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History of the Atom!
Transcript of History of the Atom!
1) If we read Dalton's notes and had to draw an atom based on what he thought, what would it look like?
2) List two ideas that the previous three scientist discovered that are still true today.
History of the Atom!
A journey about how we know, what we know!
This is what we want to know!
1. Where did the idea of atoms originate?
2. What evidence led us to the conclusion that atoms exist?
3. How has the model of the atom evolved over time?
What do we know? Discuss....
1) The sum of the protons and neutrons in the nucleus is called?
2) Atoms of the same element, but different neutrons are called?
What do we know...Discuss...
1. Can you give an description of the Gold Foil Experiment? You might want to try...hint....hint....
2. If you had to draw a picture of the atom accord to Rutherford, what would it look like?
What do we know, Discuss...
1) What did Dalton and Mendeleev have in common?
2) Discuss the locations of
periods, and then groups. What do the group and period #'s indicate about atoms?
What do we know? Discuss...
1. Who first thought up the concept of atoms?
2. What were Lavoisier's major contributions?
3. Are any of these two scientists ideas still true today?
Say hello to Democritus!
(460 B.C. - 370 B.C.)
A Greek philosopher
He is considered the
"Father of Modern Science"
He proposed a question...
Can things be divided into
smaller and smaller pieces
So like all good ideas, what did the world do with Democritus's
idea? They forgot it for 2000 years....
What really happened was Democritius's
ideas were lost when famous philosophers
like Aristotle and Plato presented the
"Captain Planet" approach to nature
They proposed the idea that matter was
made of four different "elements"
Earth, Fire, Wind, Water - Fast Forward...
Democritus arrived at the conclusion that eventually
there had to be something that could not be divided
any further. He called these parts "atoms", from the Greek
word "Atomos" meaning unsplittable. These "atomos" were....
* Made of different materials and different shapes
* Infinite in number, always moving, and could constantly
join together in different ways.
Antoine Lavoisier (1743-1794)
Aka A-Town - known an the Father of Modern Chemistry!
Fun FACTS! -
* Tax Collector - It's how he funded many
of his experiments, also why he was guillotined
during the French Revolution
Married 13 year old Marie-Anne Pierette
Paulze. She helped with his experiments!
Lavoisier first proposed The Law of Conservation of Mass - atoms are not created or destroyed. They
are always conserved in a reaction.
He did this by studying burning candles inside a sealed container.
Responsible for discovering & naming both Hydrogen & Oxygen and realized they reacted with other chemicals. Ex. Rust
Put together a list of true elements, atoms that could not be broken down any further.
Said "Matter may change form and shape, but the mass will NEVER CHANGE!"
John Dalton (1766-1844)
* Born into a Quaker Family
* Kept a weather journal that
spanned 57 years and over
200,000 weather observations!
* Was the first person to
figure out that colorblindness
was due to pigments in the eye!
* Dalton published the Law of Multiple Proportions describing the relationship between the relative numbers of atoms and their masses.
* After testing, Dalton refined Democritus's theory into an Atomic Theory of his own!
1) Elements are made of extremely small particles called atoms.
2) Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
3) Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
4) In chemical reactions, atoms are combined, separated, or rearranged.
Dalton's Atomic Theory
Have we changed any of Dalton's Ideas
or are they all still true today?
Dalton was an exceptional meteorologist. In studying the weather, he determined that evaporated water existed independently of the air around it. He wondered how water and air could be in the same place at once.
He performed many experiments on mixtures of gases to determine how they coexisted.
His research yielded one of the gas
laws - Dalton's Law of Partial Pressure
J.J. Thomson - AKA Double J
(1856 - 1940)
* Noble Prize Winner in 1906
* Was knighted and is "Sir J.J.
* Was a gifted teacher!
Thomson is credited with
the discovery of the
because this went
against what Dalton
How'd he do it? I'm so
glad you asked! Let me introduce the Cathod Ray Tube! At the
time, scientist could see the beam of light, but didn't know what it was!
So what's the Big Deal with Double J..
When experimenting with cathode ray tube, Thomson discovered the particles that made up the beam change position when a magnet was held nearby.
* That meant that particles had a charge!
* Thomson discovered that these "corpuscles" were 1800 times smaller than a hydrogen atom - the smallest thing known to scientist at the time.
