Chem chap 9
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Bohr's theory of an Atom
when an atom absorbs energy in the form of heat, light or electricity it often re emits that energy as light.
Bohr's theory (model)
Orbit- is a circular path around the shell of the nucleus at definite distance (fixed energy) in which electron moves (revolves)
Drawbacks of Bohr's Model
Not fully successful in explaining line spectrum (emission, spectrum) exhibited by (colors) different elements with different atomic number (number of electrons)
Quantum Mechanical Theory (Wave theory)
Orbital- is a three dimensional space around the nucleus where the probability of locating an electron is maximum at one particular time
orbitals are represented by a number (1,2,3,4..) and a letter (s,p,d,f..)
Distribution of electrons of an element into various orbitals of increasing enery
Pauli's Exclusion Principle
A maximum of only two electrons with opposite spin can be accommodated into any given orbital
orbitals with fixed definite amount of energy
orbitals with equal (same) amount of energy
Degenerate orbitals (equal amount of energy) are singly full with parallel spin before they are paired up with opposite spin
Each orbiral is represented as a square box
stands for the number of electrons in the outermost shell orbit.
Electrons of the outermost shell
corresponds to group number of an element
stands for the number of shells into which electrons are distributed
Periodic Trend in properties of Elements in Period table.
Atomic size-----increases-------- decreases
Metallic character--- increases----- decreases
Nonmetallic-------- decreases----- increases
Ionization energy--- decrease------ increases
Metals tend to lose electrons and for positive ion (Na+, Mg2+, Al3+)
Bigger atoms can easily lose electrons to form cation (positive ion)
Non metals tend to gain electrons to form negative ions (F1-, O2-, N3-)
- is the energy required to remove electrons from neutral gaseous atom.
- further from the nucleus
What is the most reactive metal of the period table?
Fr-Francium (lower left side)
What is the most reactive of NON metal of the periodic table
Fluorine (upper right corner)
Compare the size
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