Atomic Structure & Coulomb's Law - AP Chem Unit 1, Topic 5a

Summary

This educational video script explores the history and development of atomic structure theory. It begins with JJ Thompson's discovery of electrons and the plum pudding model, then moves to Rutherford's gold foil experiment revealing the nucleus with protons. Robert Millikan's oil drop experiment determined the charge of an electron, while Niels Bohr introduced energy levels and quantization. James Chadwick discovered neutrons, and the script concludes with a discussion on atomic structure, emphasizing the importance of charge magnitude and distance in understanding electrostatic forces, as explained by Coulomb's law.

Takeaways

• 🔬 JJ Thompson's cathode ray tube experiment led to the discovery of electrons and the plum pudding model of the atom.
• 🌟 Ernest Rutherford's gold foil experiment with alpha particles resulted in the discovery of the nucleus and the identification of protons.
• 💧 Robert Millikan's oil drop experiment determined the charge of an individual electron to be approximately 1.592 x 10^-19 coulombs.
• 🌌 Niels Bohr proposed that electrons exist in quantized energy levels and can jump between these levels, but cannot exist between them.
• 🚫 James Chadwick discovered neutrons, uncharged particles in the nucleus with a mass similar to protons.
• 💥 The development of atomic theory led to the creation of the first nuclear weapon within 13 years of Chadwick's discovery.
• 🌐 Atoms consist of a nucleus containing protons and neutrons, with electrons orbiting in an electron cloud.
• 📏 The majority of an atom is empty space, with the nucleus being extremely small compared to the overall size of the atom.
• 🔐 The ease of removing an electron from an atom is influenced by the magnitude of the positive charge and the distance of the electron from the nucleus.
• 🔗 Coulomb's law explains the attractive force between charged particles, showing that greater charge magnitude and shorter distances result in stronger forces.

Q & A

What did JJ Thompson discover about atoms using a cathode ray tube?

JJ Thompson discovered that atoms contained negatively charged particles, which he called electrons, using a cathode ray tube. He observed that these particles were deflected towards a positively charged metal plate.

What is the Plum Pudding model of the atom?

The Plum Pudding model, proposed by JJ Thompson, suggested that electrons were randomly distributed within a positively charged 'gel' that made up the rest of the atom, similar to plums in a plum pudding.

What was Ernest Rutherford's contribution to atomic theory?

Ernest Rutherford proposed the existence of a dense, positively charged nucleus within the atom after observing that alpha particles were deflected when shot at a thin gold foil.

What did Rutherford's gold foil experiment reveal about the structure of atoms?

Rutherford's gold foil experiment revealed that atoms have a dense, positively charged nucleus, which contradicted the Plum Pudding model and led to the Rutherford model of the atom.

What was Robert Millikan's contribution to understanding the charge of electrons?

Robert Millikan determined the charge of an individual electron through his oil drop experiment, calculating it to be approximately 1.592 x 10^-19 coulombs.

How did Niels Bohr's theory differ from the Plum Pudding model regarding electron behavior?

Niels Bohr theorized that electrons existed in specific energy levels and orbited the nucleus in a manner similar to planets around the sun, which was a significant departure from the random distribution suggested by the Plum Pudding model.

What is the concept of quantization in relation to electron energy levels?

Quantization refers to the idea that electrons can only exist in specific, discrete energy levels and cannot exist in between these levels, similar to steps on a staircase.

Who discovered neutrons and how did this impact our understanding of the atom?

James Chadwick discovered neutrons, uncharged particles in the nucleus with similar mass to protons. This discovery led to the understanding that atoms consist of protons, neutrons, and electrons.

Why is it easier to remove an electron from hydrogen compared to helium?

It is easier to remove an electron from hydrogen because there is only one proton attracting the electron, resulting in a weaker electrostatic force compared to helium, which has two protons attracting its electrons.

How does Coulomb's law relate to the attraction between charged particles in an atom?

Coulomb's law states that the attractive force between charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them, helping to explain why electrons are held in the atom.

Why is it easier to remove an electron from lithium compared to helium, even though both have a +2 charge?

It is easier to remove an electron from lithium because the outermost electron in lithium is farther from the nucleus, resulting in a weaker attractive force compared to the outermost electron in helium.

