Models of the Atom Timeline

Summary

This video script traces the evolution of atomic theory from ancient Greek philosophers to modern quantum mechanics. Democritus and Leucippus first proposed indivisible 'atoms', but Aristotle's four elements theory was more accepted. John Dalton's experiments in 1808 confirmed atoms as basic units. JJ Thompson's discovery of electrons led to the 'plum pudding' model, which was later refined by Rutherford's gold foil experiment revealing a concentrated nucleus. Niels Bohr's planetary model was succeeded by Erwin Schrodinger's quantum mechanical model, depicting electrons as probabilistic orbitals. The script concludes by acknowledging the ongoing refinement of atomic models as scientific understanding deepens.

Takeaways

• 📚 The concept of atoms originated from ancient Greek philosophers Democritus and Leucippus, who proposed that all matter was made of uncuttable particles called 'atomos'.
• 🔬 Aristotle's competing theory of matter being composed of earth, water, air, fire, and ether was more popular at the time, overshadowing the atom theory.
• 🧪 John Dalton introduced the first scientific experiments in 1808, suggesting atoms as indivisible and like tiny balls that combine to form different substances.
• 🌐 J.J. Thompson's discovery of electrons challenged Dalton's model, proposing the 'plum pudding model' where electrons are scattered within a positively charged substance.
• 💥 Ernest Rutherford's gold foil experiment revealed a concentrated positive charge at the atom's center, leading to the 'nuclear model' of the atom.
• 🌀 Niels Bohr's model depicted electrons as planets orbiting a sun-like nucleus, a concept that was later refined by quantum mechanics.
• 🚫 Quantum mechanics, particularly through the work of Erwin Schrodinger, showed that electrons do not orbit in fixed paths but form probabilistic 'orbitals'.
• 🔬 Further discoveries by Rutherford and Chadwick identified protons and neutrons as the subatomic particles within the nucleus.
• 🔍 The quantum mechanical model is the most accurate representation of atoms, though it can be complex for simple explanations.
• 🎨 For simplicity, many educational materials use a hybrid model that combines elements of the Bohr and quantum mechanical models to illustrate atomic structure.
• 🔍 As scientific understanding evolves, the models of atoms are subject to change and refinement to more accurately reflect atomic behavior.

Q & A

Who were the first people to discuss the concept of atoms?

The first people to discuss the concept of atoms were the ancient Greek philosophers Democritus and his teacher, Leucippus.

What did Democritus believe atoms were?

Democritus believed that atoms were tiny, uncuttable particles that all matter was made of, and that they came in different sizes and shapes.

What was Aristotle's opposing view to Democritus' atomic theory?

Aristotle proposed that different things were made of different amounts of the elements earth, water, air, fire, and ether, which was an opposing view to Democritus' atomic theory.

Why did people initially not believe in Democritus' atomic theory?

People initially did not believe in Democritus' atomic theory because it was not supported by experimental evidence, and Aristotle's ideas were more popular at the time.

Who conducted the first scientific experiments that supported the atomic theory?

The British chemist John Dalton conducted the first scientific experiments that supported the atomic theory in 1808.

How did John Dalton envision atoms?

John Dalton envisioned atoms as tiny, indivisible balls that arranged in different combinations to make different substances.

What discovery challenged Dalton's view of atoms being indivisible?

JJ Thompson's discovery of electrons within atoms challenged Dalton's view, showing that atoms were not indivisible but made up of even smaller particles.

What model of the atom did JJ Thompson propose?

JJ Thompson proposed the plum pudding model of the atom, where electrons were scattered throughout a positively charged substance, like blueberries in a muffin.

What was Ernest Rutherford's discovery regarding the structure of the atom?

Ernest Rutherford discovered that atoms have a nucleus where all the positive charge is concentrated, and that atoms are mostly empty space with electrons orbiting around the nucleus.

What was Niels Bohr's model of the atom?

Niels Bohr proposed a model where electrons orbit the nucleus in circular paths, similar to planets around the Sun.

How did Erwin Schrodinger's work differ from Bohr's model of electron orbits?

Erwin Schrodinger introduced the concept of electron orbitals, which are regions where electrons are likely to be found, rather than fixed circular orbits.

What are the two subatomic particles that make up the nucleus of an atom?

The two subatomic particles that make up the nucleus of an atom are protons and neutrons.

What is the current understanding of how electrons behave around the nucleus?

The current understanding is that electrons do not orbit the nucleus in fixed paths but rather move in a way that can be described by quantum mechanics, forming orbitals of various shapes.

