atom – smallest piece of an element nucleus › very dense, almost all the mass of the atom, but...
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ATOM – smallest piece of an element
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Nucleus› Very dense, almost all the mass of the atom,
but very small› Protons – positively charged, one AMU› Neutrons – no charge (neutral), one AMU
Energy levels› Electrons – e- -negatively charged, very small› First energy level – only two electrons› Later energy levels – eight electrons
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Element Name
Hydrogen Helium Lithium sodium
# protons 1 2 3 11
# electrons 1 2 3 11
# neutrons 0 2 3 11
Atomic Number 1 2 3 11
Atomic Mass Number
1 4 6 22
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ATOMS – smallest piece of an element› GROUND STATE – overall zero charge› Equal numbers of protons and electrons
IONS – atoms with charges!› Electrons have been stolen… the
imbalance of protons (positive) and electrons (negative) results in a charged particle
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Chlorine has 17 protons and 17 electrons The chloride ion stole an electron from another
atom… it now has 17 protons and 18 electrons It has a negative charge because it has more
electrons than protons
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# protons
# electrons
Charge(protons – electrons)
Cation, anion or neutral atom?
Symbol
Name
4 4 0 Neutral Be Beryllium
4 2 2+ Cation Be2+ Beryllium
17 17 0 Neutral Cl Chlorine
17 18 1- Anion Cl- Chloride
7 7 0 Neutral N Nitrogen
7 10 3- Anion N3- Nitride
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How can we determine what charge an ion will have?
The OCTET rule… atoms want to be like noble gases and have eight electrons in their valence (outer) energy level
We can predict charges with groups of the periodic table
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Groups of atoms that share electrons with each other, but then steal more!› Or electrons they were sharing were stolen
from them…› Names do NOT end in -ide
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Ions with opposite charges are attracted to each other like magnets› We call this attraction an ionic bond› Compounds formed by ionic bonds are called
ionic compounds
Charges are shown with little numbers up = superscript… K1+
Numbers of ions in the formula are shown with little numbers down = subscript… O2
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We balance the charges of the ions› Potassium fluoride
K1+ + F1- -> KF
› Lithium oxide Li1+ + O2- -> Li2O
› Magnesium bromide Mg2+ + Br1- -> MgBr2
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IONIC Compounds MOLECULAR Compounds
Steal electrons = ionic bond Share electrons = covalent bond
Ions and polyatomic ions Atoms
Metal + Non-metal Non-metal + Non-metal
Formula unit – balanced charges Molecule – numbers of atoms
Second element ends in –ide Second element ends in –ide
NO prefixes YES prefixes
Na2O – sodium oxideMgCl2 – magnesium chlorideKOH – potassium hydroxide
CO – carbon monoxideN2O – dinitrogen oxide
Si3N4 – trisilicon tetranitride
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Naming acids is similar to naming ionic compounds… › Cl- is chloride
HCl is hydrochloric acid
› SO42- is sulfate
H2SO4 is sulfuric acid
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Not this mole…
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This mole…
6.02 x 1023
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Amedeo Avogadro, 1811 - proposed that the volume of a gas at a given pressure and temperature is proportional to the number of molecules or atoms of the gas, no matter how large or small each atom or molecule is
› In other words, more molecules = more
volume
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Many scientists… Jean Perrin, JJ Loschmidt, Robert Millikan, Michael Faraday… over many years were involved in experiments that led to the determination of the number of molecules
In 1906, Jean Perrin proposed naming the number in honor of Avogadro… › Avogadro’s number = 6.02 x 1023
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One mole of a substance has a gram mass equal to the atomic mass (AMU)of that substance› Carbon-12 has a mass of 12 AMU
One mole of Carbon-12 has a mass of 12 g
› One molecule of H2O has a mass of 18 AMU One mole of H2O has a mass of 18 g So if you have 18 g water, you have…
6.02 x 1023 molecules of water
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Substance
Atomic mass (AMU)
Molar Mass (kg)
Total mass
# moles # molecules
Helium 4.0 AMU 4.0 g 4.0 g 1 mol 6.02 x 1023
Helium 4.0 AMU 4.0 g 8.0 g 2 mol12.04 x 1023 =
1.20 x 1024
Helium 4.0 AMU 4.0 g 2.0 g ½ mol 3.01 x 1023
CO2
C = 12.0 AMU O = 16.0 AMU
+O = 16.0 AMU
44.0 AMU
44.0 g 44.0 g 1 mol 6.02 x 1023
CO2 44.0 AMU 44.0 g 11.0 g ¼ mol 1.51 x 1023
NaCl
Na = 23.0 AMU+ Cl =35.5 AMU 58.5 AMU
58.5 g 175.5 g 3 mol18.06 x 1023 =
1.81 x 1024
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Switching between units› Atomic mass <-> molar mass <-> moles› Kilometers <-> Meters <-> Centimeters
Unit conversion factors100 m = __?__ cm
100 m x 100 cm = 10,000 cm 1 m
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1 hour = ______ seconds1 hr x 60 min x 60 sec = 3600 seconds
1 hr 1 min
1 year = ______ seconds1 yr x 365 days x 24 hr x 60 min x 60 sec = 31,536,000
seconds 1 yr 1 day 1 hr 1 min
60 miles/hr = ________ feet/second60 mi x 5280 ft x 1 hr x 1 min = 88 feet/sec
1 hr 1 mi 60 min 60 sec