Ch 2 Chemical Bonding and Lewis Structure Flashcards
compound
combinations of two or more diff elements in defined proportions, no overall changers
anion
species possessing overall negative charge
non isolable
cation
species possessing overall positive charge
non isolable
diff names for ions containing multiple atoms
complex ions, polyatomic ions, molecular ions
ionic bonds
opp charged ions held tgth by electrostatic forces
trend in electronegativity
higher negativity towards fluorine, most electronegative
covalent bonds
mutual attraction of a pair of electrons to nuclei or adjacent atoms, shared electrons
metallic bonds
electrons shared simultaneously atoms, flow, elemental metals or metal alloys - metallic bonds
what electronegativity difference leads to ionic vs covalent
0>x - 0.4 slightly polar, 0.5 - 2.0 polar, 2.1< ionic
relationship between trends in electronegativity and atomic radius etc
higher electronegativity up table as atomic radius decreases, therefore electrons held more tightly to nucleus and ^ attraction
electron affinity, ionization energy increases along with electronegativity
electron affinity
energy released when electron added to neutral atom to form neg charged ion
ionization energy
energy required to remove most loosely bound electron of an isolated, gaseous atom, positive ion, or molecule
homonuclear diatomic species
molecules containing non polar covalent bonds, atoms in the bond have same electronegativity
molecules containing non polar covalent bonds
homonuclear diatomic species
polar covalent bonds
electrons polarized towards atom ^ electronegativity
ionic compounds
ions held together w/ electrostatic forces, when melted, conduct electricity due to freely moving anions and cations
common rxn group 1 and group 17
alkali metals x halogens (17) - alkali metal halides, one electron transferred alkali metal atom to halogen
redox reaction
reduction-oxidation, oxidized - loses an electron, reduced - gain an electron, total elec lost = total gained
closed shell
atom has same # electrons valence shell as noble gas in the same row, generally 8, full valence shell
octet
closed valence shell w 8 electrons
bond order
bonds between atoms
bond length
distance between two nuclei participating in bond
bond dissociation energy
energy needed to completely seperate bonded atoms
relationship bond order, length, dissociation energy
higher bond order, shorter bond length, higher bond dissociation energy
heteronuclear diatomic molecule
electrons not shared equally, polar
bond dipole
unequal distribution of electrons, partial positive and partial negative charge (delta plus or minus)
how to rep bond dipoles
delta plus or minus and arrow with cross on tail
percent ionic character definition and how to calculate
ratio of actual bond dipole (measured) to calculated bond dipole if the pair purely ionic
% ionic character = (measured dipole moment X-Y / calculated dipole momend of X+Y-) x 100
what % ionic character ionic?
more than 50% ionic character ionic
importance of arrangement of atoms and bonds
allows us to predict physical properties and chemical reactivity of different chem compounds
octet rule
want 8 electrons in valence shell, if period 3 or higher can possible expand octet IF reduces formal charge
some elements group 13 can have just 6 valence electrons
name atoms incomplete octet
electron deficient
importance electron deficient compounds
elec deficient comp of carbon, key in many reactions of organic chem. Ex tertiary butyl cation important intermediate in industrial production of rubber (polyisobutylene)
name of atoms greater than 8 valence electrons
hypervalent, or expanded octet
unpaired electrons, name and importance
free radicals, messenger molecules in living systems and reactive species in atmospheric chemistry
nitric oxide
molecule of the year 1992, signalling molecule, penetrate cell walls and trigger relaxation of vascular smooth muscle, blood vessel dilation, and increased blood flow
formal charge
difference between number of valence electrons unbonded atom and # in bonded. each bond pair counted as one electron
indicated with little charge + 1 2+ 2- with little circle around it right next to the atom
steps to drawing lewis structures
- arrange symbols, least electronegative in center
- add valence electrons
3.draw single bonds
- anions, add electrons most electronegative terminal. cations, remove electrons central atom
- additional bonds unpaired electrons
- rearrange for octets
- redraw
- label formal charges
- check electron count
- determine which one is best structure if multiple options
how to determine if best lewis structure
- formal charges minimized
- neg formal charges on more electronegative atoms
arrow heads when drawing atomic movement resonance structures
half arrow head one electron, full head two electrons of bond
resonance structures
multiple structures, same position atoms but different arrangement of electrons
true structure and resonance
true structure is weighted average of set of resonance
how to draw resonance structures
double headed arrow between
valid resonance structure
octet rule is satisfied on all atoms
best resonance structure
minimal formal charge, neg formal charge on more electronegative elements, positive on less, this is lowest energy configuration
chemically reasonable res structure
any valid resonance where magnitude formal charge small (but not necessarily minimized) represent bonding typical of various elements
what element doesn’t do double bonds
fluorine
what do resonance structures actually mean?
true structure would be a hybrid of all but thats hard to show, so resonance structures none of them are really the true structure
isomers
isomers same molecular formula DIFF arrangement of atoms (resonance same arrangement atoms, diff electrons)
resonance curvey arrow notation
1st res structure with arrows pointing to where electron pairs/bonds would move to in second
Arrow Pushing
drawing lewis with more than one central atom
pay close attention to # of electrons, probable lots resonance structures
general rules/characteristics lewis structures
all valence shown, all electrons assigned, octet rule, minimal formal charge, neg formal charge on most electroneg, actual molecular structure hybrid of all structures
oxidation state
measure of degree of electron loss of an atom in chem species.
IONIC COMPOUND - same as charge on ionic form
COVALENT BONDS - charge the atom would have after bonding electrons “given” to more electronegative atom
does formal charge or oxidation state describe electron distribution better covalent bonds?
NEITHER!!!! true charge distribution somewhere between two extremes
partial charge probably better
partial charge
bonds aren’t really purely ionic or covalent, have dipoles rep by partial positive or partial neg charge (delta + or -), magnitude of partial charge, difference in electronegativity
probably best representation of true charge distribution
bronsted-lowry acids and bases
acid is a proton donor (H+), base proton acceptor
what sort of charge should you look at to determine what sort of reaction occurs (acid base)
partial charge NOT formal
common acid in acid base reactions
hydronium ion (H3O+), bonding electrons between one of the H and O move to O creating H2O, Proton H+ move to base (ex ammonia) form bond using 2 electrons from the base
Li+ etc how many valence electrons?
base it on the highest occupied shell of non ionized form , so for Li+ it would be 0
