1. Take notes on the appropriate page in your packet
Atomic Structure
Take notes on the appropriate page in your packet

2. Atoms -The Building Blocks of Matter+ + + + - - + + - - -

3. Atoms
Smallest possible unit into which matter can be divided, while still maintaining its properties.
Made up of:
protons
neutrons
electrons - + - + + - + + - -

4. Atoms are so small that…
it would take a stack of about 50,000 aluminum atoms to equal the thickness of a sheet of aluminum foil from your kitchen.
a human hair is about 1 million carbon atoms wide.
a typical human cell contains roughly 1 trillion atoms.
a speck of dust might contain 3x1012 (3 trillion) atoms.
C-C-C-C-C-… + 999,995 more
1 trillion atoms  .

5. + Protons (+) Positively charged particles Located in the NUCLEUS
Identify the atom
Never change
1 atomic mass unit (1 amu) + - +

6. Neutrons = 1 atomic mass unit (amu)+ -
Neutral particles; have no electric charge
Located in the NUCLEUS of the atom
= 1 atomic mass unit (amu)

7. - Electrons (-) Negatively charged particles
Found outside the nucleus of the atom, in the electron shells
Mass is insignificant when compared to protons and neutrons
= # of protons in a neutral atoms
Involved in the formation of chemical bonds + - -

8. What would be the atomic number of this atom?
The number of protons in the nucleus of an atom -
What would be the atomic number of this atom? + - -

9. Atomic Number and Protons
= # of electrons
= 1 atomic mass unit (amu)

10. + The Atom’s “Center” - - -
Protons and neutrons are grouped together to form the “center” or nucleus of an atom.
Notice that the electrons are not apart of the nucleus + - - -

11. Mass Number Average Atomic Mass
The total number of PROTONS + NEUTRONS in an atom’s nucleus (always a whole number)
Expressed in Atomic Mass Units (amu)
Each proton or neutron has a mass of 1 amu
Average Atomic Mass

12. + Mass Number What would be the mass number of this atom? -  3  4
3 protons + 4 neutrons = a mass number of 7 amu
Why did we not account for the electrons when calculating the mass number?

13. Hydrogen (H) Atom - Notice the one electron in the first orbital+ -
= 1
= 0
What’s the atomic number of this atom?
What’s the mass number of this atom? - 1 + 1
Even though there are no neutrons present,
Hydrogen is still considered an atom

14. Oxygen (O) Atom
Notice the two electrons in the first orbital/level and the six in the second + -
= 8
What’s the atomic number of this atom?
What’s the mass number of this atom? - - 8 - + + + + - - + + 16 - - -

15. Sodium (Na) Atom - What’s the atomic number of this atom?
Notice the two electrons in the first orbital/level, eight in the second, and one in the third + -
= 11
= 12
What’s the atomic number of this atom?
What’s the mass number of this atom? - - - 11 - + + + + - - - + + 23 - - - -

16. Identifying an Atom Name of element followed by mass number
Example: Carbon-14
# protons? _____ # neutrons? _____ # electrons? _____
Example: Magnesium-25
Example: Potassium-39 6 8 6 6 13 12 19 20 19

17. Short hand form AZ Notation Ex. AZ X A = mass number Z = atomic number
X = Element Symbol
So…126C shows that Carbon has an atomic number of 6 (6 protons) and a mass number of 12 (6 protons and 6 neutrons)
147N: How many protons? ____ Electrons? ____ Neutrons?__
3216 S: Protons? _____ Electrons? ______ Neutrons? ____
3517Cl: Protons? ______ Electrons? _________ Neutrons? _____

18. Isotopes
All atoms of the same element have the same number of protons; however, atoms of the same element with different numbers of neutrons are called isotopes.
Notice that each of these atoms have one proton; therefore they are all types of hydrogen. They just have a different mass number (# of neutrons). - - + + + -
Hydrogen (Protium)
Hydrogen (Deuterium)
Hydrogen (Tritium)

19. Isotopic Notation…
Element Name – mass number OR Element Symbol – mass number
For example, all carbon atoms have 6 protons (definition of carbon.)
Most carbon atoms have 6 neutrons (mass number of 12.)
Carbon – 12 OR C – 12
But some carbon atoms have 8 neutrons, giving them an mass number of 14.
Carbon – 14 OR C-14

20. Ions
Atoms of an element that have a different number of protons and electrons
Atoms that gain electrons get more negative particles (form a negative ion)
Atoms that lose electrons lose some negative particles (form a positive ion)

21. Calculating Atomic Mass
The “atomic mass” is similar to the mass number; it is the decimal number found in the periodic table.
The atomic mass is the weighted average of the masses of all the naturally occurring isotopes of an element
The average considers the percent abundance of each isotope in nature
Take the percent and convert it into a decimal
Multiple the decimal by its coordinating mass number
Add the numbers together
Let’s Practice!
Calculate the average atomic mass of Neon. Below you will find 3 isotopes of Neon and each’s percent abundance.
Atomic Mass of Ne
0.9060* * *22 = =
Ne(20)
90.60
Ne(21)
0.26
Ne(22)
9.20

22. Calculating Atomic Mass
What would be the atomic mass (≈) of Hydrogen if these three isotopes
were found in the following percentages (99.9%, 0.015%, 0%) respectively? - + + + - -
Hydrogen (Protium)
Mass # = 1 amu
Hydrogen (Deuterium)
Mass # = 2 amu
Hydrogen (Tritium)
Mass # = 3 amu

23. Calculating Average Atomic Mass
Ex. An element has 3 isotopes: 24.1% of all the isotopes have a mass of amu, 48.7% have a mass of 74.61, and 27.2% have a mass of What is the average atomic mass of the element?
Convert percent to a decimal by moving the decimal 2 places to the left.
Multiple each % by its mass
Add together
The sum is the average atomic mass.

24. How to Determine % Abundance
Boron has two naturally occurring, Boron-10 and Boron What is the % abundance of each isotope?
Look up Average Atomic Mass of Boron: ________
Choose 1 isotope (the closest to the average atomic mass) and assign it a value of “x”
The other isotope is assigned a value of 1-x (100%-x)
Write the equation and solve (don’t forget to use the masses!!!)
10.811
Boron-11 = x
Boron-10 = 1-x
= 11x + 10(1-x)
= 11x + 10 – 10x
= x + 10
X = 0.811
Boron-11 = 81.1%
Boron-10 = 18.9%

25. How to determine most abundant isotope
Calcium has 3 isotopes. One has a mass of 35amu, another 41amu, and another 40amu. Which isotope is the most abundant?
Look at the atomic mass to determine most abundant isotope!