Why might the video use a simplified model of the atom for certain explanations?

The video might use a simplified model of the atom to make it easier to convey fundamental topics and concepts, even though it is not an exact representation of the quantum mechanical model.

Outlines

00:00

🔬 Early Theories of Atoms

This paragraph delves into the early conceptions of atoms by ancient Greek philosophers Democritus and Leucippus, who proposed that all matter is composed of indivisible particles called 'atomos'. Democritus envisioned atoms as having different shapes and sizes, with properties like hooks and spikes to explain the behavior of materials like iron and salt. However, these ideas were not widely accepted at the time due to the popularity of Aristotle's competing theory of the four elements. The paragraph also introduces John Dalton in 1808, who conducted the first scientific experiments suggesting matter is made of tiny, indivisible particles, which he called atoms.

05:00

🌐 Evolution of Atomic Models

The second paragraph outlines the evolution of atomic models from Dalton's indivisible spheres to more complex structures. It discusses J.J. Thompson's discovery of electrons and his 'plum pudding' model, where electrons were thought to be embedded throughout a positively charged substance. This was later challenged by Ernest Rutherford's gold foil experiment, which revealed a concentrated positive charge in the atom's nucleus, leading to the nuclear model of the atom. Niels Bohr's model introduced the concept of electrons orbiting the nucleus like planets around the Sun, which was later refined by quantum mechanics to describe electrons as occupying probabilistic orbitals rather than fixed paths.

10:02

📚 Modern Understanding of Atoms

The final paragraph discusses the current understanding of atomic structure, which includes the quantum mechanical model with its orbitals and the subatomic particles within the nucleus, namely protons and neutrons. It also touches on the practical use of simplified models, like the Bohr model, for teaching and basic explanations of atomic behavior, acknowledging that while these models are not entirely accurate, they serve as useful tools for conveying fundamental concepts in chemistry.

Keywords

💡Atom

An atom is the smallest unit of a chemical element that retains the properties of that element and cannot be broken down by chemical means. It is the central theme of the video, illustrating the historical progression of atomic theory. The script mentions Democritus' concept of 'uncuttable' particles, which is the origin of the word 'atom', and how this idea evolved over time with contributions from various scientists.

💡Democritus

Democritus was an ancient Greek philosopher who, along with his teacher Leucippus, first proposed the idea of atoms. His vision of atoms as indivisible particles of different sizes and shapes is foundational to the script's narrative on the history of atomic theory.

💡Aristotle

Aristotle was a well-known philosopher who proposed a different theory of matter, suggesting it was composed of earth, water, air, fire, and ether. His ideas were more widely accepted than Democritus' at the time, which the script uses to contrast the acceptance of different scientific theories.

💡John Dalton

John Dalton was a British chemist who is credited with the first scientific experiments that supported the atomic theory. The script describes his model of atoms as indivisible and spherical, which was a significant step in the scientific understanding of atoms.

💡Electron

Electrons are subatomic particles that carry a negative charge and are found outside the nucleus of an atom. The script discusses J.J. Thompson's discovery of electrons and their much smaller size relative to atoms, challenging Dalton's model of indivisible atoms.

💡Plum Pudding Model

The Plum Pudding Model, proposed by J.J. Thompson, depicted atoms as having electrons scattered throughout a positively charged substance, similar to blueberries in a muffin. The script uses this model to illustrate the shift from viewing atoms as indivisible to being composed of smaller particles.

💡Ernest Rutherford

Ernest Rutherford conducted the gold foil experiment, which led to the discovery that atoms have a nucleus where all positive charge is concentrated. The script explains how this finding contradicted the Plum Pudding Model and led to the Nuclear Model of the atom.

💡Nuclear Model

The Nuclear Model of the atom, also known as the Rutherford model, describes atoms as having a dense nucleus with electrons orbiting around it. The script highlights this model as a significant advancement in atomic theory, showing that atoms are not just indivisible particles but have a complex internal structure.

💡Niels Bohr

Niels Bohr was a physicist who proposed a model of the atom where electrons orbit the nucleus in fixed paths, similar to planets around the Sun. The script uses Bohr's model to discuss the early understanding of electron behavior before the development of the quantum mechanical model.

💡Orbitals

Orbitals, as described by Erwin Schrodinger, are regions around the nucleus where electrons are most likely to be found. The script explains that electrons do not move in fixed orbits but rather occupy probabilistic orbitals, which is a key concept in the quantum mechanical model of the atom.

