The History of the Atom……. Democritus was the first to theorize that all matter was composed of atoms! Democritus’ ideas were crushed by a contemporary, named……….

………………Aristotle!!!! Aristotle asked Democritus three 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?

By weighing the materials before and after... Antoine Lavoisier came up with…….. The law of Conservation of Mass This states: - Matter cannot be created or destroyed in a chemical reaction, simply converted from one form into another John Dalton ends up using this point in his theory of an atom!

Joseph Proust… Came up with the Law of Definite Proportions He had examined copper carbonate decomposition and no matter the amount he started with, whenever it decomposed it would yield 5.3 parts copper, 4.0 parts oxygen and 1.0 parts carbon John Dalton ends up using this point in his theory of an atom! Law of Definite Proportions- Elements that make up compounds (like water H 2 O) are ALWAYS in the same proportion by matter. H 2 O

It took almost 2000 years before the idea of the atom came back! John Dalton (school teacher) brought Democritus’ idea back! All matter is made of atoms! His points were: –All matter is made up of atoms (from Democritus) –Atoms are indestructible and can’t be divided into smaller particles. (not true)‏ –Atoms of one element are exactly alike, but they are different from other elements. (not exactly true)‏ –Chemical reactions rearrange atoms- no atoms form or disappear. (from Lavoisier) –Molecules and compounds always consist of a certain combination of atoms that never varies. (H 2 O)‏ (from Proust) John Dalton’s theory has been modified as we learned new information……..

Dalton thought Atoms are solid and indestructible, THEY ARE NOT. Atoms 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…..? Are these atoms or am I Losing my marbles?

THE ELECTRON……….. See Thomson’s experiment on page 102 of the Physical Science book. Scientists knew that matter was not negatively charged, so atoms couldn’t be either…. There had to be positively charged particles too!

Protons were discovered next and then were followed by Neutrons. see pgs in the Physical Science book.

Thomson’s Atom Model In Thomson’s "Plum Pudding Model" each atom was a sphere filled with a positively charged fluid. The fluid was called the "pudding." Scattered in this fluid were electrons known as the "plums."

Rutherford’s “Football Analogy” Football Stadium

TO REVIEW…. “I, Democritus, came up with the “atom” idea” “I, Dalton, proposed solid indivisible balls like marbles” “I, Thompson, said an atom is positive, with negative Electrons…. Like cookie dough or plum pudding” “I, Rutherford, came up with the idea the nucleus is Positive and the atom is mainly empty space”

Bohr' s Atom Model Electron Cloud Model

MODERN ATOMIC THEORY Subatomic Particles 3 main ones (there are others, but that’s for physics..)‏ –Electrons –Protons –Neutrons

MODERN ATOMIC THEORY Nucleus has protons (+) and neutrons (neutral)‏ Electrons (-) move around nucleus Nucleus is very TINY and takes up the least amount of space in an atom. Most of an atom is EMPTY SPACE! 1 drop of water = 6.5 x atoms (6.5 sextillion or )‏

Name of Subatomic Particle Charge of Particle Relative Mass (compared to other subatomic particles) Location in Atom

ATOMIC NUMBER= # of protons in the nucleus This number NEVER CHANGES and so it can be used to identify the element !!! PROTONS give an element its identity for example: If an atom has 6 P….it’s CARBON 7 P…….N 1 P…….? 53 P……? IF the atom is NEUTRAL this is also the # of electrons outside the nucleus.

MASS NUMBER Mass # = number of protons + number of neutrons in the nucleus. ALL the mass of an atom comes from the __________ and_____________ in the ____________ of the atom. measured in atomic mass units (amu) Example: Chlorine Mass # of chlorine: 35 amu Protons= ? (from atomic number)‏ Neutrons= ? (mass # - atomic #)‏

How to read the periodic table… Au Which is atomic #? What does that tell us? Which is mass #? What does that tell us? # P = 79 # N = (197-79) = 118 # e- = 79

Charge….d atom! If an atom has a charge… which subatomic particle would have to have changed in number? Is it the # of protons, # of electrons or # of neutrons?

ATOMIC CHARGES Ion = an atom that loses or gains one or more electrons 2 types of ions are: Cations –positively charged ions -loses one or more electrons Anions –negatively charged ions -gains one or more electrons

23 11 Na +1 # P = 11 # N = (23-11) = 12 #e- = 10 How many electrons would sodium normally have? Did sodium lose or gain an electron? How many electrons did sodium lose or gain? Is this charged atom a cation or an anion? THIS IS AN ION ( +1 CHARGE)‏

ISOTOPES Isotopes are the same element (same # of protons)‏ They are chemically alike They have different atomic masses. (because they have different # of neutrons )‏ Example: Lithium-6, and Lithium-7 are isotopes Lithium - 6 has a mass of 6amu (3 protons + 3 neutrons) Lithium - 7 has a mass of 7amu (3 protons + 4 neutrons)‏ Why doesn’t the # of protons change? Because the # of protons gives it it’s identity! Lithium! Thomson discovered that neon consisted of atoms of 2 different masses. The number of protons identifies the element and electrons have virtually no mass…. So which subatomic particle would be different and change the mass?

Example of an isotope – 1 1 H, 2 1 H, 3 1 H –All are Hydrogen because they have 1 proton. Isotope#P#N 1 1 H 1 0 mass of 1 = (1 P + 0 N)‏ 2 1 H 1 1 mass of 2 = (1 P + 1 N)‏ 3 1 H 1 2 mass of 3 = (1 P + 2 N)‏