Chem Ch. 3 Notes

400 BC — The Greek Philosophers

Debate concerning the nature of matter

Democritus

stated all matter was made of invisible ultimate particles known as atomos

Aristotle

stated all matter is continuous, no ultimate particles; was believed until the 1700s

200 to 1700 AD — The Alchemists

• 1st experimenters experimented in secret

• trying to turn base metals into gold

• discovered many useful things (medicines, gun powder)

Alchemists

1st experimenters; experimented in secret; discovered many useful things (ex. medicines, gun powder)

1600-1700 AD — The Atomists

Galileo, Boyle, Bacon, Newton | First since Democritus to believe matter was made of atoms

1782 — Antoine Lavoisier

Father of Modern Chemistry; made quantitative obs. about chem. rxns.; Law of Conservation of Matter

1782 — Law of Conservation of Matter (Mass)

In an ordinary rxn., matter cannot be created or destroyed only rearranged

1799 — Joseph Proust — Law of Definite Proportions

Most famous for his studies of iron pyrite, FeS2, also known as fools gold. He discovered that all iron pyrite consisted of 46.5% iron and 53.5% sulfur by mass.

1799 — Law of Definite Proportions

Elements that make up a compound are always in a certain proportion by mass; suggested that matter came in packages of certain sizes

1803 — John Dalton — First Atomic Theory

After studying the works of lavoisier, Proust and many others, John Dalton, an english school teacher and chemist, proposed the first atomic theory.

1803 — First Atomic Theory

John Dalton

1. All matter is made of indivisible particles (atoms)

2. Atoms of the same element are the same

3. Atoms of different elements are different

4. In a chem. rxn. atoms are only rearranged

5. Atoms of different elements combine chemically in definite Proportions to make compounds

raised many questions; why do atoms of different elements act differently?

1811 — J.J. Berzelius

Element Symbols; established modern system of chemical symbols for elements

1803 — John Dalton

Solid Atom; tiny, indivisible particle

1886 — Eugen Goldstein

Discovered Canal Rays (Anode Rays)

1886 — Discovery of Canal/Anode Rays

Eugene Goldstein; led to the development of mass spectometry

1896 — Henri Becquerel

Discovery of Radioactivity

1896 — Discovery of Radioactivity

Henri Becquerel; suggested very strongly that something was coming out of the supposedly indivisible atoms

1897 — J.J. Thomson

Discovered Electron (studied Cathode Ray Tube); determined that Cathode Rays were made of electrons with properties

1897 — Discovery of the Electron (Cathode Ray Tube with properties)

J.J. Thomson

1. e- are negative particles

2. e- from all atoms are the same

3. e- had an e/m (charge to mass) ratio of 1.759 × 10⁸ c/g

1897 — Plum Pudding Model

Positive sphere of matter with electrons embedded throughout; J.J. Thomson knew his atom still didn’t fit all of the facts

1898 — Wilhelm Wien

Discovered the Proton; Doing approx. same experiments as Thomson, discovered that Canal Rays consisted of protons with properties

1898 — Discovery of the Proton

Wilhelm Wien; properties:

1. charged +1

   1. All have the same mass of 1 amu (1.67 × 10^-24 g)

1909 — Rober Millikan

Oil Drop Experiment; discovered the charge and mass of the electron

1909 — Oil Drop Experiment

Robert Millikan;

1. The charge on each oil drop was a whole # multiple of -1

2. Used the electron charge & Thomsons e/m ratio to find electron mass of 0 amu

1910 — J.J. Thomson

Discovered Isotopes using a modified Crooke’s Tube that separated particles by mass, he discovered two different types of neon. They were chemically identical, but had different masses.

1910 — Discovery of Isotopes

J.J. Thomson; Crookes’ Tube separating neon particles by mass

Isotope

atoms of the same element that are chemically the same & have different masses; every naturally occurring element consists of mixtures of more than one isotope

1911 — Ernest Rutherford

Gold Foil Experiment; testing plum pudding model

1911 — Gold Foil Experiment

Ernest Rutherford; concluded that:

1. the atom is mostly empty space

2. the atom contains a tiny, dense, core called nucleus

1911 — Nuclear Atom

Ernest Rutherford; Tiny, dense, + core (nucleus) surrounded by empty space containing e-

1913 — Niels Bohr

Came up with the Planetary Atom - Tiny, dense + core (nucleus) surrounded by e- in energy levels that orbit nucleus

1913 — Planetary Atom

Niels Bohr;

1. e- in an atom can only exist if they have certain “allowed energies” (energy is quantized)

2. e- orbit the nucleus at a calculated distance from the nucleus determined by e- energy

1926 — Erwin Schrodinger

came up with the Electron Cloud (Quantum Mechanical) Atom

1926 — Electron Cloud Atom

Erwin Schrodinger

tiny, dense + nucleus surrounded by e- in mathmatically defined regions called orbitals

• e- do not follow nice neat paths

According to Bohr and Schrodinger

Electrons in an atom can only exist if they are in “allowed” energy levels, or shells

1932 — James Chadwick

Discovered the Neutron; while bombarding a Be atom with alpha particles, he knocked off a neutron

1932 — Discovery of the Neutron

James Chadwick; Scientists began to suspect that the atom contained a third particle, which was similar to the proton, but was neutral.

The atom consists of 2 major parts

Nucleus and Electron Cloud

Nucleus

tiny, dense, + core

Electron Cloud

set of mathematically defined regions in space around nucleus

The atom consists of three major subatomic particles

Protons, Neutrons, Electrons

Protons

+1 Charge; 1 amu

Neutrons

0 Charge; 1 amu

Electrons

-1 Charge; 0 amu

Nuclear Notation (Isotopes)

Atomic Number (Z)

# of p+ in nucleus; unique to each element

Mass Number (A)

sum of p+ and n⁰ in the nucleus of an atom; identifies the isotope

Atomic Mass/Weight

A weighted average of all naturally occurring atoms of an element

(mass isotope x % abundance) + (mass isotope x % abundance) / 100

Nuclear Radiation

Fission and Fusion; produces a lot of energy

Fission

• heavy atoms split

• produces radioactive waste

  • lower temp. required (in comparison)

Fusion

• light atoms join

• no radioactive waste produced

  • high temp. required (ex. stars are fusion reactors)

Nuclear Decay

Alpha Decay, Beta Decay, Gamma Radiation

Alpha Decay

• produces alpha particles (₂⁴He)

• stopped by clothes, skin, paper

• weakest

B

Beta Decay

• produces a beta particle (_-1⁰e or -₁⁰B) high speed, high energy electron

  • stopped by glass, thin sheets of metal, thick wood

Gamma Radiation

• produces gamma rays (high energy electromagnetic radiation)

• no charge, no mass

• stopped by thick concrete, thick sheets of lead

• strongest