Chapter 1: History of Chemistry

Who is Antoine Lavoisier?

1. Created law of conservation of mass

   • mass is neither created or destroyed

2. combustion involves oxygen

Joseph Proust

1) Law of Definite Proportions

• the proportion by mass of the elements in a specific compound is always the same

  • ex: in water, the mass of oxygen is always eight times the mass of water.

John Dalton

1) Law of Multiple Proportions

• When two elements combine with each other to form more than one compound, the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers. 

2) Atomic Theory Postulates

3) Created a periodic table organized by atomic mass but most were wrong

John Dalton’s Atomic Theory

1. Elements are made of atoms

2. Atoms of a given element are identical

3. The atoms of a given element are different from those of any other element

4. Atoms of one element can combine with atoms of other elements to form compounds

   1. A given compound always has the same relative numbers and types of atoms

5. Atoms are indivisible by chemical processes. That is atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way atoms are grouped together.

Which of Dalton’s postulates were wrong

1) Atoms are indivisible

• protons, electrons, neutrons exist

2) Atoms of a given element are identical

• isotopes = different amount of neutrons

Avogadro

Equal volumes of different gases under the same temperature and pressure contain the same # of molecules

• 22.4 L in 1 mol

Cannizzaro

Discovered approx values of atomic masses

JJ Thomson

Cathode Ray Tubes

1. When high voltage applied to a tube, a cathode ray is produced

2. Cathode ray emerges from negative electrode

   • repelled by the negative pole of an applied electric field

3. He theorized ray was a stream of negatively charged particles called electrons

Discovered the electron

Charge to mass ratio of an electron

Charge/mass = e/m = -1.76 × 10^8 C/g

e = charge on the electron in coulombs (C)

m = electron mass in grams

Plum Pudding Model

1. JJ Thomson
2. An atom is electrically neutral. It has no charge.
3. + charges and - charges are equal.
4. An atom is made out of a sphere of + charges with -negatively charged electrons embedded in it.

Robert Millikan

Charged Oil Drop Experiment

• determined magnitude of electron charge

• (Mass of drop x gravity) = (electric field x charge)

Mass of an electron

9.1 × 10^-31 kg

Ernest Rutherford

1. Shot alpha particles at a thin sheet of metal foil 

2. He expected α particles to travel through foil

   • However many alpha particles were deflected or reflected 

     • Deflections caused by a center of concentrated positive charge in the atom

     • Discovered the nucleus

Electrons equal the number of _____

protons, in neutral atoms

Isotope

different amount of neutrons

Mass number

neutrons + proton

• top number on element notation

Atomic number

number of protons

• bottom number on element notation

• top number on periodic table

Chemical behavior determined by _____

electrons

Chadwick

• Neutrons exist, no charge, isotopes exist 

• Isotope - different amt of neutrons