Outlines

00:00

🔬 Discovery of Subatomic Particles

This paragraph discusses the early exploration of subatomic particles, starting with JJ Thompson's experiments in 1897. Thompson used a cathode ray tube to observe the deflection of particles, leading to the discovery of electrons. He proposed the plum pudding model of the atom, where electrons were thought to be randomly distributed within a positively charged substance. Ernest Rutherford later refined this model through his gold foil experiment with alpha particles, which revealed a dense, positively charged nucleus within the atom. This led to the understanding that atoms consist of a nucleus containing protons and electrons orbiting around it. Robert Millikan's oil drop experiment determined the charge of an individual electron, while Niels Bohr contributed to the understanding of electron energy levels and their quantized nature.

05:01

🌌 Bohr's Atomic Model and Quantum Theory

The paragraph delves into Niels Bohr's atomic model, which suggested electrons orbit the nucleus in specific energy levels, similar to planets around the sun. Bohr's model was an improvement over previous theories, introducing the concept of quantized energy levels where electrons could only exist at certain energy states and could jump between these levels. This idea laid the groundwork for quantum mechanics. James Chadwick's discovery of neutrons in the 1930s completed the basic model of the atom, consisting of protons, neutrons, and electrons. The paragraph also explains the vast emptiness within atoms, with most of their volume being empty space, and how atoms would appear if scaled down to a football stadium analogy.

10:02

⚛️ Atomic Structure and Electrostatic Force

This section explores the forces that hold electrons in atoms, focusing on the electrostatic force between charged particles. It compares the ease of removing electrons from hydrogen and helium, explaining that a greater positive charge results in a stronger attraction to electrons. The paragraph introduces Coulomb's law, which describes the force between charged particles, and discusses how the magnitude of charge and the distance between them affect this force. It uses the example of lithium to illustrate that an electron farther from the nucleus experiences a weaker force, making it easier to remove compared to an electron in helium.

15:04

🔋 Understanding Atomic Interactions

The final paragraph emphasizes the importance of understanding atomic structure and interactions, particularly the role of distance in determining the force of attraction between charged particles. It reiterates the significance of Coulomb's law in chemistry and physics, explaining how the force of attraction decreases with increasing distance between charged particles. The paragraph concludes by summarizing the key points of the lesson and encouraging viewers to engage with the content by giving a thumbs up.

Keywords

💡Subatomic Particles

Subatomic particles are the fundamental units that make up atoms. The video discusses how these particles interact with each other, focusing on electrons, protons, and neutrons. These particles are essential to understanding atomic structure and behavior, as they determine the properties of elements and compounds.

💡JJ Thompson

JJ Thompson is credited with discovering the electron and proposing the plum pudding model of the atom. His work is foundational to the video's narrative, as it marks the beginning of our understanding of atomic structure. Thompson's experiments with cathode rays led him to the conclusion that atoms contained negatively charged particles, which he called electrons.

💡Plum Pudding Model

The plum pudding model was an early atomic model proposed by JJ Thompson. It suggested that electrons were embedded within a positively charged 'pudding' with no distinct nucleus. This model was later disproved by Rutherford's gold foil experiment, but it's an important step in the historical progression of atomic theory.

💡Ernest Rutherford

Ernest Rutherford's gold foil experiment is a pivotal moment in the video. His findings contradicted the plum pudding model and led to the discovery of the atomic nucleus. Rutherford observed that alpha particles were deflected when they hit a thin gold foil, indicating the presence of a dense, positively charged nucleus at the center of the atom.

💡Alpha Particles

Alpha particles are positively charged particles composed of two protons and two neutrons. In the video, Rutherford's use of alpha particles in his gold foil experiment is highlighted as a key method for discovering the nucleus. The deflection of alpha particles provided evidence for the existence of a dense, central nucleus within the atom.

💡Nucleus

The nucleus is the central part of an atom, containing protons and neutrons. The video explains that Rutherford's experiment led to the understanding that the nucleus is dense and positively charged. The nucleus is crucial for atomic identity and plays a significant role in chemical reactions and radioactive decay.

💡Protons

Protons are subatomic particles with a positive electric charge. They are located in the nucleus of an atom and their number determines the element's atomic number. The video discusses how protons were identified as the positive charges within the nucleus, which was a significant advancement in atomic theory.

💡Electrons

Electrons are subatomic particles with a negative electric charge. They orbit the nucleus and are much smaller than protons or neutrons. The video describes how electrons were discovered by JJ Thompson and how their properties, such as being able to occupy discrete energy levels, contribute to atomic structure and chemical behavior.

