Test 2–Scientists and Conversions Flashcard

Democritus
400 BC
Founded Atoms
Called them indivisible.
Aristotle
Refuted atoms.
Thought that all matter was continuous.
Law of Conservation of Mass
Mass is neither destroyed nor created during ordinary chemical or physical reactions.
Law of Definite Proportions
A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound.
Law of Multiple Proportions
If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers.
John Dalton
1808
Explained the law of conservation of mass, law of definite proportions and the law of multiple proportions.
Dalton’s Atomic Theory
1. All matter is composed of extremely small particles called atoms.
2. Atoms of a given element are identical size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
3. Atoms can not be subdivided, created, or destroyed.
4. Atoms of different elements combine in simple, whole number ratios to form chemical compounds.
5. In chemical reactions, atoms are combined, separated, or rearranged.
Two of Dalton’s Points Proven Wrong
Atoms ARE divisible into smaller particles.
A given element can have atoms with different masses.
Atom
Smallest particle of an element that retains the chemical properties of that element.
Joseph John Thompson
Founded electrons by observing cathode ray tubes.
Robert A. Millikan
Found that the electron is much much smaller than the smallest atom of an element.
Also discovered that the electron has a negative charge.
Atomic Structure Inferences
1. Because atoms are electrically neutral, they must contain a positive charge to balance the negative electrons.
2. Because electrons have so much less mass than atoms, atoms must contain other particles that account for most of their mass.
Ernst Rutherford, Hans Geiger and Ernest Marsden
Founded the nucleus of the atom.
Also founded the electron cloud.
Nuclear Forces
Short range proton-neutron, proton-proton, and neutron-neutron forces hold the nuclear particles together.
Atomic Number
Number of protons in a nucleus of each atom of that element.
Isotopes
Atoms of the same element that have different masses.
Mass number
total number of protons and neutrons in the nucleus of an isotope.
Nuclide
General term for any isotope for any element.
Atomic Mass Unit (Amu)
The unit that is equal to the mass of carbon-12 and is used as a relative measurement of the periodic table.
Average Atomic Mass
the weighted average of the atomic masses of the naturally occurring isotopes of that element.
Mole
Amount of a substance that contains as many particles as there are atoms in exactly 12g of carbon-12.
Avogadro’s Number
(6.022 X10tothe23rd) the number of particles in exactly one mole of a pure substance.
Molar Mass
The mass of one mole of a pure substance.
Moles–>Atoms
Amt. of element in moles X 6.022×1023=Number of atoms.
Atoms–>Moles
Number of atoms X 1/6.022×1023=Moles
Atoms–>Mass
Number of atoms X 1/(6.022×1023) X molar mass of element=Mass in grams.
Mass–>Atoms
Mass of element X 1/Molar Mass of element x(6.022×1023)=Atoms
Mass–>Moles
Mass of element x 1/molar mass of element=Moles
Moles–>Mass
Moles X molar mass of element = Mass of element
Conversion Numbers
1 mole=6.022X1023 atoms
1 mole= molar mass of element

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