Elements, Atoms, and Ions

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Elements, Atoms, and Ions
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Dalton Atomic Theory

1. Elements are composed of extremely small
   particles called atoms.
2. All atoms of a given element are identical,
   having the same size, mass and chemical
   properties.
3. The atoms of one element are different from the
   atoms of all other elements.
4. Atoms of one element can combine with atoms of
   other elements to form compounds. A given
   compound always has the same relative numbers and
   types of atoms.
5. Atoms are not created or destroyed in chemical
   reactions. A chemical reaction simply changes
   the way the atoms are grouped together.

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Law of Multiple Proportions
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Each water molecule has 2 hydrogen atoms (2 g)
and 1 oxygen atom (16 g). The mass ratio of
oxygen to hydrogen is always 81.
Law of Constant Composition
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8 X2Y
Law of Conservation of Mass
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Elements, Atoms, Molecules, Ions and Isotopes
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Atoms

• Smallest particle of an element that retains the
  chemical identity of that element.
• Composed of protons, neutrons, and electrons.
• Even the subatomic particles are made up of
  particles themselves.

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Subatomic Particles
mass p mass n 1840 x mass e-
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Units of Mass

• Particles masses measured in grams are extremely
  small.
• For convenience, atomic mass units are used to
  express masses instead.
• 1 AMU 1/12 the mass of a Carbon-12 atom
• Scientists massed a sample of carbon-12,
  determined the mass of a single carbon-12 atom,
  and divided it by 12 to find the mass of each
  proton and neutron.

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Subatomic Particles
Particle Mass Charge Location
proton 1 AMU in the nucleus
neutron 1 AMU none in the nucleus
electron 0 AMU - surrounding the nucleus
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Isotopes are atoms of the same element (X) with
different numbers of neutrons in their nuclei
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Molecule two or more atoms in a definite
arrangement held together by chemical bonds
Diatomic molecule contains only two atoms
H2, N2, O2, Br2, HCl, CO
Polyatomic molecule contains more than two atoms
O3, H2O, NH3, CH4
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Ion Atom or group of atoms with a net positive
or negative charge.
cation ion with a positive charge If a neutral
atom loses one or more electrons it becomes a
cation.
anion ion with a negative charge If a neutral
atom gains one or more electrons it becomes an
anion.
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Do You Understand Ions?
13 protons, 10 (13 3) electrons
34 protons, 36 (34 2) electrons