Thursday
October
14
2021
AIM
• Where does the mass
on the periodic table
come from?
AGENDA
• YOYO
• Rutherford’s Gold Foil
Experiment Simulation
• Isotope/AAM notes &
practice
YOYO (Do Now)
• Take out the regents
HW questions. Work
in pairs to check and
discuss each other’s
work. On the do now
sheet write “Atomic
History HW check”
HOMEWORK
• Edpuzzle-Isotopes
and Average
Atomic Mass
• Quiz corrections due Monday
Answer to History of the Atom Regent
Questions
pHet Simulation Link - Rutherford
https://phet.colorado.edu/sims/html/rutherford-scattering/lat
est/rutherford-scattering_en.html
YOYO
Look at the two images below. What similarities do you see? What
differences do you see? Write down at least 1 similarity and 1
difference that you can observe in these images.
Similarities
Differences
Looking at this picture...
Question: What do you
notice about the number
of ELECTRONS in all
three pictures?
Looking at this picture...
Question: What do you
notice about the number
of PROTONS in all three
pictures?
Looking at this picture...
Question: What do you
notice about the number
of NEUTRONS in all three
pictures?
Looking at this picture...
Question: Based on this
image, what do you think
an isotope is? What stays
the same and what
changes?
Isotopes
● An isotope is a different version of a particular
element with a different mass.
● The atomic number (# protons), and the number of
electrons DO NOT CHANGE
● The number of neutrons change - that is the only way
to change the mass of an atom without changing what
atom it is.
Changing the Subatomic Particles
● If you change the number of protons...you change the atomic
number and the element itself
● If you change the number of electrons...you change the charge
and create an ion
○ Lose electrons - become positive ion - cation
○ Gain electrons - become negative ion - anion
● If you change the number of neutrons...you change the mass of
the atom only
Isotopic Notation
● Isotopes are written with the element symbol and the mass
number.
Analyzing Isotopes
Li-6
●
●
●
●
# Protons:_____
# Electrons: _____
# Neutrons: _____
Isotopic Notation:
_______
Li-7
●
●
●
●
# Protons:_____
# Electrons: _____
# Neutrons: _____
Isotopic Notation:
_______
Li-8
●
●
●
●
# Protons:_____
# Electrons: _____
# Neutrons: _____
Isotopic Notation:
_______
Average Atomic Mass
● Average atomic mass is the average mass of all the
naturally occurring isotopes of an element
● It is a weighted average you you must take the percent
abundance into account
● This is where the atomic mass on the periodic table
comes from
1.
Bromine has 2 naturally occurring isotopes. Using the information
provided below, calculate the average atomic mass for bromine.
2. Find the average atomic mass for B if 19.9% of B atoms are B-10 with a
mass of 10.012 amu and 80.1% are B-11 with a mass of 11.009 amu.
3. Find the average atomic mass for Mg if 78.99% of Mg atoms are Mg-24
with a mass of 23.985 amu, 10.00% are Mg-25 with a mass of 24.985 amu,
and 11.01% are Mg-26 with a mass of 25.982 amu.
4. Titanium has five common isotopes: 46Ti (8.0%), 47Ti (7.8%), 48Ti
(73.4%), 49Ti (5.5%), 50Ti (5.3%). What is the average atomic mass of
titanium?