CHEM 111 UNIT 02 - Atomic Structure & Periodicity

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ATOMIC STRUCTURE AND PERIODICITY UNIT 2

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Transcript of CHEM 111 UNIT 02 - Atomic Structure & Periodicity

Page 1: CHEM 111 UNIT 02 - Atomic Structure & Periodicity

ATOMIC STRUCTURE AND PERIODICITYUNIT 2

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Atomic Structure

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THE QUANTUM MECHANICAL MODEL OF ATOMUNIT 2

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Quantum Mechanical Model of an Atom

De Broigle’s Matter-waveElectron bound to an atom

behave both as a particle and a wave.

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Quantum Mechanical Model of an Atom

Heisenberg Uncertainty Principle It 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.

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Quantum Mechanical Model of an Atom

Schrodinger’s Equation

Ψ – wave function (orbital) Ψ2 – probability distribution

of the electron

𝑯𝝋=𝑬𝝋

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Quantum Mechanical Model of an Atom

So how are the electrons moving around a nucleus?

We don’t exactly know.We can only determine the

probability of finding the electron at an area.

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QUANTUM NUMBERSUNIT 2

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Quantum Numbers

Ψ – orbital that satisfies the Schrodinger’s Equation

Ψ2 – probability distribution

Quantum NumbersNumbers that characterizes the orbitals

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Quantum Numbers

Principal 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

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Quantum Numbers

Principal Quantum Number (n)

Relates the sizeand energy of theorbitalAs n increases

the orbital gets larger the electron spends more time farther than the

nucleus The energy increases

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Quantum Numbers

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

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Quantum Numbers

Magnetic Quantum Number (ml) related to the orientation of the orbital in

space

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Quantum Numbers

s-orbital

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Quantum Numbers

p-orbital

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Quantum Numbers

d-orbital

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Quantum Numbers

f-orbital

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Quantum Number

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ELECTRON SPINUNIT 2

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Electron Spin Number

4th quantum number (ms)

Related to the magnetic properties of the atom

Can be ½ (up spin) or - ½ (down spin)

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Pauli’s Exclusion Principle

No 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 spin

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Quantum Numbers

Example. Quantum NumbersDetermine which of the following sets of quantum number are not allowed?n = 3, l = 2, ml = 2, ms = ½

n = 4, l = 3, ml = 4, ms = ½

n = 0, l = 0, ml = 0, ms = -½n = 2, l = -1, ml = 1, ms = -½

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Quantum Numbers

Example Quantum NumbersGive the maximum number of electrons in an atom for the following quantum numbers.n = 4n = 5, ml = 1

n = 5, ms = ½n = 3, l = 2

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ELECTRON CONFIGURATIONUNIT 2

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Electron Configuration

describes how electrons are distributed among the various orbitals of an atom

Aufbau’s PrincipleThe orbitals are filled in order of increasing

energy

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Electron Configuration

1s 2Energy Level (Principal Quantum #) Sub Level

(s, p, d, f )

# of e- in sub level

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Electron Configuration

Orbitals that have lower n have lower energy

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

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Electron Configuration

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Electron Configuration

Element Orbital Diagram Electron Configuration

Li(3 e-)

B(5 e-)

2s 2px

2py 2pz

1s

2s 2px

2py 2pz

1s

1s2 2s1

1s2 2s2

2p1

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Electron Configuration

Hund’s Rule for degenerate orbitals (orbitals having the

same energy), the lowest energy is attained when the number of electrons having the same spin is maximized

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Electron Configuration

Element Orbital Diagram Electron Configuration

C(6 e-) 1s2 2s22p2

2O(8 e-) 1s2 2s2 2p5

2s 2px

2py 2pz

1s

2s 2px

2py 2pz

1s

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Electron Configuration

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Electron Configuration

Condensed Electron ConfigurationMg – 1s2 2s2 2p6 3s2

Mg – [Ne] 3s2

Elements in the same group (vertical column) have the same valence electron configurations

core e-

valence e-

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Electron Configuration

Element Condensed Electron Configuration

O(8 e-) [He] 2s2 2p4

Si(14 e-) [Ne] 3s2 3p2

K(19 e-) [Ar] 4s1

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Electron Configuration

Transitional Metals

Element Condensed Electron Configuration

V [Ar] 4s2 3d3

Hg [Xe] 6s2 4f10 5d10

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Electron Configuration

Example. Electron ConfigurationGive the expanded and the condensed electron configuration and draw the condensed orbital diagram for the following elements.SulfurCadmiumHafmium

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PERIODIC TABLEUNIT 2

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Periodic Table of Elements

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PERIODIC TRENDSUNIT 2

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Atomic Radius

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Atomic Radius

Left to Rightas p+ and e-

increases, the attraction of the nucleus and valence e- increases

Up to Downas n increases, energy

level increases, its distance from nucleus increases

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Ionic Radius

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Ionization Energy

Minimum 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 electron

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Ionization Energy

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Electron Affinity

Energy 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 electron

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Electron Affinity

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Electronegativity

Measure of a tendency of atom to attract a bonding pair

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Electronegativity