Future scientist changed the name his particles to the ELECTRON!
* Later experiments led him to determine the exact mass of the electron.
* His new picture of the atom was called the "Plum Pudding Model"
What?!?! You've never had plum pudding?
Never fear, think of a chocolate chip cookie. How is this picture an excellent representation of what Thomson was talking about?
Hint: What would the parts of the cookie represent?
Ernest Rutherford (1871-1937)
Aka "E Dawg"
* Was a student of Double J!
* Won a Noble Prize
* Was on the New Zealand 100 dollar bill!
Rutherford experimented a lot with something called
Alpha particles. They are involved in Nuclear Reactions.
He set up an experiment where he fired a stream of
these positively charged alpha particles at a very thin
sheet of Gold. (Think Aluminum foil, but just made of gold!
What he expected to find was that ALL
positive alpha particles passed through the
atom, which was lots of empty space with
a few smaller electrons scattered around.
Ready for an Experiment?!?!?!
Aka "The Big Russian"
* Credited with bringing the Metric System to Russia
* Known for his long hair and beard. He only cut it
once a year!
* Youngest in a family of 11 kids!
* Mendeleev is considered to be the
"Father of the Periodic Table"
He realized that certain elements had
similar chemical reactions and chemical
* Mendeleev put elements in order by
increasing atomic mass.
When he saw repeating patterns, he
created a new row. He called these?
The names of the groups on the periodic table are important
Let's review the names really quick!
Find a piece of paper
Crumple it into a small
ball. Take aim, and throw it at me. Go ahead, I promise I won't write you up.....this time only!
So, What did we learn?
What did the paper balls represent?
What did I represent?
And finally, what happened? Did that match up with Rutherford's ideas?
Rutherford concluded that there had to be some part of the atom
that would REPEL the POSITIVELY charged Alpha particles.
As expected, MOST of the atom was empty space, but there
was something else in there, and it had a positive charge!
* Rutherford called these "Protons" and proposed that there was
a small, dense, portion of the atom where they were held, and the
much smaller electrons orbited the outside.
You may not be excited, but E-Dawg sure
It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.
- Ernest Rutherford
Niels Bohr (1885-1962)
AKA B Money
* Won a Nobel Prize
* Played professional soccer
for the Danish National
team as the goalkeeper.
* Bohr confirmed that the electrons were not stuck in the atom.
* Instead, he thought the electrons moved around the outside of the atom on "levels"
* Gave rise to the eventual
currently accepted today.
Henry Mosely (1887-1915)
* Super smart guy
* Born into a scientific
family, both his parents
* Had a promising career in science, but enlisted in the
army during World War 1 to serve his country. (England)
He died in the Battle of Gallipoli in Turkey at the
age of 27.
Mosley did work with X-Ray Crystallography. Basically shot
X-rays at particles and observed how they collided.
Mosley discovered something unique. A pattern between the atomic number of an element and the type of
Mosley had found proof that every element is different in a specific way!!!
* Mosley discovered that every element had a different
atomic number. (What does that mean again???)
* With this pattern, Mosley predicted the existence of 4 new elements that had not yet been discovered.
* It's because of Mosley that we think we've discovered
all the elements and are not missing any!
Bohr had a brilliant mind. He built upon the ideas of scientist before him, but was the first person to realize the relationship between electrons and energy.
His studies gave rise to the
study of quantum mechanics!
Don't worry, we get to study
all about it!
Last but certainly not least
Sir James Chadwick
(1891 - 1974)
AKA Jimmy Neutron
* Chadwick was an English Physicist
* Part of the Manhattan Project and creation of the Atomic Bomb!
* Previous studies had indicated that the mass of the atom was different than the # of protons.
* Chadwick also tested the nucleus by bombarding it with nuclear particles and measuring the energy given off.
* He determined that the particle
must be about the same size an a proton, but was neutral in charge.
Robert Milikan (1868-1953)
AKA - The Milk Man
Milkikan deduced the charge of a single electron using an experiment known as
the Oil Drop Experiment
This value (-1.60 x 10-19 C) is
important as many calculations are related to how strongly an atom holds on to it's electrons.
Milikan could adjust this to vary the strength of
the electromagnet and determine the total charge of each drop.