💡Robert Millikan

Robert Millikan's oil drop experiment, as mentioned in the video, allowed for the measurement of the charge of a single electron. This experiment was crucial for understanding the quantized nature of electric charge and provided a precise value for the elementary charge, which is a fundamental constant in physics and chemistry.

💡Niels Bohr

Niels Bohr's model of the atom, as discussed in the video, introduced the concept of electrons existing in quantized energy levels. Bohr's model improved upon the plum pudding model by suggesting that electrons orbit the nucleus in specific paths or shells, which was a significant step towards the modern understanding of atomic structure.

💡Quantum

The term 'quantum' refers to the discrete amounts in which certain physical properties can change. In the video, it is used to describe how electrons can only exist in specific energy levels and cannot exist between these levels. This concept is fundamental to quantum mechanics and is essential for understanding atomic transitions and the behavior of electrons.

💡Coulomb's Law

Coulomb's Law is a principle in physics that describes the electrostatic interaction between electrically charged particles. In the video, it is used to explain how the force of attraction between charged particles (like protons and electrons) depends on the magnitude of their charges and the distance between them. This law is crucial for understanding the stability of atoms and the bonds they form.

Highlights

JJ Thompson's discovery of electrons using a cathode ray tube in 1897.

Thompson's plum pudding model of the atom with electrons floating in a positively charged gel.

Ernest Rutherford's gold foil experiment that led to the discovery of the atomic nucleus.

Rutherford's conclusion that atoms contain a dense, positively charged nucleus and protons.

Robert Milliken's oil drop experiment determining the charge of an individual electron.

Niels Bohr's theory of electrons existing in quantized energy levels around the nucleus.

Bohr's concept of electrons jumping between energy levels but not existing between them.

James Chadwick's discovery of neutrons in the nucleus in the early 1930s.

The composition of an atom with protons, neutrons, and electrons.

The vast majority of an atom is empty space, with the nucleus being very small compared to the overall size of the atom.

The difficulty of removing an electron from hydrogen compared to helium due to the electrostatic force.

The ease of removing an electron from lithium compared to helium due to the increased distance from the nucleus.

Coulomb's law and its application in understanding the attractive forces between charged particles in atoms.

The importance of both charge magnitude and distance in determining the attractive force between particles in an atom.

The significance of the distance between the nucleus and electrons in lithium making it easier to remove an electron compared to helium.

The educational value of the lesson in understanding atomic structure and interatomic interactions.

