1. Notes: Atomic Structure
WCHS Chemistry

2. 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 amu)
Found outside of the nucleus
Protons are Positive
NEUTRons are NEUTRal

3. HOW WE’D DRAW AN ATOM
ELECTRONS
NEUTRONS
PROTONS

4. 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

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

6. 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)

7. 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

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

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

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

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

12. 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
= 56 36 36
= 48

13. 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)

14. Isotopes and Atomic Mass
ISOTOPES SIMULATION
Isotopes and Atomic Mass

15. 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
= 18
= 20

16. + 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 +

17. 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

18. 3 3 2 3 Li0 # protons? # electrons? Li+1 # protons? # electrons?
EXAMPLE
Li0
# protons?
# electrons?
Li+1
# protons?
# electrons? 3 3 2 3

19. FULL ATOMIC SYMBOLS → Put on your periodic table!

20. EXAMPLES
H F N 1 19 14 1 9 7

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

22. +1 1
NUCLEUS 1
NUCLEUS
- 1
OUTSIDE OF NUCLEUS

23. Charge= #P-#E
CHARGE
MASS-#P
= A-Z #P
MASS Z =