1. Symbols
Contain the symbol of the element, the mass number and the atomic number X
Mass
number
Atomic
# protons
+ # neutrons
mass number
# protons

2. F Symbols 19 9 Find the number of protons number of neutrons
number of electrons
Atomic number
Mass number
= 9 + F 19 9
= 10
= 9
= 9
= 19

3. Br Symbols 80 35 Find the number of protons number of neutrons
number of electrons
Atomic number
Mass number
= 35
= 45 Br 80 35
= 35
= 35
= 80

4. Na Symbols 23 11 Find the number of protons number of neutrons
number of electrons
Atomic number
Mass number
= 11
= 12 Na 23
= 11
= 11 11
= 23
Sodium atom

5. Na Symbols 23 11 Find the 1+ number of protons number of neutrons
number of electrons
Atomic number
Mass number
= 11 Na
= 12 23 1+
= 10 11
= 11
= 23
Sodium ion

6. Symbols
If an element has an atomic number of 23 and a mass number of 51 what is the
number of protons
number of neutrons
number of electrons
Complete symbol
= 23
= 28
= 23 V 51 23

7. Symbols
If an element has 60 protons and 84 neutrons what is the
Atomic number
Mass number
number of electrons
Complete symbol
= 60
= 144
= 60 Nd
144 60

8. Symbols
If a neutral atom of an element has 78 electrons and 117 neutrons what is the
Atomic number
Mass number
number of protons
Complete symbol
= 78
= 195
= 78
Platinum is even more rare than gold. In fact, 50 tons of ore is required to produce just 50 grams of platinum.
Platinum is a grayish-white metal that is malleable yet, like gold, is resistant to attack by air, moisture, and most solutions.
Its melting point is even higher than gold, at just over 3,000°F. It ranks 72 in abundance among the elements. Pt
195 78

9. Mass Number Isotopes Ions Relative Atomic Mass Average Atomic Mass
Masses of Atoms
Mass Number
Isotopes
Ions
Relative Atomic Mass
Average Atomic Mass
Law of definite proportions states that a chemical compound always contains the same proportion of elements by mass
Percent composition — the percentage of each element present in a pure substance—is constant
Calculation of mass percentage
1. Use atomic masses to calculate the molar mass of the compound
2. Divide the mass of each element by the molar mass of the compound and then multiply by 100% to obtain percentages
3. To find the mass of an element contained in a given mass of the compound, multiply the mass of the compound by the mass percentage of that element expressed as a decimal
Courtesy Christy Johannesson

10. Atomic Mass p+ n0 e– Ca 20 40 20 20 20 Ar 18 40 18 22 18 Br 35 80 3545 35 Ca
40.08 20 Ar
39.948 18 Br
79.904 35

11. Bohr - Rutherford diagrams
Putting all this together, we get B-R diagrams
To draw them you must know the # of protons, neutrons, and electrons (2,8,8,2 filling order)
Draw protons (p+), (n0) in circle (i.e. “nucleus”)
Draw electrons around in shells He Li
3 p+
4 n0
2e– 1e–
Li shorthand
2 p+
2 n0
3 p+
4 n0
Draw Be, B, Al and shorthand diagrams for O, Na

12. Be B Al O Na 8 p+ 11 p+ 8 n° 12 n° 4 p+ 5 n° 5 p+ 6 n° 13 p+ 14 n°
2e– 8e– 1e– Na
8 p+
8 n°
2e– 6e– O

13. Mass Number mass # = protons + neutrons always a whole number
NOT on the Periodic Table!
Neutron +
Electrons
Nucleus e-
Proton e- e-
Nucleus e- e-
Carbon-12
Neutrons 6
Protons 6
Electrons 6 e-