Transcripts

in unit 1 Section 5 we're focusing on

subatomic particles and how they

interact with each other now this story

kind of goes all the way back to around

1897 when a scientist named JJ Thompson

was able to use something called a

cathode ray tube to pass a array of

particles in there and he had a

positively charged metal plate and a

negatively charged metal plate and he

noticed that things were being deflected

in the direction of the positive plate

and so he realized that these atoms had

negative charges in them he called them

electrons and he didn't really have a

very good grasp as to what they were

like or how they reacted other than what

you see here but he he did come up with

a model being the good scientist he was

he called it the plum pudding model and

his idea looked something like this

where he thought that

these electrons were like these little

pods or these little bubbles that were

kind of floating around randomly in the

atom while the rest of the atom was this

positively charged

gel for lack of a better word it's

called The Plum Pudding model because he

said that these electrons were randomly

distributed kind of like plums in Plum

Pudding so that was his idea now over

time this got refined Ernest Rutherford

about 15 or so years later was in charge

of an experiment where he propelled

alpha particles which are very dense

positively charged particles at a very

thin piece of gold foil now this is a

little picture or kind of a cartoon of

how this worked he set up this gold foil

here and he had a device that

essentially shot these alpha particles

at the gold foil now in his idea if the

plum pudding model was correct pretty

much all of those alpha particles would

have gone straight through the gold foil

well he found that that's not exactly

what happened as you can see in this

little cartoon here some and this is

kind of exaggerated but some of those

alpha particles were deflected

and a very small fraction of these alpha

particles actually were almost reflected

completely and bounced off of the gold

foil and came back almost in the same

direction as it was shot out from which

was very surprising to him he did not

expect this to happen so I guess the

question is why were some of the alpha

particles deflected or even repelled by

the gold atoms well if we think about

this we know that the only way that

anything can be deflected off of

anything else in our

macroscopic world is if something that's

a very high density hits something else

of very high density and they bounce off

of each other

and he used this to to reason and

realize that you know these alpha

particles had a positive charge and they

were very dense they must have been

hitting something else that was

positively charged and also very dense

inside those gold atoms and so that's

why there was that reflection or that

the deflection in the gold foil

experiment he realized that inside each

one of those gold atoms there had to be

something that was very dense

something that was positively charged he

called that the nucleus and he called

those positive charges inside the atoms

protons and so this gold foil experiment

was an excellent way to demonstrate that

there are protons and they're in this

very dense nucleus of the atom so slowly

this uh understanding of the atom is

being revised and refined now we go

backward a few years and we have Robert

Milliken and he actually was focused on

the electrons he used something called

the oil drop experiment where he charged

up these little tiny droplets of oil and

he was able to determine the charge of

an individual electron

and he used this electric field in order

to do that so he calculated that the

electric charge of one electron was

about

1.592 times 10 to the negative 19th

coulombs

so there we have that value very

ingenious experiment for all the way

back there in 1908. now if we go forward

a bit more we have Niels Bohr and he was

thinking about electrons as well and his

theory his his evidence showed that

electrons

existed in these energy levels

and they were spinning around the

nucleus now he did not have an exact uh

idea as to what these energy levels

looked like but he theorized or he

hypothesized I suppose that they looked

kind of like this

or these atoms had electrons that were

basically orbiting the nucleus kind of

like planets do in the solar system this

these circular energy levels this was

his idea now today we know that energy

levels don't actually look like that

that's not what they look like but that

was his idea and this kind of gives us a

model to work with now one thing that he

got very right on here was that

electrons can jump

they can move from one energy level to

another and so this this electron here

for example in this first energy level

it can jump to the second

or to the third or one from the third

can jump to the second but they cannot

hover between levels

so they can be in the first they can be

in the second they can't be like

floating in between and that's something

we call a quantized function something

that's a Quantum function exists in one

level

or a different level

or a different level but it can't be

floating in between it's kind of like

steps on a staircase

you know that you can be standing on one

step in the staircase

or you could be standing on one above it

or one below it but you can't levitate

in between the steps

and that's kind of what we have here you

can have an electron in an energy level

one above it one below it but it can't

be floating or levitating in between and

so that's what we're talking about when

we say Quantum in this context it's a

measurement or some sort of of a

function that exists only in

discrete or complete steps not in not

not floating around in the middle or

fractional amounts

James Chadwick was yet another scientist

who discovered that there were uncharged

particles along with protons in the

nucleus and that was in the early 1930s

these were called neutrons we know that

they have no charge about the same mass

as a proton if you want to get technical

they weigh a little bit more than a

proton but but not much and this was

essentially the basis for nuclear

science Nuclear Physics they were able

to take this complete story of the atom

the protons and the neutrons and to a

lesser extent those electrons and within

you know 13 years of James Chadwick's

Discovery they were able to create the

first nuclear weapon so we have those

scientists that helped us understand the

story of the atom now today we know that

atoms are composed of protons in the

nucleus those are the positively charged

particles those have a mass of about one

atomic mass unit and then we have

neutrons like we said those don't have

any charges those are neutral and so

that's why they're called you know

neutrons because they're neutral and

they also have a mass of about one

atomic mass unit and then we have the

electrons those are much much smaller

than protons and neutrons and they're

buzzing around the nucleus in what we

