Introduction
One of the most famous formulas in the world is E=mC2, where E is energy, m is mass and C is speed of light.
Classification of Matter
Matter can be classified into different categories depending upon their physical or chemical nature.
Molecular or Particle Concept of Matter
Intensive investigation by scientists over the years led to the development of a mental model known as 'dynamic particle model'.
Effect of Temperature and Pressure on States of Matter
When we heat a solid, we add energy to the system increasing the vibration of the particles. Eventually these particles break free from their binding forces and melt. The normal melting point of a crystal is the temperature at which it melts under one atmospheric pressure. Increase in pressures usually raises the melting point.
Elements, Compounds and Mixtures
According to the chemical classification of matter there are two main categories: (i) Pure substances (ii) Mixtures.
Symbols of Elements
Even before knowing what elements were, man started extracting them from their ores. A few metals like gold, silver, iron, copper, lead, tin and mercury were used even in the 1st century A.D. A mention of them is made in the 'Charaka Samhita' - a medical treatise of ancient India. These metals were associated with a particular heavenly body.
Atomic Mass of Elements
Experimentally it is determined that the mass of an atom is very small ranging from 1.7 x 10-24 g to about 4.0 x 10-22 g. These small masses are terribly impractical to work with. Thus, it became necessary to reduce the atomic masses into simple figures.
Atomic Mass Unit Scale
The scale in which the relative atomic masses of different atoms are expressed is called atomic mass unit scale.
Solutions
Solution is defined as a homogeneous mixture of two or more chemical substances. The state of matter of a solution may be solid, liquid or gaseous.
True Solutions, Suspensions and Colloids
A true solution is a homogeneous solution in which the solute particles have diameters less than 10-7cm. i.e., the solute particles are of molecular dimensions. The particles are invisible even under powerful microscopes.
Special Properties of Colloids
Brownian movement
When a colloidal solution is viewed through a powerful microscope, the colloidal particles can be seen moving in a random zig-zag path. This zig-zag motion of colloidal particles is called Brownian movement. This random motion is due to collisions between the colloidal particles.
Dalton's Atomic Theory
John Dalton, a British school teacher, published his theory about atoms in the year 1808. His findings were based on experiments and also from laws of chemical combination.
Laws of Chemical Combination
When substances react, they do so by following certain laws. These laws are called the laws of chemical combination. These formed the basis of Dalton's atomic theory of matter.
Atoms and Molecules
Atom is the smallest particle of an element, which may or may not have independent existence. It is made up of subatomic particles like electrons, protons and neutrons. Atoms of one type of element differ from those of the other due to different number of subatomic particles.
Atomicity of a Molecule of an Element
The number of atoms, which constitute one molecule of an element, is called its atomicity.
Molecules of Compounds
A molecule of a compound consists of two or more atoms of different elements joined together in a fixed ratio.
Relative Molecular Mass
Relative molecular mass or RMM is the molecular weight of an element or an compound. It is the number of times one molecule of the substance is heavier than 1/12 the mass of an atom of carbon (C12).
Mole Concept
Since it is not possible to calculate the weight of particles individually, a collection of such particles called mole is taken for all practical purposes. Avogadro discovered that under standard conditions of temperature and pressure, (1atm and 273K) a sample of gas occupies a volume of 22.4 L.
Molar Volume
The molar volume [22.4L at STP] plays a vital role in stoichiometric calculations because it is the link between volume and mass in reactions involving gases.
Relationship between Gram Molecular Weight and Gram Molecular Volume
Gram molecular weight (GMW) is the relative molecular mass of a substance expressed in grams. It is also called gram molecule of that element.
Numericals Based on Mole Concept
Important relationships
* 1 mole of an atom = 1 gram atomic weight of an atom
* 1 mole of a molecule = 1 gram molecular weight of molecule
Empirical and Molecular Formula of a Compound
Empirical formula is the formula of a compound, which shows the simplest whole number ratio between the atoms of the elements in the compound. It does not indicate the actual number of atoms of the elements present but the simplest whole number ratio.
Summary
Element is a pure substance, which can neither be decomposed nor built from simpler substances by any physical or chemical means. It contains only one kind of atom.
