The Structure Of The Atom

Atom - Smallest particle of an element that has the same properties as that element.

• Protons are positively charged particles (+1)

• Neutrons have no charge

• Electrons are negatively charged particles (-1)

• Protons and neurons are found in the nucleus of an atom

• Electrons orbit around the atom.

• In an electrically neutral atom, # of protons equals the # of electrons

• In the nucleus of an atom, there are protons and neutrons

• Different elements = different particle counts and arrangements

Atomic Mass Unit: Unit used to express the mass of an atom

• Protons have a mass of 1 AMU

• Neutrons have a mass of 1 AMU

• Electrons (smallest) have a mass of 0.0006 AMU

Quarks: Small particles that make protons and neutrons

Atomic Number (Z) : The number of protons in an atom

• It differs for each element and is written above the periodic table

• CANNOT use # of electrons to identify an atom.

• Every atom of a given element has the same atomic number.

• When an atom loses electrons, it becomes positively charged

• When an atom gains electrons, it becomes negatively charged

  Mass Number (A): The # of protons and neutrons in the nucleus of an atom.

  • The mass number is shown as a superscript (up)

  • Atoms of the same element can have different mass numbers

  The formula for Finding # of neutrons: N = (A-Z)

  Ex: AL = 27-13=14 neutrons

  Isotopes: Atoms of the same element with different mass numbers

  • #  of protons and electrons would be the same

  • # of neurons would be different

  Atomic Mass: The mass of a single atom; approximately equal to the total mass of the protons and neutrons in an atom.

  • The mass of an electron is insignificant.

  • Mass of atom = mass of protons + mass of neutrons

  Average Atomic Mass:

  • Weighed average mass of all isotopes of an element