A Level Chemistry Revision "Relative Atomic Mass"
Summary
TLDRThis video teaches the concepts of relative isotopic mass and relative atomic mass, explaining how they are calculated using isotope data. It highlights that relative isotopic mass is a whole number without units, and relative atomic mass is a weighted mean mass also without units, derived from the abundance of isotopes.
Takeaways
- 🔬 Atoms have extremely small masses, making their direct measurement challenging.
- 📌 Scientists use relative mass to compare atomic masses, with carbon-12 as the reference point.
- 🌐 Carbon-12 is assigned a mass of exactly 12, and other atoms' masses are measured relative to 1/12 of its mass.
- 🧪 Isotopes are atoms of the same element with different numbers of neutrons, resulting in different masses.
- 🏗️ Relative isotopic mass is the mass of an isotope compared to 1/12 the mass of carbon-12.
- 📊 Relative isotopic mass is always a whole number and has no units.
- 📚 The periodic table lists the relative atomic mass of elements, which is calculated from the relative isotopic masses.
- 📈 Relative atomic mass is the weighted mean mass of an element's isotopes, taking into account their abundance.
- 🧩 The relative atomic mass is not always a whole number, reflecting the average mass based on isotopic abundance.
- 📘 To calculate relative atomic mass, use the equation involving the relative isotopic masses and the percent abundance of each isotope.
Q & A
What is the main topic of the video?
-The main topic of the video is the concept of relative isotopic mass and relative atomic mass, and how to calculate relative atomic mass from isotope data.
Why are relative masses used in chemistry?
-Relative masses are used in chemistry because atoms are extremely small and their actual masses are very tiny, making it impractical to use absolute masses in calculations.
What is the reference isotope for relative mass in chemistry?
-The reference isotope for relative mass in chemistry is carbon-12.
How is the mass of carbon-12 defined in terms of relative mass?
-In chemistry, the mass of carbon-12 is defined as exactly 12, and 1/12 of its mass is counted as 1 relative mass unit.
What are isotopes and how do they differ?
-Isotopes are atoms of the same element with a different number of neutrons, which results in different masses for each isotope.
What is the definition of relative isotopic mass?
-Relative isotopic mass is defined as the mass of an atom of an isotope compared with 1/12 the mass of carbon-12.
Why is the relative isotopic mass always a whole number?
-The relative isotopic mass is always a whole number because it is a ratio comparing the mass of an isotope to a fraction of the mass of carbon-12, which is a fixed reference.
What is the formula used to calculate the relative atomic mass of an element?
-The formula to calculate the relative atomic mass is the sum of the products of the relative isotopic masses and their respective percent abundances, divided by 100.
Why are relative atomic masses not whole numbers on the periodic table?
-Relative atomic masses are not whole numbers on the periodic table because they are weighted means based on the abundance of each isotope, resulting in a non-integer value.
Can you provide an example of calculating the relative atomic mass using the given formula?
-Yes, for chlorine with isotopes chlorine-35 (75% abundance) and chlorine-37 (25% abundance), the relative atomic mass is calculated as (35 * 0.75) + (37 * 0.25) = 35.5.
What is the significance of the relative atomic mass in the periodic table?
-The relative atomic mass in the periodic table represents the average atomic mass of an element, taking into account the natural abundance of its isotopes, and is used in chemical calculations.
Outlines
🔬 Understanding Relative Isotopic and Atomic Mass
This paragraph introduces the concept of relative isotopic mass and relative atomic mass, explaining their definitions and importance in chemistry. It emphasizes the small size and mass of atoms and how scientists use carbon-12 as a reference point, assigning it a mass of exactly 12. The paragraph also touches on isotopes, which are atoms of the same element with different numbers of neutrons, and their relative masses. The video script invites viewers to learn the definitions and apply them to calculate the relative atomic mass from isotope data.
📊 Calculating Relative Atomic Mass from Isotope Data
The second paragraph delves into the calculation of relative atomic mass, which is the weighted mean mass of an element's atoms compared to 1/12 of the mass of carbon-12. It explains that this value is derived from the relative isotopic masses of the element's isotopes and their respective abundances. The paragraph provides the formula for calculating relative atomic mass and gives examples with chlorine, thallium, and magnesium isotopes, demonstrating how to apply the formula to find the average atomic mass of these elements.
Mindmap
Keywords
💡Relative Isotopic Mass
💡Relative Atomic Mass
💡Isotopes
💡Carbon-12
💡Abundance
💡Atomic Mass
💡Weighted Mean
💡Periodic Table
💡Chlorine-35 and Chlorine-37
💡Thallium-203 and Thallium-205
💡Magnesium Isotopes
Highlights
Introduction to the concept of relative isotopic mass and relative atomic mass.
