Bonding Flashcards
2- Structure and Bonding
an attractive force between two ions or between two atoms
Chemical Bond
Why do chemical bonds form?
The compound resulting from this is more stable and lower in energy than the separate atoms
How do chemical bonds form?
Octet Rule
principle which states that atoms tend to gain, lose, or share electrons in order to achieve a full outer shell with eight electrons
except hydrogen and helium for the outer shell (1s) can occupy only 2
Octet Rule
An atom is most stable if its outer shell is either filled or contains ___, and it has NO electrons of higher energy.
eight electrons
Main-group elements in chemistry tend to adopt the electron configuration of the nearest ___.
noble gas
a chemical bond may be ___ and ___.
ionic and covalent
types of covalent bonds
polar and nonpolar
- bond formed as a result of the electrostatic attraction between ions of opposite charge
- bond formed from the transfer of electrons
- usually formed from the reaction of metals with nonmetals
Ionic Bond
compounds formed by ionic bonds
Ionic Compound
attractive forces between opposite charges
Electrostatic Attraction
bond formed as a result of sharing electrons between two nuclei
Covalent Bond
compounds formed by covalent bonds
Molecular Compounds
measure of the ability of an atom to pull the bonding electrons toward itself
Electronegativity
a covalent bond between atoms with the same electronegativity
Nonpolar Covalent Bond
a covalent bond between atoms with different electronegativities
Polar Covalent Bond
electronegativity difference of a pure covalent bond
< 0.4
electronegativity difference of a polar covalent bond
between 0.4 and 1.8
electronegativity difference of an ionic bond
> 1.8
a pair of equal and oppositely charged poles separated by a distance
Dipole
- measure of dipole
- magnitude of the charge on either atom x distance between the two charges
Dipole Moment
what molecules have dipoles
Polar Molecules
electron-dot structures
Lewis Structures
line-bond structures
Kekulé Structures
- NOT an actual charge
- used for bookkeeping of electrons
- the charge the atom would have if each bonding electron pair in the molecule were shared equally between atoms the difference between the number of valence electrons an atom has when it is not bonded to any other atoms and the number it “owns” when it is bonded
Formal Charge
formula for getting the formal charge
FC = (no. of valence e- in free atom) - (number of valence e- in bonded atom)
FC = (no. of valence e- in free atom) - (no. of bonding e- / 2) - (no. of nonbonding e-)
omitting of the covalent bonds and listing atoms bonded to a particular carbon (or nitrogen or oxygen) next to it (with a subscript if there is more than 1 of a particular atom)
Condensed Structures
- Carbon atoms are NOT usually shown.
- A carbon atom is assumed to be at each intersection of two lines (bonds) and at the end of each line.
- Hydrogen atoms bonded to carbon are NOT shown.
- Atoms other than carbon and hydrogen are shown.
Skeletal Structures
3D structures for drawing chemical structures
- Perspective Drawing
- Ball-and-Stick Model
- Space-Filling Model
shows 3D shape
Perspective Drawing
shows bond angles accurately
Ball-and-Stick Model
shows atoms in scale
Space-Filling Model
bond lies in the plane of the paper (or screen, when viewed electronically)
straight line —————-
“normal” bond
bond extends backwards, away from the viewer, so effectively “into” the paper (or screen)
dashed bond
dashed line - - - - - - - - -
bond protrudes forward, towards the viewer, so effectively “out of” the paper (or screen)
wedged bond
horizontal triangle
- geometry based on the arrangement of atoms in a molecule
- defined by bond angles
Molecular Geometry
- geometry based on valence electron pairs (bonding and non-bonding) around a central atom
= bonding electron pairs
= nonbonding/lone electron pairs - defined by bond angles
Electron Pair Geometry
model for the prediction of molecular geometry based on the minimization of electron repulsion between regions of electron density around an atom
Valence-Shell
Electron-Pair Repulsion (VSEPR) Model
The best arrangement of a given number of electron pairs (bonding and nonbonding) is the one that ____ the repulsions among them.
minimizes the repulsions
arrange the pair repulsions
lone-pair vs lone-pair repulsion > lone-pair vs bonding pair repulsion > bonding pair vs bonding pair repulsion
Without lone pairs:
electron pair geometry =
molecular geometry
Molecular geometry can
be described in terms of
___.
bond angles
assumes that the electrons in a molecule occupy overlapping atomic orbitals of the individual atoms
Valence Bond Theory
assumes the formation of molecular orbitals from the atomic orbitals
Molecular Orbital Theory
type of bond formed when atomic orbitals on neighboring atoms overlap one another
Covalent Bond
head-on overlap of atomic orbitals; stronger
Sigma (σ) Bonds
sideway overlap of atomic orbitals; weaker
Pi (π) Bonds
atomic orbitals obtained when two or more nonequivalent orbitals of the same atom combine for covalent bond formation
Hybrid Orbitals
produces the molecular geometry of the molecule
Hybridization
shape of any hybrid orbital is [same/different] from the shapes of the original atomic orbitals
different
as s character increases, bond length _ and bond strength _
bond length: decreases
bond strength: increases
inversely proportional
the greater the electron density in the region of orbital overlap, the _ and _ the bond
stronger and shorter
as s character increases, bond angle _
bond angle: increases
directly proportional
a region of space in a molecule where electrons are most likely to be found
Molecular Orbital
2 ways to combine atomic orbitals into molecular orbitals
- Additive
- Subtractive
lower energy, bonding molecular orbital
Additive
higher energy, antibonding molecular orbital
Subtractive
occurs when an electron is shared by more than 2 atoms with π bonds (p orbitals)
π Electron Delocalization
π electron delocalization structures are represented by
resonance contributors
refers to two individual line-bond structures and and their special resonance relationship is indicated by the double-headed arrow between them
Resonance Forms
The only difference between resonance forms is the placement of the _ and _.
π bond and nonbonding valence electrons
A compound with resonance forms _ jump back and forth between two resonance forms.
does NOT
has a single unchanging structure of the two individual forms and has characteristics of both
Resonance Hybrid
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