Note on History of the Atom

Transcription

1 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

2 John Dalton ( ) 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.

3 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 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..

4 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.

5 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..!!

6 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

7 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 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.

8 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: