Protons, Neutrons, Electrons/Isotopes/Average Atomic Mass

An Atom is Like… If an atom was the size of a football stadium … the nucleus (protons + neutrons) would be a marble on the 50 yard line the electrons would be smaller than gnats out in the stands Gnat-sized electron Marble -sized nucleus

Atom Facts! Important things to remember about atoms! Most of an atom is empty space Electrons are so small, we can pretend that their mass is zero The mass of an atom is from its nucleus (protons & neutrons)

Atomic Number Atomic Mass Tells you the identity of the element (Each element has a different atomic #) Atomic Mass

Practice! Given the following atomic numbers, determine the identity of the elements: Atomic # Element 16 Sulfur 9 Fluorine 53 Iodine

Protons Also tells you the number of protons (Each element has a different # of protons) Atomic Mass

Practice! Determine the number of protons for each element: Element # Protons chlorine 17 arsenic 33 oxygen 8

Isotopes Isotopes = Different versions of the same element Isotopes of Carbon

Isotope Facts! Important things to remember about the isotopes of an element! Same Element Same # Protons Different # Neutrons Different Masses

% Abundance Relative Percent Abundance = The overall percent of each isotope of an element Isotopes of Carbon

Isotope Symbols OR 11H or Hydrogen-1 1 proton 0 neutrons Mass number Hydrogen-3 OR 11H or Hydrogen-1 1 proton 0 neutrons 21H or Hydrogen-2 1 proton 1 neutron 31H or Hydrogen-3 1 proton 2 neutrons

Mass Number The mass number = # protons + # neutrons Mass Number = 3 (So, if you know the # protons, you can figure out the # neutrons, and vice versa!) Example: 31H or Hydrogen-3 # Protons = 1 Mass Number = 3 Mass number = # protons + # neutrons 3 = 1 + x x = # Neutrons = 2

Practice! Determine the # of protons and neutrons for each of the following isotopes: 168O 8 protons, 8 neutrons 2110Ne 10 protons, 11 neutrons Flourine-19 9 protons, 10 neutrons Boron-11 5 protons, 6 neutrons

Atomic Mass The Atomic Mass is the average weighted mass of the isotopes of an element Atomic Mass

Add all of the answers from step 1 above. Ave. Weighted Mass To calculate the average weighted mass (atomic mass of an element: Step 1 Multiply each isotope’s mass x its % abundance. (Make sure the % abundance is in decimal form!) Step 2 Add all of the answers from step 1 above.

Ave. Weighted Mass Calculate the average weighted mass (the atomic mass) of nitrogen. Isotope Mass Relative % Abund. Nitrogen-14 14.003 amu 99.63 Nitrogen-15 15.000 amu 0.37 Step 1 (14.003)(0.9963) = 13.951 amu (15.000)(0.0037) = 0.055 amu Step 2 13.951 + 0.055 = 14.006 amu Mass % Abund. (as a decimal)

Practice! Calculate the average weighted mass (the atomic mass) of Silicon. Isotope Mass Relative % Abund. Silicon-28 27.977 amu 92.23 Silicon-29 28.976 amu 4.67 Silicon-30 29.974 amu 3.10 Step 1: Step 2: (27.977)(0.9223) = 25.803 amu 25.803 + 1.353 + 0.929 = (28.976)(0.0467) = 1.353 amu 28.085 amu (29.974)(0.0310) = 0.929 amu

Electrons Tells you the number of electrons too! Remember! The atomic # also tells you the number of protons (so…the # protons = # electrons in an atom)

Ions! When an atom loses or gains one or more electrons, it becomes an ion. There are two kinds of ions: Cations: Ions formed when atoms lose one or more electrons – have a positive charge Ex. Ca2+, Na1+, Al3+ Anions: Ions formed when atoms gain one or more electrons – have a negative charge Ex. F1-, P3-, O2-

Practice! Determine the number of electrons for each element: Element # Electrons S 16 S2- 18 Al 13 Al3+ 10

Finished!