surface will have a shine.
- All are solids except mercury Hg which is a liquid.
- All have a silvery colour except gold and copper.
- Good conductors of heat and electricity.
- Form positive ions by lending electrons.
- Shows an affinity for non metals.
- Some metals react with Dil. Hydrochloric acid yielding hydrogen.
What is not a pure substance, That means a substance consisting of more than one kind of molecules or atoms is considered as a mixture. ( A pure element can have different Isotopes)
There are different types of mixtures.
1. Homogeneous Mixtures
The composition of ingredients in a homogeneous mixture will be the same in two or mare samples taken.
Eg : - All true solutions, Air, clear tap water, sea water , blood plasma , brass (an alloy of zinc and copper) 18 carat gold are examples. Ingredients cannot be separately seen even through a microscope.
2. Heterogeneous mixtures
Often the separate substances can be seen with the naked eye or through a microscope. Eg :- Soil, mortar, muddy water, rocks, cloud
3. Collids
Dispersed solid or liquid particles are so small and cannot be seen separately. If a beam of light is passed through the medium the light will scatter. When a colloid is formed by two liquids, oil and water, it would be an emulsion.
For more click Pure substances and Mixtures .
This is a group of two or more atoms chemically bonded together to form a pure substance. Atoms may be of the same kind as in di atomic gases. A molecule of oxygen has two atoms of the same kind.
Eg. Oxygen O2, Carbon dioxide CO2, Water H2O , Glucose C6 H12O 6
A solution that contains a definite number of moles
Molecular weight of a pure chemical, taken in grams consists of one mole (mol) of molecules
1 mol of any chemical substance will give the same number of molecules which is equal to the Avagadoro number. This denoted by the symbol … NA.
NA. = 6.02 x 10 23 particles
Usually this refers to an acid becoming neutral by the addition of a base.
Eg 1.:- HCl + NaOH → Na Cl + H2O
1 mol + 1mol → 1 mol + 1 mol
Eg 2:- H2SO4 + 2 NaOH → Na2 S O4 + 2 H2O
1 mol + 2mol → 1 mol + 2 mol
Acids may also be neutralized by carbonates and the metals above H in the activity series.
Eg 3:- 2 HNO3 + CaCO3 → Ca (NO3)2 + H2 O + CO2
Eg 4 :- 2 HCl + Zn → ZnCl2 + H2
i. The element
The atmosphere contains nearly 79% of Nitrogen 20% of oxygen excluding water vapour and suspended dust etc, . Although the gas is quite stable under normal conditions, during lightening, it combines with Oxygen to form oxides. NO2, N2O4, and NO.
This is mainly used to manufacture ammonia which is necessary to make fertilisers. These fertilisers get bound to the soil and the effect of getting washed away is at a minimum.
ii. Nitrogen cycle
Nitrogen is an essential element for organisms. Yet it cannot be taken in directly. Nitrogen is present in the soil as nitrates . KNO3 , NaNO3 and Ca(NO3)2, NH4NO3 etc,. These are absorbed as aqueous solutions by the plants to build body tissue. Animals get this from plants. When the animals and plants die Nitrogen is returned to the soil as nitrates. This is known as the Nitrogen cycle.
