1. Sec Atomic Structure

2. From the advances in atomic theory, we have a pretty solid basis for determining the structure of an atom
Structure of atom: describes location of all subatomic particles
Nucleus?
Location of protons, electrons, neutrons?

3. Atomic Structure: Protons and neutrons located in a densely packed nucleus in the center of the atom- electrons are located outside of nucleus in areas of probability that can be modeled by an electron cloud
Protons- what charge?
Electrons- what charge?
Neutrons- what charge?

4. Atomic identity and the way certain atoms behave are primarily based on the number and organization of protons and electrons

5. Protons in an Atom
An atom’s identity is determined by the number of protons it contains
Identity= what element it is
Each element on the periodic table has a unique number of protons- therefore the number of protons an atom has will determine its identity
Ex: Every atom with 6 protons is carbon; every atom with 9 protons is fluorine

6. Number of protons in an atom is its atomic number on the periodic table- whole number found above element’s symbol
Periodic table- elements ordered in increasing atomic number (number of protons)
Atomic number can be written as a subscript on the left side of an element’s symbol:

7. Neutrons and Mass Number
When discussing the mass of things as tiny as subatomic particles, it is impractical to use grams- instead we will use a special unit called:
Proton mass=
Neutron mass=
Electron mass=

8. Electron’s mass is so small compared to the mass of protons and neutrons, we choose to ignore it (0.054% the mass of proton/neutron)

9. Mass number of an atom =
number protons + number of neutrons
Why do we not include number of electrons when calculating mass number?
Mass number is not found on periodic table- you will be given this info if you need it

10. Number of neutrons an atom contains is not on the periodic table either- how would you determine the number of neutrons an atom contains?
Mass number can be written as a superscript to the left of an element’s symbol, or as a number after the element’s name:

11. Formation of Ions
Atoms are neutrally charged- what does this mean about the number of protons and electrons?
When an atom is charged, it is no longer called an atom, it is called an ion
What do you think changes in order for an atom to become an ion?

12. Charge= number of protons- number of electrons
If number of electrons > number of protons, charge is ____________
If number of electrons < number of protons, charge is ____________
Anion=
Cation=
The charge of an ion is written as a superscript on the right side of the element’s symbol:

13. Element Symbols
Breakdown of atomic number, mass number, and charge when writing symbol:

14. Isotopes
Anyone remember what an isotope is?

15. Isotopes= atoms of the same element that have different numbers of neutrons
If the number of neutrons are different, what else changes?
What stays the same between isotopes of the same element?

16. The existence of isotopes disprove part of Dalton’s atomic theory (points 2 and 3 in 4.1 notes)
Dalton (point 3): atoms of same element have identical properties
Isotopes: atoms of same element, but have different properties- number of neutrons and mass number

17. Dalton (point 2): Atoms cannot be changed into different types of atoms
Isotopes: some isotopes are radioactive- they will decay (meaning they will eject protons and neutrons) until they become stable- when they decay they turn into new elements

18. In order to determine which isotope is being discussed, mass number is used when writing the symbol or when writing out the name
Ex: Writing the symbol/name of hydrogen isotope with 0 neutrons:
Symbol/name of hydrogen isotope with 1 neutron:

19. Symbol Name Atomic Number Mass Number Charge Protons Neutrons
Electrons
Magnesium- 25 +2 82
126

20. Average Atomic Mass
Some isotopes are more common in nature than others
Average atomic mass- found on the periodic table, typically as a decimal below the element’s symbol
Average atomic mass= a weighted average of all the masses of all the isotopes of a particular element

21. Average atomic mass= weighted average?
This means it is calculated based off of the abundance of each isotope in nature as well as the mass of each isotope
If isotope A is more abundant that isotope B, which isotope will affect the average atomic mass more? Why?

22. Mass Number vs. Average Atomic Mass
# protons + # neutrons
Always a whole number
For one specific isotope
Not found on periodic table
Average Atomic Mass
An Average
Not a whole number
Weighted average of all isotopes
Found on periodic table

23. Calculating average atomic mass
You will typically be given the abundance of each isotope as a percentage- must change this percentage to a decimal when using it for a calculation
Average atomic mass= (isotope A abundance x isotope A mass) + (isotope B abundance x isotope B mass) + …
When calculating average atomic mass, use the actual mass of the isotope, not the mass number

24. Example- Calculating Average Atomic Mass
Find the atomic mass of chlorine if chlorine-35 has a mass of amu and chlorine-37 has a mass of amu and is present 24.22% of the time.
Remember- percentages of isotopes must add up to 100
This means that chlorine-35 has what abundance?
Isotope
Mass
Percent
Decimal