Chemistry- Some Basic Concepts of Chemistry

What is Chemistry?

Chemistry is the study of matter, its physical and chemical properties and the physical and chemical changes its undergoes under different conditions.

Application of Chemistry

Knowledge of chemistry has been used in applied sciences such as medicine, dentistry, engineering, agriculture and in daily home use products.

Nature of Chemistry/ Classification of Chemistry

Chemistry is traditionally classified further into five branches

Organic Chemistry is the study of the properties and reactions of the compounds of carbon. Ex- CH₄ C₂H_6. Inorganic Chemistry is the study of substances which are not organic. Ex- H₂0, NH_3. Physical chemistry deals with the studies of properties of matter. It is the study of atoms, molecules and fundamental concepts related to electrons, energies and dynamics therein. Analytical Chemistry. Biochemistry.

Pure Substances

Pure substances have definite chemical composition. They have the same properties regardless of their origin. Ex- Pure metal, distilled water

Mixtures

Mixtures have no definite composition and hence no definite properties. Ex- paint, concrete

Elements

Elements are pure substances which cannot be broken down into simple substances by ordinary chemical changes. Ex- Na, K, Ca

Compounds

Compounds are pure substances which can be broken down into simpler substances by ordinary chemical changes. Ex- H2O, CO2

Mixtures and classification of mixtures

A mixture contains two or more substances in no fixed proportion and may be separated by physical methods. Mixtures are further divided into homogenous and heterogenous mixtures.

Physical properties

Physical properties are those which can be measured or observed without changing the chemical composition of the substance. Ex- colour, odour, melting point, boiling point, density etc.

Chemical properties

Chemical properties are the properties where the substances undergo a chemical change and thereby exhibit change in chemical composition. Ex- Burning of magnesium ribbon in the presence of oxygen to form magnesium oxide.

Mass and Weight

The SI unit of mass is kg. The mass of a body does not vary as its position changes. The weight of a body is result of the mass and gravitational attraction. It varies because the gravitational attraction of the earth for a body varies with distance from the centre of the earth. The mass of a body is more fundamental property than its weight. 1kg=1000g=10^³g.

Length

The SI unit of length is m. The fractional units of the SI unit of length are used for small quantities. Ex- nanometer (nm), picometer (pm). 1 nm= 10^-9m and 1 pm= 10^-12m

Volume

Volume is the amount of space occupied by a three dimensional object. The SI unit of volume is metre³ or m³. A volumetric flask is used to prepare a known volume of a solution.

Density

Density of a substance is its mass per unit volume. The SI unit of density is kg/m³ or kgm^-3.

Temperature

Temperature is a measure of the hotness or coldness of an object. The SI unit of temperature is Kelvin (K).

Law of Conservation of Mass

Antoine Lavoisier is said to be the father of modern chemistry. The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. Therefore, Total mass of reactants=Total mass of products. A

Law of Definite Proportions

A given pure compound always contains the same proportion of elements by weight. Irrespective of the source, a given pure compound always contains the same elements in the same proportion.

Law of multiple proportions

It was proposed by John Dalton. The law of multiple proportion states that when two elements A and B combine with each other to form more than one compound, the masses of element B that combine with element A are in the ration of small whole number. Ex- Water and hydrogen peroxide.

Gay Lussac Law of Gaseous Volumes

When gases combine or are formed during a chemical reaction they do so in a simple ratio by volume provided that all the gases are at the same temperature.

Avogadro Law

Avogadro Law states equal volumes of equal gases at the same temperature and pressure contain equal number of molecules.

Dalton’s Atomic Theory

1.Matter consists of tiny indivisible particles called atoms. 2.Atoms of same elements have the same properties including mass. Atoms of different elements differ in mass. 3.Compounds are formed when atoms of different elements combine in a fixed ratio. 4.Chemical reactions involve only the reorganization of atoms. Atoms are neither created nor destroyed in a chemical reaction.

Atomic mass

Atomic mass is the mass of an atom. It is very small. Ex- The mass of one hydrogen atom= 1.6736 × 10 ^-24 g.

Average atomic mass

Many naturally occurring elements exist as a mixture of more than one isotope. Isotopes have different atomic masses. Therefore, we should know the average atomic masses. Ex- Average atomic mass of hydrogen= 12.011u.

Molecular Mass

Molecular mass is the sum of average atomic masses of all the atoms of elements which constitute the molecule. Molecular mass of a substance is the mass of one molecule of that substance relative to the mass of one carbon-12 atom.

Formula Mass

Mole concept

One mole is the amount of substance that contains as may entities or atoms as there are atoms in exactly 12 g or 0.012 kg of the carbon-12 isotope.

Molar Mass

Moles and Gases