CHEM 111 UNIT 02 - Atomic Structure & Periodicity

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Transcript of CHEM 111 UNIT 02 - Atomic Structure & Periodicity

ATOMIC STRUCTURE AND PERIODICITY

ATOMIC STRUCTURE AND PERIODICITYUNIT 2ELECTROMAGNETIC RADIATIONUNIT 2Electromagnetic Radiationa method of transfer of energy through spaceExamplesVisible LightMicrowaveX-rayLight as a waveCharacteristicsWavelength ()Distance between two adjacent peaksFrequency ()The number of complete wavelengths, or cycles, that pass a given point each second

Light as a wavec speed (m/s)c = 3.00 108 m/s for EMR wavelength (m)f frequency (Hz)

Electromagnetic RadiatonExample. Frequency of Electromagnetic RadiationAn FM radio station broadcasts at 99.5 MHz. Calculate the wavelength of the corresponding radio waves.Electromagnetic Spectrum

THE NATURE OF MATTERUNIT 2Light as a particleMax PlanckDiscovered that EMR energy can be released/absorbed only in discrete chunksQuantumThe smallest quantity of energy that can be emitted/abosrbed.

Light as a particlen integerh Plancks constant frequency of the lightPhotoelectric EffectHigh frequency (high energy) lights can cause metals to emit electrons.

But low frequency (low energy) lights cannot.

Photoelectric EffectImplicationLight can behave as a particle. EMR is a stream of tiny energy particlesPhotonparticle of energyquantum of light

Dual Nature of LightLight can behave both as a wave and a particle.Dual Nature of LightExample. The Energy of a PhotonMicrowave radiation has a wavelength of 1.0 cm. Calculate the frequency and the energy of the single photon of this radiation.Dual Nature of LightExample. WavelengthCuCl, when burned, emits 4.41 10-19 J per photon. What is the wavelength and the color of the resulting radiation?Dual Nature of LightExample. Number of photonsCalculate the number of photons.THE ATOMIC SPECTRUM OF HYDROGENUNIT 2The Atomic Spectrum of HydrogenContinuous Spectrumrainbow of colors

Line SpectrumA spectrum containing radiation of specific wavelengths

THE BOHR MODELUNIT 2Electrons in hydrogen atom move around the nucleus in certain allowed circular orbitsElectrons have fixed energy called energy levelsThe Bohr Model

The Bohr ModelEnergy levels available to the electron in Hydrogen atom

Z nuclear charge (+1 for Hydrogen)n level of the orbit radiusIf n = 1, it is at ground stateIf n > 1, it is at an excited state

The Bohr ModelExample. Electron QuantizationCalculate the energy required to excite the hydrogen electron from n = 1 to n = 2. Calculate the wavelength of the light that must be absorbed by a hydrogen atom in its ground state to reach its excited state.Atomic Structure

THE QUANTUM MECHANICAL MODEL OF ATOMUNIT 2Quantum Mechanical Model of an AtomDe Broigles Matter-waveElectron bound to an atom behave both as a particle and a wave.

Quantum Mechanical Model of an AtomHeisenberg Uncertainty PrincipleIt is impossible for us to know simultaneously the exact momentum and the exact position of a particle in space.The more precisely the position of the particle is measured or determined, the less precisely its momentum can be known, and vice versa.

Quantum Mechanical Model of an AtomSchrodingers Equation

wave function (orbital)2 probability distribution of the electron

Quantum Mechanical Model of an AtomSo how are the electrons moving around a nucleus?We dont exactly know.We can only determine the probability of finding the electron at an area.QUANTUM NUMBERSUNIT 2Quantum Numbers orbital that satisfies the Schrodingers Equation2 probability distribution

Quantum NumbersNumbers that characterizes the orbitals

Quantum NumbersPrincipal Quantum Number (n)can have positive integers Azimuthal Quantum Number (l)can have integral values from 0 to (n-1)Magnetic Quantum Number (ml)can have integral values from l to l

