A Neutron walked into a bar and asked how much for a drink. The bartender replied, “ for you, no charge.
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Jaime- Internet Chemistry Jokes

Atoms: The Building Blocks of Matter

-Atom: the smallest particle of an element that retains the chemical properties of that element
-Named by Democritus
-Means “ indivisible ”

-Discoveries made by people like Dalton,
Thomson, Millikan, Rutherford, and Bohr
-Subatomic particles:
 Protons
 Neutrons
 Electrons

-Nucleus
 Protons and neutrons


Majority of the mass
 Strong nuclear force holds it together
-Electron shells or orbitals
Electrons
 Most of the volume

-Electron:
 Negative charge
 Tiny, very light particles
 Electron cloud
-Proton:
 Positive charge
 At least one in every atom
 Much greater in size and mass than electrons
 Nucleus
-Neutron:
 Neutral (no) charge
 About the same size and mass as protons
 Nucleus

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-Atomic Number #protons
Atomic Number
Atomic Symbol
Atomic Mass
-Atomic Mass (or mass number) =
#protons + #neutrons

-If an atom is electrically neutral, then #protons
= #_________

-Determine the number of protons, neutrons, and electrons in the following neutral atoms:
 Sodium
 Carbon
 Chlorine
 Helium
 Arsenic

-Determine the number of protons, neutrons, and electrons in the following atoms:
 Sodium (Na): p + :11 e :11, n 0 :12
 Carbon (C ): p + :6 e :6, n 0 :6
 Chlorine (Cl): p + :17 e :17, n 0 :18
 Helium (He): p + :2 e :2, n 0 :2
 Arsenic (As): p + :33 e :33, n 0 :42

Objectives:
1. Identify and describe the discoveries and research of Democritus, Dalton, Rutherford,
Thomson, Bohr, and Schrodinger
2. Describe the law of conservation of mass and law of multiple proportions
3. Describe the atomic theory and its individual components

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Greek Philosophers
Aristotle- viewed the entire known universe as being made up of five distinct “ elements ” (earth, fire, air, water, and ether) which mixed to form anything of substance
Democritus asked- If you break a piece of matter in half again and again, how many breaks will you have to make before you can break it no more? Democritus thought that it ended at some point, a smallest possible bit of matter. He called these particles atoms. (370 BC)
People believed Aristotle for almost 2000 years

 Dalton- English chemist, meteorologist, and physicist
 He studied the atomic mass of elements by studying water and carbon dioxide and decided atoms are tiny, hard spheres
 He used ideas made by scientists before him-
Democritus, Lavoisier , and Proust- to come up with his atomic theory

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1803: Dalton- Created the Atomic Theory
Atomic Theory:
1) All matter is composed of atoms
2) Atoms of a given element are identical in size, mass, and other properties
3) Atoms can not be subdivided, created, or destroyed ( law of conservation of mass) (Subdivided part has been disproven)
4) Atoms of different elements combine in simple wholenumber ratios to form compounds (law of multiple proportions)
5) In reactions, atoms are combined, separated, or rearranged

Atoms of different elements combine in simple whole- number ratios to form compounds
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Examples:
NaCl
H
2
O

Atoms can not be created or destroyed
• Example:
How can you explain chemical reactions?
*Atoms are rearranged, separated, combined
2H
2
O + O
2
--> 2H
2
O
2

 Dalton proposed that atoms cannot be divided
 Nuclear fission- a nuclear reaction in which the nucleus of an atom splits into two smaller parts, releasing tremendous amounts of energy
▪ Nuclear power plants

 Many scientists agreed on this theory and it stayed unchanged until 1890
 Scientists that followed used Dalton ’ s theory and expanded on it

 Dmitri Mendeleev – first to organize elements according to their properties and mass
 Predicted the existence and properties of elements not yet discovered
 Left blank spots
 Father of the modern periodic table

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Discovered electron using cathode ray
Thomson studied cathode rays and found that they were
 negatively charged because they were deflected in magnetic fields.
Came up with “ Plum pudding ” model

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British Scientist 1911
Re-ordered the periodic table in order of increasing atomic number instead of mass.
Problems with the Mendeleev table disappeared.

 Discovered proton and a nucleus by hitting gold foil with helium (alpha) particles
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Discovered much of the atom is “ empty space ”
He hit gold foil with fast-moving helium (alpha) particles

(positively charged particles)
Expected particles to pass through because the mass and
 charge were uniformly distributed
,
were deflected into all directions
Concluded that a very small, dense area in the center was positively charged the rest is empty space.

 Discovered the neutron
 Studying gamma rays pointed at hydrogencontaining compounds, found that something was in the nucleus besides protons
 It had no charge
 Created Bohr model

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Studied electrons and their behavior
Determined electrons have dual properties
They act like matter because they have mass and volume BUT they also act like light because they can be bent or diffracted
Became known as quantum theory

370 BC- Democritus
Coined term atom
1803- Dalton
Atomic Theory
1890- Thomson
Discovered electron
1919- Rutherford
Discovered proton
1925- Shrodinger
Electron dual theory
1932- Bohr
Discovered neutron

-Isotopes: atoms of the same element that have different masses.

 Same # of protons and electrons, but differ in # of neutrons
Different ways to depict which isotope you have:
(p + n)
A
Z
X element symbol atomic number
(p)

6p +
8nº

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Mass of atom determined by protons and neutrons
Actual Mass of:
Proton: 1.673 X 10 -27 kg
Neutron: 1.675 X 10 -27 kg
Electron: 9.109 X 10 -31 kg
Mass of oxygen-16 atom= 2.657 X10 -23 g

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- Instead of using EXACT mass of an atom in kg, scientists use the relative atomic mass
Relative Atomic mass measured in atomic mass units (amu)
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Proton= 1.007276 amu
Neutron= 1.008665 amu
Electron= 0.0005486 amu

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Average atomic mass = Σ (mass of isotope × relative abundance)
Carbon-12 is the isotope this formula was based upon
 Ex: One type of copper atoms weighs in at 62.93 amu, the other has a mass of 64.94 amu. The lighter isotope is more common with 69.09% occurrence.

 Average atomic mass of copper = (62.93 amu
× 0.6909) + (64.94 amu × 0.3091)= 63.55

A certain atom has a nucleus containing six protons and eight neutrons and has six electrons orbiting the nucleus.
This atom is a form of the element-
A) silicon
B) carbon
C) magnesium
D) calcium