Electrons and Energy

Red Book: 5.1-5.2Blue Book:13.1-13.2

Rutherford’s Failure

Rutherford’s model could not describe behavior of atoms

Think About It: Why do

certain atoms react while others don’t? Why

do some fireworks

glow red and others green?

Bohr’s Atom

Hypothesis: each electron exists in a certain “orbit” or “energy level”

Electrons can never exist in between

Higher energy levels are further from the nucleus

Quanta

A quantum (pl. quanta) is the amount of energy required for an electron to move up an energy level

Quantum Mechanical Model

Also called “electron cloud model”

Mathematically-based

Quantum Mechanical Model

Determines allowed electron energies and how likely it is to find an electron in various locations around the nucleus

Dense cloud = high probability

Atomic Orbitals

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

Why It’s Important:

The exact location of each electron

controls the atom’s properties!

“Address” of Electron

Each electron will be foundOn a PRINCIPAL ENERGY LEVEL In one of several SUBLEVELSOn an ORBITAL

Principal Quantum Numbers

Each principal energy level is assigned a principal quantum energy number, n

n can be 1, 2, 3, or 4, etc…

Sublevels

Each principal energy level has specific sublevels where an electron can be found

# of sublevels corresponds to principal quantum number Level 1 has 1 sublevel Level 2 has 2 sublevels…

Sublevels

Sublevels are given letter designations (according to shape)

spdf

Why s, p,d, and f?

The orbital names (s, p, d, f, g, h,...) are derived from the characteristics of their spectroscopic lines: sharp, principal, diffuse and fundamental, the rest being named in alphabetical order. For mnemonic reasons, some call them spherical & peripheral.

Atomic Orbitals

s sublevel – 1 orbitalsp sublevel – 3d sublevel – 5f sublevel – 7

Atomic Orbitals

Each orbital can hold one pair of electrons

Each member of the pair has an opposite spin

How many total How many total electrons in each?electrons in each?

1st Principal Energy Level

• 1 sublevel (s)

• 2 electrons in s orbital

• 2 total

2nd Principal Energy Level

• 2 sublevels (s and p)

• 2 electrons in s orbital• 6 electrons in p orbitals

• 8 total (10 combined with 1st)

3rd Principal Energy Level

• 3 sublevels (s, p and d)

• 2 electrons in s orbital• 6 electrons in p orbitals• 10 electrons in d orbitals

• 18 total (28 combined with 1st and 2nd)

4th Principal Energy Level

• 4 sublevels (s, p, d and f)

• 2 electrons in s orbital• 6 electrons in p orbitals• 10 electrons in d orbitals• 14 electrons in f orbitals

• 32 total (60 combined with 1st, 2nd, and 3rd)

Electron Arrangement

Blue Book: 13.2Red Book: 5.2

Electron Configuration

Way that electrons are arranged in various orbitals

Arrangement governed by three rules

Aufbau Principle

Electrons first occupy sublevels/orbitals of lowest energy

Sublevels from some principal energy levels overlap others

Aufbau Diagrams

Display the order in which sublevels/orbitals are filled (to achieve the most stable configuration)

Aufbau Principle

Pauli Exclusion Principle

Each orbital holds, at most, two electrons.

Two occupy the same orbital, two electrons must have opposite spins.

This is written or

Hund’s Rule

In each sublevel, one electron enters each orbital until each has one with the same spin direction

Not until all orbitals have one electron can any have two

Orbital Filling Diagrams

Show which orbitals are filled by electrons

Writing Electron Configurations

Electron Configurations

Sublevels are filled in the following order:

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s

Electron Configurations

Contain 3 items:Number represents energy levelLetter represents sublevelSuperscript represents number of electrons

1s2

Electron Configurations

Additional segments needed for each sublevel

1s2 2s2

Electron Configurations

1s2 2s2 2p6

Electron Configurationsof Specific Elements

In a neutral element, the number of electrons is equal to the number of protons.

Electron Configurations

Hydrogen

Oxygen

Neon

Silicon

Calcium

Superscripts add up to the total number of

electrons!