1. Aim: How are atoms different from each other?
Do Now:
Take out a calculator and reference tables.
Describe the difference between protons, neutrons, and electrons.

2. Protons, Neutrons and Electrons
Particle
Charge
Mass
Location
Symbol
Proton +1
1amu
Nucleus
Neutron
Electron -1
1/1836 amu or
0 amu
Outside the nucleus

3. What’s an amu?
amu stands for atomic mass unit. The mass of a proton is approximately 1.67 x grams. Because it is so small, it is more convenient to use a different scale. So, the mass of one proton is expressed as 1 amu.
A neutron has approximately the same mass as a proton, so it is also expressed as 1 amu.
An electron has such a tiny amount of mass compared to protons and neutrons that it is usually rounded to 0 amu.

4. Why are protons important?
Each atom of a specific element has the same number of protons as every other atom in that element.
The number of protons in the nucleus of an atom is called the atomic number.
Elements in the periodic table are arranged by atomic number. Therefore, the number of protons in an atom of an element determines where it is placed on the table.

5. Using the Periodic Table of Elements
How many protons does _________ have?
Zinc
Neon
Tin
Tungsten
Radium
***Note – The periodic table in the reference tables does not tell you the name of the element – only its symbol. The name of the element can be found on Table S***

6. How else can we use this information?
Remember – The mass of a proton is 1amu. The mass of a neutron is also 1amu. The mass of an electron is about 0amu. We can use this information to calculate the atomic mass of an atom of a particular element.
So, if an atom of oxygen has 8 protons, and 8 neutrons, its mass is 16amu.
This information can also be found on the periodic table of elements.

7. What is the mass of…
Hydrogen?
Magnesium?
Chromium?
Cobalt?

8. Calculating the number of neutrons
We can calculate the number of neutrons by subtracting the atomic number from the atomic mass. (Round the mass to the nearest whole number)
How many neutrons does _________ have?
Beryllium?
Molybdenum?
Uranium?

9. Why isn’t atomic mass listed as a whole number?
Not every atom of an element is the same. Some atoms contain more neutrons than others. These atoms are known as isotopes.
The atomic mass listed on the periodic table is an expression of the ratio of all the atomic masses that can be found of that element.

10. Calculating the Mass of an Element
Atomic mass can be calculated from the mass and the abundance of naturally occurring isotopes.
Example: Carbon has two naturally occurring stable isotopes % are C-12, while the remaining 1.108% are C-13. To find the atomic mass of carbon, we use the following set up:
Convert the % to decimal numbers and multiply the mass by its decimal abundance.
12amu x = amu
13amu x = amu
Add the masses of isotopes.
11.87amu amu = 12.01amu

11. The Rules of Reading and Writing an Isotope
Isotope symbols use the same letters
The mass of the isotope is written on the top left of the symbol.
The atomic number is written on the bottom left of the symbol.
Sometimes only the mass of the symbol is written.

12. What is the mass, atomic number, and number of neutrons of…

13. Activity
Complete the questions on the worksheet you were given.

14. Homework #
Review Book – page 11. Answer questions