Science: Physical Science

Science: Physical Science

Bohr’s Model Lewis Structure

Niels Bohr Gilbert N. Lewis

Born in Denmark20th Century

physicist (scientist)Worked on the

Manhattan Project during World War II. This is the project that produced the first atomic bomb.

Born in the USA20th Century

physicist (scientist)Home-schooled until

the age of 13 when he entered the preparatory school of the University of Nebraska.


BOHR’S MODEL DRAWING

LOOKS VERY MUCH LIKE THE SOLAR SYSTEM HELPS US UNDERSTAND ELECTRON

CONFIGURATION HELPS US UNDERSTAND WHY AND HOW SOME

ELEMENTS WILL BOND WITH OTHER ELEMENTS


Shells: Basics

Let's cover some basics of atomic shells:

a. The center of the atom is called the nucleus.

b. Electrons are found in areas called shells.

c. c. Shells are areas that surround the center of an atom.


Bohr’s Model:

Step by Step

Directions

Important Things to

Remember

A. Each shell corresponds to a period on the Periodic Table.

B. You MUST load each shell before you move on to the following one.

C. The number of electrons on each shell can only be up to the number of elements found on the corresponding period. Example: The first shell can only have a maximum of 2 electrons because there are only 2 elements on the first period of the table (Hydrogen and Helium)


Bohr’s Model:

Step by Step

Directions

1. Locate the element on the Periodic Table and write the information about the element.

2. Draw the nucleus and write the number of protons and neutrons inside the nucleus.

3. Draw the correct amount of shells outside the nucleus based on the row number where the element is found.

4. Start loading electrons on each shell, beginning from the inside and moving to the outside.



Element: HeliumAtomic #: 2Atomic Mass: 4.003

Bohr ‘s Model: Example 1

Protons: 2 Neutrons = 4 – 2 (Atomic Mass – Protons)Electrons: 2

P= 2N= 2


Element: NeonAtomic #: 10Atomic Mass: 20.183

Bohr ‘s Model: Example 2

Protons: 10Neutrons = 20 – 10 (Atomic Mass – Protons)Electrons: 10 (2 on the inner shell / 8 on the outer shell)

P= 10N= 10

Lewis Structure

Important things to remember

Octet Rule (Lewis Rule of Eight)

When atoms combine to form molecules, they generally each lose, gain, or share valence electrons until they attain or share eight.

Number of valence electrons is the same as number of the group where the element is found (don’t count transition metals). Example: Hydrogen = 1 valence electron, Calcium = 2 valence electrons, Carbon = 4 valence electrons.


Lewis Structure

Step by Step Directions

1) For the example we will use HCN2) Calculate the number of valence electrons

that move around it. We have: 1 + 4 + 5 = 10

3) Add a pair of bonding electrons between

every two atoms. H : C : N4) Add the rest of the electrons to the outer

atoms, until they meet the octet rule . Hydrogen is an EXCEPTION. It only needs 2 electrons around it.

H C N

So far, Nitrogen satisfied the octet rule and we have placed the 10 valence electrons. However, Carbon only has 2 valence electrons. What’s next?


Lewis Structure

Step by Step Directions

5) Nitrogen will have to share electrons with Carbon. We can move 4 electrons.

H C N6) We now have 8 electrons around each

atom and a total of 10 valence electrons.

7) Next, we need to replace each pair of bonding electrons with a simple line to show the bond.

H C N


Lewis Structure

Example using Carbon dioxide - CO2

1) Carbon is in Group 4 (if we don’t count the transition metals).

2) Oxygen is in Group 6 (if we don’t count the transition metals).

3) Thus we have: C = 4 valence electrons; O = 6 valence electrons. Multiply 6 x 2 = 12 (remember there are 2 Oxygen atoms in Carbon dioxide. Total = 16.

4) Add a pair of bonding electrons between every 2 atoms.

O C O5) We used 4 electrons out of 16. We

need to start placing the other electrons to satisfy the octet rule.


Lewis Structure

Example using Carbon dioxide - CO2 – Cont’

6) Place electrons around the outer atoms

O C O 7) The Oxygen met the octet rule but not the Carbon atom. Each Oxygen shares 2 electrons with the Carbon.

O C O 8) Replace the bonding electrons with simple lines.

O C O


O C O

O C O

C O

C O

O C O

O C O

C O

C O

O C O

You are done!

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