1. OF PROTONS, NEUTRONS AND ELECTRONS IN AN ATOM
DETERMINE THE NUMBER
OF PROTONS, NEUTRONS AND ELECTRONS IN AN ATOM

2. Counting the Pieces Atomic Number = number of protons
# of protons determines kind of atom.
the same as the number of electrons in the neutral atom.

3. Counting the Pieces Mass Number = the number of protons + neutrons.
All the things with mass.
NOT on the periodic table

4. Isotopes
Atoms of the same element can have different numbers of neutrons.
different mass numbers.
called isotopes.

5. Writing Isotopes Two ways: Hyphen notation
Name of element – mass number
Ex:
carbon- 12
carbon -14
uranium-235

6. Nuclear Symbol Notation
Contain the symbol of the element, the mass number and the atomic number.
Mass
number X
Atomic
number

7. Na Symbols 24 11 Find the number of protons number of neutrons
number of electrons
Atomic number
Mass Number
Name 24 Na 11

8. Na Symbols 24 11 Find the number of protons = 11
number of neutrons = 13
number of electrons = 11
Atomic number = 11
Mass Number = 24
Name = sodium – 24 24 Na 11

9. Br Symbols 80 35 Find the number of protons number of neutrons
number of electrons
Atomic number
Mass Number
Name 80 Br 35

10. Br Symbols 80 35 Find the number of protons = 35
number of neutrons = 45
number of electrons = 35
Atomic number = 35
Mass Number = 80
Name = bromine - 80 80 Br 35

11. Symbols
if an element has an atomic number of 34 and a mass number of 78 what is the
number of protons
number of neutrons
number of electrons
symbol
Name

12. ANSWERS
if an element has an atomic number of 34 and a mass number of 78 what is the
number of protons = 34
number of neutrons = 44
number of electrons = 34
Name = selenium – 78 78 Se 34

13. Symbols if an element has 91 protons and 140 neutrons what is the
Atomic number
Mass number
number of electrons
Name
symbol

14. ANSWERS if an element has 91 protons and 140 neutrons what is the
Atomic number = 91
Mass number = 140
number of electrons = 91
Name = Protactinium - 140 Pa
140 91

15. Average Atomic Mass
A weighted average of all naturally occuring isotopes of an element.
There is a formula used to calculate average atomic mass:
= (mass of isotope 1) (% abundance/100)
(mass of isotope 2) (%abundance/100)
+...________________________________

16. Unit for Atomic Mass The atomic mass unit (amu)
amu definition - one twelfth the mass of a carbon-12 atom.
Each isotope has its own atomic mass relative to the carbon-12 atom

17. Atomic Mass
You try…
Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of amu and 30.9% has a mass of amu.

18. Answer
(62.93 amu) (69.1% / 100) = amu +(64.93 amu) (30.9% / 100) = amu amu

19. Atomic Mass
Magnesium has three isotopes % magnesium-24 with a mass of amu, 10.00% magnesium-25 with a mass of amu, and 11.01% magnesium-25 with a mass of amu. What is the atomic mass of magnesium?

20. Answer
( amu) (78.99% / 100) = ( amu) (10.00% / 100) = ( amu) (11.01% / 100) = amu

21. Atomic Mass Is not a whole number because it is an average.
are the decimal numbers on the periodic table.