Timberlake LecturePLUS 2000

Characteristics of Atoms

• Atoms are composed of protons, neutrons, and electrons.

• Protons and neutrons are located in the nucleus (center of the atom).

• Electrons are located outside of the nucleus.

Quantum Model

• We learned about:– Dalton’s atomic theory– J.J. Thompson’s plum pudding model of the atom– Rutherford’s model of the atom– Bohr model of the atom

• The model used today is called the quantum model

Orbitals are represented by a letter (s, p, d, f, …)

Timberlake LecturePLUS 2000

Describing Electrons

• There are two ways to express the number and location of electrons in an atom:– Orbital Diagrams– Electron Configurations

Timberlake LecturePLUS 2000

Orbital Diagrams

• Visual representation of how electrons are placed in orbitals.

• Electrons are represented by arrows.

• In an orbital diagram, electrons have opposite spins (designated by opposite arrow directions).

Timberlake LecturePLUS 2000

Blank Orbital Diagram

• Fill in the lowest energy orbitals first!

Incr

easi

ng e

nerg

y

1s

2s

3s

4s5s6s7s

2p

3p

4p5p6p

3d

4d5d

7p 6d

4f5f

Timberlake LecturePLUS 2000

Electron Configuration

• Tells us the most likely position of where electrons can be found.

• It is like the address of an electron.

• Electron configurations are used instead of orbital diagrams because they are less cumbersome.

Timberlake LecturePLUS 2000

Steps for filling in an Orbital Diagram

1. Identify the number of electrons.

2. Fill in the orbital diagram using the following rules:A. Aufbau Principle-Fill in the lowest energy orbitals

first.B. Pauli Exclusion Principle-Each orbital (block) can

contain 2 arrows. The arrows must be pointed in opposite directions.

C. Hund’s Rule Every orbital in a subshell must have one electron in it before any one orbital can be filled with a second electron.

Timberlake LecturePLUS 2000

Orbital Diagrams:Example #1

• Draw an orbital diagram for H.• Hydrogen has 1 electron.

1s 2s 2p 3sThe electron configuration is then:

1s1

Timberlake LecturePLUS 2000

Orbital Diagrams:Example #2

• Draw an orbital diagram for B.• Boron has 5 electrons.

1s 2s 2p 3sThe electron configuration is then:

1s22s22p1

Timberlake LecturePLUS 2000

Orbital Diagrams:Example #3

• Draw an orbital diagram for C.• Carbon has 6 electrons.

1s 2s 2p 3sThe electron configuration is then:

1s22s22p2

Timberlake LecturePLUS 2000

Orbital Diagrams:Example #4

• Draw an orbital diagram for O.• Oxygen has 8 electrons.

1s 2s 2p 3sThe electron configuration is then:

1s22s22p4

Timberlake LecturePLUS 2000

Practice

Draw an orbital diagram and write the electron configuration for the following elements:

1. He 2. Li 3. N 4. F 5. S

Timberlake LecturePLUS 2000

He

• Helium has 2 electrons.

1s 2s 2p 3s

The electron configuration is then:1s2

Timberlake LecturePLUS 2000

Li

• Lithium has 3 electrons.

1s 2s 2p 3s

The electron configuration is then:1s22s1

Timberlake LecturePLUS 2000

N

• Nitrogen has 7 electrons.

1s 2s 2p 3s

The electron configuration is then:1s22s22p3

Timberlake LecturePLUS 2000

F

• Fluorine has 9 electrons.

1s 2s 2p 3s

The electron configuration is then:1s22s22p5

Timberlake LecturePLUS 2000

S

Sulfur has 16 electrons.

1s 2s 2p 3s 3p

The electron configuration is then:1s22s22p63s23p4

Timberlake LecturePLUS 2000

More Practice

Write the electron configuration for each:A. Cl

B. Sr

C. I

Timberlake LecturePLUS 2000

Solution

Write the electron configuration for each:A. Cl (17 electrons)

1s2 2s2 2p6 3s2 3p5

B. Sr (38 electrons)1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2

C. I (53 electrons)1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5

Noble Gas Abbreviated Notation

He

Ne

Ar

Kr

Xe

Example

• Write the noble gas abbreviated electron configuration for oxygen (O).

1.) The noble gas that occurs before O is He.2.) Start with [He].3.) Finish writing the electron configuration from

helium: [He]2s22p4

Example

• Write the noble gas abbreviated electron configuration for Silicon (Si).

• The noble gas that occurs before Si is Ne.• Start with [Ne].• Finish writing electron configuration from Ne:

[Ne]3s23p2

Example

• Write the noble gas abbreviated electron configuration for Gallium (Ga).

• The noble gas that occurs before Ga is Ar.• Start with [Ar].• Finish writing electron configuration from Ar:

[Ar]4s23d104p1

Write the Noble-Gas abbreviated electron configuration for the

following:a.) S:

b.) Cd:

c.) Fe:

d.) Br:

Write the Noble-Gas abbreviated electron configuration for the

following:a.) S: [Ne]3s23p4

b.) Cd: [Kr]5s24d10

c.) Fe: [Ar]4s23d6

d.) Br: [Ar]4s23d104p5