Download A or `Mass Number` - Uplift Pinnacle Prep

WHAT DO THESE BOXES MEAN??
Number of protons/
Atomic Number
All atoms of the
same element
have the same
number of
protons
THE ATOM…THROUGH THE YEARS
THE ATOM…THROUGH THE YEARS
IF WE MADE A SCALE MODEL OF AN ATOM
AND WANTED TO USE COWBOY STADIUM AS
OUR ELECTRON CLOUD, THE NUCLEUS OF THE
ATOM WOULD BE THE SIZE OF THE ERASER ON
THE END OF YOUR PENCIL. AN ELECTRON
WOULD STILL BE SMALLER THAN THE POINT ON
A STRAIGHT PIN.
AVERAGE MASS OF SUBATOMIC
PARTICLES
Subatomic Electric
Particle
Charge
Electron
-1
Mass
Number
(amu)
0
Atomic Mass Unit
Proton
+1 -24
1 amu = 1.66 x 10 g
Neutron
0
Location
1
Electron
cloud
Nucleus
1
Nucleus
Isotopes
ATOMS OF THE SAME
ELEMENT WITH DIFFERENT
NUMBERS OF NEUTRONS
(THEREFORE HAVE
DIFFERENT MASSES).
TWO ISOTOPES OF SODIUM
ISOTOPE SYMBOL
X: element symbol
ISOTOPE SYMBOL
A: Mass Number
#protons + # neutrons in the
nucleus
Always larger than Z
ISOTOPE SYMBOL
Z: Atomic number
#protons
ISOTOPES OF SODIUM
23
11
Na
24
11
Na
2 WAYS TO WRITE ISOTOPE SYMBOL
23
11
Na
Or Sodium-23
EXAMPLE PROBLEM
• Write the isotope symbol for the
chemical element that has 6 protons
and 8 neutrons
WORK IT OUT!
• Take out Whiteboards and
Markers
• Talk over answer with partner
• Raise board when directed
#1
• Write the isotope symbol for the
chemical element that has 17
protons and 16 neutrons
33
17
Cl
or
Chlorine-33
#2
How many protons are in the
isotope 54Cr? (Chromium-54)
24 (like every atom of
Chromium)
#3
How many neutrons are in the
isotope 42Ca?
22 neutrons
#4
How many electrons are in the
isotope 23Na?
11 electrons
QUICK BREAK …
BY THE END OF THE CLASS TODAY
I WILL BE ABLE TO…
•calculate the average
atomic mass of an element
using isotopic composition
AVERAGE ATOMIC MASS
•the weighted average of
the atomic masses of all
naturally occurring
isotopes of an element.
Where can we find the average
atomic mass of each element?
WHAT IS THE DIFFERENCE??
• The A or ‘Mass
Number’ is the mass of
that specific isotope
• The number on the
periodic table is the
average of all the
existing isotopes
• Example of Carbon
LET’S TAKE A LOOK AT PENNIES…
The US mint estimates that of all the
pennies currently in circulation 66.5% of
them are “new” (post-1982) pennies and
33.5% are ‘old’ pennies. A ‘new’ penny
weighs 2.5g and an old penny weighs 3.1
g. Use this information to determine the
average mass of a penny.
HOW DO WE CALCULATE THE AVG.
MASS OF A PENNY?
Penny Year
Mass (grams)
Percentage
in Circulation
Post-1982
2.5g
66.5%
Pre-1982
3.1g
33.5%
2.5 + 3.1 = 5.6
5.6 ÷ 2 = 2.8 grams
WE MUST TAKE INTO CONSIDERATION THE
PERCENTAGES OF EACH TYPE OF PENNY!
Penny Year
Mass (grams)
Percentage
in Circulation
Post-1982
2.5g
66.5%
Pre-1982
3.1g
33.5%
(2.5 x 0.665) + (3.1 x 0.335) = 2.7 grams
WHAT IS THE AVERAGE ATOMIC MASS
OF COPPER??
Isotope
Copper-63
Copper-65
Mass
Number
63
65
Percentage
Natural
Abundance
69.17%
30.83%
(63 x 0.6917) + (65 x 0.3083) = 63.61 grams
YOU TRY:
Rubidium has two common
isotopes, Rubidium-85 and
Rubidium-87. If the abundance of
Rubidium-85 is 72.2% and the
abundance of Rubidium-87 is
27.8%, what is the average atomic
mass of rubidium?
QUIZ TIME