Unit 9- Chemical Bonds Flashcards
chem bonds
forces that hold the atoms together in substance
- ionic bonding: cation + anion (ionic cpd)(transfer of e-)
- covalent bonding: nonmetal eles (molec cpd)
Lewis Electron-Dot Symbol
Symbol of ele surrounded by dots which represent their ve-
- cations: most have no ve- shown
- anions: most hve 8 ve-
lattice energy
energy required to sep 1 mol of ionic solid into its gaseous ions
LE= (k|Q1Q2|)/r
Q1 and Q2 = ionic charges
r = distance between ions in the solid
- use Q1Q2 for LE but when all the same, use r
covalent bonding
results from atoms sharing an e- pair
bond length
the distance between the nuclei of 2 bonded atoms
Lewis Structures
show how the ve- are arranged in a molec or polyatomic ion
bonding pairs
e- shared between 2 atoms and are rep by lines
lone pairs
entirely on one atom and are rep by 2 dots
octet rule
atoms share e- until each atom is surrounded by 8 e-
- single bond: share 1 pair e-
- double bond: share 2 pair e-
- triple bond: share e pair e-
bond order
the # of e- pairs shared between 2 atoms
- as bond order incs, length of bond decs and strength of bond incs
skeleton structure
shows which atoms are bonded to each other
central atom
bonded to 2 or more other atoms
- usually farthest left and down on periodic table
terminal atom
bonded to 1 other atom
* H and F are always terminal
writing Lewis Structure
- start with the skele structure
- sum the ve-
- substract 2e- for each bond in skele structure
- count the # of e- needed to satisfy octet rule (if # needed > # remain, add 1 bond for each additional 2e- needed )
- place remaining e- as lone pairs to satisfy octet rule
bond polarity
- UNEQUAL sharing leads to a POLAR covalent bond
- EQUAL sharing leads to a NONPOLAR covalent bond
dipole movements
measure of the unequal sharing of e-
- zero for nonpolar
- NOT zero fro polar
polar covalent bond symbol
δ with a +/- to show charges
Electronegativity
measure of the ability of an atom to attract the shared e- in a chem bond
- inc up and right
H= 2.1
C= 2.5
N= 3.0
O= 3.5
F= 4.0
- diff in electroneg shows if polar or not and comparison to other molecule shows length of arrow. longer = more polar
Formal charges
a charge assigned to atoms in Lewis structures by assuming the shared e- are divided equally between the bonded atoms
formal charge= # of ve - # of lone pair e - # of bonds
comparing Lewis Structures
- SMALLEST formal charges are FAVORED (more stable)
- adjacent atoms w/ formal charges of the SAME sign are much LESS favorable
- neg formal charge on MORE electroneg atoms are FAVORED
resonance structures
differ only in the distribution of the ve-
- indicated by double handed arrow
avg structure
avg of all resonance structures
- resonance structures contribute equally
bond order
avg of the bonds
(ex: 1 double bond and 1 single bond = 3/2 = 1.5)
electron deficient molec
central atoms from Group 2A and 3A do not have enough ve- to complete an octet
odd e- molec
species with odd # of e-
expanded valence shell molec
have more than 8e- about an atom in Lewis structure (extra e- on central atom)
- only 3rd period elements or later
- formula: ZFn (where Z= P, S, Cl, As, Se, Br, Te, I, or Xe and Fn= terminal atom)
Oxides of heavier elements
have a central atom from the 3rd or later periods
bond energies (bond dissociation energy)(D)
the energy required to break 1 mol of bonds in a gaseous species
- Always endothermic
- deltaH reaction = sum(bond energies of bonds broken) - sum(bond energies of bonds formed)
- lewis structured need to be written
- bond energies (except of diatomics) are avg energies
