Chapter 5

Section 5.1

Models of the Atom

Essential Questions:

1. What is the Bohr model of the atom?

2. How are electrons distributed in the atom?

The Bohr Model

• Neils Bohr

-electrons found only in specific circular path

–orbits around the nucleus.

• Each electron orbit has fixed energy

–called energy level

Hydrogen

Elements are the new building blocks

Hydrogen

Oxygen-8

Carbon-6

Energy Levels

• Fixed energy levels of electrons are similar to rungs of a ladder.

• The lowest possible energy level is called its ground state.

• Just like a person an electron can climb from one rung (energy level) to another.

• Electrons can NOT be found in between rungs (energy levels).

• To move from one level to another an electrons must gain or lose energy.

Quantum

• Amount of energy required to move an electron from one energy level to another.

• The amount of energy an electron gains or loses in an atom is not always the same.

• Less energy is required to move between higher energy levels because they are closer together.

Quantum Mechanical Model

• No exact electron path

• Determines energies of an electrons

•

• Electron location is based on how likely it can be found at a particular location.

Atomic Orbitals

• Region of space in which there is a high probability of finding an electron

• Energy levels are labeled by numbers, n= 1, 2, 3, 4, 5, 6 or 7

• Each energy level has orbitals

• Orbitals are labeled by letters and different letters have different shapes

• (S, P, D, F)

Summary of Principal Energy Levels, Sublevels, and Orbitals

Principal energy level Number of

sublevels

Type of sublevel

n = 1 1 1 s (1 orbital)

n = 2 2 2 s (1 orbital), 2p (3 orbtials)

n = 3 3 3s (1 orbital), 3p (3 orbtials), 3d

(5 orbitals)

n = 4 4 4s (1 orbital), 4p (3 orbtials), 4d

(5 orbitals), 4f (7 orbitals)

Maximum number of electrons

n = 1 : 2 electrons

n = 2 : 8 electrons

n = 3 : 18 electrons

n = 4 : 32 electrons

Chapter 5.2 Electron Arrangement in atoms

Electron Configuration

• Arrangement of electrons in orbitals around the nucleus of an atom

• 3 rules

–Aufbau principle

–Pauli exclusion principle

–Hund’s rule

Aufbau Principle

• Electrons enter the lowest energy level first.

Pauli Exclusion Principle

• An orbital can hold at most 2 electrons, if 2 electrons are present they must have opposite spins

• An up or down arrow indicates the electron’s spin ↑ or ↓,

• An orbital with paired electrons is written as

↑↓

Hund’s Rule • One electron goes into each orbital of one type

until they all have 1 e-, then the e- can start to double up.

Orbital filling

Electron

Element 1s 2s 2px 2py 2pz 3s Configuration

H □ □ □ □ □ □

□ □ □ □ □ □

□ □ □ □ □ □

□ □ □ □ □ □

□ □ □ □ □ □

□ □ □ □ □ □

Orbital filling

Electron

Element 1s 2s 2px 2py 2pz 3s Configuration

H □ □ □ □ □ □

□ □ □ □ □ □

□ □ □ □ □ □

□ □ □ □ □ □

□ □ □ □ □ □

□ □ □ □ □ □

Electron Configuration

Exceptional Electron Configuration

• There are always exceptions to the rules

• Cr : 1s2 2s2 2p6 3s2 3p6 3d5 4s1

• Cu :1s2 2s2 2p6 3s2 3p6 3d10 4s1

• Exceptions due to subtle electron interactions in orbitals with similar energies

Chapter 5.3 Physics & the Quantum Mechanical Model

Light • The study of light led to the quantum mechanical model

• Newton: light consists of particles

• Huygens: light travels in waves

C = λ ν

Wavelength

Speed of light = 3.00 x 108 m/s

frequency

***Wavelength and frequency of light are

inversely proportional

Electromagnetic Spectrum

What color in the visible spectrum has the longest wavelength?

Red

Which color

in the visible

spectrum

has the

highest

energy?

Violet

Calculations Calculate the wavelength of the yellow light emitted

by a sodium lamp if the frequency of the radiation is 5.10 x 1014 Hz (5.10 x 1014 /s) and the speed of light is 3.00 x 108 m/s.

c = λ v 3.00 x 108 m/s = λ • 5.10 x 1014 /s

λ = 3.00 x 108 m/s

5.10 x 1014 /S

λ = 5.88 x 10-7 m

Atomic Spectra

• Electrons climb the energy ladder when they absorb energy. To fall back down the ladder, they give off light energy.

• Each discrete line in an emission spectrum correspond to 1 exact frequency of light emitted by the atom.

Atomic emission spectrum =

fingerprint

An explanation of atomic spectra

The light emitted by an

electron moving from a

higher to a lower energy

level has a frequency

directly proportional to

the energy change of the

electron.

n = 1

n =2

h •ν

h •ν

E = h ν

Energy

Planck’s constant

frequency

Quantum Mechanics

The motions of subatomic particles and atoms as waves

Photoelectric effect:

• Einstein used Newton idea’s said light could be described as quanta of energy that behave as particles

• Light quanta = photons