The Building Blocks of Matter: Atoms Matter Anything that has mass and takes up space (volume)

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The Building Blocks of Matter: Atoms


  • Anything that has mass and takes up space (volume)

    • Examples:
      • A brick has mass and takes up space
      • A desk has mass and takes up space
      • A pencil has mass and takes up space
      • Air has mass and takes up space


  • Smallest possible unit into which matter can be divided, while still maintaining its properties.

  • Made up of:

    • protons
    • neutrons
    • electrons
  • The solar system is commonly used as an analogy to describe the structure of an atom

Atoms are so small that…

  • it would take a stack of about 50,000 aluminum atoms to equal the thickness of a sheet of aluminum foil from your kitchen.

  • if you could enlarge a penny until it was as wide as the US, each of its atoms would be only about 3 cm in diameter – about the size of a ping-pong ball

  • a human hair is about 1 million carbon atoms wide.

  • a typical human cell contains roughly 1 trillion atoms.

  • a speck of dust might contain 3x1012 (3 trillion) atoms.

  • it would take you around 500 years to count the number of atoms in a grain of salt.

Let’s Experiment

  • In order to try to gain an idea of how small an atom really is, you will complete the following activity.

    • Cut a strip of 11 in. paper in half.
    • Discard one half.
    • Cut the remaining piece in half.
    • Continue cutting and discarding the strips as many times as you can.
    • Make all cuts parallel to the first one. When the width gets longer than the length, you may cut off the excess, but that does not count as a cut.


  • How many cuts were you able to make?

  • Do you think you could keep cutting the paper forever? Why or why not?

Protons (+)

  • Positively charged particles

  • Help make up the nucleus of the atom

  • Help identify the atom (could be considered an atom’s DNA)

  • Equal to the atomic number of the atom

  • Contribute to the atomic mass

  • Equal to the number of electrons


Electrons (-)

  • Negatively charged particles

  • Found outside the nucleus of the atom, in the electron orbits/levels; each orbit/level can hold a maximum number of electrons ( 1st = 2, 2nd = 8, 3rd = 8 or 18, etc…)

  • Move so rapidly around the nucleus that they create an electron cloud

  • Mass is insignificant when compared to protons and neutrons

  • Equal to the number of protons

  • Involved in the formation of chemical bonds

Hydrogen (H) Atom

  • Notice the one electron in the first orbital

Oxygen (O) Atom

  • Notice the two electrons in the first orbital/level and the six in the second

Sodium (Na) Atom

  • Notice the two electrons in the first orbital/level, eight in the second, and one in the third

The Atom’s “Center”

  • Protons and neutrons are grouped together to form the “center” or nucleus of an atom.


    • Particles that make up protons and neutrons

Sub-Atomic Particles Weight Comparison (protons, neutrons, electrons)

Sub-atomic Particles Size Comparison (protons, neutrons, electrons, & quarks)

Atomic Number

  • The number of protons in the nucleus of an atom

Mass Number

  • The total number of protons and neutrons in an atom’s nucleus

  • Expressed in Atomic Mass Units (amu)

    • Each proton or neutron has a mass of 1 amu

Building Atoms

  • Using the whiteboard and the proton, neutron, and electron pieces, build the following atoms, and determine their atomic and mass numbers.

Atom Builder

  • Using the interactive website link below, practice building atoms.



  • Gravitational Force

  • Electromagnetic Force

  • Strong Force

  • Weak Force

Gravitational Force

  • The force of attraction of objects due to their masses

  • The amount of gravity between objects depends on their masses and the distance between them

Electromagnetic Force

  • The force that results from the repulsion of like charges and the attraction of opposites

  • The force that holds the electrons around the nucleus

Strong Force

  • The force that holds the atomic nucleus together

  • The force that counteracts the electromagnetic force

Weak Force

  • This force plays a key role in the possible change of sub-atomic particles.

    • For example, a neutron can change into a proton(+) and an electron(-)
  • The force responsible for radioactive decay.

    • Radioactive decay  process in which the nucleus of a radioactive (unstable) atom releases nuclear radiation.


  • Atoms that have the same number of protons, but have different numbers of neutrons

  • Examples

Atomic Mass

  • The weighted average of the masses of all the naturally occurring isotopes of an element

  • The average considers the percent abundance of each isotope in nature

  • Found on the periodic table of elements

  • Example


  • Charged particle that typically results from a loss or gain of electrons

  • Two types:

    • Anion = negatively charged particle
    • Cation = positively charged particle

Building Ions

  • Using the whiteboard and the proton, neutron, and electron pieces, build the following ions, and determine their atomic and mass numbers.

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