General chmistry_lec01

BITS Pilani, Pilani Campus

Welcome

CHEM F111 : General Chemistry

BITS Pilani Pilani Campus

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General Chemistry (Overview of handout) Upload Handout from ID website

• Quantum theory • Atomic structure and spectra • Chemical bonding • Spectroscopy:

• Vibrational • Electronic • NMR

• Chemical thermodynamics • Chemical Kinetics

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• Coordination compounds • Octahedral • Tetrahedral • Square planar geometries

• Conformation • Stereochemistry • Types of reactions:

• Elimination • Addition • Substitution • Pericyclic

• Aromatic compounds


Books

Text Books T1: Elements of Physical Chemistry: 6th Edition, Oxford University Press, Oxford, reprinted in 2015, P.W. Atkins and Julio de Paula, T2: Organic Chemistry, 10th Edition, John Wiley & Sons, Inc. New York, 2011, T. W. Graham Solomons and Craig B. Fryhle,

Reference Books: R1: Physical Chemistry, David Ball R2: Concise Inorganic Chemistry, 5th Edition, Blackwell Science, Oxford, 1999, J. D. Lee, R3: Inorganic Chemistry: Principles of Structure and Reactivity, 4th Edition, Huheey, Keiter R4: Organic Chemistry, 6th Edition, PHI, New Delhi, 1992, R. T. Morrison and R. Boyd,


General Chemistry (Evaluation components)

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Component Duration Weightage

(%)

Date and Time Remarks

Mid-

Semester

test

90 min. 30 Will be

announced

by ID

Closed

book

Tutorials 10 min. 25 Continuous Closed

book

Compre.

Exam.

3 hours 45 02/12 AN Partially

open book


Tutorial: Evaluation components

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Tutorial Hour • Clarification of doubts •Further discussion and interactions •Problem solving •Periodical and continuous evaluation: Two types: 10 min.

• Quiz: A set of objective type questions (different types), which the student will have to answer and submit during the tutorial class.

• Assignment: A set of problems will be assigned periodically, of which one to be solved in the tutorial hour of the following week.

Assignment/Lecture slides/Notices will be uploaded on the Nalanda (upon activation). Please register yourself on Nalanda


Lecture slides can be downloaded from Department of chemistry website: BITS Pilani Pilani Campus Academic Departments Password: BITSPILANI Chemistry Pedagogy Course related announcements

http://www.bits-pilani.ac.in/pilani/pilaniChemistry/courserelated


CLASSROOM RULES

7 BITS Pilani, Pilani Campus

Quantum Theory: Background

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Classical Mechanics:

Describes the motion of macroscopic objects,

from pendulum, projectiles to parts

of machinery, as well as astronomical objects,

such as spacecraft, planets, stars, and galaxies.

Galileo

Euler

Newton Laws of motion

Lagrange

Hamilton

unaltered for three centuries till end of 19th Century BITS Pilani, Pilani Campus

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Classical Mechanics: Consequences

1. Predict a precise trajectory for particles with precisely

specified locations and momenta at each instant.

2. Any kind of motion can be excited to any arbitrary value

of the energy

3. Waves and Particles are distinct concepts

Certain Phenomena were unexplainable ???

? Black body radiation

? Photoelectric effect

? Electron diffraction

? Line spectra of atoms

……….Foundation of Quantum Mechanics BITS Pilani, Pilani Campus

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Black body

• Study of Interaction of light with matter was in progress.

(How light was emitted or absorbed ??)

• Any object radiates energy, when heated. The amount of

energy emitted, and its frequency distribution depends on

the temperature and on the material.

Actual black bodies don't exist in nature

• Black Body: A perfect absorber and a perfect emitter:

Theoretically it can be approximated as a small hollow

cavity with a tiny hole for light to escape.


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• Such solid black bodies, when heated to glowing emitted a

continuous spectrum composed of all wavelengths of light,

called Black Body/cavity radiations.

• The distribution of absorbed or emitted radiation depends

on the absolute temperature, not on the body material.

Black body radiation-the phenomena

Inte

nsi

ty (

I) o

r P

ow

er

de

nsi

ty

Wavelength

At constant T, Intensity increases as λ

increases, attains a maximum value and

then decreases.

Not all the wavelengths of light are

emitted equally.

?


• With increase in T, the λmax shifts towards shorter wavelength.

λmax T = b b = 2.9 mmK

[Wien’s Displacement Law]

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Observations: Two Radiations Law

Used to estimate the

temperature of Sun and

Earth

• (λ, T) increases with increase in T.

