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Section 2: The Structure of Atoms

Section 2: The Structure of Atoms. 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

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Section 2: The Structure of Atoms

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  1. Section 2: The Structure of Atoms

  2. 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

  3. 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

  4. 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

  5. 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)

  6. 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

  7. 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?

  8. Atomic Masses • Moles and grams are related, you can convert between moles and grams

  9. Atomic Masses • Examples:

  10. 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

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