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Chemistry Review: Atoms
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Atoms are made up of a nucleus containing
protons and neutrons and orbitals
containing electrons (2, 8, 8,...).
The outermost electrons are known as
valence electrons.
Ions
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Ion: Valence electrons are lost
or gained in order to have a
full outer shell. This results in
a charge.
➲ Metals lose electrons to form
cations.
➲ Nonmetals gain electrons to
form anions.
Intramolecular Bonds
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Ionic Bonds: A force of attraction between
a cation and an anion (aka a transfer of
electrons).
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Ex. NaCl
Intramolecular Bonds
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Covalent Bonds: neither atom is willing to
give up electrons so the electron pairs are
shared (i.e. two non-metals).
ex. H2 (g) , CH4 (g)
Intramolecular Bonds
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Double and triple bonds can result if 2 or 3
pairs are shared.
 ex. O2, N2, CH2CH2
Number of bonds
• Non metals
always make a
certain number
of covalent
bonds (based
on their need
for valence
electrons).
Electronegativity
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Elements have varying electronegativity
(EN) or the affinity (want for) electrons.
Non-polar covalent bond: the atoms
involved have similar electronegativities, so
the electrons are shared equally.
(ex. C-H).
Electronegativity
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Polar covalent bonds: the atoms
involved have different electronegativities
so there is uneven sharing of electrons.
This results in a separation of charge.
(ex. O-H)
Electronegativity
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the more electronegative atom (often O,
N, S) will pull the electron pair towards it
more often and gain a partial negative
charge.
➲ The electrons spend more time away from
the more electropositive atom (often H),
so it has a partial positive charge.
Polar Covalent Molecules
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If the molecule is asymmetrical and has a
polar covalent bond, the molecule will also
be polar.
➲ ex. H2O, CH3OH
Non-polar Covalent Molecules
• Non polar molecules occur when a
molecule has non polar covalent bonds
OR because of the symmetrical
arrangement of polar covalent bonds.
Intermolecular Bonds
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The partial charges on polar
covalent molecules result in
attraction between molecules.
Ex. Hydrogen bonds: the
attractive force between an
electronegative atom and an
electropositive hydrogen atom
that is bonded to either
nitrogen, oxygen, or fluorine.
Organic Compounds
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Organic compounds: “chemicals of life”,
contain a lot of Carbon ex. C6H12O6 (usually
also hydrogen, but not always)
Hydrocarbons: only contain C and H, ex. CH4
Inorganic compounds do not contain Carbon
ex. HCl
Organic Compounds
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Carbon atoms attach to each other to form
chain and ring structures that are the
backbones of the major biological molecules
(carbohydrates, lipids, proteins, and nucleic
acids).
Functional Groups
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Other elements attach to the carbon
backbone of organic compounds.
These groups are more reactive and give
certain chemical properties to the
molecule.
Functional Groups
• ex. -OH, -COH, -CO
and -COOH are polar
because of the highly
electronegative oxygen
atom, making
compounds that contain
them (alcohols and
sugars) highly soluble
in water.
Water
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Water is inorganic (no Carbon) but is an
important chemical to life because it
comprises a large part of living organisms.
Water
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It is polar covalent, which makes it a versatile
solvent.
Like dissolves like: Other polar
molecules/functional groups are hydrophilic
and will dissolve,
Nonpolar molecules/functional groups are
hydrophobic and will not.