Section 2: The Structure of Atoms
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Transcript of Section 2: The Structure of Atoms
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Section 2: The Structure of Atoms
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What is in an atom?
• The three main subatomic particles are distinguished by mass, charge, and location in the atom: electrons, protons and neutrons
• Proton is a subatomic particle that has a positive charge and that is located in the nucleus of an atom
• Neutron is a subatomic particle that has no charge and that is located in the nucleus of an atom
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What is in an atom?
• Each element has a unique number of protons– An element is defined by the number of protons
• Unreacted atoms have no overall charge– A charged atom is called a ion
• The electric force holds the atom together
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Atomic Number and Mass Number
• Atoms of each element have the same number of protons, but they can have different numbers of neutrons
• The atomic number equals the number of protons
• The mass number equals the total number of subatomic particles in the nucleus
• Video
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Isotopes
• An isotope is an atom that has the same number of protons as other atoms of the same element do but that has a different number of neutrons
• Isotopes of an element vary in mass because their numbers of neutrons differ
• The number of neutrons can be calculated: Neutrons = Mass number (A) – Atomic number (Z)
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Atomic Masses• Because working with such tiny masses is
difficult, atomic masses are usually expressed in unified atomic mass units (u)
• Average atomic mass is a weighted average
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Atomic Masses
• The mole is used for counting small particles– 1 mol = 602,213,670,000,000,000,000,000
particles– Avogadro’s number: 6.022 x 1023
• Video: What is a mole?
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Atomic Masses
• Moles and grams are related, you can convert between moles and grams
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Atomic Masses
• Examples:
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Atomic Mass
• Compounds also have molar masses– To find the molar mass of a compound, you can
add up the molar masses of all of the atoms in the molecules of the compounds
• Video: Atomic Mass