1. Atomic properties Atomic number, atomic symbol, mass number, isotopes

2. HOW DO WE DESCRIBE AN ATOM  We’ve already discussed what makes up an atom  Proton  Neutron  Electron  Now we need to find a way to describe the properties of an individual atom

3. DESCRIBING THE ATOM  Let’s take a look at the periodic tables around the room.  On each periodic table are several things 1. Symbol for the element 2. Name of the element 3. Numbers that describe the element

4. HOW DO WE NAME AN ELEMENT  The first thing we will exam is the naming of elements  Finding the names of elements is like doing a giant word search  EXAMPLE: What is the name of the element with the symbol He ?

5. ANSWER  He is the symbol for the element: HELIUM

6. TRY THESE 1. Br 2. Li 3. Zn 4. B 5. Ag 6. K

7. ANSWERS 1. Br - Bromine 2. Li - Lithium 3. Zn - Zinc 4. B - Boron 5. Ag - Silver 6. K – Potassium  Let’s look at #5 and #6

8. FIND THE SYMBOL FROM THE NAME  It’s usually easier to find the name of the element when you have the symbol. It’s harder to find the symbol when you have the name.  Try these: 1. Mercury 2. Xenon 3. Iron

9. ANSWERS 1. Mercury - Hg 2. Xenon - Xe 3. Iron – Fe  REMINDER: For your periodic table  You may use this on your quizzes  You must fill in your own information

10. WHAT DEFINES AN ATOM One particle defines what an atom (or element is)  This particle is the PROTON  The number of protons in an atom tells us what element is.

11. ATOMIC NUMBER  Atomic number : the number of protons in an atom Example: Find Hydrogen (H) on your periodic table  The atomic number of hydrogen is 1.  What is the atomic number for He?

12. ATOMIC NUMBER  The periodic table is arranged in order of increasing atomic number.  Find the atomic number for these: 1. Sulfur 2. Uranium 3. Gold

13. ATOMIC NUMBER 1. Sulfur - 16 2. Uranium - 92 3. Gold – 79  If you ever change the number of protons, you change the atom into a different element.

14. MASS NUMBER  Mass number : the sum of an element’s protons and neutrons. Remember, electrons don’t have an atomic mass  On your periodic table, this is found below the symbol of the element  EXAMPLE: The mass number for H (hydrogen) is 1.008

15. UNITS  The unit for the mass unit is the atomic mass unit (amu)  Therefore:  Hydrogen has a mass number of 1.008 amu

16. FIND THE MASS NUMBER  Find the mass number for the following: 1. Cl 2. Pd 3. Sr

17. MASS NUMBER AND ISOTOPES  Notice that not all the mass numbers are whole numbers  A lot of them have decimals  WHY?

18. ISOTOPES  The reason is that not every atom in an element has the same number of neutrons  ISOTOPE : atoms of the same element with different numbers of neutrons  Isotopes of atoms is what is responsible for radiation  The mass number is an average of all the different isotope masses

19. SYMBOLS  How do we show how many protons and neutrons are in a symbol.  EXAMPLE:  An element has 10 protons and 10 neutrons, how do we show it?  First, what is the element?

20. SYMBOLS Ne 20 10 Number of protons Number of protons + neutrons

21. WRITE THE SYMBOL FOR THESE 1. 35 protons and 45 neutrons 2. 40 protons and 51 neutrons 3. 78 protons and 117 neutrons

22. HOW MANY PROTONS AND NEUTRONS  40 Ar 18  56 Fe 26  238 U