1. The Atom
EQ: How are the subatomic particles of an atom calculated? How is the Bohr model drawn for elements?

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

3. Atoms
Smallest possible unit into which matter can be divided, while still maintaining its properties.
Made up of:
protons
neutrons
electrons - +
For example, what is the
smallest possible unit
into which a long essay can be
divided and still have some meaning? - + + - + + - -

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.
if you could enlarge a penny until it was as wide as the US, each of its atoms would be only about 3 cm in diameter – about the size of a ping-pong ball
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.
it would take you around 500 years to count the number of atoms in a grain of salt.
C-C-C-C-C-… + 999,995 more
1 trillion atoms  .
Is made of approximately 3 trillion atoms
Just one of these grains

5. + Protons (+) Positively charged particles Located in the NUCLEUS
The identity of the atom…they NEVER change!
Equal to the atomic number of the atom
Equal to the number of electrons in a neutral atom
Protons + Neutrons = Mass Number + - +

6. Neutrons Protons + Neutrons = Mass Number-
Neutral particles; have no electric charge
Located in the NUCLEUS of the atom
Protons + Neutrons = Mass Number

7. - Electrons (-) Negatively charged particles
Found outside the nucleus of the atom, in the electron shells
Move so rapidly around the nucleus that they create an electron cloud
Mass is insignificant when compared to protons and neutrons
Equal to the number of protons in a neutral atoms
Involved in the formation of chemical bonds
2n2 to determine number of electrons per shell + - -

8. + 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 + - - -

9. 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? + - -

10. Mass Number
The total number of PROTONS + NEUTRONS in an atom’s nucleus
Not found on the periodic table.
Expressed in Atomic Mass Units (amu)
Each proton or neutron has a mass of 1 amu -
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? (Like counting the weight of a flea on a dog) -

11. 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? _____

12. Sub-Atomic Particles Weight Comparison (protons, neutrons, electrons)
Neutron = x10-27 kg Proton = x10-27 kg Electron = x10-31 kg - - +
1839 electrons = 1 neutron
1836 electrons = 1 proton +
How do you think the mass of a neutron
compares to that of a proton?
1 neutron ≈ 1 proton

13. Hydrogen (H) Atom - Notice the one electron in the first orbital = 1 +
= 0 -
How many
more electrons
can fit in the 1st
orbital/ level?
2n2 +
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
How many
more electrons
can fit in the 2nd
orbital/ level? - - - + + + + - - + + - - -

15. Sodium (Na) Atom
Notice the two electrons in the first orbital/level, eight in the second, and one in the third + -
= 11
= 12 - - -
How many
more electrons
can fit in the 3rd
orbital/ level? - + + + + - - - + + - - - -

16. 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)

17. Isotopic Notation…
Atoms with extra neutrons are like a person born with extra fingers! Still human, but a little bit different!
Often, atoms with extra neutrons are unstable and break apart (called radioactivity!). The more extra neutrons, the more unstable they are.
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

18. Time to Play….
ATOMIC DOMINOES

19. Atoms, Isotopes, & Ions
Atom: no overall charge- neutral, the number of protons EQUALS the number of electrons.
Isotopes: atoms of an element with the same number of protons, but different number of neutrons.
Ion: carries a charge, the number of electrons DO NOT equal the number of protons.
Protons don’t change, they are the IDENTITY of the atom
Electrons are either gained or lost
Gained: the overall charge is negative
Lost: the overall charge is positive

20. Subatomic Particles: Atoms, Isotopes, Ions

21. What would be the atomic mass (≈) of Hydrogen if these three isotopes
Isotopes & Atomic Mass
“mass number” is simply Protons + Neutrons in a specific atoms nucleus, represented using a whole number.
“atomic mass” decimal number found in the periodic table.
reflects the average of all the naturally occurring isotopes based on the percent abundance of each isotope - - - + + +
Hydrogen (Protium)
Mass # = 1 amu
Hydrogen (Deuterium)
Mass # = 2 amu
Hydrogen (Tritium)
Mass # = 3 amu
What would be the atomic mass (≈) of Hydrogen if these three isotopes
were found in the following percentages (99.9%, 0.015%, 0%) respectively?

22. Calculating Average Atomic Mass
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.

23. Ex. An element has 3 isotopes: 24
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?

24. 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!
The mass number of the most abundant isotope can be used when no mass number is given.

25. Calculating % Abundance
Assign one isotope a value of x, and the other a value of 1 - x
Due to the fact that the 2 isotopes should add up to 100% or 1
Multiply the mass by the assigned x value
Add together and set equal to the average atomic mass.
Solve for x (multiply by 100 to convert to %)
Plug in x value to solve for 1 – x. (multiply by 100 to convert to %)

26. Silicon has two isotopes, Si-29 and Si-28
Silicon has two isotopes, Si-29 and Si-28. Find their percentages in nature.
Average atomic mass Si =
[(29)(x) ] + [(28)(1 – x)] =
29x + 28 – 28x =
x + 28 =
x = = 8.55 % Si – 29
1 – = = % Si - 28

27. Law of Definite Proportions & % mass
The law of definite proportions confirms that the percent composition of each element in any size sample of a given compound will be the same.
% mass/composition calculation
Determine the total mass of the sample.
Divide the individual mass of the element by the total mass of the sample.
Multiply by 100 to make a %
This percent correlates to
the ratio of the elements
in the compound.

28. A 78 g sample of an unknown compound contains 12. 4 g hydrogen
A 78 g sample of an unknown compound contains 12.4 g hydrogen. What is the % by mass of hydrogen in the sample?

29. If hydrogen composes 11% of a 100 g sample of water, what is the mass of hydrogen in the sample?