Name_________________________ Date_____________

Note on History of the Atom

� Why is learning about the atom important….? • The atom was considered to be an “imaginary” thing, something that people laughed at!

• Roosevelt trusted Einstein, and funded his secret research known as the “Manhattan Project”

• In a few short years, the idea of an invisible atom had been developed into a city-destroying weapon - the atomic bomb! They figured out they could split atoms apart, and this would release tons of energy!

� The History of the Atom……. o Democritus was the first to suggest that all matter was made of ______________! o The name atom comes from his Greek word,

“______________”, which means not dividable or whole! o Democritus’ ideas were crushed by another Greek Philosopher, named……….

………………______________________!!!!

� Aristotle didn’t believe in atoms o Aristotle asked Democritus questions:

� If we are made of atoms, what holds us together?

� Why can’t we see these atoms?

� Why don’t we fall down like a bag of marbles?

� What’s in between atoms?

� Democritus was unable to answer these questions……. o And so, people continued to think that matter was continuous - your body, the world around us

was one continuous piece…. o This philosophy continued for centuries…….

� Many years later…. o Middle Ages: 5th -16th Century o Alchemy: medieval “chemistry” o All matter made of 4 elements –

_____________ , _____________ , _____________, ____________

� During the 1700’s and 1800’s…. • Scientists were doing large, observable, basic experiments

• They were doing experiments with stoves, pots, ovens, and basic glassware!

• With observable properties came explanations!

• _____________________-the act of reasoning from factual knowledge or evidence

� John Dalton…… (1766-1844)

o A __________________________! o Described what was seen by scientists in terms of _____________________!

� John Dalton theorized that these substances were made of atoms!

o THE ATOMIC THEORY OF MATTER! (1803)

� All _____________________ are made of tiny, solid, indestructible particles known as atoms

� All atoms of one element are the _______________

� Atoms of _________________ elements are different

� Atoms of different elements form compounds in whole number ratios

� Atoms are not created or destroyed in chemical reactions, only how they are combined to form compounds

• John Dalton’s theory was wrong in one respect……..

�John Dalton’s theory was wrong in one respect……..

Atoms are not solid and indestructible like marbles….. � They contain different parts……. � However, scientists did not know this until parts of the atom were discovered…..

What part of the atom do you think was discovered first…..?

�THE _____________________…! Why do you think it was the first part of the atom to be discovered…..?

________________________________________________________________

�Benjamin Franklin in the Early 1800’s! o Lots of basic work with _________________ o Matter has charge! o There are two types of “_____________” in the world:

� + charged objects � charged objects

� Ben Franklin is the first to come up with these names positive & negative. o Franklin didn’t know that these charges were part of the ________________.

�J.J. THOMSON � In 1897, Thomson used a ___________________________________________ (CRT)

to prove that an atom had a ________________________ particle known as an electron’

� He believed that __________________ were distributed throughout an atom

� This model is known as the “__________________________________________”.

Electrons are stuck throughout an atom just like plums are stuck throughout pudding.

Plum Pudding is an English dessert

� Cathode Ray Tube, or Crooke’s Tube

� This was one of the very first experiments to be done with electricity! � __________________ designed this tube in 1879. � The cathode ray (travels from cathode to anode) inside glows � Crookes was convinced this beam consisted of charged particles

� So what are Cathode Rays….?

♣ ________________________, in 1897, answered this question!

♣ Thomson used a Crooke’s tube and two charged plates above and below the beam

♣ Which way do you think the beam bent….?

♣ The Beam was attracted to _____________plate,

and was deflected from _______________ plate!

♣ The beam could also be deflected with a magnet

♣ From this, he said that the beam was made

of ___________________ charged particles,

called ______________________!

♣ He was looking at electrons, which are part of the atom!

�The cathode ray tube was the beginning to the modern day…..

____________________

�Who puts all of this information together into “The Big Picture”?

• J.J. Thomson theorized that these negative and positive particles were part of the

atom!

• We are all made of charge!

• He develops the first working model of the atom,

known as the ______________________________________!

