Models of Atom 1) The concept of atom was born in Greece about 450 BC 2) Democritus, Greek scientist proposed that matter and motion are discontinuous and could not be infinitely divided. At some point a fundamental indivisible particle would emerge and he called it as Atomos (atom). 3) In 350 B.C., Aristotle argued that matter and motion are continuous. He believed that the smallest particle can be further divided. His view prevailed for almost 21 centuries

Dalton Model of the Atom In seventeenth century, Robert Boyle, British scientist, concluded from experiments, that a gas was made of tiny particles In 1803, John Dalton proposed that matter is discontinuous as Democritus suggested. But he offered experimental evidence. CO 2 H 2 O

Atomic Theory 1) An element is composed of tiny, indivisible, indestructible particles called atoms 2) All atoms of an element are identical and have the same properties. 3) Atoms of different elements combine to form compounds 4) Compounds contain atoms in small whole number ratios 5) Atoms can combine in more than one ratio to form different compounds

Thomson Model of the Atom Thomson discovered a negatively charged particle, called an Electron (e - ) and a positively charged particle called a Proton (p + ) Thomson proposed a subatomic model of the atom (plum pudding model). Mass of an electron = 9.11 x Mass of proton = 1.67 x

Rutherford Model of the Atom

Rutherford Model of the Atom 1) The most of  -particles passed through foil because an atom is largely empty space with electrons moving about. 2) The center of the atom is the atomic nucleus containing protons 3) Compared to the atom, the nucleus is tiny and has very high density 4) Negatively charged electrons are distributed about positively charged nucleus. Diameter of atom = 1 x cm Diameter of atom = 1 x cm Rutherford also predicted neutral particles along with protons

Discovery of Neutrons In 1932 James Chadwick discovered the neutrons (n 0 ) Subatomic Particle SymbolLocationRelative charge Relative mass Electron Proton Neutron e-p+n0e-p+n0 Outside nucleus inside nucleus Inside nucleus /1836 1

Atomic Notation

Isotopes For most elements, the number of neutrons in the nucleus varies Definition of isotope: Atoms of the same element that have different number of neutrons in the nucleus are called isotopes.

Isotopes

Atomic mass Carbon mass = 1.99 x “ Carbon-12 has been chosen as reference standard” Unit for Atomic mass is amu Atomic mass unit is equal to 1/12 the mass of carbon-12 atom Atomic mass: The average mass of naturally occurring isotopes

Calculation of Atomic mass 12 C mass = amu, Abundance= 98.89% 13 C mass = amu, Abundance = 1.11% Unit values of abundance for both isotopes: 98.89/100 = for 12C 1.11/100 = for 13C 12C mass = amu x = amu 13C mass = amu x = amu Carbon (average)mass = amu

Periodic table An element in the periodic table Atomic number Symbol Atomic mass 6 C C 12.01

The Quantum concept of energy Continuous energy level Quantized energy level

Bohr Model of the atom Electrons orbit around the atomic nucleus just as planets orbit around the sun The electrons travel in a fixed energy orbit, energy level

Energy levels of electron

Energy levels and sublevels 4 4s,4p,4d, 4f 3 3s, 3p, 3d 2 2s, 2p 1 1s The number of subshells corresponds to the number of main energy level

Energy levels and sublevels

Electron Configuration 7s 6s 6p 6d 5s 5p 5d 5f 4s 4d 4d 4f 3s 3p 3d 2s 2p 1s Energy level, Lower level are filled first

Presentation of configuration 2p 2 Electron configuration of Oxygen: 1s 2 2s 2 2p 4 Practice Br, Fe and Au

Quantum mechanical model of the atom 1) Uncertainty principle: It is impossible to determine the location and energy of electron- Heisenberg, Germany 2) The region of high probability (~95%) for finding an electron of given energy is called an “orbital”

Quantum mechanical model of the atom

d-Orbitals