CSU’s Gen Chem 111 Test 3 – Flashcards

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question
what forms ionic bonds?
answer

oppositely charged ions

question
what forms covalent bonds?
answer
positively-charged atomic nuclei and the negatively-charged electrons between them
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what does chemical bonding do?
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Chemical bonding lowers the potential energy between positive and negative particles
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nonpolar covalent
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no electronegativity difference
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polar covalent bond
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less than 1
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ionic bond
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above 1 electronegative difference

metals and nonmetals

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types of covalent bonds
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nonmetal and nonmetal

metalloid and nonmetal

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what is bond polarity?
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a measure of how equallyelectrons are shared

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what happens in a completely nonpolar covalent bond
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the electrons are shared equally

;;EN = 0

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what happens in a nonpolar covalent bond?
answer

;The electrons are shared fairly equally between the two atoms that are bonded, and ;EN ; 0.4

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what happens in a polar covalent bond?
answer

;The electrons are pulled more strongly to one atom than to the other atom, and ;EN = 0.4 ; 1.7

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what happens in an ionic bond?
answer

;The electrons are transferred
;;EN ; 1.7

question

Which is the most polar bond?

(a) N - H
?
(b) F - N
?
(c) O - H
?
(d) I - Cl

answer
O-H
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what makes up a lewis electron dot symbol?
answer

 

consists of the chemical symbol for an element surrounded by dots
Chemical symbol represents nucleus + core electrons
Each dot represents a valence electron

 

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why do we use lewis dot diagrams?
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used to show and track the valence electrons (e.g. during a chemical reaction)
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how to build a lewis diagram
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Figure out the total #  of valence electrons.

 

 

Make sure to adjust if it’s a cation (remove electrons) or an anion (add electrons).
Figure out how the atoms are connected.
The central atom is generally less electronegative than the atoms around it (except for H).
Start by connecting them all with single bonds.
Complete the octets of the atoms bonded to the central atom first (but for Hydrogen only use 2 electrons).
If there aren’t enough electrons for the central atom, try giving it multiple bonds.
Place any left over electrons on the central atom.

 

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What is the octet rule?
answer

 

Octet = eight valence electrons

 = four pairs of valence electrons

 = eight v. e. means full s and p subshells

 = filled outer level

 

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what is formal charge?
answer
It’s the charge that an atom would have if all the bonding electron pairs were shared equally.
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what is the formal charge equation?
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Formal charge = (# of valence electrons in isolated atom) – (# of electrons assigned in the Lewis structure)
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what is the most stable lewis structure?
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1) has atoms that bear formal charges closest to zero, and (2) any negative formal charges are on atoms that are more electronegative.
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what is more important: the octet rule or formal charge
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satisfying the octet rule is more important than minimizing formal charges.
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exceptions to the octet rule
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Odd number of valence electrons in molecule
Less than an octet (H, Be, B, Al common)
More than an octet (n = 3 and above since d orbitals available

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what is a resonance structure?
answer

describing
molecular structures with
‘delocalized’ electrons

Bonds in the molecule have:
• Equal bond strengths
• Equal bond lengths
• Equal bond dipoles

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what does bond order equal?
answer


electron pairs/

atom sets

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what does VSEPR stand for
?
answer
Valence-Shell Electron-Pair Repulsion Theory
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what is vsepr?
answer
Model explaining/predicting the geometric shape of
molecules:
Electron ‘groups’ are as far apart as possible
Requires an appropriate Lewis structure
Number of bonding groups and nonbonding groups are arranged in
optimal geometric arrangements
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what determines the electron group arrangement?
answer
total number of groups.
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what are the types of groups in molecules?
answer
Bonding groups (X) = # of surrounding atoms (regardless of bond order)
• Nonbonding groups (E) = # of lone pairs
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two electron groups:
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electron group arrangement: linear

Molecular shape (AX2): Linear
2 bonded atoms
0 lone pairs
180° bond angle

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three electron groups
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electron group arrangement: trigonal planar

Molecular shape (AX3): Trigonal planar
3 bonded atoms
0 lone pairs
120° bond angles

Molecular shape (AX2E): Bent (V shaped)
2 bonded atoms
1 lone pair
~120° bond angle

question

four electron groups

 

answer

electron group arrangement: tetrahedral

Molecular shape (AX4): Tetrahedral
4 bonded atoms
0 lone pairs
109.5° bond angles

Molecular shape (AX E): Trigonal pyramidal

3 bonded atoms
1 lone pair
~ 109.5° bond angles

Molecular shape (AX2E2): Bent

2 bonded atoms
2 lone pairs
~ 109.5° bond angles

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five electron groups
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electron group arrangement: trigonal bipyramidal
Axial and equatorial positions are nonequivalent

Molecular shape (AX5): Trigonal bipyramidal
5 bonded atoms
0 lone pairs
90° and 120° bond angles

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Five Electron Groups
Electron-group arrangement: Trigonal bipyramidal
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Molecular shape (AX4E): Seesaw
4 bonded atoms
1 lone pair
~90° and ~120° bond angles

Molecular shape (AX E ): T-shaped
3 bonded atoms
2 lone pairs
~ 90° bond angles

Molecular shape (AX2E3): Linear
2 bonded atoms
3 lone pairs
~ 180° bond angle

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Six Electron Groups
Electron-group arrangement: Octahedral
answer

