Overview
This lecture explains how to determine the properties of atoms and ions, such as element name, symbol, atomic number, mass number, protons, neutrons, electrons, and charge, using a periodic table and given information.
Determining Atomic Properties from Chemical Symbol and Mass Number
- The chemical symbol (e.g., Na) identifies the element on the periodic table (Na is sodium).
- The isotope name combines the element name and the mass number (e.g., sodium-22).
- The atomic number equals the number of protons and is found above the element symbol on the periodic table (Na: atomic number 11).
- The number of neutrons = mass number − atomic number (sodium-22: 22 − 11 = 11 neutrons).
- The ion charge determines electron count: a 1+ charge means one more proton than electrons (11 protons, 10 electrons for Na⁺).
Using Protons and Neutrons to Find Other Properties
- Given the number of protons, look up the element on the periodic table (44 protons: ruthenium).
- Atomic number = number of protons (44).
- Mass number = protons + neutrons (44 + 56 = 100; ruthenium-100).
- Ion charge = protons − electrons (44 protons, 40 electrons: 4+ charge, written as Ru⁴⁺).
Solving for Ions with a Negative Charge
- Iodine-131 (1− charge): atomic number is 53 (I), mass number is 131.
- Number of neutrons = 131 − 53 = 78.
- Net charge 1− means one more electron than protons (53 protons, 54 electrons).
Determining Properties from Symbol and Neutron Count
- Mg²⁺ with 13 neutrons: Mg is magnesium, atomic number 12.
- Mass number = protons + neutrons = 12 + 13 = 25 (magnesium-25).
- 2+ charge means two more protons than electrons (12 protons, 10 electrons).
Key Terms & Definitions
- Isotope Name — element name plus mass number (e.g., sodium-22).
- Atomic Number — number of protons in an atom; found on the periodic table.
- Mass Number — sum of protons and neutrons.
- Ion Charge — difference between protons and electrons; written as +/−.
- Neutron Number — mass number minus atomic number.
- Electron Number — protons minus charge (for cations), protons plus charge (for anions).
Action Items / Next Steps
- Practice solving atomic property problems using different given information and a periodic table.