1. Chapter 4.3
The Atom

2. The Atom
The smallest particle of an element that retains its identity in a chemical reaction

3. Three Kinds of Subatomic Particles
Electrons
Negatively charged
Surround the nucleus
Protons
Positively charged
In the nucleus
Neutrons
Neutrally charged

4. Three Kinds of Subatomic Particles
Remember: the mass of one proton is about the same as the mass of one hydrogen atom!

5. Structure of the Atom Atoms are made up mostly of empty space
At the center of the atom is the nucleus
Central core made up of protons and neutrons
Contribute most of the mass of an atom
Positively charged

6. Structure of the Atom
Surrounding the nucleus are orbitals of negatively charged electrons
Today, known as the electron cloud

7. What makes one atom different from another?
The number of protons!
A difference in number of protons changes the actual element
You can change the number of electrons and neutrons and still have the same type of element

8. Reading the Periodic Table

9. How do we know how many subatomic particles are in each element?
Protons – Look at the atomic number!
Electrons – Atoms are neutrally charged, so the number of protons = number of electrons

10. How do we know how many subatomic particles are in each element?
Neutrons – The mass of the atom is made up of protons and neutrons
# neutrons = mass number – atomic number
Mass number is not the same as atomic mass, it is rounded to a whole number!

11. Shorthand Notation

12. Bohrs Atomic Model 1915 Protons and Neutrons are in the nucleus
Electrons are outside the nucleus in specific orbitals
Electrons can move from one orbital to another, and release energy as electromagnetic radiation.

13. Drawing Bohr’s Models
Atomic model that shows the electrons surrounding the nucleus in orbitals
How many electrons can fit in each orbital?

14. Drawing Bohr’s Models n = principal quantum number
The number of the energy level or orbital

15. Drawing Bohr’s Models
Use the principal quantum number to calculate the number of electrons in each orbital

16. Lewis dot structures
Valence electrons – electrons in the highest occupied energylevel/orbital of an atom
Maximum of 8 valence electrons
Use the periodic table to determine!

17. Why are valence electrons so important?
Tells us the chemical properties of an element
They are responsible for the formation and breaking of bonds

18. Lewis dot structures
We use Lewis dot structures to show the number of valence electrons within an element

19. Do Now!
Find Neon on your periodic table. What is the atomic number and mass number? How many protons, neutrons, and electrons does Neon have? What is the shorthand notation and hyphenated notation for Neon?

20. Do Now!
What is an isotope? How does one isotope differ from another?

21. Calculating Atomic Mass

22. Isotopes
Many elements have at least two or more naturally occurring isotopes
Some isotopes are found more than others
We call this it’s percentage abundance

23. Average Atomic Mass
The atomic masses found on the periodic table is the weighted average of the isotopes of an element
An isotope with a larger percent abundance will contribute more to the weighted average than an isotope with a smaller percent abundance

24. Convert percentages into decimals
What if you had two isotopes of an element: one with a mass of 15 amu and 25% abundance and another with a mass of 10 amu and 75% abundance?
Convert percentages into decimals
Divide by 100
Multiply the mass of each isotope by its percent abundance in decimal form
Add the numbers together
Ex:
25% → 0.25
75% → 0.75
(15 amu x 0.25) = 3.75
(10 amu x .75) = 7.5
= amu

25. Practice! There are 3 naturally occurring isotopes of hydrogen
Hydrogen – 1 has a mass of amu and has a percent abundance of %
Hydrogen – 2 has a mass of amu and has a percent abundance of 0.015%
Hydrogen – 3 has a mass of amu and is so rarely found in nature it’s percent abundance is considered negligible

26. Practice! Chlorine has two naturally occurring isotopes
Chlorine – 35 has a mass of amu and it’s percent abundance is 75.77%
Chlorine – 37 has a mass of amu and it’s percent abundance is 24.23%

27. Some tips Check your periodic table to see if you are correct!
Write out ALL your work!
Do not round anything until the problem is finished!
Round your final answer to TWO decimal places