Chapter 9 Flashcards Preview

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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

17

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

Delta H of reaction formula

sum of bonds broken + sum of bonds formed