Explanation of the challenges in measuring the mass of atoms due to their extremely small size.
Introduction of carbon-12 as the reference standard for relative atomic mass in chemistry.
Definition of relative mass as being relative to carbon-12, with carbon-12 having a mass of exactly 12.
Discussion on isotopes as atoms of the same element with different numbers of neutrons and masses.
Use of copper isotopes as an example to illustrate relative isotopic masses.
Definition of relative isotopic mass as the mass of an isotope compared to 1/12 the mass of carbon-12.
Points to learn about relative isotopic mass: uniqueness to each isotope, whole number values, and unit-less nature.
Introduction of relative atomic mass as the weighted mean mass of an element's atoms compared to carbon-12.
Explanation of how the weighted mean accounts for the abundance of each isotope.
Clarification that relative atomic mass has no units and is typically not a whole number.
Equation for calculating relative atomic mass using the relative isotopic masses and their abundances.
Example calculation of chlorine's relative atomic mass with its two isotopes and their abundances.
Example calculation of thallium's relative atomic mass with its isotopes and abundances.
Final example calculation of magnesium's relative atomic mass considering its three isotopes and their abundances.
Summary of the ability to define and calculate relative atomic mass from isotope data after the video.
Transcripts
I am welcome back to precise lessons by
the end of this video you should be able
to define relative isotopic mass and
relative atomic mass you should then be
able to calculate relative atomic mass
from isotope data now this video is all
about the masses of atoms the problem is
that atoms are extremely smaller so
they've got extremely small masses
here's the mass of one atom of hydrogen
and it concedes a tiny number scientists
solved this problem by using relative
mass masses and chemistry are relative
to carbon-12 which is an isotope of
carbon we call these relative masses
because their relative to carbon-12 in
chemistry we say that atoms of carbon-12
have a mass of exactly 12 and then 1/12
of the mass of this atom is counted as 1
at GCSE we saw that isotopes are atoms
of the same element with a different
number of neutrons and different masses
the good example is copper which has got
two main isotopes atoms of one of the
isotopes have a relative mass of 63 and
atoms of the other isotope have a
relative mass of 65 we call these values
relative isotopic masses relative
isotopic mass is defined as the mass of
an atom of an isotope compared with 1/12
the mass of carbon-12 you need to learn
that definition as you could be asked in
your exam now there are several points
that you need to learn about relative
isotopic mass firstly there's one
relative isotopic mass for each isotope
of an element secondly relative isotopic
mass is always a whole number it's never
a decimal and lastly relative isotopic
mass has got no units coming up welcome
to look at relative atomic mass
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okay now if you look in your periodic
table you can see that the mass number
for copper is actually 63 point 5 this
is called the relative atomic mass and
we calculate this value from the
relative isotopic masses here's the
definition of relative atomic mass and
again you need to learn this definition
relative atomic mass is the weighted
mean mass of an atom of an element
compared with 1/12 or mass of carbon-12
now the mean is weighted for the
abundance of each isotope in other words
how common an isotope is then again
relative atomic mass has got no unit if
you look at your periodic table you can
see that virtually all of the relative
atomic masses are not whole numbers and
that's because relative atomic mass is a
mean we can't let relative atomic mass
using this equation relative atomic mass
equals the relative isotopic mass of
isotope 1 multiplied by the percent
abundance of isotope 1 added to the
relative isotopic mass of isotope 2
multiplied by the percent abundance of
isotope 2 and then all divided by 100 in
the exam you could be asked to calculate
relative atomic mass given data on
isotopes so let's try some examples
chlorine has two isotopes chlorine 35
with an abundance of 75 percent on
chlorine 37 with an abundance of 25
percent calculate the relative atomic
mass for chlorine so pause the video now
and try this yourself putting the
numbers into the equation it gives us a
relative atomic mass of 35 point 5 for
chlorine here's another example thallium
has two isotopes thallium 2o 3 with an
abundance of 29.5%
and thallium 205 with an abundance of
70.5% calculate the world of atomic mass
of thallium so pause the video now and
try this yourself okay putting the
numbers into the equation it gives us a
relative atomic mass for thallium of 204
point four here's one final example
magnesium has three isotopes magnesium
24 with an abundance of 79 percent
magnesium 25 with an abundance of 10% on
magnesium 26 with an abundance of 11%
calculate the relative atomic mass of
magnesium now as you can see we've
adjusted the equation to take into
count the three isotopes so pause the
video now and try this question yourself
okay putting the numbers into the
equation it gives us a value for the
world of atomic mass of magnesium of
twenty four point three okay so
hopefully now you should be able to
define relative isotopic mass and
relative atomic mass you should then be
able to calculate relative atomic mass
from isotope data
[Music]
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