Gen CHEM 1 lecture 1.ppt

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    LectureNo.1(The Electronic Structure of Atoms)

    Lecturer:Prof. Allan N. Soriano,Ph.D. Ch.E.

    Email:[email protected]

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    Content

    Atomic Models

    Quantum Mechanics

    Electronic Configuration

    Periodic Relations of Elements

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    Atomic Models

    Democritus (400 BC)

    He theorized that matter could not be divided into

    smaller and smaller pieces, and eventually the smallestpossible piece would be obtained.

    He named the smallest piece of matter atomos

    meaning not to be cut.

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    Atomic Models (Cont.)

    Aristotle (350 BC)

    He modified an earlier theory that matter was madeof four elements: earth, fire, waterand air.

    He also rejected the idea of atomism of matter.

    Fire

    Air

    Water

    Earth

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    Atomic Models (Cont.)

    John Dalton (1800)

    He proposed a modern model based on experimentation.

    Daltons Atomic Theory:

    1. Elements are composed of extremely small particles called

    atoms. All atoms of the same element are alike, and atomsof different elements are different.

    2. The separation of atoms and the union of atoms occur in

    chemical reactions. In these reactions, no atom is created or

    destroyed, and no atoms of one element are converted intoan atom of another element.

    3. A chemical compound is the result of the combination of

    atoms of two or more elements. A given compound always

    contains the same kinds of atoms combined in the same

    proportions.

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    Atomic Models (Cont.)

    Daltons Billiard Ball Model:

    Atoms are solids and indivisible.

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    Atomic Models (Cont.)

    J. J. Thomson (1900)

    He discovered electron and proposed a model of theatom called Plum Pudding Model.

    Atoms were made

    from a positively

    charged substancewith negatively

    charged electrons

    scattered about.

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    Atomic Models (Cont.)

    Ernest Rutherford (1910)

    He proposed that atoms are mostly empty space andnegative electrons orbit a positive nucleus using the

    Gold Foil Experiment.

    The Gold Foil Experiment.

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    Atomic Models (Cont.)

    Rutherfords Model:

    A nucleus exists in

    the center of the

    atom.The nucleus contains

    protons and neutrons

    which together

    account for the mass.Electrons, which occupy most of the total volume

    of the atom, are outside the nucleus and move

    rapidly around it.

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    Atomic Models (Cont.)

    Neils Bohr (1913)

    He proposed an improved atomic model.

    The Bohrs Model.

    Electrons move in

    definite orbits aroundthe nucleus.

    These orbits, or

    energy levels are

    located at certaindistances from the

    nucleus.

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    Atomic Models (Cont.)

    Nuclear Bohr Model of Hydrogen Atom:

    Electrons normally

    exist in the lower

    energy state (ground

    state).

    When an electron

    jumps into higherenergy state it is

    said to be in an

    exited state.

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    Atomic Models (Cont.)

    Werner Heisenberg (1925)

    Theorized that it is impossible to know

    simultaneously both the velocity and position of a

    particles (Heisenberg Uncertainty Principle).

    The probable location of an electron is based on

    how much energy the electron has.

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    Atomic Models (Cont.)

    Electron Cloud Model:

    Electron cloud is a

    space in which electron

    are likely to be found.Electrons whirl about

    the nucleus billion of

    times in 1 second.

    They are not movingaround in random

    pattern.

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    Quantum Mechanics

    Electromagnetic Radiation

    Light travels through space in a wave motion.

    THE WAVE NATURE OF LIGHT

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    Quantum Mechanics (Cont.)

    Defini t ions

    Wavelength ()the distance between two

    similar points on two successive waves. It

    should be expressed in meters. (1nm = 10-9 m).

    Am pli tud e (a)height of a crest or depth of

    a trough.

    Intensity (br ightness) of Radiat ion

    is proportional to the square of amplitude (a2).

    Speed o f l igh t (c)

    equivalent to 2.998 x 108

    m/sec.

    c =

    Frequency ()is the

    number of waves that pass a

    given spot in a second, this is

    the reciprocal of second (1/s =hertz).

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    Colors of Visible Spectrum:

    Color Wavelength, nm

    Violet 400450

    Blue 450500

    Green 500570Yellow 570590

    Orange 590620

    Red 620750

    Quantum Mechanics (Cont.)

    Sample Problem:

    What is the frequency of red light with a wavelength of

    700nm and violet light with a wavelength of 400nm?

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    Quantum Mechanics (Cont.)

    Heinrich Hertz

    Generated electromagnetic waves with long wavelengthslarger than those of visible light and who demonstrated that

    long wavelength radiation exhibits the same phenomena as

    light does.

    Electromagnetic

    Radiation

    (Spectra).

