Bohr – Rutherford Atomic Model

Neils Bohr improved Rutherford’s model by placing electrons in distinct energy levels or “shells” rather than an electron “cloud”

Bohr & Rutherford combined their theories to create the current simplified atomic model

The atom is made up of three sub-atomic particles:

ProtonsElectronsNeutrons

Bohr – Rutherford Atomic Model:

The Atom:Sub-Atomic

ParticleCharge Mass Location

Proton

Electron

Neutron

+

-none

1 amu

negligible

1 amu

nucleus

outside nucleus

nucleus

education.jlab.org/ qa/atom_model.html

The Atom:

nucleus

electron neutron

proton

Nucleus: Contains protons & neutrons Overall positive charge (+) Contains nearly all mass (dense)

Electrons: Located outside

nucleus Easily moved, lost or

gained Negative charge (-)

Every atom has a symbol & two numbers associated with it.

Ex.

The Atom – Important Info:

C 12

6

Mass Number

Atomic Number

•The mass of an atom

•The bigger number•The number of protons & neutrons

•The number of protons•The smaller number

Since atoms are neutral, the number of protons (+)

equals the number of electrons (-)

For the following atom, state the…i) mass numberii) atomic numberiii) # of protonsiv) # of electronsv) # of neutrons

O 16

816

8

8

8

16 – 8 = 8

For the following atom, state the…i) mass numberii) atomic numberiii) # of protonsiv) # of electronsv) # of neutrons

Na23

1123

11

11

11

23 – 11 = 12

For the following atom, state the…i) mass numberii) atomic numberiii) # of protonsiv) # of electronsv) # of neutrons

Ar40

1840

18

18

18

40 – 18 = 22

Cu64

2964

29

29

29

64 – 29 = 35

For the following atom, state the…i) mass numberii) atomic numberiii) # of protonsiv) # of electronsv) # of neutrons

For the following atom, which statement is TRUE?

P 3115

A) The atomic number is 31.

B) The atom has 15 neutrons.

C) The atom has 16 electrons.

D) The atom has 15 protons & 15 electrons.

Given a neutral atom, which statement is TRUE?

A) An atom always has the same number of electrons as neutrons.

B) Electrons & neutrons are found in the nucleus.

C) The atomic number states the number of neutrons.

D) An atom has the same number of electrons as protons.

Atoms are made up of: Protons Electrons Neutrons

Protons & Neutrons are located in the nucleus

Electrons are located outside the nucleus

An atom’s atomic number is equal to the number of protons (smaller number)

An atom is neutral, therefore the number of protons & electrons are equal

An atom’s mass number is equal to the protons & neutrons together (bigger number)

Activities: Physical Science Worksheet #7

Once you’ve completed the

worksheet, continue with the rest of the

lesson

Recall, in the Bohr-Rutherford atomic model, electrons are located outside the nucleus

Electrons are organized into:Electron shells or Energy levels orOrbitals

Electrons:

Be familiar with all the terms, especially the

first two

Each electron shell differs in size & the number of electrons it can hold (capacity)

Electrons:

Electron Shell

Capacity

1st 2 electrons

2nd 8 electrons

3rd 8 electrons*

4th 2 electrons*

Shows maximum # of electrons in

each shell

Shells can be partially filled or empty

*Simplified – 3rd shell holds 18 electrons4th shell holds 32 electrons

Is a picture of an atom, showing its protons, electrons & neutrons.

Ex.

Bohr – Rutherford Diagram:

Protons =

Electrons=

Neutrons=

334

3 P+

4 N0 2 e- 1 e-

Li73

Draw a Bohr-Rutherford diagram for:

Protons =

Electrons=

Neutrons=

9910

9 P+

10 N0 2 e- 7 e-

F199

Draw a Bohr-Rutherford diagram for:

Protons =

Electrons=

Neutrons=

556

5 P+

6 N0 2 e- 3 e-

B115

Draw a Bohr-Rutherford diagram for:

Protons =

Electrons=

Neutrons=

121212

12 P+

12 N0 2 e- 8 e-

Mg2412

2 e-

Draw a Bohr-Rutherford diagram for:

Protons =

Electrons=

Neutrons=

191920

19 P+

20 N0 2 e- 8 e-

K 3919

8 e- 1 e-

Be 9 4

Which of the following diagrams best represents the Bohr-Rutherford model of…

A)

4 P+

5 N0 2 e-3 e-

B)5 P+

4 N0 2 e- 2 e-

C)4 P+

5 N0 2 e- 2 e-

Draw a Bohr-Rutherford diagram for each of the following atoms:

P 3115

N 147

Al 2713

15 P+

16 N02 e-

8 e-5 e-

7 P+

7 N0 2 e-5 e- 13 P+

14 N02 e-

8 e-

3 e-

The Neutron

The Rutherford-Bohr model of the atom did not answer the question:

“What holds the nucleus together given that it is made up of entirely of positive protons?”

The Neutron

In 1932, James Chadwick discovered that a third sub-atomic particle called the neutron holds the protons in the nucleus together.

Neutrons are located in the nucleus and have no charge…they are neutral.

Nucleus: Contains protons & neutrons Overall positive charge (+) Contains nearly all mass (dense)

Electrons: Located outside

nucleus Easily moved, lost or

gained Negative charge (-)

Electrons are located outside the nucleus in electron shells

In the… 1st shell – 2 electrons 2nd shell – 8 electrons 3rd shell – 8 electrons* 4th shell – 2 electrons*

In Bohr-Rutherford diagrams: Place Protons & Neutrons in nucleus Place Electrons in appropriate shells

Find the number of Protons,

Electrons & Neutrons

Activities: Physical Science Worksheet #8