Area under the curve at T = Total Power per unit surface area (M)

M is proportional to 4th power of absolute temperature and is

proportional to Energy density. M = σT4 = ∫( (λ, T) dλ (W/m2) = 5.6697 x 10-8 Wm-2K-4 [Stefan-Boltzmann Law]


Blackbody Radiation: Explanation

I. Rayleigh-Jeans Explanation (1900-1905) attempts to describe the emission spectrum from a black

body at a given temperature through classical arguments.

Assumptions: Black body cavity is made up of charged particles which behaves as tiny oscillators by thermal accelerations and emit radiations.

The electromagnetic field thus generated can be considered as a collection of waves of all possible frequencies.

Average Kinetic energy of each component (per degree of freedom) of an oscillator was assumed to be kT based on classical equipartition principle.


Rayleigh-Jeans Law

Quite Successful at long wavelengths.

Θ Rayleigh_Jeans Law predicts an Ultraviolet catastrophe that does not occur in real.

Energy density associated with radiation of wavelength from λ to

λ+dλ : dE = dλ = (8πkT/λ4) dλ ; : Energy Density

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Energy density rises without

bound as λ decreases.

Infinite energy density at

short wavelengths or Oscillators of short wavelength

(UV) are excited even at room

temperature.( UV Catastrophe!)


Crucial Assumption: • An oscillator of frequency ν cannot be excited to any arbitrary energy, but to only to integral multiples of a fundamental unit or quantum of energy hν; h = 6.626 x 10-34 Js, the Planck constant. ΔE=nhν i.e. Energy of an oscillator is quantized • The average energy is different from that in classical physics.

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Blackbody Radiation: Explanation

II. Planck’s Explanation (1900-1909) attempts to describe the emission spectrum from a black

body at a given temperature through Quantization hypothesis.


Planck Radiation Distribution Law

dE=dλ = (8π/λ4) dλ (hc/λ) [e(hc/λkT) -1]-1

c is speed of light, k is Boltzmann’s constant and h is Planck’s constant.

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Average

energy

Planck proposed empirical formula describe the curve of blackbody radiation exactly for all wavelengths.

Planck expression reproduces the experimental distribution with h = 6.63 x 10 –34 Js


Planck Law: Success story

dE = (8πhc/λ5) dλ [e(hc/λkT) -1]-1

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Planck's hypothesis: An oscillator cannot be excited unless it

receives an energy of at least hν (as this is the minimum amount

of energy an oscillator of frequency ν may possess above zero).

For high frequency oscillators (large ν, low ), the amount of

energy hν is too large to be supplied by the thermal motion of the

atoms in the walls, and so they are not excited.

At small , ehc/kT faster than 5

(Exponential is large)

Energy density 0 as 0

UV Catastrophe

avoided


The Magic of Planck’s formula

dE = dλ = (8π/λ4) (hc/λ) [e(hc/λkT) -1]-1 dλ

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exp (hc/λkT) = 1 + hc/λkT +1/2(hc/λkT)2 + ……

Dropping

= (2 π5k4/15h3c2)T4 = T4

Stefan Boltzman Law

Differentiate d/dλ = 0 for calculating max (at low λ)

maxT = hc/5k (constant) Wien’s Law

Rayleigh-Jeans formula

M = ( (λ, T) dλ

For long wavelengths,

when hc/λ << kT


Photoelectric Effect


Failure of Classical Physics to Explain

Photoelectric Effect

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• No electrons are ejected if the

frequency of radiation is below a

threshold value characteristic of

the metal.

Electron emitted should

depend on intensity and not on

frequency.

The Facts The Believes

• For frequencies above the

threshold value, emission of

electrons is instantaneous, no

matter how low the intensity of

the light. (Absence of time lag)

The energy of the incident light

is spread over as a wave front and

some time will be required by an

electron to absorb enough energy to

escape.

• Kinetic energy of emitted

electrons varies linearly with the

frequency, and is independent of

light intensity.

K.E. should depend on the

amplitude of the oscillation of the

incident radiation.


Photoelectric Effect: Einstein Explanation

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Particle Character of Light

If the minimum energy required to

remove an electron from the metal

surface is (work function), then if h < , no emission of electrons

occurs.

Threshold frequency 0 given by = h0

For > 0, Ek = h = h( 0).

1/2mv2 = h = h( 0).

Light of frequency may be

considered as a collection of

particles, called photons, each of

energy h.


General chmistry_lec01

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