Empirical Formula and Molecular Formula Introduction
Summary
TLDRThis video explains the differences between molecular and empirical formulas, emphasizing how to derive one from the other. The molecular formula shows the total number of atoms of each element in a compound, while the empirical formula represents the simplest ratio of these atoms. Through examples like ethene and cyanotriazide, the video demonstrates simplifying ratios to find empirical formulas. It also highlights that some molecular formulas can't be simplified, and multiple compounds can share the same empirical formula. The video concludes with practical advice for students encountering these concepts.
Takeaways
- 🔬 The molecular formula shows the number of atoms of each element in a compound.
- 🧪 The empirical formula represents the simplest or most reduced ratio of atoms in a compound.
- ⚛️ Ethene (C4H8) has a molecular formula that can be simplified to an empirical formula of CH2.
- 📉 To find the empirical formula, divide the number of atoms of each element by the greatest common divisor.
- 🔗 For cyanotriazide (C3N12), the empirical formula is CN4 after simplification.
- 📐 Even if a molecule has more than two elements, the basic method of finding the empirical formula is the same.
- 🔎 Some compounds, like P3N5 or C5H12, cannot be simplified, making the molecular and empirical formulas identical.
- 🔄 Different molecular formulas can share the same empirical formula, as seen with compounds like C2H4, C3H6, and C4H8, all of which simplify to CH2.
- 📘 If the molecular formula can't be simplified, the empirical formula remains the same.
- 📝 The molecular formula provides the actual number of atoms, while the empirical formula shows the simplest ratio.
Q & A
What is the difference between a molecular formula and an empirical formula?
-A molecular formula shows the exact number of atoms of each element in a compound, while an empirical formula represents the simplest whole-number ratio of these atoms.
How do you determine the molecular formula for ethene?
-For ethene, you count the atoms in the molecule. Ethene has 4 carbon atoms and 8 hydrogen atoms, so its molecular formula is C4H8.
What steps are involved in converting a molecular formula to an empirical formula?
-To convert a molecular formula to an empirical formula, you first write the ratio of the atoms. Then, simplify the ratio by dividing by the largest common factor to get the simplest whole-number ratio.
How do you find the empirical formula for ethene based on its molecular formula C4H8?
-For C4H8, the ratio of carbon to hydrogen is 4:8. Dividing both by the greatest common factor (4), the simplest ratio is 1:2, giving the empirical formula CH2.
Can a molecular formula and empirical formula be the same? Provide an example.
-Yes, if the molecular formula cannot be simplified, the empirical formula is the same as the molecular formula. For example, the molecular formula P3N5 is already in its simplest form, so the empirical formula is also P3N5.
How is the empirical formula for cyanotriazide (C3N12) determined?
-For cyanotriazide, the ratio of carbon to nitrogen is 3:12. Dividing both by 3, the simplest ratio is 1:4, resulting in the empirical formula CN4.
What happens when the molecular formula has more than two elements? How do you find the empirical formula in such cases?
-If a molecular formula has more than two elements, you divide each subscript by the largest number that can divide all of them. For example, for C5H10O5, divide each subscript by 5, yielding the empirical formula CH2O.
Why might multiple compounds share the same empirical formula?
-Many compounds can have the same empirical formula if they share the same simplest ratio of atoms. For instance, C4H8, C2H4, and C3H6 all have the empirical formula CH2 because they all have twice as many hydrogen atoms as carbon atoms.
Why is it important to know both the molecular and empirical formulas of a compound?
-The molecular formula gives the exact composition of the compound, which is necessary for understanding its structure and properties, while the empirical formula provides a simplified ratio, useful for comparing compounds and identifying common patterns.
How do you simplify ratios to find an empirical formula when dealing with complex molecular formulas?
-To simplify ratios, you identify the greatest common factor of all subscripts in the molecular formula and divide each subscript by that number to obtain the simplest whole-number ratio for the empirical formula.
