exam #3: study guide (bonding & intermolecular forces)

**chemical bonds:**

\- compounds are __a chemical combination of two or more elements in exact ratios__ (result of a chemical bond, which is a lasting attraction between atoms, formed from a chemical reaction)

\- valence electrons are the __outermost electrons of an atom__

\- atoms bond according to their __electronegativities__ (achieving stability by having full sets of valence electrons)

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**octet rules:** a rule of thumb for non-transition metals (end up with 8 valence electrons)

\- main group elements (__groups 1, 2, 13-18__)

\- **DO NOT** USE FOR __TRANSITION METALS__!

\- max. electrons would be __2 per PEL__

\- atoms would __lose, gain, or share__ electrons order to achieve an octet

\- atoms with an octet are more stable and have less energy overall

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**BARF:**

\- __breaking a bond__ requires absorption of energy

\- __release of energy__ forms a bond

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**types of bonds:**

\- __ionic bonds__ occur as a result of losing and gaining electrons

\- __covalent bonds (or molecular bonds)__ form from the sharing of electrons

\- __metallic bonds__ occur uniquely between atoms of metals

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**forming an ionic bond:**

__when metals react they__

\- lose e-

\- become positively charged

\- have smaller radii

\- acquire the e- configuration of a noble gas

__when nonmetals react they__

\- gain e-

\- become negatively charged

\- have larger radii

\- acquire the e- configuration of a noble gas

so, ionic bonds typically form from metal + nonmetal because the ions are of opposite charge and are attracted to each other.

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**ionic solids:**

\- we call solid compounds formed through ionic bonds ionic solids

__properties:__

\- solid, crystalline structure—organized structure

\- high melting points

\- electrical conductors when melted or in solution

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**covalent bonds:**

\- 2 nonmetals or a metalloid & nonmetal

\- sharing of e-

__nonpolar__

\- equal sharing

__polar__

\- unequal sharing

typically illustrated as a line drawn between atoms

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**multiple covalent bonds:**

one pair - 2

two pairs - 4

three pairs - 6

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**covalent “solids”:**

\- self-explanatory: compounds formed with covalent bonds

__properties:__

\- soft

\- low melting point

\- poor conductors of heat and electricity

__**special type: network solid**__

\- continuous covalently bonded compound

\- extremely hard

\- very high melting point

\- poor conductors

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**metallic bonds:**

\- formed by the attraction of a single metal’s electrons and positively charged nuclei

\- one of the reasons why metals are conductive are that they easily lose their electrons

\- in a pure metal, the valence electrons can move freely between atoms, creating a “sea of electrons”

\- metallic solids = metals

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**nonpolar covalent:** difference of 0.4 or less

**polar covalent:** difference between 0.4 and 1.8

**ionic:** difference greater than 1.8

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**SNAP:**

symmetric = nonpolar, asymmetric = polar (rotational)

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__**intermolecular forces:**__ forces that act between molecules (van der waals forces)

__intramolecular forces:__ forces that act within a single molecule (a.k.a. bonds)

__dipole-dipole forces:__

\- dipole—polar molecules

\- “di” = two, + poles

\- oppositely charged poles of different atoms will attract

__hydrogen bonding:__ special type of dipole-dipole interaction

\- hydrogen is particularly attracted to nitrogen, oxygen, and fluorine (the most electronegative atoms)

\- stronger than dipole-dipole interaction

__london dispersion forces:__ (weakest type of intermolecular force)

\- caused by random movement of electrons to create temporary dipoles in molecules

\- same attraction between poles then repeats the process with the next atom/molecule

\- typically occurs in nonpolar molecules and single atoms (noble gases)

\- scales with number of electrons/size of molecules and atoms

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