7.2 the bohr theory of the atom - mrvscienceandmath.com · niels bohr he used this property of...

7.2 The Bohr Theory of the Atom

John Dalton

Michael Faraday • showed that atoms could gain electric charges

J.J. Thompson The atomic theory was once again revised, to include his ideas:

In 1911, Rutherford proposed his nuclear model of the atom

Ernest Rutherford

Nucleus = protons + neutrons

THE MODERN VIEW OF THE ATOM


It is composed of electrons, protons and neutrons

ELECTRONS:

•Orbit (move around) the nucleus

•Charge of -1 (negative)

•Symbol is e

• They can be shared or transferred between the atoms



Protons:

• In the nucleus

•Charge of +1 (positive)

•Symbol is p

• They CAN’T be shared or transferred between the atoms = they are locked in the nucleus



Neutrons:

• In the nucleus

•Charge of 0 (no charge)

•Symbol is n

• They CAN’T be shared or transferred between the atoms = they are locked in the nucleus


The relative size of the nucleus and atom!

Inside the Atom

Niels Bohr He studied gaseous samples of atoms, which were made to glow by

passing an electric current through them.

Niels Bohr He used this property of elements, as well as discoveries by other scientists of

the time, to solve the problems with Rutherford’s model of the atom.

Based on his observations, Bohr proposed that

electrons surround the nucleus ONLY in specific “energy levels” or “shells.”

Each “energy level” or “shell” has only certain amount of energy!

The electrons can only move from shell to shell (stair to stairs)

Think of these electron shells as stairs

The electrons can only move from shell to shell (stair to stairs) = you can never find them between the shells (between the stairs)


The electron in the closest shell to the nucleus have the LOWEST energy =

It is on the lowest step of the stairwell


The electrons in the furtermost shell to the nucleus have the HIGHEST energy =

It is on the highest step of the stairwell


So the electrons closer to the nucleus have less energy than the electrons further from the nucleus

1. Which electron has higher energy?

2. If the blue electron wanted to reach the shell in which the red electron is, would the light be given off or not?

• Each shell can hold ONLY certain number of electrons

First shell:

2 electrons

Second shell:

8 electrons

Fourth shell:

18 electrons

Third shell:

8 electrons

The Number of Shells for an Element

• The number of shells (orbits) in an atom depends on the number of electrons in that atom

First shell:

2 electrons

Second shell:

8 electrons

Fourth shell:

18 electrons

Third shell:

8 electrons


For example, an element with six electrons has two electrons in

the first shell and four electrons in the second shell

Second shell:

8 electrons

Fourth shell:

18 electrons

Third shell:

8 electrons


First shell:

2 electrons

Draw 3 electrons

Draw 11 electrons

Draw 14 electrons

Draw 20 electrons

Drawing electrons – The Bohr Model of the Atom

CHAPTER 7 VOCABULARY

VOCABULARY WORD

VOCABULARY WORD

SUBATOMIC PARTICLES

SHELLS (ORBITS)

ATOMIC NUMBER

ATOMIC MASS (Mass Number)

POSITIVE ION

NEGATIVE ION

ION CHARGE

BOHR DIAGRAM

IONIC COMPOUND

the number of protons in the nucleus OR the number of electrons (in a neutral atom)

Atomic Number

What is the ATOMIC NUMBER of

gold?

the number of protons in the nucleus + the number of neutrons

ATOMIC MASS (Mass number)

What is the ATOMIC MASS of

potassium?

UNITS for ATOMIC MASS =

MASS NUMBER =

# of protons + # of neutrons

ATOMIC NUMBER =

# of protons (or # of electrons)

# of neutrons = MASS NUMBER – ATOMIC NUMBER

Standard Atomic Notation

• Elements are written to show the Atomic Mass Number and the Atomic

Number

Determine the number of protons, neutrons, and electrons present in potassium. Write the

symbol for this element using Standard Atomic Notation.

potassium - 39 # of protons = Atomic Number = Z = 19

# of neutrons = Mass Number – Atomic Number

= A – Z = 39 – 19

= 20 neutrons

# of protons + # of neutrons = Mass Number = A = 39

# of electrons = # of protons = 19

Determine the number of protons, neutrons, and electrons present in a cation of K – 39.

Write the symbol for this element using standard atomic notation.

potassium # of protons = Atomic Number = Z = 19

# of neutrons = Mass Number – Atomic Number

= A – Z = 39 – 19

= 20 neutrons

# of protons + # of neutrons = Mass Number = A = 39

# of electrons = # of protons – 1 = 18

How many protons and neutrons do the following elements have? What is their atomic mass (mass number)?

Carbon Oxygen Sodium

Atomic mass = #of protons + #of neutrons

Determine the number of protons, neutrons, and electrons present in K – 39. Write the symbol

for this element using standard atomic notation.

potassium - 39 # of protons = Atomic Number =

# of neutrons = Atomic Mass Number – Atomic Number

= = neutrons

# of protons + # of neutrons = Atomic Mass Number =

# of electrons (in NEUTRAL ATOM) = # of protons =

Determine the number of protons, neutrons, and electrons present in each of the atoms. Write

a symbol for each element using Standard Atomic Notation.

# of protons:

Standard Atomic Notation:

# of protons: # of protons:

# of electrons: # of electrons: # of electrons:

# of neutrons: # of neutrons: # of neutrons:

Standard Atomic Notation: Standard Atomic Notation:



# of protons:

Standard Atomic Notation:

# of protons: # of protons:

# of electrons: # of electrons: # of electrons:

# of neutrons: # of neutrons: # of neutrons:

Standard Atomic Notation: Standard Atomic Notation:

7.4 Using the Bohr Theory

BOHR DIAGRAMS • There is a pattern to the arrangements of electrons

in atoms

Atoms have SHELLS of electrons around the nucleus

BOHR DIAGRAMS

• Now you know how to FIND the number of electrons in an atom and

how to DRAW them

Niels Bohr showed how electrons are arranged in an atom = A BOHR MODEL DIAGRAM

A BOHR MODEL DIAGRAM

Other BOHR MODEL DIAGRAMs • Some diagrams show the electrons as dots.

• Others just have figures indicating the number of electrons in each shell.

BOHR DIAGRAMS Practice (worksheet)

Draw Bohr Diagrams for:

hydrogen

sodium

phosphorus

neon

calcium

First shell: 2 electrons

Second shell: 8 electrons

Fourth shell: 8 electrons

Third shell: 8 electrons

BOHR DIAGRAMS Practice (worksheet)

Draw Bohr Diagrams for:

hydrogen

Sodium ion

Phosphorus ion

Neon ion

calcium ion

First shell: 2 electrons

Second shell: 8 electrons

Fourth shell: 8 electrons

Third shell: 8 electrons

7.2 the bohr theory of the atom - mrvscienceandmath.com · niels bohr he used this property of...

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