electron arrangement in an atom

8/12/2019 Electron Arrangement in an Atom

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Electron Arrangement in an Atom

ENGR. YVONNE LIGAYA F. MUSICO


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Characteristics of Electrons

Extremely small mass

Located outside the nucleus

Moving at extremely high speeds in a

sphere

Have specific energy levels


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Energy of Electrons

When atoms are heated, bright lines

appear called line spectra

Electrons in atoms arranged in discrete

levels.

An electron absorbs energy to jump to a

higher energy level.When an electron falls to a lower energy

level, energy is emitted.


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Loss and Gain of Energy

G

a

I

n

L

o

s

s


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Bohr Model

First model of the electron structure

Gives levels where an electron is most

likely to be foundIncorrect today, but a key in

understanding the atom


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Quantum Mechanics

Describes the arrangement and space

occupied by electrons in atoms


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Quantum Mechanics

Describes the arrangement of electrons

in atoms in terms of:

Main or principal energy levels (n)

Energy subshells

Orbitals (space occupied within the

atom)


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Quantum Mechanical Atom

Electrons in atoms have quantized energies

Electrons in atoms are bound to the nucleus

by electrostatic attractionElectron waves are standing matter waves

standing matter waves have quantized

energies, as with the "electron on a wire"model


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Electron standing matter waves are 3 dimensional

The electron on a wire model was one

dimensional; one quantum number wasrequired to describe the state of the electron

A 3D model requires three quantum numbers

A three-dimensional standing matter wave

that describes the state of an electron in anatom is called an atomic orbital


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The energies and mathematical forms of the orbitals can becomputed using the Schrdinger equation

quantization isn't assumed; it arises naturally in

solution of the equationevery electron adds 3 variables (x, y, z) to the

equation; it's very hard to solve equations with lots ofvariables.

energy-level separations computed with theSchrdinger equation agree very closely with thosecomputed from atomic spectral lines


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Quantum numbers

Specify the address of each electron in anatom

UPPER LEVEL


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Quantum Numbers

The principal quantum number, n

determines the size of an orbital (bigger n =

bigger orbitals)

largely determines the energy of the orbital

(bigger n = higher energy)

can take on integer values n = 1, 2, 3, ...,

all electrons in an atom with the same valueof n are said to belong to the same shell


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Quantum Numbers

The principal quantum number, n spectroscopists use the following names for shells

n Shell Name

1 K

2 L

3 M

4 N

5 O

6 P

7 Q


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Number of Electrons

Maximum number of electrons in any

electron level = 2n2

n =1 2(1)2 = 2

n =2 2(2)2 = 8

n =3 2(3)2 = 18


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Quantum Numbers

The principal quantum number, n


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Quantum Numbers

The azimuthal quantum number, designates the overall shape of the orbital within a

shell

affects orbital energies (bigger = higher energy)

all electrons in an atom with the same value of lare

said to belong to the same subshell

only integer values between 0 and n-1 are allowed

sometimes called the orbital angular momentumquantum number

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Quantum Numbers

The azimuthal quantum number, spectroscopists use the following names for subshells

Subshell name

0 s - sharp

1 p - principal

2 d - diffuse

3 f - fundamental


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Quantum Numbers

The magnetic quantum number, m

The number of possible m

values determines the number of

orbitals in a subshell.

possible values of m

Number of orbital

in this subshell0 0 1

1 -1, 0, +1 3

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

3 -3, -2, -1, 0, +1, +2, +3 7

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Quantum Numbers


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Quantum Numbers


px py pz

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Quantum Numbers

The magnetic quantum number, mOrbitals combine to form a spherical shape.

2s

2pz2py

2px

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Quantum Numbers

The spin quantum number, msseveral experimental observations can be

explained by treating the electron as though it

were spinning

spin makes the electron behave like a tiny magnetspin can be clockwise or counterclockwise

spin quantum number can have values of

+1/2 or -1/2

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Quantum Numbers

The spin quantum number, ms

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Electron Configuration

The statement of how many electrons an

atom has in each of its subshells.

a list showing how many electrons are ineach orbital or subshell in an atom or ion

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Pauli Exclusion Principle

Limits the number of electrons in any

orbital to not more than two

Each orbital can hold TWO electrons withopposite spins.

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Hunds Rule

Priciple of Maximum Multiplicity

Within a sublevel, place one e-per orbital beforepairing them.

Empty Bus Seat Rule

RIGHTWRONG

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Aufbau Principle

Electrons fill the

lowest energy

orbital first.

Lazy Tenant Rule

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Methods of Illustrating Electronic Configuration

s p d f Notation

the distribution of electrons using this

method indicates the energy level andsublevels that are filled.

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Energy sequence

1s 2s 3s 4s 5s 6s 7s2p 3p 4p 5p 6p 7p

3d 4d 5d 6d 7d

4f 5f 6f 7f

Note:

s 2p 6

d 10

f 14

A way to remember the filling order of subshells, write

subshells designations and follow the diagonal arrows starting

from left.

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s p d f Notation

1s2

main shell

subshell

number of electrons


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Orbital diagram

using arrows to represent electrons and

boxes for orbitals. (Pauli exclusionprinciple and Hunds Rule should be

followed)


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Orbital diagram

1. write the electron configuration in subshell

notation2. draw a box for each orbital.

Remember that s, p, d, and f subshellscontain 1, 3, 5, and 7 degenerate orbitals,

respectively.

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Orbital diagram

Remember that an orbital can hold 0, 1, or 2electrons only, and if there are two electrons

in the orbital, they must have opposite(paired) spins (Pauli principle )

3. within a subshell (depicted as a group ofboxes), spread the electrons out and line up

their spins as much as possible (Hund's rule )

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Orbital diagram

Example:

1.) 9F2.) 13Al

3.) 2He

4.) 12Mg

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Learning Check

Using the periodic table, write the complete

electronic configuration using electron

notation for each:A. Cl

B. Sr

C. I

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Solution

Using the periodic table, write the completeelectronic configuration using electronnotation for each:

A. Cl1s22s2 2p63s23p5

B. Sr

1s2

2s2

2p6

3s2

3p6

4s2

3d10

4p6

5s2

C. I

1s22s2 2p63s23p64s23d10 4p65s2 4d105p5

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Paramagnetic and Diamagnetic

Paramagnetic

- When there is unpaired electron

- configurations with unpaired electrons are attracted to

magnetic fields (paramagnetism )

Diamagnetic

- When all electrons are paired

- configurations with only paired electrons are weaklyrepelled by magnetic fields (diamagnetism )

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Some other important terms

Differentiating electron

- the last entering electron in the electron configuration

Valence Shell

- the outermost shell

Valence Electron

-all the electrons in the outermost shell or valence shell


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Psuedocore Electrons

electrons in d and f subshells outside the

noble gas core are called pseudocore

electrons

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Examples of electron configurations containing

pseudocore electrons

Atom Core Psuedocore Valence Full

Configuration

Fe Ar 3d6 4s2 [Ar] 3d64s2

Sn Kr 4d10 5s25p2 [Kr] 4d105s25p2

Hg Xe 4f145d10 6s2 [Xe] 4f145d106s2

Pu Rn 5f6 7s2 [Rn] 5f67s2


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End Here

Thanks for listening.

electron arrangement in an atom

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