Flashcards in Chapter 9 Deck (23):
1
why do chemical bonds form
they lower potential energy between charged particles that compose atoms
2
ionic bond
metal + nonmetal bond and the metal transfer 1 or more electrons to nonmetal
3
covalent bond
nonmetal + nonmetal; electrons are shared, not transferred
4
metallic bonding
metal + metal; simplest form is electron sea model where atoms in metal lattice pool their valence electrons and are delocalized over the entire metal
5
lattice energy
energy associated with formation of crystalline lattice; always exothermic so lattice energy is always negative
ionic radii increase as we move down the column
6
ionic bond properties
ionic solids:
high melting points
nonconductive
solutions of ionic compounds conduct electricity
7
bond length and strength
double bond is shorter and stronger than single
triple bond is shorter and stronger than double
8
difference in direction and melting point for covalent vs ionic
covalent = shares a specific pair of electrons
ionic = non directional and share an array of ions
molecular compounds have lower melting and boiling points than ionic compounds
9
electronegativity
atom's ability to attract electrons in a chemical bond
10
periodic trends for electronegativity
increases across period
decreases down a column
flourine = most electronegative
Francium = lease electronegative
11
degree of polarity depends on..
difference between electronegativity of two bonding atoms
greater difference = more polar
12
dipole moment
measure of the separation of positive and negative charge
13
percent ionic character
increases with electronegativity difference
no bond is 100% ionic
ratio of bond's actual dipole moment to dipole moment it would have if electron was completely transferred
14
resonance structures
two or more Lewis structures for the same molecule
write out both structures with double headed arrow between
only resonance hybrid structures exist in nature
15
formal charge
charge the atom would have if all bonding electrons were shared equally
16
formal charge formula
formal charge = # of val electrons - (# of lone pair electrons + 1/2# of bonding electrons
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how to determine most appropriate skeletal structure or resonance structure
1. sum of all formal charges in neutral molecule must be 0
2. sum of all formal charges in ion must equal charge of ion
3. small or zero formal charges on individual atoms are better than large ones
4. when formal charge can't be avoided, negative formal charge should be on most electronegative atom
18
odd electron species
molecules or electrons w/ odd # of electrons (called free radicals)
can't write a good Lewis structure for these, but generally don't exist in nature
19
incomplete octets
Boron = only has 6 electrons`
20
expanded octets
any element in third row and beyond usually have up to 12 (sometimes 14) electrons
typically octets are expanded to lower formal charge
21
bond energy
energy required to break 1 mole of the bond in the gas phase
22
exo vs endo bonds
break bonds = endothermic (positive)
form bonds = exothermic (negative)
23