Atomic Theory

Atoms and Subatomic Particles

• Atom: the smallest unit of measurement for anything

  • They are neutral-charged, and individual particles have different charges + mass

  • Atoms can be broken down into 3 subatomic particles: proton, neutron (protons and neutrons make up the nucleus), and electrons

    • Proton

      • positively charged subatomic particle that is found inside of the nucleus

      • the atomic number of an element represents the number of protons in said element

    • Neutron

      • contain no charge

      • have the same mass as protons (not the same number)

      • found inside of the nucleus

      • the number of neutrons is equal to the mass number subtracted by the number of protons

        • #n = mass number - #p

    • Electrons

      • negatively charged subatomic particles found outside of the nucleus (for test purposes think of planets surrounding the sun)

      • chemical reactions occur as the result of interactions between electrons

  • Neutral atoms contain the same number of protons and electrons. If there is an imbalance, then the atom becomes an ion

    • Ions and Charges:

      • Charge = #protons - #electrons

      • An atom charge is displayed to the right, above a symbol (C^+3)

        • O^-2 means that there are 2 more negative units (electrons) than positive units (protons)

      • All atoms are neutral unless a charge is displayed

      • Ion = an atom with a positive or negative charge

• Mass Number: The number of protons + the number of neutrons

  • For example, carbon has 6 protons and 6 neutrons, so the mass number would be 12

  • The mass number on the periodic table is always rounded to the nearest whole number

  • In certain atoms recognized as isotopes the mass number of the atom is different

    • The number of neutrons can vary in a natural sample

      • Carbon-13 has 1 more mass unit than usual, meaning the number of neutrons is 7 instead of the usual 6

    • Isotope = atoms of an element with a different number of neutrons (mass) than the periodic table

      • Written as the element name and the atomic mass (Carbon-13)

      • Most elements have 2+ isotopes

• Different ways to express specific parts of an element:

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• Finding different subatomic particles:

  • Protons: Look at the atomic number on the periodic table (usually in the bottom left corner or the very top of an element box)

  • Neutrons: Find the mass number (in the top left corner or the very bottom of the element box) and subtract it from the atomic number/the number of protons

  • Electrons:

    • Isotope: electron charge = atomic number - e

      • C^-4: -4 = 6 - e

    • Non-isotope: the same number as protons

Drawing Bohr Model Atoms

• Electrons are found in orbits (shells) surrounding the nucleus (planets revolving around the sun)

• Each shell has a fixed number of electrons that it can hold

  • Shell 1: 2 electrons

  • Shells 2 and 3: 8 electrons

  

Lewis Dot Diagrams

• Based on the valance electrons of an atom

  • Valance electrons: outermost shell of electron rings

    • Need 8 valance electrons to be stable

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Bill Nye Discussion + The Structure of Atoms

• Relationship between atoms and elements

  • atom: element:: piece of pasta: spaghetti

    • In this scenario, the atom acts as the smallest unit of an element while still being that element. A piece of pasta is the smallest unit of spaghetti that still remains spaghetti

      • atom = unit, element = type

      • atoms are not building blocks! they are the element!

• Atoms are mostly empty spaces, but things can’t get through them. Why?

  • think of a fan with blades moving extremely fast

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    • electrons move so fast (so fast that they seem everywhere at once) that things are unable to pass through

• No one really knows what protons/neutrons really look like due to the size, so we just guess