1. Atomic Symbols
protons + neutrons =
mass #
atomic # =
protons

2. Elements are identified by atomic number (protons).
Neutrons
Electrons 19 20 S 17
39Ca 14 6 39 K 19 19 33 16 16 16 16 20 20 19 20 20 6 6 8 C 6

3. H H H Isotopes 1 2 1 3 1 element: same or different mass:
_________:
same # of protons & electrons,
BUT different # of neutrons 1 H 2 1 H 3 1 H
protium
deuterium
tritium

4. Quick (but challenging) Quiz!
1. The number of protons in the nucleus is…
the mass number.
the atomic number.
the same as the number of neutrons.
the total of protons and neutrons.

5. Quick (but challenging) Quiz.
2. The mass number is…
the number of protons.
the number of neutrons.
the total of protons and electrons.
the total of protons and neutrons.

6. Quick (but challenging) Quiz.
3. Isotopes of an element have…
the same mass number.
different atomic numbers.
the same number of protons but different mass numbers.
the same number of protons but different numbers of neutrons.

7. Quick (but challenging) Quiz.
4. How many neutrons are in an atom of potassium–40 ? (40K)
(Atomic Number = 19)
19 neutrons
21 neutrons
40 neutrons
59 neutrons