1. Anatomy of the Atom
Atomic Structure

2. Forces in the Nucleus The nucleus is positive (p+ and no)
REMEMBER:
The nucleus is positive (p+ and no)
Like charges repel each other…so shouldn’t the p+ in the nucleus repel each other?
But…when 2 p+ are close together in the nucleus there is a strong attraction between them. The same holds true for neutrons.

3. Atomic Number
atomic number - the number of protons in the nucleus of each atom of a given element.
The number of p+ identifies the element.
Atomic Number increases from left to right on the periodic table.

4. Electrons
The number of electrons in a neutral atom is equal to the number of protons in that atom.
e- = p+

5. # of neutrons = mass number – atomic number
mass number - the number of p+ & no in the nucleus of an atom.
# of neutrons = mass number – atomic number

6. Isotope Notation Carbon-12 Nuclear Notation Hyphen Notation
Uses the elements symbol followed by a hyphen & the mass number.
C-12
Carbon-12

7. Example:
Determine the number of p+, n0, and e- in an atom of Carbon-12.

8. Changes in the Atom
Changing electrons

9. Electrons
The number of electrons in a neutral atom is equal to the number of protons in that atom.
e- = p+
Electrons can be lost or gained.
This process is called ionization.
When electrons are lost or gained, ions are formed.

10. Ions ion- an atom with a positive or negative charge.
cation- an atom with a positive charge
Cations are formed when an atom loses negatively charged electrons.
Ca+2 is formed when calcium loses 2 electrons.
Ca+2 has 2 less electrons than protons.
the lithium atom
the lithium ion

11. Ions anion- an atom with a negative charge
Anions are formed when an atom gains negatively charged electrons.
N-3 is formed when nitrogen gains 3 electrons.
N-3 has 3 more electrons than protons.

12. Metals vs. Nonmetals Metals form cations. Na Na+ + 1e-
Nonmetals form anions.
Cl + 1 e Cl-

13. Changes in the Atom
Changing neutrons

14. Isotopes
isotope- two or more atoms having the same atomic number (same #p+) , but different mass numbers (due to different #no). nuclide- general term for a specific isotope of an element.

15. Isotopes

16. How many protons, neutrons & electrons are there in the following?
Cl Cl-1
Br S-2
N Fe+3

17. Atomic Mass Determination
Average Atomic Mass - the weighted average of atomic masses of the naturally occurring isotopes of an element.
The atomic mass is expressed relative to the value of exactly 12u for a carbon-12 atom.
Atomic Mass Unit – amu or u

18. What is a weighted average?
Example: Your grade in math might be 75% tests and 25% homework. What would your grade be if you had a test average of 80% and a homework average of 100%?
Normally, you would average 80% & 100% to get 90%.
However, with a weighted average, it is 85%.

19. Calculating Average Atomic Mass
atomic mass of each isotope X percent natural abundance (in decimal form)

20. Percent Natural Abundance
Percent Natural Abundance- the relative proportions expressed as percentages, in which isotopes of an element are found in nature.

21. Calculating Average Atomic Mass
Ex: Uranium has two isotopes, uranium-235 and uranium Uranium-235 has an atomic mass of amu and a percent natural abundance of 0.720%. Uranium-238 has an atomic mass of amu and a percent natural abundance of %. Calculate the average atomic mass of naturally occurring uranium.