💡Quantum Mechanical Model

The Quantum Mechanical Model is the current and most accurate way to describe the behavior of electrons in atoms. The script mentions that while this model is complex, it is essential for understanding atomic structure and that simpler models are sometimes used for ease of explanation.

Highlights

Ancient Greek philosophers Democritus and Leucippus were the first to discuss the concept of atoms, proposing that all matter is made of tiny, indivisible particles called 'atomos'.

Democritus visualized atoms as having different shapes and sizes, with iron atoms having hooks and salt atoms having spikes, based on their physical properties.

Aristotle's opposing theory of matter, composed of earth, water, air, fire, and ether, gained more acceptance due to his popularity.

John Dalton's scientific experiments in 1808 provided the first evidence that matter is made of tiny particles, introducing the atomic theory.

Dalton's atomic model depicted atoms as indivisible, spherical particles, differing from Democritus's model.

J.J. Thomson's discovery of electrons in the late 1800s challenged Dalton's model, suggesting atoms are divisible and composed of smaller particles.

Thomson's 'plum pudding model' proposed atoms as positively charged substances with electrons embedded like blueberries in a muffin.

Ernest Rutherford's gold foil experiment revealed the atomic nucleus, concentrating all positive charge at the center and leaving mostly empty space.

Rutherford's nuclear model contradicted Thomson's, placing a positive charge nucleus at the atom's center with electrons in orbit.

Niels Bohr's 1913 model introduced electron orbits around the nucleus, like planets around the Sun, a significant advancement in atomic theory.

Bohr's model was initially accepted but later challenged by new experimental evidence and quantum mechanics.

Erwin Schrödinger's quantum mechanical model described electrons not as orbiting bodies but as probabilities, forming orbital shapes.

Schrödinger's model introduced the concept of electron orbitals, which are regions of space where electrons are likely to be found.

Rutherford and Chadwick's discoveries of protons and neutrons refined the understanding of the atomic nucleus.

The quantum mechanical model is the current understanding of atoms, with electrons in orbitals and a nucleus of protons and neutrons.

Despite the quantum mechanical model's accuracy, simplified Bohr model representations are often used for ease of understanding in basic atomic discussions.

The evolution of atomic models reflects the ongoing refinement of scientific understanding as new evidence and experiments emerge.

