Chapter 4; Molecular Geometry, Polarity, And Intermolecular Forces Of Attraction Flashcards
what is electron geometry
relative position of the groups of electrons on the central atom
what groups does the electron geometry include
single bond
double bond
a triple bond
a nonbonding pair
what is molecular geometry
relative position of the atoms in a molecule; determine by the electron geometry
what does the VSEPR theory predict about groups of electrons
predicts that groups of electrons on the central atom are oriented to maximize distance between them
depending on the number of groups of electrons what are main three names
two groups; linear
three groups; trigonal planar
four groups; tetrahedral
what are the angles for a linear, trigonal planar, and tetrahedral group
linear - 180
trigonal planar - 120
tetrahedral - 109.5
what is molecular geometry determined by
based on the number of bonding versus nonbonding groups on the central atom
what is the electron and molecular geometry for 2 electron groups
electron - linear
molecular - linear
what is the electron and molecular geometry for 3 electron groups
electron - trigonal planar
molecular - trigonal or bent (2 bonding and 1 nonbonding group)
what is the electron and molecular geometry for 4 electron groups
electron - tetrahedral
molecular - tetrahedral, trigonal pyramidal (3 bonding and 1 nonbonding groups), or bent (2 bonding and 2 nonbonding groups)
how to find a molecular bond angle
angle (0 - 360)
what is molecular polarity
- determines how molecules interact with each other at the molecular level
- molecular level interactions determine their macroscopic properties
what is a covalent bond
two atoms sharing valence electrons
is sharing valence electrons always equal in covalent bonds
no; one atoms may attract the electrons in a bond more closely towards it nucleus
what is electronegativity
ability of an atom, when part of a covalent bond, to draw electrons towards its nucleus
as the atomic # increases what happens to the protons and electrons
atomic # increases = more protons in atoms = attract electrons
what does negativity attract.
what does positive attract
negative attracts positive
positive attracts negative
in the periodic table which ways does electronegativity increase in the periodic table
down to up
left to right
when increasing electronegativity do the atoms get smaller or bigger
smaller
as go down a group it adds energy levels, so the electron cloud gets bigger = further away the less get pulled to nucleus
what determines if a bond is polar or non polar
electronegativity differences
in an electron density diagram that shows polar and non polar molecules, what color is high density
red
in an electron density diagram that shows polar and no polar molecules what color is low density
blue
in an electron density diagram that shows polar and non polar molecules, what color is neutral
green to yellow
atom with a greater electron density has a partial negative charge
s^-
atom with a lesser electron density has a partial positive charge
s^+
what is a dipole
separation of partial charges
what type of covalent bonds are used with dipoles
polar bonds
what are some facts about non polar bonds regarding electronegativity
- form between atoms of similar electronegativity
- even electron distribution
- no partial charges or dipoles
if there is a electronegativity difference of 0.5 and less (x<0.5) what does this make it
non polar covalent bond
if there is an electronegativity difference of greater than 0.5 and less than 2.0 (0.5<x>2.0), what does this make it</x>
polar covalent bond
if there is an electronegativity difference of greater than 2.0 (x>2.0), what does this make it
ionic bond
can entire molecules be polar and non polar
yes
how can entire molecules be polar or nonpolar
polar molecules have overall charge separation
non polar molecule have even distribution of electros
- side note; polar and non polar molecules have very different physical and chemical properties
a non polar molecule can be a molecular with all […] bonds, or a molecule with […] geometry and […] polar bonds/bond dipoles
non polar
symmetrical
identical
non polar molecules with non polar bonds
hydrocarbon compounds
diatomic elements
non polar molecules with polar bonds
- identical polar bonds in symmetrical molecules
- bond dipoles cancel
- three symmetrical shapes; linear, trigonal planar and tetrahedral
a molecule is non polar if
1. all the bonds are […] or
2. the […] geometry is […] (the central atom has no nonbonding electrons) AND all the bonds are […}
nonpolar
molecular
symmetrical
a polar molecule can be
- a molecule with one […] bond
- a molecule with […] molecular geometry and more than […] polar bond
- a molecule with […] molecular geometry and nonidentical polar bonds
polar
nonsymmetrical
one
symmetrical
what is a covalent bond
result of intramolecular forces of attraction
what are intermolecular forces of attraction
attractions between molecules in liquid and solid states
intermolecular bonds are weaker than
covalent bonds
intermolecular and intermolecular forces of attraction determine […] properties of a compound; […],[…],[…]
physical
boiling point
melting point
solubility
do polar molecules have permanent or temporary dipoles
permanent
do non polar molecules have permanent or temporary dimples
can form temporary
intermolecular forces of attraction form between a […] charge on one molecule and the […] partial charge on another
partial
opposite
what is the order of the types of intermolecular forces of attraction from weakest to strongest
dispersion forces (or London forces)
dipole - dipole forces
hydrogen bonding
dispersion forces - or London forces are…
- common to all compounds and elements
- also called London forces
- weakest intermolecular force of attraction and * only one available for non polar compounds *
how does a dispersion force form
electrons in a non polar compound may shift, forming a temporary dipole
- temporary dimple induces another temporary dipole in a nearby molecule
- weak attraction between temporary dipole and induced dipole = dispersion force
compounds with larger molecules have […] dispersion forces than compounds with smaller molecules
stronger
propane (C3H8) > methane (CH4)
(more opportunities for electrons to shift)
elements with larger atoms have […] dispersion forces than elements with smaller molecules
Iodine (I2) > fluorine (F2)
dispersion forces are (core concept)
- the only forces of attraction in elements and non polar compounds
- dispersion forces result from induced temporary dipoles
what are dipole dipole forces
- form between oppositely charged ends of polar molecules
- form between permanent dipoles
- are stronger than dispersion forces
dipole dipole intermolecular forces …
- exist between polar molecules that have a permanent dipole
- they are stronger than dispersion forces
hydrogen bonding forces are dipole dipole forces between molecules with […] bond dipoles, which are
H-F
H-O
H-N
form between the partial positive pole of one molecule (H) and partial negative pole of another (F, O, N)
how to depict a hydrogen bonding force
use dotted line between H (one molecule) and N,O, or F (another molecule) or dashes
e.g. H-F …. H-F
there is donor and receptor
how to determine the strongest intermolecular force of attraction
are polar molecules present
no - dispersion force
yes = are H-O H-N or H-F bonds present
no - dipole dipole forces
yes - hydrogen bonding forces
side note;
in a molecule with hydrogen bonding forces can also have dispersion forces
what are the intermolecular forces of molecules that are bonded to H such as F, O, N
hydrogen bonding
what are the intermolecular forces of attraction of molecules that are polar
- dipole dipole
- London dispersion forces
what are the intermolecular forces of attraction in molecules that are non polar
side note; molecules that contain only C and H are non polar
London dispersion forces
hydrogen hydrogen bonds with
F, O, N
FON
