Era of Chemistry

  THEORIES OF ACIDS AND BASES. There are three basic theories of acid and bases. Arrhenius Theory Bronsted-Lowry Theory Lewis Theory Arrhenius Theory According to the Arrhenius theory, Acid - Any species that increases the concentration of H+ in aqueous solution. Base - Any species that increases the concentration of OH- in aqueous solution. Limitations of Arrhenius Theory It can only describe acid-base chemistry in aqueous solutions.Can not apply in non aqueous and gas phase reactions. Can not apply for certain compounds to explain their acid-base properties. Bronsted-Lowry Theory According to the Bronsted-Lowry theory, Acid - Any species that is capable of donating a proton (H+). Base - Any species that is capable of accepting a proton (OH-). Lewis Theory According to the Lewis theory, Acid - Any species that is capable of accepting a pair of electrons. Base - Any species that is capable of donating a pair of electrons.

  DALTON'S ATOMIC MODEL John Dalton was an English scientist and a school teacher. In 1808 he formulated a precise definition of the invisible building blocks of matter that we call 'atoms'. Dalton's atomic theory based on four assumptions. Elements are made out of extremely small,indivisible particles called 'atoms'. All atoms of a given element are identical in mass and size but the atoms of one element are different from the atoms of all other elements. Atoms of one element can not be changed into atoms of a different element by chemical reactions;atoms are neither created nor destroyed in chemical reactions. Compounds are formed by union of two or more atoms of different elements in simple mumerical ratio. He suggested that all matters was made up tiny spheres that were able to rebounce around with perfect elasticity and called them as atoms. Dalton's atomic model is called as the Golf ball model. John Dalton Atomic Model