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Atom. Definition: the smallest particle of any element that retains the properties of that element. Practice quiz question:. What is the smallest particle of magnesium that retains the properties of magnesium?. Interesting side note….

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Atom

Atom

  • Definition: the smallest particle of any element that retains the properties of that element.


Practice quiz question

Practice quiz question:

What is the smallest particle of magnesium that retains the properties of magnesium?


Interesting side note

Interesting side note…

  • Atoms are fantastically durable. Because they last so long, atoms really get around!

  • Every atom you possess has almost certainly passed through several stars and been part of millions of organisms on its way to becoming you.


Interesting side note1

Interesting side note…

  • It has been suggested that up to a billion of each person’s atoms once belonged to Shakespeare. Another billion came from Beethoven. You probably have some atoms from any historical figure you can think of!


Nowadays with the use of tunneling electron microscopes we can sort of see atoms

Nowadays, with the use of tunneling electron microscopes, we can sort of “see” atoms…

image of copper atoms


Atom

This is an image of silicon atoms arranged on a face of a crystal. It is impossible to "see" atoms this way using ordinary light. The image was made by a Scanning Tunneling Microscope, a device that "feels" the cloud of electrons that form the outer surface of atoms, like a phonograph needle feels the grooves in a record.


Atom

These electron microscopes were invented in the mid-1900’s. How did scientists figure out atomic structure without being able to look at any atoms?


The history of atomic theory

The History of Atomic Theory


But first

But first…

What is a theory in science?

A theory is a well-tested explanation of what happens in nature.

In layman’s terms, if something is said to be “just a theory,” it usually means that it is a mere guess, or is unproven. But in scientific terms, a theory implies that something has been well-tested and verified many times by multiple groups of scientists.


And while we re at it

And while we’re at it…

A scientific law is a statement of something that seems to be true in the natural world.

Example: The Law of Gravity. Newton could use this law to predict the behavior of a dropped object, but he couldn't explain why it happened.


Einstein s theory of relativity explains gravity as a curve in the fabric of space time

Einstein’s Theory of Relativityexplains gravity as a curve in the fabric of space-time:


Remember

Remember!

A law states or describes what happens in nature.

A theory explains what happens.

Both are well-tested by experiments.

Memory hint: “explanation starts with an “e” and “theory” has an “e”.


True or false

True or False?

The difference between a scientific law and a scientific theory is that a law has been proven, but a theory has not been proven.


The history of atomic theory1

The History of Atomic Theory


Democritus

Democritus

  • ancient Greek philosopher, not scientist

  • first to suggest that matter is made of tiny particles called “atomos”

  • “atomos” = Greek for “indivisible”

  • ideas were rejected by Aristotle, who was very influential, and therefore forgotten for two thousand years.


Democritus atomic model atoms were small hard particles that were different shapes and sizes

Democritus’ atomic model:atoms were small, hard particles that were different shapes and sizes


Atom

John Dalton:First to propose an atomic theory based on science:1. Each element is composed of small particles called atoms.2. All atoms of a given element are identical*; the atoms of different elements are different.3. Atoms are not created or destroyed in chemical reactions.4. Compounds are formed when atoms of more than one element combine.


Atom

John Dalton:First to propose an atomic theory based on science:1. Each element is composed of small particles called atoms.2. All atoms of a given element are identical*; the atoms of different elements are different.3. Atoms are not created or destroyed in chemical reactions.4. Compounds are formed when atoms of more than one element combine.* We now know this part is not true!


Dalton s atomic model a tiny sphere that is indivisible

Dalton’s atomic model:a tiny sphere that is indivisible


Atom

ELEMENT

1

ELEMENT

2

ELEMENT

3

ELEMENT

4

Atomic Theory


Atom

+

+

Atomic Theory


J j thomson

J.J. Thomson:

  • First to suggest that there were particles smaller than the atom.

  • Discovered the electron.

  • Developed the “plum pudding model.”


Atom

Thomson’s “plum-pudding” model:the atom is composed of electrons surrounded by a cloud of positive charge to balance the electron's negative charge


Ernest rutherford

Ernest Rutherford

  • gold foil experiment

  • discovered the nucleus, and realized that it was very dense and positively charged

  • suggested that most of the atom is empty space


Atom

Gold Foil Experiment:Rutherford shot tiny positively-charged alpha particles through a thin sheet of gold foil

What Rutherford expected:

What really happened:


Atom

Gold Foil Experiment:Some of the alpha particles bounced back. “It was as if you fired a 15-inch cannon ball at a piece of tissue paper and it came back and hit you.”

What Rutherford expected:

What really happened:


Atom

Such huge deflections could mean only one thing: some of the alpha particles had run into massive concentrations of positive charge and, since like charges repel, had been hurled straight back by them.


Atom

Rutherford’s atomic model:All of the positive charge is crammed inside a tiny, massive nucleus about ten thousand times smaller than the atom as a whole. The atom is mostly empty space.


Animation of rutherford s experiment

Animation of Rutherford’s experiment

  • http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf


Neils bohr

Neils Bohr

  • Discovered that electrons move in Orbits around the Nucleus like Planets.

  • Pictures the atom as a small positive nucleus with electrons orbiting around it; electrons can jump from orbit to orbit when they absorb or emit energy.


Bohr s model of the atom

Bohr’s Model of the Atom

Protons and neutrons are in the nucleus, which only takes up one

millionth of a billionth of the volume of the atom. The electrons are

in the electron cloud, which constitutes almost all of the volume of the atom.


In fact if an atom were expanded to the size of a cathedral

In fact, if an atom were expanded to the size of a cathedral,

the nucleus would be about the size of a housefly!


Subatomic particles to know

Subatomic Particles to Know


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