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    Max Plank

    Proposed the quantum theory of radiant energy.

    Suggested that radiant energy could be absorbed orgiven off only in definite quantities called quanta.

    E = hv = hc /

    hPlanks constant (6.626 x 10-34J-s)

    THE PARTICLE NATURE OF LIGHT

    Quantum Mechanics (Cont.)

    Albert Einstein

    Proposed that Planks quanta were discontinuous bits of

    energy called photons.

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    Quantum Mechanics (Cont.)

    Sample Problem:

    Consider a violet light with a wavelength of 400nm.

    (a) Calculate the energy, in joules, of one photon

    of this light.

    (b) Calculate the energy in kilojoules of one moleof such photons.

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    Isaac Newton

    Showed that visible (white light) from the sun can bebroken down into its various component by a prism.

    ATOMIC SPECTRA

    Quantum Mechanics (Cont.)

    Defini t ions

    Continuous Spectrumspreading out

    into a wide range band of the white light.

    Emission SpectrumWhen an elementabsorbs sufficient energy (from a flame or

    electric arc), it emits radiant energy in the

    form of light. When this radiation is passed

    through a prism, it separates into a

    component wave length.

    Absorption Spectrumwhen

    continuous radiation (white light)

    passes through a substance, certain

    wavelengths of radiation may beabsorbed. These wavelengths are

    characteristics of a substance that

    absorbs the radiation and pattern of

    these lines are referred to as an

    absorption spectrum.

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    Quantum Mechanics (Cont.)

    Every element has its own unique line spectrum,

    therefore these spectra are characteristics of an

    atoms electronic structure .

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    Quantum Mechanics (Cont.)

    Bohrs Theory:

    1. The electron of the hydrogen atom can exist only in certaincircular orbits (energy levels or shell).

    2. The electron has a definite energy characteristic of the orbit

    in which it is moving.

    3. When an electron of an atom is as close to the nucleus, it isin the condition of the lowest energy called the ground state.

    When an atoms are heated in an electric arc or Bunsen

    burner, electron absorbs energy and jump to outer levels,

    which are higher energy states (excited state).

    4. When an electron falls back to a lower level, it emits a

    definite amount of energy. The energy difference between

    the high-energy state and low-energy state is emitted in the

    form of a quantum of light.

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    Quantum Mechanics (Cont.)

    E = -RH / n2

    Where: Eenergy of the electron

    RHRydberg Constant (2.180 x 10-18J)

    nenergy level

    E = h = EhiElohv = -RH[(1/nhi

    2)(1/nlo2)]

    v = [RH/h] [(1/nlo2)(1/nhi

    2)]

    Sample Problem:What are the frequency and wavelength of the line

    in the hydrogen spectrum that corresponds to an

    electron transition from n=3 level to n=2 level?

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    Quantum Mechanics (Cont.)

    The Relat ion ship

    between Electro n

    Transi t ion s of a

    Hydrogen Atom

    and th e Spectral

    Lines.

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    The Relationship between Electron Transitions of a

    Hydrogen Atom and the Spectral Lines:

    Quantum Mechanics (Cont.)

    Since electron transitions to n=1 level (Lyman series) releasemore energy than those to the n=2 level (Balmer series), the

    wavelength s of the lines in Lyman series are shorter thanthose of the Balmer series.

    Balmer series occur in visible region.

    The lines in the Lyman series occur in the ultraviolet region.

    The lines of the Paschen series (n=3) occur at wavelengthslonger than Balmer series. It appears in the infrared region.

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    Louis De Broglie

    He reasoned that if light could show the behavior ofparticles (photons) as well as waves, then perhaps an

    electron, which Bohr had treated as particle, could behavelike a wave. (Dualistic Nature of Light).

    QUANTUM MECHANICAL MODEL

    Quantum Mechanics (Cont.)

    Erwin Schrdinger

    Formulated wave equation that relates the energy of theelectron to its position in the atom.

    Solutions of these equations give rise to quantum

    numbers.

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    QUANTUM NUMBERS set of numbers that describes an

    electron orbital

    Quantum Mechanics (Cont.)

    1. First Quantum Number (Principal)(n)indicates the

    main energy level by the electron. It defines the total energy

    of the electrons and has values from (1 to 7).

    2.Second Quantum Number (Azimuthal)(l)it describes

    the way the electron moves around the nucleus or the shape

    of the probability distribution. The values range from 0 to (n-1).

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    Quantum Mechanics (Cont.)

    n l Spectral Lines

    1 0 stype (sharp)

    2 0

    1

    s

    ptype (principal)

    3 0

    1

    2

    s

    p

    dtype (diffuse)

    4 01

    2

    3

    sp

    d

    f type (fundamental)

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    Quantum Mechanics (Cont.)