Molecular shape (AX6): Octahedral
6 bonded atoms
0 lone pairs
90° bond angles

Molecular shape (AX E): Square pyramidal

5 bonded atoms
1 lone pair
~ 90° bond angles

Molecular shape (AX4E2): Square planar

4 bonded atoms
2 lone pairs
~ 90° bond angles

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summary of vsepr theory (steps) used to predict chemical properties
answer

molecular formula

lewis structure (count all e groups around central atom)

electron-group arrangement (note positions of any lone pairs and double bonds

bond angles (count bonding and nonbonding e groups seperately)

molecular shape

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valence bond theory
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uses wave behavior of the electrons to explain bonding

Bonds form when the orbitals of two atoms that
contain electrons overlap.

why H-H forms H2

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Bond strength and orbital overlap
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greater the orbital overlap - the stronger the bond
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overlap depends on :
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shape and direction of the orbitals
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bonds are oriented:
answer
in the
direction that maximizes
the overlap
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hybridized atomic orbitals
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Mathematically ‘mix’
isolated atomic orbitals
to obtain hybrid
orbitals
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number of atomic orbitals =
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number of hybrid orbitals
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type of hybrid orbitals depends on types of
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atomic orbitals mixed
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Sigma (σ) bonds:
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result from end-to-end overlap of orbitals
– Produces a region of high electron density directly along bond axis
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Pi (π) bonds:
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result from side-to-side overlap of orbitals
– Produces two regions of electron density above and below bond axis
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bond order and types:
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Single bond: one σ bond
• Double bond: one σ and one π bond
• Triple bond: one σ and two π bonds
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Determining Geometries of Axn Molecules
answer
1. Draw the Lewis Structure
2. Determine the total number of electron domains
around the central atom A.
3. Determine the electron domain geometry
(arrange the electron domains so that repulsions
among them are minimized).
4. Use the resulting arrangement of the bonded
atoms to determine the molecular geometry.
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How the Type of Electron Pair
Affects Bond Angles
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Repulsive force of electron domains/volume
occupied by electron domains:
Nonbonding > triple > double > single
pairs bonds bonds bonds
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Nonbonding pairs experience less blank blank than bonding pairs
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nuclear attraction
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multiple bonds contain
higher blank blank blank compared with single bonds
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electronic-charge density
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memorize table 11.1
answer
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physical properties of sigma and pi bonding
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Sigma bonds allow free rotation of the atoms around the bond axis

 

Pi bonds restrict rotation around the bond axis (π orbitals must
remain aligned parallel to form bond)

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macroscopic observations of gas
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conforms to shape and volume of container

high compressiblilty

high ability to flow

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macro observations of liquid
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conforms to shape of container; volume limited by surface

very low compressibility

moderate ability to flow

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macro observationsof solid
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maintains its own shape and volume

almost none compressibility and ability to flow

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Intramolecular forces (bonding forces)
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These forces exist within each molecule.
– They influence the chemical properties of the substance.
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Intermolecular forces (nonbonding forces)
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These forces exist between molecules.
– They influence the physical properties of the substance.
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phase changes require what
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changes in the energy of matter (You are not breaking bonds – just the weaker
intermolecular forces break)
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sublimation
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solid to gas
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deposition
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gas to solid
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comparison of bonding forces
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Ionic: cation to anion

covalent: nuclei shared e- pair

metallic:cations delocalized electrons

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comparison of nonbonding (intermolecular) forces
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ion-dipole: ion charge-dipole charge

h bond: polar bond to H-dipole charge (high EN of N,O, and F)

dipole-dipole: dipole charges

ion induced dipole: ion charge - polarizable e cloud

dipole - induced dipole: dipole charge - polarizable e cloud

dispersion (london): polarizable e clouds

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bonding and nonbonding forces are just electrostatic attractions. therefore:
answer
Bonding forces tend to be stronger (large charges - close together)
– Nonbonding forces tend to be weaker (partial charges – further apart)
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ion- dipole forces
answer
Most commonly occur in ionic
solutions (i.e. salt water)
– Charge of the ion and partial charges
of the polar molecules are attracted
– In salt water – ions are solvated by
water (hydration)
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dipole-dipole interactions
answer
Dipoles in polar molecules are attracted
• Attraction creates directional orientations in these substances
(oppositely-charged poles point at each other)
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why is hydrogen bonding a special case?
answer

H-bonding is a dipole-dipole force where there is an attraction between a H
atom bonded to an atom of high electronegativity (N, O, and F) and the
negative end (lone pair) of a nearby N, O, or F atom

H-bonding is only present in molecules
with N-H, O-H, or F-H bonds (the presence of N,O,F
and H is not enough)

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charge induced dipole forces
answer
Polarizability - distortion (or squishiness) of an electron cloud
• Increases down a group - size increases and the larger electron clouds are
further from the nucleus
• Decreases left to right across a period - increasing Zeff shrinks atomic size and
holds the electrons more tightly
question
dispersion (london) forces
answer

Instantaneous dipoles caused by the random motion of
electrons
• Present in all substances, even noble gases like He
– this is the only force for nonpolar substances
• Dispersion forces tend to be the dominate intermolecular force in
most substances
• Stronger forces exist in more polarizable molecules, or molecules
that have more electrons
– strength of the force tends to scale with mass

Stronger forces exist between molecules with more ‘surface area’
to touch, if they have the same mass

question
ions present in these particle forces
answer

ionic bonding (ions only)

ion dipole forces (ion + polar molecule)

 

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ions not present in these interacting particle forces:
answer

dipole dipole forces (polar molecules)

polar and nonpolar: dipole induced dipole forces

nonpolar molecules only: dispersion forces only

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