1. Protons, Neutrons and Electrons
SWBAT: Calculate the number of protons, neutrons and electrons in a given atom

2. Atomic Structure
Quantum Mechanical Model of the Atom describes the current accepted model of the nuclear atom
The nucleus contains the protons and neutrons
The electrons are found outside the nucleus in atomic orbitals
According to Thomson since the atom is neutral in charge…… if there are electrons there must be equal numbers of protons

3. Atomic Structure The mass of the proton is 1amu
The mass of the neutron is 1amu
The mass of the electron is 1/1840amu (very, very, very, very, very, small mass)
So……. We say the atomic mass of the atom is the protons + neutrons.
 Since protons + neutrons = atomic mass and the protons and neutrons are in the nucleus, the nucleus contains the atomic mass of the atom

4. Calculate atomic mass, protons, neutrons, electrons
What is the atomic mass of this atom?
How many electrons does this atom have?
How many protons does this atom have?
How can we tell what element this atom belongs to?

5. Atomic Number The number of protons an atom has is the atomic number
On the periodic table the atoms are arranged by increasing atomic number.
How many protons does Boron have?
How many electrons does Boron have?
Atomic #

6. Atomic Mass Atomic Mass is the number of protons + neutrons
The Atomic Mass can also be found on the periodic table.
Why is it a decimal?
It’s an average of all the atomic masses of the isotopes for that element

7. Sodium – 23 2 ways to write elements Shorthand Element Name
56 is the atomic mass
26 is the atomic number
Protons =
Electrons =
Neutrons =
The 23 is the atomic mass
Sodium – 23
Protons =
Electrons =
Neutrons =

8. How to calculate the protons, neutrons and electrons
Lithium – 7
What color are the electrons?
What color are the protons?
What color are the neutrons?
What is the top number?
What is the bottom number?
Protons = 3
Electrons = 3
Neutrons = 4

9. Periodic Table Atomic # = protons (#protons = #electrons)
Atomic mass = protons + neutrons
(it’s a decimal because its an average mass of all the isotopes of that element)

10. Complete the missing boxes
Element Name
Shorthand
Atomic Mass
Atomic # p+ e- n0
Carbon - 13 27 13 20
Nitrogen - 15 8 9 37
Magnesium - 22

11. Isotopes
An isotope is an atom from the same element that has different number of neutrons.
Because it has different number of neutrons the atomic mass is different
Nitrogen – 14 vs. Nitrogen – 15 vs. Nitrogen – 16
What is the atomic mass on the periodic table for Nitrogen?
Which isotope of Nitrogen occurs most often in nature?
Nitrogen – 14. Why? The average atomic mass is closest to Nitrogen – 14. On the periodic table its 14.01amu

12. Isotopes What is the difference between the following atoms?
Carbon - 12
Carbon - 13
Protons?
Electrons?
Neutrons?
6 protons
6 electrons
and …. 6 neutrons
Protons?
Electrons?
Neutrons?
6 protons,
6 electrons
……… 7 neutrons

13. Atomic Mass
Mass Number – The mass of one specific atom. Atomic Mass – The Average of all the atoms of an element.

14. What is amu? amu stands for atomic mass unit
1 amu is equal to 1/12 the mass of a carbon – 12 atom
Scientists found the mass of a carbon - 12 atom (very common carbon isotope) then divided it by 12 to get 1

15. Atomic Mass – Weighted Average
A weighted average is an average resulting from the multiplication of each component by a factor reflecting its importance.

16. Atomic Mass – Weighted Average
Lets say you took a test and earned a 100%. You also had one homework assignment and forgot to turn it in so you got a zero. Finally, you know that in the class tests are worth 80% of your grade and homework is worth 20%. Should you have a 50% F in the class?  Can you figure out what your grade should be?

17. Atomic Mass – Weighted Average
This is an example of a weighted average. The atomic mass is also a weighted average.
It is based on the relative abundance of each isotope of an element.

18. Atomic Mass – Weighted Average
Calculate the atomic mass of Carbon. Carbon – 12 has a relative abundance of 98.89%. Carbon – 13 has a relative abundance of 1.11%.