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Atomic Structure & the Periodic Table
Atomic Theory
• Democritus- 440 B.C.
• He proposed that if you kept cutting something in half you would
eventually end up with an ______________ particle. Which he called an
atom
• Greek: Atomos - _____________
• Dalton- 1808
• In search of understanding why elements combine in specific ratios he
discovered through his experiments that this happens because they are
made of ________________ atoms.
• His theory states 3 things
1. Atoms are small and cannot be _______________,
___________________or ___________________.
2. Atoms of the ____________ element are all alike.
3. Atoms join with other atoms to make _________ substances.
Atomic Structure
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•
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Atoms are extremely __________________.
Atoms contain a ______________________.
Atoms are made of subatomic particles
• ____________________
• ____________________
• ____________________
Protons
• ______________________charged particles (____).
• Found in the nucleus.
• All protons are identical
• Each proton= 1 ________ (atomic mass unit)
• Every atom of an element has the _________ number of protons.
Neutrons
• Particles that have ________________
• Found in nucleus
• All neutrons are identical
• Protons & Neutrons are the most massive particles in the atom but
located in a ____________ small area (nucleus)
Electrons
• _______________charged particles (____)
• Located outside of the nucleus in __________or levels called atomic clouds.
• Their mass is so small that it is usually considered ___________.
• It takes more than 1,800 electrons to equal the mass of one proton.
• However electrons occupy most of an atoms ______________.
Some things to remember:
• In an atom, the number of protons equals the number of electrons. As a result, the
positive charge from protons equals the number of electrons which makes the atom
______________.
• All atoms of an element have the _____________ atomic number.
.
The Periodic Table
Periodic Table Key:
Atomic Number
 Tells us the number of __________________ in an atoms nucleus.
Atomic Mass
• Atoms are too small to be measures in everyday units of mass (grams).
• Scientists use units knows as _________________mass units (amu).
• A proton or a neutron has a mass equal to about ____________________.
• Atomic Mass is equal to the ______________ of protons and neutrons in an atom.
Isotopes
• The number of neutrons in an atom can vary.
• Atoms with the same number of protons and a different number of neutrons are called
____________________.
• We identify and isotopes by the atoms mass.
Arrangement of electrons
 The first ring can only hold _____ electrons

The 2nd and 3rd rings can both hold _________electrons