!Electrons in Atoms

Chapter 13.1 and 13.2

Atomic Models

• !Atomic models help explain the nature of elements—part of atomic theory– We can not see atoms,

so how do we know they exist?

!Scanning Tunneling Microscope

• !Can “see” atoms! Can even be used to rearrange individual atoms!

!Thompson’s Plum Pudding Model

• Thompson imagined a positively charged ball of “pudding” with electrons (which he discovered) as the “plums” inside

Niels Bohr’s Model• 1913: !Bohr imagined electrons follow

circular orbits around the nucleus, like a solar system

Energy Levels

• !The energy level of an electron is the region around the nucleus where the electron is moving

!Energy Levels are Fixed

• !Energy levels are like rungs on a ladder– !Electrons exist on rungs– !Electrons can jump

between rungs– !Electrons can’t exist

between rungs

It takes energy to jump between energy levels

• !Quantum: The amount of energy required to move from one energy level to another– Part of the Quantum Theory

Neils Bohr

• "If quantum mechanics hasn't profoundly shocked you, you haven't understood it yet."

Light and Atomic Spectra

• !Spectrum: a series of energies (like light) arranged according to wavelength, or frequency

!Atomic Emission Spectrum

• !Every element (vapor) emits light when it is excited by the passage of electric discharge.

Atomic Emission Spectrum

• !Passing this light through a prism creates a spectrum, different for every element.– !Each line

represents one exact amount of energy

More on Quantum Theory:• Subatomic particles don’t

follow the rules of classical physics– Gravity doesn’t apply!– Time doesn’t apply!– Can move without

occupying space!– Superposition—can’t

locate position!– Order of operations don’t

always apply!

Neils Bohr

• "If quantum mechanics hasn't profoundly shocked you, you haven't understood it yet."

The Quantum Mechanical Model

• Erwin Schrodinger, in 1926, used quantum theories to solve a mathematical equation concerning the location and energy of an electron.

• (But not both at once)

!Electron Orbitals—Quantum Theory

• !The area where an electron is likely to be found. (90% chance)

• !An orbital can contain two electrons.

Energy levels and

orbitals•!Types of orbitals

!s orbital = sphere shaped (1 type)

!p orbitals = dumbell shaped (3 types)

!d orbitals = clover shaped (5 types)

Electron Configurations

• High energy = unstable, higher energy levels, further away from nucleus

• Low energy = stable

• Three major rules tell you how to find where electrons will be:

!Rule 1: Aufbau Principle• !Electrons enter orbitals of

lowest energy first.

!Rule 2: Pauli Exclusion Principle

• !An atomic orbital is one or two electrons– To be in the same orbital, two electrons must be

“opposite”

!Rule 3: Hund’s Rule

• !Electrons in the same energy level must enter each orbital until all the orbitals contain one electron with parallel spins.

!Electron Cloud

• !All the electrons in all the orbitals.