What is in an atom? The Three Primary Subatomic Particles... n Protons n Neutrons n Electrons
Which Particle is Where? n Nucleus Protons Neutrons n Electron clouds –Swarm around the nucleus –Not in nice clear orbitals as seen in this picture
Protons n # of protons = the atomic number n Atomic number = # of protons n # of protons determines which element it is! n Who is element # 15? n How many protons does lithium have? n What is the atomic number of tin?
Neutrons n Number of neutrons can vary, even for the same element. n Isotopes –same # of protons –different # of neutrons n Elements have many different isotopes –Carbon-14, Uranium-238 n Neutrons affect the atomic mass
Atomic Mass n Sum of the protons and neutrons n Electrons are not included –Too small n What is the atomic mass of this atom?
What about the electrons? n A neutral atom has no charge. n positive charges = negative charges. n A neutral atom has the same # of electrons as protons n How many electrons does this atom have?
What if the atom isn’t neutral? n If an atom is not neutral, then it has a charge. n Ion –Charge particle n This atom has: 3 protons (+++) 2 electrons (--) n It is written as Li +
Your Periodic Table has the answers n How many protons? n How many neutrons? n How many electrons (if the atom is neutral?)
SUMMING UP… n How many protons? –The atomic number n How many neutrons? –Atomic mass minus atomic number n How many electrons (if the atom is neutral?) –Same as # of protons
Make sure you have these definitions in your notes!! n Ion: n Isotope: n Atomic number: n Atomic mass: