Download 1.1 Inside the Atom

Chapter 1 Section 1
Introduction
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Atoms are the smallest particles of an element that still have the elements
properties
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Building blocks of all matter
Parts of the Atom
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Nucleus
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Center of the atom
Contains most of the atom’s mass even though it is very small
Protons: particle in the nucleus that has a positive electric charge
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Neutron: particle in the nucleus that has no electric charge
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This gives the atoms their unique properties
Atoms typically have the same number of protons and neutrons
Outside the Nucleus “cloud”
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Electrons: particles outside the nucleus that has a negative electric charge
Almost no mass
• Atoms have the same number of protons and electrons
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Charges cancel out
Atomic Number vs Mass Number
• Atomic Mass Unit (amu)  SI unit
• Mass of 1 proton  1.7 × 10 -24 g  1
amu
• Atomic Number: the number of protons
in an atom
• Mass Number: the number of protons
plus the number of neutrons in an atom