Notes: Atomic Structure WCHS Chemistry

Protons are Positive NEUTRons are NEUTRal WHAT’S INSIDE AN ATOM? Amu = Atomic mass units WHAT’S INSIDE AN ATOM? Protons - positive charge Mass = 1 amu Found in the nucleus Neutrons - neutral charge Electrons - negative charge Mass = 0 (really is 0.00054 amu) Found outside of the nucleus Protons are Positive NEUTRons are NEUTRal

HOW WE’D DRAW AN ATOM ELECTRONS NEUTRONS PROTONS

ATOMIC NUMBER Atomic Number = # of protons (+) Symbol = Z How is the periodic table arranged? Atomic Number → Number of protons Used to identify an element NEVER CHANGES IN AN ELEMENT! O = Cl = 3 = 20 = 8 17 Li Ca

THE KEY ON YOUR PERIODIC TABLE Atomic Number (Z) = # of protons

ATOMIC MASS # Atomic Mass Number = # protons + # neutrons for a SINGLE ATOM Symbol = A Tells what is in the nucleus REMEMBER!!!! → An electron has a mass of ZERO. SO…. all the mass of the atom comes from the NUCLEUS (protons + neutrons)

Mg 12 24 EXAMPLE: Magnesium Symbol = Z = But what is mass (A) ? → ** We will round to the nearest whole number in this class!** 12 24

Cl 17 35 EXAMPLE: Chlorine Symbol = Z = A = ** We will round to the nearest whole number in this class!** 17 35

THE KEY ON YOUR PERIODIC TABLE Atomic # (Z) = # of protons Symbol Name Atomic Mass (A) = # of protons & neutrons (what’s in the nucleus)

Cl 17 35 EXAMPLE: Chlorine Symbol = Z = A = PROTONS # of Neutrons = ? PROTONS + NEUTRONS 35 - 17 = 18 NEUTRONS

A = # Protons + # Neutrons Z = # Protons Then, # Neutrons = A - Z ! # OF NEUTRONS A = # Protons + # Neutrons Z = # Protons Then, # Neutrons = A - Z !

Kr Kr Z = A = 84 #P = #N = Z = A = #P = #N = 20 36 36 36 + 20 = 56 36 EXAMPLES Kr Z = A = 84 #P = #N = Kr Z = A = #P = #N = 20 ISOTOPE 36 36 36 + 20 = 56 36 36 84 - 36 = 48

PLURAL!!!! ISOTOPES Isotopes = Same elements but have different atomic masses Due to # of neutrons! REMEMBER!!!!! → #protons CANNOT change ***EVERY ATOM IS AN ISOTOPE*** 2 have to be compared Periodic table has the average mass of all the isotope forms! (NOT the “correct” mass)

Isotopes and Atomic Mass ISOTOPES SIMULATION Isotopes and Atomic Mass

35Cl Z = A = 35 #P = #N = 37Cl Z = A = 37 #P = #N = 17 17 17 17 EXAMPLES 35Cl Z = A = 35 #P = #N = 37Cl Z = A = 37 #P = #N = 17 17 17 17 35 - 17 = 18 37 - 17 = 20

+ ATOMS **Elements are on the periodic table as ATOMS** Atoms = Neutral or zero charge So, in an atom, # protons (+) ALWAYS = # electrons (-) Atomic # = # of protons = # of e-’s Ex: Carbon +

IONS Ions = Charged particles They have gained or lost ELECTRONS! Negative ion → atom has GAINED electrons Has more - than + Anion Positive Ion → Atom has LOST electrons Has more + than - Cation

3 3 2 3 Li0 # protons? # electrons? Li+1 # protons? # electrons? EXAMPLE Li0 # protons? # electrons? Li+1 # protons? # electrons? 3 3 2 3

FULL ATOMIC SYMBOLS → Put on your periodic table!

EXAMPLES H F N 1 19 14 1 9 7

IONIC SYMBOL ISOTOPE SYMBOL EXAMPLES Cl- Li+ Al3+ Ca2+ O2- EX: 35Cl 6Li 30Al 40Ca 16O

+1 1 NUCLEUS 1 NUCLEUS - 1 OUTSIDE OF NUCLEUS

Charge= #P-#E CHARGE MASS-#P = A-Z #P MASS Z 55 133-55 = 78 54