Outlines
🔬 Introduction to Molecular and Empirical Formulas
This paragraph introduces the concepts of molecular and empirical formulas. It explains that the molecular formula provides the exact number of atoms for each element in a compound, while the empirical formula presents the simplest ratio of those atoms. Using ethene (C4H8) as an example, it shows how the molecular formula gives the number of carbon and hydrogen atoms, and then demonstrates how to simplify this into the empirical formula (CH2) by dividing the atom counts by their greatest common factor.
🧪 Cyanotriazide: A Cool-Looking Molecule
This section uses the example of cyanotriazide (C3N12) to illustrate how to calculate both the molecular and empirical formulas. It explains that by simplifying the ratio of carbon and nitrogen atoms (3:12) to its lowest terms (1:4), we can derive the empirical formula CN4. It highlights the similarity in the process, regardless of the number of elements involved.
Mindmap
Keywords
💡Molecular Formula
💡Empirical Formula
💡Ratio
💡Simplification
💡Atoms
💡Compound
💡Carbon
💡Hydrogen
💡Nitrogen
💡Greatest Common Divisor (GCD)
Highlights
Introduction to molecular, formula and empirical formula, explaining their differences and how to write an empirical formula from a molecular formula.
Molecular formula tells how many atoms of each element are in a compound, using ethene as an example.
For ethene, the molecular formula is C4H8, which means it contains 4 carbon atoms and 8 hydrogen atoms.
The empirical formula simplifies the ratio of atoms in a compound, reducing C4H8 to CH2 by dividing both elements by 4.
Empirical formula represents the simplest or most reduced ratio of atoms in a compound.
Example with cyanotriazide: The molecular formula is C3N12, simplified to an empirical formula of CN4 by dividing both by 3.
In compounds with more than two elements, the empirical formula is derived by simplifying the ratios of all elements involved, such as in C5H10O5, which simplifies to CH2O.
Some molecular formulas cannot be simplified further, making the empirical formula identical to the molecular formula, such as in P3N5 and C5H12.
If the ratio of atoms cannot be reduced, the molecular formula is also the empirical formula.
Many different compounds can share the same empirical formula, as seen with C2H4, C3H6, and C6H2, all of which have CH2 as their empirical formula.
The empirical formula is about finding the simplest ratio of atoms, not necessarily a unique representation of a compound.
The molecular formula gives the total number of atoms, while the empirical formula provides the reduced ratio.
Empirical formulas are often the same across different compounds with similar atomic ratios, particularly in hydrocarbons.
Teachers often provide unsimplifiable molecular formulas in exercises to test understanding of empirical formulas.
Many molecular formulas that cannot be simplified directly result in the same empirical formula.
Learning the difference between molecular and empirical formulas helps in understanding how elements bond and form compounds.
Transcripts
this is an introduction to molecular
formula and empirical formula we'll talk
about what they are what the differences
are between them and we'll learn how you
write an empirical formula when you're
given a molecular formula to start with
here's a molecule of a compound ethene
let's see how to write a molecular
formula and an empirical formula for
ethene
now i often like to think of molecular
formula as the regular formula which you
may already be familiar with
the molecular formula tells us how many
atoms of each element are in a compound
so ethene here has two elements carbon
and hydrogen
for carbon it has one two three four
atoms so we do c4
and then for hydrogen we've got one two
three four five six seven eight
eight hydrogens
c4h8 tells us how many atoms and of what
type are in this compound
now empirical formula over here is all
about the ratio of different types of
atoms in a compound okay
so here we have four carbons and eight
hydrogens let's write this as a fraction
or as a ratio okay so we got four
carbons
four carbon over
eight
hydrogen
now what's special about the empirical
formula
is it tells us
the simplest or most reduced ratio
of the atoms in a compound so if this
ratio or fraction here were on your math
homework how would you write this in the
simplest or most reduced form
okay
you'd think
what was the largest number that you
could divide both of these by and in
this case it's four we can divide the
top by four
and we can divide the bottom by four and
when we do that we'll get four divided
by four will give us
one carbon
over
eight divided by four which is two
hydrogens
and this is now the simplest or most
reduced form of this fraction ratio
now
we write the empirical formula based on
this
simplified ratio okay so it's going to
have one carbon
c we don't write anything after it
because it's just one and then h
two hydrogens
h2
so ch2 is the empirical formula that
represents the simplest or most reduced
ratio of the atoms in the compound
whereas a molecular formula tells us how
many atoms of each element are in the
compound let's look at another
here's a molecule of the compound
cyanotriazide i think this molecule has
a really cool shape it looks like
something out of star trek or something
okay so for the molecular form
how many atoms of each element do we
have here in this compound okay so we
got carbon
and we have one two three of them so c3
and then we got nitrogen and we got one
two three four five six seven eight nine
10 11 12
n 12. that is our molecular formula c3
and 12.