Transcripts

as scientists have done experiments and

learned more and more about atoms

they've changed the way they think about

atoms so in this video we're going to

look at a timeline of the different ways

that scientists have pictured or

imagined atoms over the years now the

first people to really talk about the

idea of atoms were the ancient Greek

philosopher Democritus and his teacher

Leucippus they lived about 2,500 years

ago and Democritus he said something

like this he said imagine you have an

object like say a slice of bread and you

cut that in half and then you take half

of that and you cut it in half and then

you take half of that and you will you

get the idea eventually he said you're

going to come to something that you

can't cut in half anymore and he called

these objects he called them a Hamas

which means uncuttable and it's where we

get the word atom from Democritus

imagined that all matter all stuff was

made of these tiny uncuttable particles

and he imagined that the atoms came in

different sizes and different shapes he

imagined for example that iron atoms had

hooks which is how they could hold

together so strongly and he thought that

salt atoms had spikes on them because he

felt that salt tasted sharp so

Democritus was right but people didn't

really take to his ideas part of the

reason was because around the same time

the well-known philosopher Aristotle

proposed his own idea of what matter was

made of he said that different things

were made of different amounts of the

elements earth water air fire and ether

this is kind of like Captain Planet if

you're old enough to get that reference

and more people believed Aristotle maybe

just because he was so popular already

so Democritus and leucippus they were

right all along but

here's the thing they weren't scientists

they couldn't do experiments in the

laboratory to prove that they were right

and because of this some people think

that their idea it was just kind of a

lucky guess they couldn't actually prove

what they thought so you know how can

you tell whether it's right or wrong

ideas about atoms remain that way for

about 2,000 years until in 1808 the

British chemist John Dalton came up with

the first scientific experiments that

showed that matter was made of tiny

little particles this is kind of how

John Dalton pictured Adams he imagined

them sort of as tiny little balls that

arranged in different combinations to

make different things and he imagined

that these atoms were indivisible you

couldn't cut them into smaller pieces

now at first nobody believed Dalton but

over the course of the 1800s

more and more scientists did begin to

believe what he had to say but then in

the 1900s the early 1900's people's idea

about atoms started to change one of the

key things cause this change was that in

the late 1800s JJ Thompson discovered

that atoms have electrons and he

discovered that electrons are much much

smaller than atoms so while Dalton

thought that atoms were tiny and

indivisible JJ Thompson said no no

they're not indivisible because they're

made up of electrons which are much

smaller

so JJ Thompson pictured the atom as sort

of like a blueberry muffin

he called this the plum pudding model JJ

thompson imagined that if you took an

atom and split it open you'd see tiny

electrons stuck

throughout the inside of it just the way

blueberries are stuck in the dough of a

blueberry muffin and Thompson thought

that what's the dough in a blueberry

muffin that it was like a positively

charged substance so you had negative

electrons stuck in like a positively

charged dough and together the positive

and negative charge balanced the two

things balanced balanced each other out

so that the atom was electrically

neutral but the big change from Dalton's

model to Thompson's model was showing

that atoms weren't actually indivisible

that they were made of even smaller

things now not too much longer in the

gold foil experiment

Ernest Rutherford discovered that Adams

had a nucleus that all the positive

charge in an atom was concentrated right

in its center and that besides that in

the electrons atoms were pretty much

empty space

so JJ Thompson thought the positive

charge was all distributed throughout

like dough in a muffin but Rutherford

showed that all this positive stuff was

concentrated right here in the center

and this is what we call the nuclear

model of the atom because it has a

nucleus sometimes people call this the

Rutherford model now so far we've been

talking a lot about the positive charge

and the nucleus of an atom but we

haven't talked too much about what's

actually going on with these electrons

in the atom in 1913 the physicist Niels

Bohr came up with his model of the atom

he reasoned that there is a nucleus in

the middle just like Rutherford had but

that electrons instead of just sort of

being randomly distributed throughout

the atom Bohr said that the electrons

were sort of like planets around a Sun

that they were spinning around the

nucleus in circular orbits so here a

picture of some of the electrons and

here the orbit

imagine that they're spinning around the

nucleus in these circles all right now

people thought Bohr's idea for the

electrons made a lot of sense at first

but then in the 1920s additional

experiments showed that it wasn't

exactly the way electrons really move

and a variety of physicists particularly

the physicist Erwin Schrodinger showed

that electrons weren't really spinning

in orbits but it's more like they were

hyperactive flies and they were buzzing

around the atom sketching out different

shapes it's kind of if you did like

time-lapse photography on a hyperactive

fly and you saw that over a long period

of time it sketched out a particular

design and whereas Bohr called these

circular paths

he called them orbits Schrodinger called

the hyperactive sketch out shapes

he called them orbitals here's a

circular orbital - but electrons didn't

only make circles this is actually a

sphere because it's a circle in three

dimensions here is another shape another

type of orbital that electrons could

also make looks like this sort of two

teardrops next to each other

so in the quantum mechanical model

electrons don't orbit the nucleus they

buzz around the atom sketching out

different shapes now let's focus on the

nucleus here over the same amount of

time and a little bit later scientists

were discovering the two subatomic

particles that make up the nucleus so we

can refine this picture a little bit

more in 1919

Ernest Rutherford discovered protons

there they are

and then in 1932 James Chadwick

discovered new Tron's so the really

correct view of the quantum mechanical

model shows the orbitals being sketched

out by the electrons but then also show

the subatomic particles protons and

neutrons here in the nucleus now this is

pretty much how we think about atoms

today but as scientists learn more and

more about atoms as they do more

experiments they're going to find that

this model isn't exactly a perfect

representation of what atoms are really

like and they're quite likely to change

this and refine it even more now as I

said this quantum mechanical model is

like the really accurate way to describe

ABS but the thing is with these orbitals

it can really be kind of a pain

sometimes to describe simple things that

atoms are doing using electron orbitals

and so a lot of times in these videos

when I talk about atoms I'm actually

going to be sort of using a cross

between the very correct quantum

mechanical model and the sort of

outdated Bohr model just because for our

purposes a lot of the simple things

we're going to be talking about the Bohr

model it works just fine so already

you've probably seen me draw atoms like

this where you see the the electron

orbits at different angles and sometimes

particularly when we're talking about

bonding we're going to be drawing atoms

like this with the protons and neutrons

here and the nucleus and then electrons

in different rings different orbits on

the outside of the atom we're going to

find that thinking about the atom like

this is very useful for simple tasks

talking about bonding and stuff but keep

in mind that when we're discussing atoms

they actually aren't exactly like this

and they're much more like the quantum

mechanical model so keep in mind that

I'm lying to you a little bit but I'm

lying to you in order to make it easier

to convey some fundamental topics