sometimes call the electron cloud now

you can see how much smaller

and how much less massive they are than

protons and neutrons about one eighteen

hundred and twentieth of the mass of

those particles in the nucleus they have

a negative charge now this is a picture

that you've probably seen before where

you have you know neutrons and protons

in the middle electrons buzzing around

there is a major it's I say that there's

a little problem that's actually a

rather a major problem with this picture

and the fact is the picture is not drawn

to scale

in fact it's not even close to scale

because if you wanted to draw or

visualize an atom that actually was

drawn to scale you might need something

that's about the size of this football

stadium here so let's imagine that we're

going to make the model of an atom the

size of that football stadium right

there now if that's the case the nucleus

is going to be a dime on the 50-yard

line

so imagine a dime on the 50-yard line

well the electrons would be grains of

sand buzzing around in those outside

stands

that's what you'd have to have in order

to have an atom drawn essentially to

scale now that tells us that the vast

majority of an atom is empty space over

99.9999999

of an atom is empty space which means

you know you're made of atoms so almost

all of you would be empty space almost

all of me would be empty space if you

were to extract all the empty space out

of a person you'd have someone that

weighed basically the same as they do

now except they'd be about the size of

a grain of sand

and they would be

pure protons electrons and neutrons

but of course that's not how a matter is

in our in our world at least

now

let's take a look at two relatively

simple atoms in fact these are for all

practical purposes the two simplest

atoms that exist hydrogen and helium and

you can see these of course these are

not drawn to scale this is just a little

cartoon that I made to help us visualize

these now imagine or ask yourself from

which of these atoms would it be easier

to remove an electron

so think about that and

the answer is it is easier to remove an

electron from hydrogen

and do you see why that is we have

basically two types of particles here we

have protons that are positively charged

and we have electrons that are

negatively charged I've left out the

neutrons because they don't have a

charge and so there's no real

positive or negative attractive Force

there

so

it's easier to take one away from

hydrogen because there's less attractive

Force there's only one positive charge

here that's holding in the electron

whereas over here we have two protons

that are holding in the electrons

now

the idea here is that the greater the

magnitude of the charge the greater the

attraction

so what we have here is what's sometimes

called an electrostatic force

basically that just means the positive

attracting the negative

and the more positive and more negative

charge you have the stronger they tend

to attract each other so these here in

helium would be more strongly attracted

a plus two to a minus two will have the

stronger traction than a A plus one

minus one so it's relatively easier

or easy to remove that electron from

hydrogen

now let's look at two other atoms we

have hydrogen and helium but let's let's

change gears here and this time let's

look at Helium and lithium so helium and

lithium look kind of like this once

again not really drawn to scale just

just an idea here to help us visualize

I'm going to ask the same question from

which of these atoms would it be easier

to remove an electron

now you notice we have another factor in

play here because it's true that we have

a plus two and a minus two for the

helium and a plus three and a basically

a minus three for this lithium but

notice what else we have over here there

is a new energy level this last electron

in lithium is farther away from the

nucleus

so since it's farther away from the

nucleus it has less of an attraction

it's kind of like having two magnets

next to each other and you know that if

you have two magnets that are very close

well they'll snap together very readily

but if you have those two magnets that

are farther apart well there's less of

an attraction it's kind of the same idea

here

the greater the distance the lower the

attraction so the answer is it's easier

to remove this electron from lithium

than it is to remove this last electron

from Helium so I want you to think about

those two factors we've just talked

about there's the magnitude of the

charge

and the distance between the charged

particles

now this brings us to a very important

Concept in chemistry that helps us

understand atomic structure this is

called Coulomb's law

and this is a law that we use from

physics and the F stands for the

attractive forces between any two

charged particles now this K stands for

a constant but notice we have two other

types of variables here we have the Q q1

and Q2 are the magnitude of charge of

each of the two charged particles

and then the d stands for the distance

between the two charged particles now if

we think about this from a mathematical

point of view you can see that if these

values for Q go up

then the force goes up as well

so what this tells us is more strong of

a charge greater magnitude of charge

means we have a stronger attractive

Force

that's why the plus two and minus 2 had

a stronger traction than the plus one

minus 1.

like we had in that example earlier

now D is for distance and notice it's in

the denominator so that tells us that if

the distance is higher

you know this denominator gets larger

that's going to make this whole value

smaller

so what that tells us is that the

greater the distance

the less the attractive force and that

tells us why lithium since its last

electron was was farther away

would have a lower attractive Force okay

and this is just an introduction to

Coulomb's law we'll get more into detail

with this and learn some more things

about this in future lessons this is

just an introduction to it right now now

let's go back to these two atoms we

looked at uh here a minute ago and let's

explain

why it's easier

for lithium to lose that last electron

then for helium to lose that electron

so what is the deciding force is it the

magnitude of charge

or is it the distance

well you can see it's the distance this

this electron here is farther away

from the nucleus than we have in helium

lithium's outermost electron is in that

second occupied energy level it's

located a greater distance from that

nucleus than in the case for helium in

its outermost electron which is only in

the first occupied energy level

so as we think about Coulomb's law and

the parts of an atom and how they're

attracted to each other this really

helps us to understand how atoms and the

parts of an atom interact with each

other hope you enjoyed this lesson hope

you learned something from it and if you

did please give me a thumbs up and I

hope to see you again on my channel in

the future