Lesson 3 Flashcards
(45 cards)
In a chemical reaction, the mass of the substances produced is equal to the mass of the substances reacted
Law of conservation of mass
-Foundation of stoichiometric calculations
• Allows chemist to determine the amounts of reactants or products involved in a chemical reaction
Law of conservation of mass
-Also called the law of definite composition
-Any sample of a given compound will always be composed of the same
elements in the same proportion by mass:
Law of definite proportion
- For elements that can form different compounds, the masses of the second element that can combine with a fixed mass of the first element are in a ratio of small whole numbers
Law of multiple proportion
Law of multiple proportion
Example: N and 0 can combine to produce different compounds in
different whole number ratio:
A. NO
B. NO2
C. N₂O
Dalton’s atomic theory
Book = A new System of Chemical Philosophy
• Proposed an atomic theory of matter that can explain
chemical observations as predicted by the three fundamental laws
Dalton atomic theory(READ)
Postulates:
1. Matter is made up of extremely small indivisible particles called atoms.
2. Atoms of the same element are identical and are different from those other elements:
3. Compounds are formed when atoms of different elements combine in certain whole-number ratios
4. Atoms rearrange only during a chemical reaction to form new compounds.
-There are various basic elements from which all matter is made -Everything is composed of small atoms moving in a void
Democritus(460-370 B.C.)
-Some atoms are round, pointy, oily, have hooks, etc. to account for their properties
-Ideas rejected by leading philosophers because void = no existence
Democritus (460-370 B.C.)
-Introduced his ideas in 1803
-Each element is composed of extremely small
-particles called atoms All the atoms of a given element are identical, but
they differ from those of any other element
John Dalton (1766-1844)
-Atoms are neither created nor destroyed in any chemical reaction
-A given compound always has the same relative numbers and kinds of atoms
John Dalton (1766-1844)
Discovered electron 1897-Cathode Ray Experiment
Joseph John Thomson (1856-1940)
-Plum Pudding model 1904
•Electrons in a soup of positive charges
Joseph john thomson(1856-1940)
Discovered isotopes 1913
Joseph john thomson
Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle: the electron
Conclusion from the Study of Electron
A. Cathode rays have identical
properties regardless of the element used to produce them. All elements must contain identically charged electrons.
B. Atoms are neutral, so there must be positive particles in the atom to
balance the negative charge of the electrons
C. Electrons have so little mass that atoms must contain other particles that account for most of the mass
Nucleus Theory, 1910
•alpha particle gold foil experiment
Ernest Rutherford (1871-1937)
-An atom’s mass is mostly in the nucleus
-The nucleus has a positive charge (Moseley)
-Electrons in fixed orbit
Ernest Rutherford (1871-1937)
Electrons are
Negative charge
Proton are
Positive charge
Neutron are
Neutral charge
Alpha particle gold foil experiment:
-Particles shot through thin sheet of gold
-Most shots went straight through
-A small amount were deflected
-Hence…. The atoms must be made of mostly empty space with a small dense nucleus
Rutherford found that most (99%) of the alpha particles that he shot at the gold went straight through
From these experiments Rutherford concluded that the atom had a dense positive core, with the rest composed of mostly empty space with the occasional negatively charged electron
Nuclear model
Planetary Model 1913
- Nucleus surrounded by orbiting electrons at different energy levels
-electrons exist in several distinct layers or levels
-Electrons have definite orbits
Niels Bohr (1885-1962)
