Empirical Formula and Molecular Formula Introduction

Summary

This 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

00:00

🔬 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.

05:03

🧪 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.

Keywords

💡Molecular Formula

The molecular formula indicates the exact number of atoms of each element in a compound. It is referred to as the 'regular formula' in the video and is essential for understanding the specific composition of molecules. For example, the molecular formula of ethene is C4H8, which shows there are 4 carbon atoms and 8 hydrogen atoms in the compound.

💡Empirical Formula

The empirical formula represents the simplest whole-number ratio of atoms in a compound. It simplifies the molecular formula by reducing it to its lowest terms. In the video, ethene’s empirical formula is shown to be CH2, derived from dividing the molecular formula's subscripts (C4H8) by their greatest common divisor.

💡Ratio

A ratio is a mathematical relationship between two quantities. In the context of the video, it refers to the ratio of atoms in a compound. The empirical formula is based on the most reduced ratio of these atoms. For example, the ratio of carbon to hydrogen in ethene is 4:8, which reduces to 1:2, giving the empirical formula CH2.

💡Simplification

Simplification involves reducing a fraction or ratio to its most basic form by dividing both the numerator and denominator by their greatest common divisor. In the video, the molecular formula of cyanotriazide (C3N12) is simplified to the empirical formula CN4 by dividing both subscripts by 3.

💡Atoms

Atoms are the smallest units of chemical elements that form compounds. The video frequently refers to the number of carbon, hydrogen, and nitrogen atoms in different compounds to explain molecular and empirical formulas. For instance, in ethene, there are 4 carbon atoms and 8 hydrogen atoms.

💡Compound

A compound is a substance formed when two or more elements chemically bond. The video focuses on different compounds such as ethene (C4H8) and cyanotriazide (C3N12) to explain the difference between molecular and empirical formulas.

💡Carbon

Carbon is one of the elements frequently used in the video to illustrate molecular and empirical formulas. In compounds like ethene (C4H8), carbon atoms are counted to determine both the molecular formula and the simplified empirical formula.

💡Hydrogen

Hydrogen is another element used to demonstrate the difference between molecular and empirical formulas. The video shows that ethene has 8 hydrogen atoms (C4H8), and after simplification, its empirical formula is CH2, indicating a 2:1 ratio of hydrogen to carbon.

💡Nitrogen

Nitrogen is used in the video when discussing cyanotriazide (C3N12). The number of nitrogen atoms helps determine both the molecular formula and its empirical formula (CN4), showing how the ratios of atoms are simplified.

💡Greatest Common Divisor (GCD)

The GCD is the largest number that can divide two or more numbers without leaving a remainder. It is used in the video to simplify ratios for empirical formulas. For example, the GCD of 4 and 8 (in C4H8) is 4, leading to the empirical formula CH2.

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