Introduction To Introduction To AtomsAtoms

Section 1: Development of Section 1: Development of The Atomic TheoryThe Atomic Theory

Atomic Theory VideosAtomic Theory Videos https://www.youtube.com/watch?v

=thnDxFdkzZs

https://www.youtube.com/watch?v=QbWKF9uDF7w

Cool Visual: Cool Visual: http://www.timetoast.com/timelines/history-of-the-atomic-model--36

Atoms…Atoms…

……Are the smallest particles into Are the smallest particles into which an element can be divided which an element can be divided and will remain the same and will remain the same substancesubstance

……Make up elements (which Make up elements (which combine to form compounds)combine to form compounds)

……often called the building blocks of often called the building blocks of mattermatter

Atoms…Atoms…

……Were not seen prior to 1981 when the Were not seen prior to 1981 when the scanning tunneling microscope was scanning tunneling microscope was inventedinvented

……comes from the Greek word atomos, comes from the Greek word atomos, meaning indivisiblemeaning indivisible

However…However…

The atomic theory has been around for The atomic theory has been around for more than 2000 years!more than 2000 years!

Refresh your Refresh your memory…memory…

What’s a theory?What’s a theory?

A theory is an explanation for a broad range of hypotheses and observations that have been supported by testing

Let’s Tour The History Let’s Tour The History of The Atomof The Atom

First Stop…GreeceFirst Stop…Greece

Democritus proposed Democritus proposed (around 440 BC)…(around 440 BC)…

……that if a person continued to cut that if a person continued to cut a coin in half over and over again, a coin in half over and over again, they would eventually end up they would eventually end up with an uncuttable piecewith an uncuttable piece

……the name for the atomthe name for the atom

Aristotle disagrees. He Aristotle disagrees. He thought (around mid 300 thought (around mid 300 BC, after Democritus)…BC, after Democritus)…

……particles could be divided particles could be divided indefinitelyindefinitely

It’s All Greek To Me!It’s All Greek To Me!

So Who Thought Up So Who Thought Up The Atomic Theory?The Atomic Theory?

Let’s move to Britain!Let’s move to Britain!

……and about 2000 and about 2000 years have passed.years have passed.

……in the 1700’s, scientists have in the 1700’s, scientists have learned that elements combine in learned that elements combine in specific proportions based on massspecific proportions based on mass

What are combined elements with a What are combined elements with a constant mass ration called?constant mass ration called?

(Hint: Ch 4)(Hint: Ch 4)

Compounds!

Dalton’s Theory Dalton’s Theory Stated…Stated… All substances are All substances are

made of atoms. made of atoms. Atoms are small Atoms are small particles that cannot particles that cannot be created, divided, be created, divided, or destroyedor destroyed

Atoms of the same Atoms of the same element are exactly element are exactly alike, and atoms of alike, and atoms of different elements different elements are differentare different

Atoms join with other Atoms join with other atoms to make new atoms to make new substancessubstances

So, is the atom really So, is the atom really the smallest particle ?the smallest particle ?

We thought so until 1897 (yes, just We thought so until 1897 (yes, just 110 years ago!) Another British 110 years ago!) Another British scientist, J.J.Thomson, discovered scientist, J.J.Thomson, discovered that there were small particles that there were small particles inside the atom, therefore, the inside the atom, therefore, the atom could be divided into atom could be divided into smaller parts!smaller parts!

Thompson Thompson experimented with the experimented with the cathode ray tube and cathode ray tube and discovered…discovered…

Thompson concluded, Thompson concluded,

And he is credited with the And he is credited with the discovery of the electron! discovery of the electron!

He is known for the “plum pudding” He is known for the “plum pudding” or “chocolate chip cookie” model or “chocolate chip cookie” model of the atom.of the atom.

A Few Years Later…A Few Years Later…

A student of Thompson’s named A student of Thompson’s named Ernest Rutherford decided to Ernest Rutherford decided to check out Thompson’s theory check out Thompson’s theory himself so he set up an atomic himself so he set up an atomic shooting galleryshooting gallery

Meet RutherfordMeet Rutherford

Bye-Bye Plum Bye-Bye Plum Pudding!Pudding! Rutherford came up with his own Rutherford came up with his own

model of the atommodel of the atom He is credited with the discovery He is credited with the discovery

of the proton and nucleusof the proton and nucleus Rutherford's model came to be Rutherford's model came to be

known as the “solar system” known as the “solar system” modelmodel

Jumping Electrons!Jumping Electrons!

Niels Bohr (who Niels Bohr (who worked with worked with Rutherford) Rutherford) suggested suggested that electrons that electrons travel around travel around the nucleus in the nucleus in definite pathsdefinite paths

Jumping Electrons!Jumping Electrons!

Bohr also proposed Bohr also proposed that the that the electrons could electrons could jump between jump between pathspaths

Electron Clouds and Electron Clouds and Current TheoryCurrent Theory

The exact The exact movement of movement of an electron an electron cannot be cannot be predicted but, predicted but, according to according to current theory, current theory, there are there are regions of the regions of the atom where atom where the electrons the electrons are more likely are more likely to be found. to be found. These are These are called electron called electron clouds.clouds.

Chadwick…1932Chadwick…1932

Credited with the discovery of the Credited with the discovery of the neutron which is located in the neutron which is located in the nucleus with the protonsnucleus with the protons

The Atom Through The Atom Through Time…Time…

History of the periodic History of the periodic table…table… Mendeleev – created the first Mendeleev – created the first

periodic table, ordered by periodic table, ordered by increasing atomic massincreasing atomic mass

Mosley – rearranged the periodic Mosley – rearranged the periodic table in order of increasing table in order of increasing atomic #, this is the way the atomic #, this is the way the current table is arrangedcurrent table is arranged

Let’s summarizeLet’s summarize

In what two parts of an atom is In what two parts of an atom is most of its mass located?most of its mass located?

Most of the mass of an atom is located in its nucleus

Let’s summarizeLet’s summarize

What are the two differences between the What are the two differences between the atomic theory described by Thompson atomic theory described by Thompson and described by Rutherford?and described by Rutherford?

The differences in the theories are that Thompson’s model had the negatively charged particles in the positive material but Rutherford’s model had them moving around the positive material. Thompson’s model does not have a nucleus in the atom but Rutherford’s does.

Let’s summarizeLet’s summarize

Identify the difference in how Bohr’s Identify the difference in how Bohr’s theory and the modern theory theory and the modern theory describe the location of electrons.describe the location of electrons.

Bohr’s theory was that electrons move in definite paths around the nucleus. The modern theory states that the path of an electron cannot be known. Only the areas of the atom where electrons are likely to be found can be described.

Draw an atom:Draw an atom:

Now that we know a little more Now that we know a little more about the atom lets draw one.about the atom lets draw one.– First, close your notebook and try First, close your notebook and try

from memory!from memory!– Draw one atom you remember from Draw one atom you remember from

today and tape it to the correct today and tape it to the correct cabinet around the roomcabinet around the room