1. ATOMIC STRUCTURE

2. ESSENTIAL QUESTION…..
How can you identify an element and/or isotope based on its subatomic particles?

3. What is an atom composed of?
COMPOSED OF THREE SUBATOMIC PARTICLES:
PROTON (POSITIVELY CHARGED)
NEUTRON (NO CHARGE)
ELECTRON (NEGATIVELY CHARGED)
BOTH IN THE NUCLEUS
ALL FOUND OUTSIDE THE NUCLEUS (ELECTRON CLOUD)

4. ABOUT THE PARTICLES….. PROTONS (p+) NEUTRONS (n0) ELECTRONS (e-)
Proton is nearly 2000 times more massive than the electron, but equal in charge and opposite in sign to the electron
Number of protons in the nucleus is electrically balanced by an equal number of electrons
NEUTRONS (n0)
Mass almost exactly equal to that of the proton
ELECTRONS (e-)
Mass of electron much less than the mass of a proton and neutron
Equal number of protons and electrons = NEUTRAL ATOM

5. Properties of Subatomic Particles
Symbol
Location
Charge
Relative mass
Actual mass (g)
Electron e-
Around nucleus 1– 1
1840
9.11×10-28
Proton p+
Nucleus 1+
1.673×10-24
Neutron n0
nucleus
1.675×10-24

6. Na 11 ATOMIC NUMBER 22.990 Sodium
REPRESENTS THE NUMBER OF PROTONS IN AN ATOM
ELEMENTS ARRANGED BY INCREASING ATOMIC NUMBER
UNIQUE TO A GIVEN ELEMENT
SINCE ALL ATOMS ARE NEUTRAL, ATOMIC NUMBER ALSO TELLS US THE NUMBER OF ELECTRONS IN AN ATOM
USUALLY FOUND AT THE TOP OF THE ELEMENT’S SYMBOL 11 Na
22.990
Sodium

7. Learning Check 1
State the number of protons for atoms of each of the following:
A. Nitrogen (N)
1) 5 protons 2) 7 protons 3) 14 protons
B. Sulfur (S)
1) 32 protons 2) 16 protons 3) 6 protons
C. Barium (Ba)
1) 137 protons 2) 81 protons 3) 56 protons
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8. MASS NUMBER
THE TOTAL NUMBER OF PROTONS AND NEUTRONS IN THE NUCLEUS OF AN ATOM
MASS NUMBER – ATOMIC NUMBER = # NEUTRONS
ROUND THIS NUMBER TO THE NEXT WHOLE NUMBER TO DETERMINE THE MASS NUMBER 11 Na
22.990
Sodium
Example: Sodium (Na)
Mass Number = 23
Atomic Number = 11
______
12 neutrons -

9. Practice From the Periodic Table
Complete the following chart:
Name
Symbol
Mass Number
# protons
# neutrons
# electrons
Lithium Mg 26 16

10. ISOTOPES DALTON THOUGHT THAT…..
Atoms could not be divided(indivisible)….atoms can be divided
All atoms of an element are IDENTICAL….not really!!
Atoms of an element have same number of p+ and e-, but the number of n0 may be different

11. ISOTOPES ISOTOPES ARE…
Atoms of the same element with the same number of protons, but different numbers of neutrons.
Atoms of the same element (same atomic number) with different mass numbers

12. THE ISOTOPES OF HYDROGEN
All atoms have the same number of protons (p+=1)…….
….but different number of neutrons in the nucleus (which means these isotopes will have different mass numbers!!)

13. Z X ISOTOPIC NOTATION A (the total number of protons + neutrons)
A = mass number
(the total number of protons + neutrons)
Z = atomic number
(the total number of protons)
X = element symbol

14. READING ISOTOPIC NOTATION46
21 Sc
46 = mass number
(the total number of protons (21) + neutrons (25))
21 = atomic number
(the total number of protons (21))
Sc = element symbol
(In a neutral atom, the number of electrons (21) is equal to the number of protons)

15. Another way of writing an isotope46
21 Sc or Scandium-46
Name of the element followed by the mass number
(This format does not include the atomic number)

16. 16 31 65 8 15 30 Practice O P Zn 8 p+ 15 p+ 30 p+ 8 n 16 n 35 n
O P Zn
8 p p p+
8 n 16 n 35 n
8 e e e-
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17. practice An atom has 14 protons and 20 neutrons.
A. Its atomic number is
1) ) ) 34
B. Its mass number is
C. The element is
1) Si 2) Ca 3) Se
D. Another isotope of this element is
1) 34X 2) 34X 3) 36X
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18. Isotopes Most elements found as a mixture of isotopes
Relative abundance of each isotope is constant
Example: Potassium in bananas
93.25% of K atoms have 20 n0
6.7302% of K atoms have 22 n0
0.0117% of K atoms have 21 n0
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19. Isotopes Isotopes of an element differ in mass
The more neutrons in an isotope, the greater the mass
Still, isotopes of an element have the same chemical behavior
Why? Chemical behavior depends on the number of e-, not n0 or p+
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20. Calculating Atomic Mass
Percent abundance of isotopes
Mass of each isotope of that element
Average Atomic Mass=
mass isotope1(percent abundance1) + mass isotope2(percent abundance2) + …
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21. Atomic Mass of Magnesium
Isotopes Mass of Isotope Abundance
24Mg = 24.0 amu %
25Mg = amu %
26Mg = amu %
Average atomic mass of Mg = 24.3 amu Mg
24.3
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22. Learning Check AT7
Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the atomic mass of gallium?
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23. Solution AT7 68.9 amu x 60.2 = 41.5 amu for Gallium-69 100
Atomic mass Ga = amu
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