Chemistry Unit 1

Democritus

• Greek philosopher

• matter divided into smaller pieces forever?

• idea smallest piece of matter indivisible

• named smallest piece of matter atomos

atomos meaning

not to be cut

Aristotle’s elements

fire, air, water, earth

Democritus beliefs about atoms

• atoms small hard particles

• made of same stuff

• different shapes and sizes

• always moving

• capable of joining together

• infinite in number

Dalton’s model

experiments → acceptance of existence of atoms

Dalton’s 5 postulates

1. All elements are composed of indivisible particles called atoms

2. Atoms can not be created or destroyed

3. Atoms of the same element are exactly alike, same masses

4. Atoms of different elements are different

5. Atoms combine to form compounds in small whole number ratios

• became one of modern foundations of chemistry

• #’s 2 & 3 proven false

Timeline of Atomic Theory

1. Greek model, Democristus (400 BC)

2. Aristotle’s 4 elements

3. Dalton Model (1803)

4. Thompson Model (1897)

5. Rutherford Model (1911)

6. Bohr Model (1922)

7. Wave Model (current)

Thompson

• 1897

• atom made of smaller particles

• electric current through gas

• gave off rays of - charged particles

• electrical field deflects electron beam

• ratio of charge to mass is constant

Plum Pudding Model

• atoms made of + charged substance

• - charged particle scattered throughout

• like raisons in plum pudding

Conclusions drawn by Thompson

• particle smaller than atom must exist

• atom is divisible

• must be positively charged particles in the atom

Thompson’s name for electrons

corpuscles

Rutherford’s gold foil experiment

• + charged particles at thin gold foil

• x-ray paper around

• most of radiation made it through

• some bounced off → must be + charge in atom

• sometimes change course slightly

Gold Foil experiment conclusions

• atoms mostly open space

• small, dense, + charged center

• center = nucleus

• nucleus tiny compared to atom

• - charged particles scattered around edge

Bohr Model

• 1913

• Niels Bohr

• electrons move in orbits around nucleus

• each electron in specific energy level (distance from nucleus)

Isotopes

Atoms of the same element that have different numbers of neutrons (diff. masses)

Four most abundant elements on Earth

• Oxygen

• Silicon

• Aluminum

• Iron

Four most abundant elements in body

• Oxygen

• Carbon

• Hydrogen

• Nitrogen

Law of constant composition

a compound always contains the same relative numbers of atoms

What are natural materials

mixtures of pure substances

Pure substances are

either elements or combinations of elements called compounds

A given compound always has

the same proportions of the elements

A compound is

a distinct substance that is composed of the atoms of two or more elements and always contains the same relative number of those elements

A chemical formula is

a formula that shows how many atoms of what element are in a compound.

If the nucleus is the size of a grape the first electron is

one mile away

An Ion is

a charged atom

Line of best fit must go through (0,0) because

when a subject exhibits neither of the characteristics shown it is at the point (0,0)

Atomic mass exceptions in the periodic table

• Tellurium and Iodine

• Potassium and Argon