Chapter 3

Substances are made of atoms

Natural Philosophy

Heraclitus versus Parmenides

Heraclitus – everything is in the process of change

Parmenides – Change is impossible

Natural Philosophy

In 400 BCE, Democritus stated, All matter consists of tiny particles called átomos, which are not created and cannot be destroyed.

This was the beginning of the atomism.

Natural Philosophy

The fight wasn’t over. Plato disagreed.He thought that the beauty of the world

had to be caused by more than mere atoms.

He proposed a system of changing elements; water, fire, earth, air.

Natural Philosophy

Aristotle disagreed with both Democritus and Plato. He proposed a system called Hylomorphism.

Hylomorphism is a system of ever changing states of matter.

Natural Philosophy

Atomism was lost until the 16th CenturyThough it was still not a hard science, it

was part of a belief system called alchemy.

Thankfully, Robert Boyle put an end to the mess when he wrote The Skeptical Chemyst.

“Nature works by means of bodies unseen.”

Lucretius

The Elements

Atomic Theory

Three laws provide supporting evidence of atoms.– Law of Definite Proportions– Law of Conservation of Mass– Law of Multiple Proportions

Law of Definite Proportions

Every compound is composed of specific elements and whole-number ratios of those elements.

Water H20 - 2 Hydrogen: 1 Oxygen

Law of Conservation of Mass

Matter cannot be create or destroyed by normal physical or chemical processes

i.e.- What goes in, must come out!

Law of Multiple Proportions

The same elements can bond in differing whole-number ratios to form different compounds.

Methanol CH3O

Ethanol C2H5O

Dalton’s Atomic Theory

It contained five principles based on current knowledge of atoms.

We have summarized those principles in the following statements:

Dalton’s Atomic Theory

1. All matter is made up of tiny indestructible particles called atoms.

2. All atoms of one type (element) have the same mass and properties.

3. Atoms of different types (elements) have different masses and properties.

Dalton’s Atomic Theory

4. In Chemical reactions, atoms rearrange, but are not changed, created, or destroyed.

5. When different elements combine, they do so in some ratio of whole numbers.

Chapter 3

Structure of Atoms

Atomic dessert

In 1897 J.J. Thomson was able to control light in a vacuum through the use of magnets.

He concluded that the charge of the beam was negative.

He also new that the charge was due to movement of something inside atoms

He concluded that atoms contain subatomic particles with + and - charges.

Atomic Dessert

He created the “plum pudding” model of the atom

The Atom was a big positive charge, with very small particles of negative charges embedded in it.

Radioactive Man

In 1907, Ernest Rutherford performed “The Gold Foil Experiment”

Radioactive Man

Conclusion: Atoms have a hard, positively charged center called a nucleus.

The center was packed with tiny particles called PROTONS.

Most of the atom is empty space, while the tiny, tiny electrons float around outside.

Subatomic Particles

POSIT IVECHARG E

PROT ONS

NEUT RALCHARG E

NEUT RONS

NUCLEUS

NEG AT IVE CHARG E

ELECT RONS

AT OM

NUCLEUS ELECTRONS

PROTONS NEUTRONS NEGATIVE CHARGE

POSITIVE CHARGE

NEUTRAL CHARGE

ATOM

Atomic Numberequals the # of...

equal in a neutral atom

Elephants and Fleas

Today, we believe that the atom has three subatomic parts:

PROTON – positive charge in the nucleus

NEUTRON – no charge in the nucleus

ELECTRON – negative charge, orbiting the nucleus

Elephants and Fleas

Atomic Number – number of protonsAtomic Mass – number of protons +

number of neutrons

Why aren’t electrons added into the mass of the atom?

Isotopes

ISOTOPE - atoms of the same element that have a different number of neutrons

This happens rather frequently, that is why the atomic mass on the periodic table is not a whole number. It is an average of the different isotopes for that element.

Chapter 3

Electron Configurations

The not so great “greats”

Dalton, Thomson, and Rutherford were great men of science, but they had yet to understand the atom.

It wasn’t until Niels Bohr began to think about Hydrogen that were started to understand how complex an atom really is.

Bohr: What is it good for?!

Bohr, using a technique called Line Emission Spectrums, saw that electron didn’t just fly randomly around the nucleus. In fact, they are in distinct orbits called ENERGY LEVELS.

Bohr: What is it good for?!

If you put energy into an electron, it will change energy level into an EXCITED STATE. It will eventually drop back down to it’s GROUND STATE and give off energy in the form of light.

The colors of chemistry

Electromagnetic Spectrum – radiation moving at the speed of light ranging from low-energy radio waves to high-energy cosmic rays; includes visible light

It is often referred to as “light”The spectrum is created by the

“jumping” of electrons between orbits

Visible Spectrum

The more energy a wave has, the higher the frequency

Red has the lowest frequency, therefore it has the lowest energy

The most energetic color is violetROY G BIV

Electrons are wavicles.

Bohr model of the atom shows electrons orbiting a nucleus.– Electrons are particles

When we attempt to observe an electron, it changes position– Electrons are waves

De Broglie to the rescue

In 1924, Louis De Broglie suggested that electrons do not travel in perfect orbits, but rather in orbitals.

The resulting image was an “electron cloud.”

Electron Configuration Rules

Take notes on Hog Hilton and work on board.