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Chapter 3 pages 65-89
3-1
Vocab
Law of conservation of mass- mass is neither destroyed or created in Chemical reactions
or physical changes
Law of definite proportions- Chemical compound contains same elements in same
proportions by mass Ex. NaCl always 39.34%=Na
60.66%Cl
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
Daltons Atomic Theory
1) All matter made up of atoms
2) Atoms of same element have same size, mass, and other properties
3) Atoms cannot be subdivided created or destroyed
4) Atoms of different elements combine in whole number ratios
5) Atoms are combined, separated, or rearranged in chemical reactions
Not all of Daltons theories have been proven true
Important concepts
All matter composed of atoms
Atoms of any one element differ from an atom from another element
Modern Atomic Theory
1)All matter is composed of atoms
2)Atoms of any one element differ in properties from atoms of another element
remain unchanged
3-2
Electron DiscoveryEnglish scientist J. Joseph Thompson discovered that atoms have negatively charged
particles in them while studying the passage of electricity through a gas in a cathode ray
tube. He called these particles corpuscles but today we call them electrons.
This finding is important because it was the first finding that showed particles of the atom
had charges.
Discovery of the atomic nucleus
Scientist Ernest Rutherford conducted an experiment in which he bombarded a thin sheet
of gold foil with alpha particles. He expected that the alpha particles would pass through
the foil without being effected. When the experiment was over, he was surprised to see
that some of the alpha particles actually bounced right back at him. He found that about 1
in 8000 did this. After thinking about this for a long time, he concluded that the particles
must have hit a small tightly packed bundle of particles with a positive charge.
Rutherford suggested that this bundle was the nucleus. He also suggested that the
electrons orbited around the nucleus.
This discovery was important because it revealed more about the atoms structure.
Charge and mass of electrons
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
Vocab
Atom- the smallest particle of an element that retains the chemical properties of that
element
Nuclear Forces- Short range proton neutron, proton proton, and neutron neutron forces
hold the nuclear particles together
3-3 page 75
Vocab
Atomic number- the number of protons in the nucleus of each atom of that element
Isotopes- atoms of the same element that have different masses
Nuclide- a general term for any isotope of any element
Mass Number- the total number of protons and neutrons in the nucleus of an isotope
Atomic Mass Unit- Exactly 1/12 the mass of a carbon 12 atom
Average Atomic Mass- The weighted average of the atomic masses of the naturally
occurring isotopes of an element
Mole- the amount of a substance that contains as many particles as there are atoms in
exactly 12g of carbon -12
Avogadros number- 6.022x1023 – is the number of particles in exactly one mole of a pure
substance
Molar mass- the mass of one mole of a pure substance
Refer to Table 3-11 Page 82 for mass mole atom conversion equations
- C6 – Atomic # or # of protons
Mass # = neutrons + protons 12