Quiz 1: Isotopes, Ions, and Average Atomic Mass 9th Grade Chem

This quiz will cover isotopes, ions, and average atomic mass. You will have 20 minutes to take it in class. It will be all fill in the blank and calculation-based questions. BRING A PENCIL AND A CALCULATOR!

• Mass number: Protons+neutrons

  • when given the mass number, subtract the amount of protons from the mass number (see atomic number), and what you’re left with is the amount of neutrons

• Atomic number: protons

  • The larger number on the periodic table

• Atomic mass: average of the relative amounts of each isotope

• Electrons: Negatively charged particles, found outside of the nucleus of an atom

• Protons: positively charged particles, found in the nucleus of an atom

• Neutrons: uncharged particles, found in the nucleus of an atom

• Neutral atoms: have the same amount of electrons and protons; neutrons differ

• Isotopes: atoms of the same element with the same amount of protons and a differing amount of neutrons

  • the notation for this is has in subscript:

    • on the top left corner before the chemical symbol, the mass number

    • on the bottom left corner before the chemical symbol, the atomic number

      • Ex:

        

  • It can also be written with the element name, a dash, and then following that the mass number

    • Ex: Carbon-12

• Ions:

  • there is not an equal amount of protons and electrons

  • if there are more protons than electrons, the charge is positive

    • Ex: Helium has a charge of +2. I know that it has 2 protons, but because it has a charge of +2, there are 2 more protons than electrons. Therefore, it has 0 electrons.

  • if there are more electrons than protons, the charge is negative

    • Ex: nitrogen has a charge of -3. I know that it has 7 protons, but because it has a charge of -3, there are 3 more electrons than protons. Therefore, there are 10 electrons.

• Calculating average atomic mass (AAM): (atomic mass of isotope #1)(fractional abundance of isotope #1)+(atomic mass of isotope #2)(fractional abudnace of isotope #2)

  • fractional abundance is the percentage of a particular isotope in the total sample of atoms, written as a decimal

  • remember sig figs!!!

• Significant figures

  • When multiplying/dividing sig figs, whichever # has the least amount of sig figs, you’ll round there

  • when adding/subtracting sig figs, line it up all the way. Whichever one is the shortest, go from there