Quantum NumbersPrincipal Quantum Number (n)

Relates the sizeand energy of theorbitalAs n increasesthe orbital gets largerthe electron spends more time farther than the nucleusThe energy increases

Quantum NumbersAzimuthal Quantum Number (l)related to the shape of the orbital

Quantum NumbersMagnetic Quantum Number (ml)related to the orientation of the orbital in spaceQuantum Numberss-orbital

Quantum Numbersp-orbital

Quantum Numbersd-orbital

Quantum Numbersf-orbital

Quantum Number

ELECTRON SPINUNIT 2Electron Spin Number4th quantum number (ms)Related to the magnetic properties of the atomCan be (up spin) or - (down spin)

Paulis Exclusion PrincipleNo two electrons can have the same set of quantum numbers (n, l, ml, ms)

Each orbital can have a maximum of two electrons, one up-spin, and another down spinQuantum NumbersExample. Quantum NumbersDetermine which of the following sets of quantum number are not allowed?n = 3, l = 2, ml = 2, ms = n = 4, l = 3, ml = 4, ms = n = 0, l = 0, ml = 0, ms = -n = 2, l = -1, ml = 1, ms = -Quantum NumbersExample Quantum NumbersGive the maximum number of electrons in an atom for the following quantum numbers.n = 4n = 5, ml = 1n = 5, ms = n = 3, l = 2ELECTRON CONFIGURATIONUNIT 2Electron Configurationdescribes how electrons are distributed among the various orbitals of an atom

Aufbaus PrincipleThe orbitals are filled in order of increasing energy

Electron Configuration1s 2Energy Level (Principal Quantum #)Sub Level(s, p, d, f )# of e- in sub levelElectron ConfigurationOrbitals that have lower n have lower energy

Orbitals that have lower l have lower energy s < p < d < f

Electron Configuration

Electron ConfigurationElementOrbital DiagramElectron ConfigurationLi(3 e-)B(5 e-)2s2px2py2pz1s2s2px2py2pz1s1s2 2s11s2 2s2 2p1Electron ConfigurationHunds Rulefor degenerate orbitals (orbitals having the same energy), the lowest energy is attained when the number of electrons having the same spin is maximizedElectron ConfigurationElementOrbital DiagramElectron ConfigurationC(6 e-)1s2 2s22p22O(8 e-)1s2 2s2 2p52s2px2py2pz1s2s2px2py2pz1sElectron Configuration

Electron ConfigurationCondensed Electron ConfigurationMg 1s2 2s2 2p6 3s2

Mg [Ne] 3s2

Elements in the same group (vertical column) have the same valence electron configurationscore e-valence e-Electron ConfigurationElementCondensed Electron ConfigurationO(8 e-)[He] 2s2 2p4Si(14 e-)[Ne] 3s2 3p2K(19 e-)[Ar] 4s1Electron ConfigurationTransitional Metals

ElementCondensed Electron ConfigurationV[Ar] 4s2 3d3Hg[Xe] 6s2 4f10 5d10Electron ConfigurationExample. Electron ConfigurationGive the expanded and the condensed electron configuration and draw the condensed orbital diagram for the following elements.SulfurCadmiumHafmiumPERIODIC TABLEUNIT 2Periodic Table of Elements

PERIODIC TRENDSUNIT 2Atomic Radius

Atomic RadiusLeft to Rightas p+ and e- increases, the attraction of the nucleus and valence e- increasesUp to Downas n increases, energy level increases, its distance from nucleus increases

Ionic Radius

Ionization EnergyMinimum energy required to remove an electron from the ground state of the isolated gaseous atoms

X(g) X+(g) + e-

The higher the IE, the harder it is to remove an electronIonization Energy

Electron AffinityEnergy associated with the addition of an electron to an atom in gaseous state

X(g) + e- X-(g)

Measures the ease of an atom to accept an electronElectron Affinity

ElectronegativityMeasure of a tendency of atom to attract a bonding pairElectronegativity