Atomic Structure & Model

– The Basics

I. Atomic Structure

A. Atomic Structure Review

II. Bohr Model

A. Electron Energy Shells

1. Electrons are arranged in shells around the nucleus in predictable locations

a. The shell closest to the nucleus must fill all seats before seats farther from the nucleus are filled.

II. Bohr Model

Shell Number Available Seats

1 2 electrons

2 8 electrons

3 8 electrons

4 18electrons

II. Bohr Model

2 Atoms are more stable when their outer shell is full.

3 Atoms that do not have a full outer shell tend to gain or lose electrons. This results in a full outer shell and therefore, stability. This is called the octet rule.

4 Periodic table periods (aka the rows) share the same number of shells.

II. Bohr Model

B. Valence Electrons

1. Valence Electrons are electrons located on the outmost energy shell of an atom.

2. They are responsible for creating bonds with other atoms.

3. Periodic table families (aka the columns) share the same number of valence electrons.

II. Bohr Model

II. Bohr ModelC. Drawing Bohr Models

1. Find your element on the periodic table.

2. Determine the number of electrons (it is the same as the atomic number).

3. Find which period your element belongs to.

a. Elements in the 1st period have one energy levelb. Elements in the 2nd period have two energy levelsc. Elements in the 3rd period have three energy levels,

etc. etc..

II. Bohr Model

4. Draw a nucleus with the element symbol inside.

5. Draw the number of energy shells around the nucleus.

6. Add the correct number of electrons to each shell.a. Remember…

Shell Number

Available Seats

1 2 electrons

2 8 electrons

3 8 electrons

4 18 electrons

II. Bohr Model

7. Check your work! Find what family your element belongs to!

a. Elements in the 1st family have one valence electron.

b. Elements in the 2nd family have two valence electrons.

c. Elements in the 3rd family have three valence electrons, etc., etc..

Bohr-ing Practice ;-)• For an Atom of Hydrogen:

• 1 Electron!• Simple, you just draw the first electron

here

Bohr-ing Practice ;-)

• For an Atom of Helium:

• 2 Electrons!

• Simple, you just draw the second electron

here

Bohr-ing Practice ;-)• For an Atom of Lithium:

• 3 Electrons!

• But wait a minute…We said that only 2 Electrons can fit into the first level

• So What do we do when it’s full????

Bohr-ing Practice ;-)

• For an Atom of Lithium:

• 3 Electrons!• Simple, you just draw the third Electron

here