ATOMIC THEORY Defining the Atom An atom is the smallest particle of an element that retains its identity in a reaction. An atom is the smallest particle.

ATOMIC

THEORY

Defining the Atom

An atom is the smallest particle of an element that retains its identity in a reaction.

The basic building blocks of matter that make-up everyday objects.

How small is an atom?

About a million atoms stacked on top of each other = the thickness of a sheet of paper.

Copyright © 2010 Ryan P. Murphy

About 5 million atoms make up a period at the end of a sentence.


Video Link! The size of atomshttp://www.youtube.com/watch?v=yQP4UJh

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http://www.youtube.com/watch?v=yQP4UJhNn0I

http://www.youtube.com/watch?v=yQP4UJhNn0I

DemoCritus

Early Greek Scholar-was the first to suggest the existence of atoms

He believed that atoms were indivisible and indestructible.

Never developed a theory lacked experimental support

John Dalton’s Atomic Theories-All matter is composed of tiny indestructible particles called atoms.-Atoms cannot be made or destroyed.-All atoms of the same element are identical.-Different elements have different types of atoms.-Chemical reactions occur when atoms are rearranged.-Atoms of different elements can mix together to form compounds.

Dalton’s Theory Revised

Most of Dalton’s theory is still accepted today EXCEPT that atoms are known to be divisible.

Atoms can be broken down into 3 subatomic particles: electrons, protons and neutrons.

J.J. Thomson

Used a cathode ray tube to prove the smallest particles present must have a negative charge.

http://www.youtube.com/watch?v=RW_zfKOU9uM&feature=related




-


+

-


+

-

Like charges (-) (-) repel. The Electron is negative.


+

-


+ -


+

-


+

-

Opposite charges attract (+) (-). The electrons are negative.

What did this study find?J.J. Thompson discovered the ELECTRON!!!


+

-

J.J. Thomson

Atoms were electrically neutral, so there must be a + particle to cancel out the – charge from the electron.

Developed the Plum Pudding Model (positive ball containing scattered electrons)

Ernest Rutherford

Former student of Thomson, DISPROVED the Plum Pudding Model of the atom.

The Gold Foil Experiment: Sent a beam of + charges (alpha particles) through a piece of very thin gold foil.

Angles of deflection were measured.


Turn Sound On







Rutherford

Results: Most of the alpha particles passed straight through, most of the foil must be regions of “empty” space – not a + sphere like Thomson believed.

+ charges and the atoms mass must be found in the center discovered the nucleus

The Nuclear Atom

In Rutherford’s atomic model, the protons and neutrons are located in the nucleus.

The electrons are distributed around the nucleus and occupy almost all the volume of the atoms.

Video! Rutherford’s Gold Foil Experimenthttp://www.youtube.com/watch?v=5pZj0u_

XMbc


http://www.youtube.com/watch?v=5pZj0u_XMbc

http://www.youtube.com/watch?v=5pZj0u_XMbc

• Neils Bohr Model (1913): Depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus– .


The atom consists of three fundamental particles ---


Proton + (positive charge)






+





++

Neutron 0 (neutral charge / no charge)


Neutron 0 (neutral charge / no charge)


Neutron 0 (neutral charge / no charge).


– A neutron walks into a video store.


– He asks the clerk “How much are the movies?”




“For you…”“No

Charge.”



“For you…”“No

Charge.”



Electron – (negative charge)


ATOMIC STRUCTURE

Particle

proton

neutron

electron

Charge

+ ve charge

-ve charge

No charge

1

1

nil

Mass

ATOMIC STRUCTURE

the number of protons in an atom

the number of protons and neutrons in an atom

He2

4 Atomic mass

Atomic number

number of electrons = number of protons

HELIUM ATOM

+N

N

+-

-

proton

electron

neutron

shell

Why are atoms electrically neutral?

What atom is this? How can you tell?


Answer! (2 Protons) Atomic #2


Answer! (2 Protons) Atomic #2 (Helium)


Answer! (2 Protons) Atomic #2 (Helium)


• Review! To find # of protons and electrons


• Review! To find # of protons and electrons– It is the atomic number, or count the P+ or E-.


• Review! To find # of protons and electrons– It is the atomic number, or count the P+ or E-.


• Review! To find # of protons and electrons– It is the atomic number.– What is this atoms Atomic number?


• Answer!


• Answer! Count the 11 Protons or 11 Electrons


• Answer! Atomic Number 11.– What element is #11


• Answer! Atomic Number 11.– What element is #11 Sodium


• Review! To find # of neutrons


• Review! To find # of neutrons– Subtract the atomic number from the atomic mass to

determine the difference.



determine the difference.– How many neutrons does Lithium have?




Atomic Mass




Atomic Mass

Atomic Number




Atomic Mass

Atomic Number6.94 amu – 3 =


• Answer! 6.94 – 3 = 3.94

Atomic Mass



• Answer! 6.94 – 3 = 3.94 or 4 neutrons

Atomic Mass



Complete the following table in your notes

Atomic # Mass # # of Protons

# of Neutrons

# of Electrons

9 10

14 15

47 22

55 25

ATOMIC THEORY Defining the Atom An atom is the smallest particle of an element that retains its identity in a reaction. An atom is the smallest particle.

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