now for the empirical formula we want to
take this first
and write it as a ratio okay so three
carbons over 12 nitrogen and we want to
ask ourselves how can we simplify this
as much as possible what's the biggest
number that we can divide both of these
by
in this case the largest number is three
we can divide both the top
and the bottom by three
and that will give us
one carbon over four nitrogen is the
most simplified ratio of elements for
this compound
and now we write the empirical formula
using this most simplified ratio so
we'll have c
1 so we don't put anything after it and
then we have n
4 so cn4 is the empirical formula here
now not every compound or molecule has
only two elements here so we can't
always get an empirical formula by just
simplifying a fraction
but even when we have a molecular
compound that has more than two elements
the basic math steps we use are still
totally the same
check out this molecular formula that
has carbon hydrogen and oxygen in it we
want to write an empirical formula for
it we can't really write this as a
fraction like we did with the previous
ones but we'll look at these numbers 5
10 and 5 and ask what's the largest
number that we can divide all three of
them by
for c5 h1005 that number will be five
we want to divide everything by five so
for the empirical formula we'll get c
5 divided by 5 gives us 1 so we don't
put anything after it
h
10 divided by 5 gives us 2 so we'll do h
2 and then o
5 divided by 5 gives us 1 again so we
don't put anything after it here so this
is the empirical formula for this
molecular formula
we just want to ask what's the largest
number that we can divide each of these
subscripts by in the molecular formula
to get the empirical formula
now with some molecular formulas you
just can't simplify them anymore
for example
p3 and 5 okay there's no number that we
can divide both of these by to simplify
it further the same is true for
c5h12 there's nothing we can divide both
5 and 12 by
when this happens
we keep this in mind that if the ratio
of atoms in the molecular formula can't
be simplified anymore
the empirical formula is the same as the
molecular formula so for p3n5 its
empirical formula is p3n5
and for c5h12 its empirical formula is
just
c5h12
don't get confused by this teachers and
textbooks love to give you molecular
formulas that you can't reduce anymore
and then ask you what the empirical
formula is this freaks a lot of students
out don't be freaked out by it just
remember that if you can't simplify the
molecular formula anymore there's
nothing wrong it just means that the
empirical formula is going to be exactly
the same as a molecular formula now
finally i want to mention that many
different compounds can all have the
same empirical formula
early in the video we saw the molecular
formula c4h8
has ch2 as its empirical formula
but many other compounds also have ch2
as their empirical formula
c2h4
c3h6
c5h10
and c6h2
all
have ch2 as their empirical formula the
empirical formula as we've said is all
about the most simplified ratio of atoms
in a compound
so whenever we have a molecular formula
with just carbon and hydrogen where we
have twice as many hydrogens as carbons
c2h4 c3h6
the empirical formula will always be ch2
so many many molecular formulas can have
the same empirical formula keep that in
mind so now you've learned about the
difference between molecular formula and
empirical formula the molecular formula
tells us the total number of atoms of
each element that are in a compound and
the empirical formula is the simplest or
most reduced ratio of those atoms
we saw that some molecular formulas just
can't be simplified anymore so the
empirical formulas are the same as the
molecular formulas and finally we saw
that
many compounds with different molecular
formulas can all have the same empirical
formula so now that you've learned this
you might want to go on to the writing
empirical formula practice problems or
you might want to watch my video called
what's the point of empirical formula
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