Chemistry

ATOMIC STRUCTURE
Different models of atom
(1) Dalton's atomic model.
Dalton’s atomic model is one of the fundamentals of physics and chemistry. This theory of atomic
composition was hypothesized and partially confirmed by the English chemist and Physicist John Dalton.
Dalton came with his Atomic theory as a result of his research into gases. He discovered that certain
gases only could be combined in certain proportions even if two different compounds shared the same
common element or group of elements. Through deductive reasoning and experimentation, he made an
interesting discovery. His findings led him to hypothesize that elements combine at the atomic level in
fixed ratios. This ratio would naturally differ in compounds due to the unique atomic weights of the
elements being combined.
This was a revolutionary idea but further experimentation by himself and others confirmed his theory.
The findings became the basis of Dalton’s Atomic Laws or Model. These laws focus on five basic
theorems.
(1) Pure Elements consist of particles called atoms.
(2) Atoms of an element are all the same for that element. That means gold is gold and oxygen is oxygen
down to the last atom.
(3) Atoms of different elements can be told apart by their atomic weights.
(4) Atoms of elements unite to form chemical compounds.
(5) Atoms can neither be created or destroyed in chemical reaction. The grouping only changes.

Characteristics of waves :
Amplitude : Maximum displacement from mean position it remains constant with distance except
stationary or standing waves.
Wavelength : It is the distance between two adjacent crest or troughs.
Frequency (µ or ν) : The no of waves passing through a point in 1second, unit-sec–1 or Hz
Wave number ( or ) µ ν : No. of waves present in unit distance.
1 /λ per metre ,per cm etc.
Velocity : linear distance travelled by wave in one second.
v = µλ