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The Structure of the Atom

The Structure of the Atom. The Building Block of Matter. Atoms are the smallest particles of an element that retains the chemical properties of that element. Parts: Nucleus – small region in the center of the atom. (+ charged protons, = charged neutrons)

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The Structure of the Atom

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  1. The Structure of the Atom The Building Block of Matter

  2. Atoms are the smallest particles of an element that retains the chemical properties of that element • Parts: • Nucleus – small region in the center of the atom. (+ charged protons, = charged neutrons) • Electron Cloud – large region, compared to nucleus, where electrons are found.

  3. Size of nucleus vs. electron cloud If an atom was the size of a sports stadium, the nucleus would be the size of a marble! Subatomic Particles: • Protons : + charge, relative mass = 1.007 atomic mass units (amu); round to 1 • Neutrons: = charge, relative mass = 1.009 atomic mass units (amu); round to 1 • Electrons: - charge, relative mass = 0.0005 atomic mass units (amu); round to 0 (not factored in when figuring total mass of an atom)

  4. Structure of Subatomic Particles • Subatomic particles composed of fast moving points of energy called quarks Quark Calculations(for protons and neutrons) Each proton is 2 up quarks and 1 down quark 2(2/3) – 1(1/3) = 4/3 – 1/3 = 3/3 or +1 Each neutron is 2 down quarks and 1 up quark 2(-1/3) + 2/3 = 0 Each electron is composed of 2 down quarks 3(-1/3) = -1

  5. Isotopes • Atoms with the same number of protons & electrons but a different number of neutrons. • They are the same element, but have different masses. • All isotopes are used to calculate atomic mass (reason why weight is a decimal). • Most elements consist of a mixture of isotopes.

  6. Atomic Number • Number of protons in the nucleus (also the number of electrons) • Typically the number on top of the symbol on the Periodic Table. 13 Atomic Number 26.981

  7. Mass Number • Number of protons + number of neutrons in an atom. • When solving for number of neutrons: round mass number properly, subtract atomic number from mass number.

  8. Element Symbols • Hyphen Notation: Element symbol – Mass # (rounded) Example: Helium  He-4 • Nuclear Symbol: Superscript Mass Number, Subscript Atomic Number, Symbol Example: 4 He 2

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