Atom Basics
The Subatomic Particles Protons (p+) : Have +1 Charge Have a mass of 1 amu (atomic mass unit) Electrons (e-): Have a -1 charge Have a mass of 0.0005 amu Neutrons (n0): Have no charge Have a mass of 1 amu
Atomic Structure FAIL
Electron Cloud Model Nucleus Rest of the atom Incredibly small Contains all the protons and neutrons Nucleus is very dense Rest of the atom Mostly empty space The electrons move around in the empty space No Specific Orbits Use a cloud to show the probability of finding an electron = orbital
How do we describe atoms? Every element has its own atomic number Atomic number is on top in the blocks in the periodic table Atomic Number = Z = number of protons
How do Protons and Electrons Relate? If an atom has no charge then… The number of electrons must equal the number of protons. If the atom has a charge then its called an ion Positively charged ions = cations Negatively charged ions = anions
How do Protons and Electrons Relate? How do atoms become charged? Comes from imbalance in protons and electrons Only the number of electrons changes Protons are buried deep in the nucleus and so they don’t change. Positive charge Lost electrons Negative charge Gained electrons
What about neutrons? Imagine three atoms: What element are they? Atom 1: 6 protons, 6 electrons, 6 neutrons Atom 2: 6 protons, 6 electrons, 7 neutrons Atom 3: 6 protons, 6 electrons, 8 neutrons What element are they? All the same element but the atoms aren’t the same Isotopes – Atoms with the same number of protons but different numbers of neutrons
How do we tell the atoms apart? Atom 1: 6 protons, 6 electrons, 6 neutrons Atom 2: 6 protons, 6 electrons, 7 neutrons Atom 3: 6 protons, 6 electrons, 8 neutrons Mass Number = protons + neutrons Symbol = A Not every isotope is represented evenly.
How do we adjust for different isotopes? Average atomic mass – weighted average of the masses of all the isotopes. Bottom number on Periodic Table
Average Atomic Mass Carbon has two naturally occurring isotopes: Carbon with a mass number of 12 – 98.93% Carbon with a mass number of 13 – 1.07% (12 amu * 0.9893) + (13 amu * 0.0107) = 12.0107 amu
What is the shorthand? X = symbol of the element A = mass number Z = atomic number Q = charge (left off if not charged) Also see just X–A C-13
Practice What is the atomic number? What is the atomic mass? What is the mass number? How many protons? How many neutrons? How many electrons?