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    Quantum Mechanics (Cont.)

    3.Third Quantum Number (Magnetic)(ml)it defines the

    possible orientation of the electrons in space. The values are

    froml through 0 to +l.

    4.Fourth Quantum Number (Spin)(ms)it takes intoaccount the spinning of the electron around its own axis as it

    moves about the nucleus. The spin is either clockwise or

    counterclockwise. The values are +1/2 (clockwise) and -1/2

    (counterclockwise).

    l ml

    Number of orbitals (2l + 1)

    0 0 1

    1 -1, 0, +1 3

    2 -2, -1, 0, +1, +2 5

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    Hunds Rule

    When filling a set of degenerate energy levels, the

    electron enter the orbitals singly, with spins in the same

    direction (same as s number), until the set is half filled,before they pair up with opposite spins.

    Quantum Mechanics (Cont.)

    Concepts:

    Paulis Exclusion Principle

    Each electron within a given atom must have a

    unique set of the four quantum numbers.

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    Quantum Mechanics (Cont.)

    Aufbaus Principle

    Electrons will

    successively occupy

    the available orbitalson order of

    increasing energy.

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    Quantum Mechanics (Cont.)

    Example:

    Write the

    possible set of

    quantum

    numbers for theelectrons in:

    (a) 3s

    (b) 3d

    (c) 4f

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    Quantum Mechanics (Cont.)

    Atomic Orbital Shapes:

    sand pOrbitals

    dOrbitals

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    Electronic Configuration

    Electronic Configuration

    Refers to the arrangement of electrons in energy

    levels.

    Methods of Writing

    1.Orbital method

    2.Shell method3.Arrow Rectangular method

    4.Core Method

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    Electronic Configuration (Cont.)

    Example (neutral atom):

    Write the electronic configuration using the fourmethods of the following elements:

    (a) Br

    (b) Ca

    Example (monoatomic ions):

    Give the electronic configuration of:

    (a) V4+

    (b) Cl

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    Magnetism

    Paramagneticsubstances that contain net

    unpaired electrons and are attracted by a magnet.

    Ex. Li

    Diamagneticsubstances that do not contain net

    unpaired electrons and are slightly repelled by amagnet.

    Ex. Mg

    Quantum Mechanics (Cont.)

    Related Concepts:

    P i di R l ti f El t

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    Periodic Relations of Elements

    Periodic Classifications of Elements

    Elements may be classified according to their

    electronic configurations.

    1.The Noble GasesThey are also known as Inert Gases or

    Group O elements. They are colorless monoatomic gases,

    which are chemically unreactive and diamagnetic. They have

    outer configurations of ns2np6(except for Helium).

    2.The Representative ElementsThese elements are foundin the A families of the periodic table. They exhibit a wide

    range of chemical behavior and physical characteristics. The

    chemistry of these elements depends upon the valence

    electrons.

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    3.The Transition ElementsThey are found in the B families

    of the periodic table. All of these elements are metals andmost of them are paramagnetic and form highly colored,

    paramagnetic compounds.

    4.The Inner-Transition ElementsThese elements are foundat the bottom of the periodic table, but they belong to the 6th

    and 7thperiods after the elements of group IIIB. All inner-

    transition elements are metal and are paramagnetic. Their

    compounds are also paramagnetic and colored.

    Periodic Relations of Elements (Cont.)

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    Periodic Variation in Physical Properties

    1.Atomic Radiusone-half the distance between the nuclei of

    the two atoms in an elemental substance.

    Periodic Relations of Elements (Cont.)

    TREND:

    LEFT RIGHT decreases

    TOP BOTTOM increases

    f (C )

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    2.Ionic Radiusone-half the distance between the nuclei of a

    metal and a non-metal.

    Periodic Relations of Elements (Cont.)

    TREND:

    LEFT RIGHT decreases*

    TOP BOTTOM increases

    positive ions are smaller thanthe metal atoms from which they

    are formednegative ions are larger than

    the nonmetal atoms from which

    they are formed

    *this happens when comparing both

    metals and non-metals but by

    comparing the metals and non-metals, nonmetalshave larger ionic radius than metals.

    P i di R l ti f El t (C t )

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    3.Ionization Energythe minimum energy required to remove

    an electron from a gaseous atom in its ground state.

    Periodic Relations of Elements (Cont.)

    TREND:LEFT RIGHT increases

    TOP BOTTOM decreases

    4.Electron Affinitymeasure of the energy change when

    electron is added to a neutral atom to form a negative ion.

    TREND:LEFT RIGHT increases

    TOP BOTTOM decreases

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    END of Lecture No. 1