• This rejected ____________________ idea that atoms were solid particles like

marbles that weren’t made of smaller pieces

�Thomson Analogy - ___________________________ Draw:

�Why is Thomson’s model wrong….?

♣ A scientist named Ernest Rutherford figured it out!

♣ He shoots big heavy alpha (_) particles (with + charge) at ultrathin gold foil

♣ He expected most to go through the atom.

♣ Very few were deflected, and some even bounced straight back!

♣ Rutherford described this as a bowling ball being sent at a piece of paper, full

speed, and bouncing back!

�ERNEST RUTHERFORD � In 1908, he performed his famous _____________________________________.

� His experiment proved that an atom is mostly ________________________.

� It also proved that an atom has a small and dense positively charged center called

a _________________________.

�The Gold Foil Experiment….

� Rutherford’s “nuclear” model! Draw:

� What is going on….? � Most of the ______________ particles are going straight through!

� A few of the _____________________________ are bouncing off of something!

� Alpha particles are _______________and _________________________!

o What could they be bouncing off of ?

o They must be bouncing off of something that is….

_____________________________________

Rutherford theorized that all of the protons weren’t scattered about, like in a chocolate

chip cookie, but were all ___________________________ into a tiny, dense __________________,

which he called the ________________________!

�Rutherford Analogy - __________________ Draw:

�What is the relative size of the atom….? ♣ An atomic model the size of Busch Stadium and parking would contain a pea sized nucleus containing

95.95% of the atoms mass.

♣ The _____________ at the pitcher’s mound would be the ____________________, and an

_______________ crawling on the parking lot outside would be an ________________________!

♣ The atom is mostly…..

♣ _______________________________________! _______________________________!

� Structure of the Atom o Inside Nucleus:

� Protons (p+) - have ____________, _______________ charge, & determine identity of ___________________

� Neutrons (n) - have _________________, ___________ charge o Outside Nucleus:

� Electrons (e-) - ________________ charge, ________ mass

� Number of particles in neutral atom • # p+ usually = # e-

• Atomic Number = # p+

• Mass Number = # p+ + # n

� So is this the final model of the atom today… __________! o A scientist named ________________________, a great friend of Einstein, noticed

something weird about _____________________.

o A hydrogen atom consists of ____________________ orbiting ______________….

o Atoms can give off light when they are excited with _________________!

o Think about light bulbs, neon lights, headlights….

With one electron, how many different types of energy or colors of light do you think

hydrogen can give off….?

� NEILS BOHR � He wondered about the exact location of _______________in an atom.

� He concluded in 1913 that an electron had a certain amount of energy

which keeps an electron moving around the nucleus in a region called an

__________________ level.

� He described an atom much like the ___________________________ in

that electrons orbit around the nucleus in energy levels just as

_________________orbit around the sun

� Bohr Analogy - ______________________ Draw:

� Bohr came up with a new model for the atom…

� Bohr suggested that _____________ could move to many locations or “_____________levels”

within the atom!

� The electron was _______________ to more than one location in the atom!

� In Bohr’s Model of the atom, electrons orbit the nucleus like planets orbit the sun. It is called

THE ____________________________MODEL.

� When electrons jump up to different energy levels, they eventually fall back down and give off

_______________________!

� Electrons in Energy Levels Level maximum number

of electrons

1 ____

2 ____

3 ____

4 ____

� WAVE MODEL or ELECTRON CLOUD-Modern Atomic Theory � In 1926, it was stated that it is impossible to know the exact

location and motion of an electron or small particle= Heisenburg Uncertainty Principle.

� Electrons don’t orbit the nucleus in simple, well-defined paths. This is why chemists often show electron orbitals as

cloudy regions. The more dots in the cloud, the more likely an electron would be found there.

� Electron Cloud Analogy - _____________________________

� Electron Cloud Model

• Electrons not in fixed orbits (like Bohr’s model), instead is areas or

“clouds”

• Shows where we are most likely to find an electron

• Most current model

Draw the 4 different Models: