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THE ATOM
NUCLEAR MODEL OF THE ATOM
• An atom is an electrically neutral particle
• Composed of protons, neutrons, and electrons.
• Atoms are spherical in shape
• Have a tiny, dense nucleus of positive charge surrounded by one or more negatively charged electrons
• Nucleus contains 99.7 % of the mass of an atom.
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BASIC STRUCTURE OF THE ATOM
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SUBATOMIC PARTICLES
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SUBATOMIC PARTICLES
• Most of the atom consists of fast-moving electrons traveling through the space around the nucleus.• Atoms are neutral in charge• The number of protons = the number of electrons
• Atomic Number: • The number of Protons in the nucleus • determines the identity of an atom• No two types of atoms have the same number of protons
• An Element consists of atoms with the same number of protons.
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ATOMIC NUMBER(Z): THE NUMBER OF
PROTONS IN THE NUCLEUS OF EACH ATOM OF THE ELEMENT
• Atomic Number = Protons• Elements are arranged in the periodic table
from left to right in order of increasing atomic number.• Atomic number identifies the element
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ISOTOPES AND MASS NUMBER
• Atoms can have different mass.• Naturally occurring elements are a mixture of
atoms that have different numbers of neutrons. • Atoms with the same number of protons, but
different number of neutrons are called Isotopes.
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HYDROGEN HAS THREE ISOTOPES:
• Protium 1 proton 1 electron 0 neutrons• Deuterium 1 proton 1 electron 1 neutron• Tritium 1 proton 1 electron 2 neutrons
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ISOTOPES AND MASS NUMBER
• Isotopes: atoms of the same element that have different masses. • Same number of protons• Different number of neutrons • Different Mass• Atoms of different isotopes have different
masses so identity is given by name and name and mass.mass.
• Mass Number = protons and neutrons
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ISOTOPE (NUCLEAR) SYMBOLS:
Consists of three parts1. the symbol of the element2. the atomic number of the element 3. the mass number of the specific isotope.
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NUCLEAR SYMBOL•Read as Helium-4
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ISOTOPE NAMES
Element Name-Mass NumberHelium-4Potassium-39Hydrogen-3
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NEUTRONS = MASS NUMBER – ATOMIC NUMBER
Atomic Number: _________Mass Number: __________# of Protons: _________# of Electrons: _______# of Neutrons: ________Name of Isotope: ____________
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EXAMPLE
Atomic Number: _________Mass Number: __________# of Protons: _________# of Electrons: _______# of Neutrons: ________Name of Isotope: ____________
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EXAMPLE
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Atomic Number: _________Mass Number: __________# of Protons: _________# of Electrons: _______# of Neutrons: ________Isotope Name: _________
DRAW THE ISOTOPE SYMBOL FOR CALCIUM WITH 21 NEUTRONS.
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COMPARING POTASSIUM ISOTOPES
Potassium-41• protons = ________• electrons = ______• neutrons = _______
Potassium-40• protons = ________• electrons = ______• neutrons = _______
Potassium-39• Protons = __________• Electrons = _________• Neutrons = __________
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RELATIVE ATOMIC MASSES
• Atomic masses measured in grams are very small. • Example: An atom of Oxygen-16 has a mass of 2.657 x 19-23grams.
• It is most convenient to measure mass in relative atomic masses.
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TO SET UP A RELATIVE SCALE OF ATOMIC MASSES:
1. One atom is chosen and assigned a relative mass value,
2. All the other masses are expressed in relation to this defined standard.
• Carbon-12 is the chosen standard.• A single atom of C-12 is assigned a mass
of exactly 12 atomic mass units(u).
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AN AMU
• One amu is exactly 1/12th of the mass of a carbon-12 atom or 1.660 5402 x 10-24grams.
• The atomic mass of a carbon-12 atom is exactly 12 u. • Atomic Mass: The mass of an atom expressed in
atomic mass units.
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AVERAGE ATOMIC MASS
• Atomic Masses given for the elements on the periodic table are weighted averages for the naturally occurring mixtures of isotopes, called average atomic mass.
• Average Atomic Mass depends on mass and relative abundance of the isotopes.
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TO CALCULATE AVERAGE ATOMIC MASS:
1. Atomic mass x relative abundance 2. Add results.
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EXAMPLE PROBLEM:
Naturally occurring copper consists of 69.17% Cu-63, mass of 62.939 598u and 30.83% Cu-65, mass of 64.927 793u• 0.6917 x 62.939 598u = 43.535u• 0.3083 x 64.927 793u = 20.017
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