Bonding and Chemical Reactions Flashcards
Molecules
atoms of elements comibing
Chemical Bonds
bonds between atoms formed via interaction of valence electrons from both atoms
Octet Rule
atoms bond with atoms to form 8 electrons in its outermost shell to resemble the structure of noble gases
Incomplete Octet
Hydrogen (2 ve)
Lithium (2 VE)
Beryllium (4VE)
Boron (6VE)
Expanded Octet
Any element in period 3 or higher
Odd number of electrons Exception to Octet Rule
molecules with odd number of VE cannot distribute electrons to give eight to each atom
ex: NO, nitric ocide
Ionic Bond
ELECTRONS from an atom with LOW IONIZATION ENERGY (usually metal) TRANSFER to atom with HIGH ELECTRON AFFINITY (usually nonmetal)
they are held together due to the opposite charges formed between the ions
lattice structures consisting of repeating rows of cations and anions
Covalent Bonding
electron pair is SHARED between two atoms, with SIMILAR values of ELECTRONEGATIVITY
usually nonmetals
individually bonded molecules, not lattice structures
Nonpolar vs Polar Covalent Bond vs Coordinate Covalent
NonPolar: electron pair is shared equally
Polar: electron pair is shared nonequally
Coordinate: if both shared electrons are contributed by only one of the atoms
Cation
atoms that loses electrons, positive charge
Anion
atom that gains electrons, negative charge
Ionic Compound Properties
Very high melting and boiling points (due to strength of electrostatic force)
Readily dissolve in polar solvents
Good aqueous conductors
Crystalline Lattice of Ionic Bonds
repeating units of positive and negative ions to maximize attractive forces and minimize repulsive forces
Energy required to form ions through transfer of electrons is _____ than the energy released forming an ionic bond. Making it ____ to form ions.
greater; unfavorable
Covalent compounds contain relatively ___ intermolecular interactions. Leading to the following properties:
weak;
Low melting and boiling points
poor conductors in aqueous state
Covalent bonds allow for ___ bonds with other atoms to fill the valence shell of an atom
multiple
Bond Orders for Single, Double and Triple bonds
Single: 1
Double: 2
Triple: 3
Property of Covalent: Bond Length
average distance between two nuceli in a bond
as number of shared electron pairs INCREASES, bond length DECREASES
Triple < Double < Single
Property of Covalent: Bond Energy
energy required to break a bond and separate compounds in gaseous atomic states
greater the shared pairs, the more energy required to break bonds and the stronger the bond!
Triple > Double > Single
Property of Covalent: Polarity
when two atoms have a relative difference in electronegativities
atom with the higher electronegativity hogs the electrons more
Dipole
a polar bond, positive end has less electronegative atom and negative end has the more electronegative atom
Non Polar Covalent Bond
equal distribution of electrons with identical/near identical electronegativity atoms
Diatomic atoms, bonds between atoms with a deltaElectronegativity less than 0.5
Polar Covalent Bond
atoms with different electronegativities (0.5-1.7 so it doesnt form ionic bond)
Dipole Moment
occurs for polar covalent bonds
vector point towards partial negative
p =q * d
p = dipole moment q = magnitude of charge d = displacement vector
Debye Units
columbs - meters ; measurement of dipole moment
Coordinate covalent bonds
shared electrons originate from same atom
one lone pair attacks another atom with unhybridized p-orbital
typically bound in lewis acid/base reactions
Lewis Acid
compound which accepts lone pair of electrons
Lewis Base
compound which donates lone pair of electrons
Bonding vs Non Bonding Electrons
B: electrons involved in the covalent bond in Valence shell
NB: electrons in Valence shell not involved in covalent bond
Lone Pairs
electron pairs in valence shell that are associated with only one nucleus and not shared or bonded
Most stable arrangement is one that…
minimizes the number and magnitude of formal charges
Steps of Drawing Lewis Structure
1) Draw arrangement of elements, least electronegative atom in center
2) Count all valence electrons of the atoms and sum them together
3) Draw single bonds between atoms, each constitutes 2 valence electrons
4) Complete octets of all atoms by adding VE pairs
5) place extra electrons on central atom
6) if octet of central is not filled, create double.tripple bonds using said lone pairs
Terminal Positions of Lewis Structure
H, F, Cl, BR, I
Formal Charge =
V - N nonbinding - N bonding
N nonbonding = number of nonbonding electrons
N bonding = number of bonds
V - normal number of electrons in the atoms valence shell usually
Resonance structures/Resonance Hybrid
all possible lewis structures of a molecule ; actual structure is a hybrid of all structures known as resonance hybrid
Stability of Resonance Structures
1) lewis structure with small or no formal charge is most stable
2) lewis structure with less separation between opposite charges is prefered
3) lewis structure in which negative formal charhes are placed on electronegative atoms is more stable
Lewis Structures: Exception to Octet rule
remember all after period 3 and H, He, Li, Br, B can have more or less thant four bonds and electrons on central atom!
extra electrons go to d subshell
VSEPR Theory
three dimensional arrangement of atoms surrounding central atom is determined due to repulsions between bonding and non-bonding electrons to orient them as far as possible to minimize repulsive forces
Predicting Geometrical Structure
1) Draw Lewis Structure
2) Total number of bonding and nonbonding electron pairs in the Valence shell of central atom
3) orient so electron pairs are as far as possible
Linear
180 degrees, 2 Electron density areas
Trigonal Planar
120 degrees, 3 electron density areas
Tetrahedral
109.5 , 4 electron density areas
Trigonal Bipyramidal
90, 120, 180 , 5 electron density areas
Octahedral
90, 180, 6 electron density areas
Electronic vs Molecular Geometry
E: spatial arrangement of all pairs of electrons around the central atom (bonding and non bonding)
M: spatial arrangement of only bonding pairs of electrons ; which MCAT focuses on
Ideal Bond Angle
angle between bonds
nonbonding pairs exert more repulsion than bonding pairs as they are closer to the nucleus
A compound with polar bonds may be polar or nonpolar depending on __
spatial orientation of the polar bonds in the molecule ; if dipole moments cancel each other out (vector sum = 0) then a nonpolar compound is made
Molecular Orbital
when two atoms bond to form a compound, the atomic orbitals interact
Bonding vs Antibonding Orbitals
B: sign of both atomic orbitals are the same
AB: sign of atomic orbitals are different
Sigma Bond
orbitals overlapping head to head
free rotation about axes
Pi Bond
orbitals overlap so two parallel electron clouds are formed
no free rotation due to electron densities are parallel
Intermolecular Forces
impact physical properties like melting and boiling point
1) Van der Waals
2) Dipole - Dipole
3) Hydrogen
van der Waals
unequal distribution of electron density causing rapid polarization/counterpolarization forming negative and positive portions on molecules leading to temporary attraction between neighboring molecules
weakest force, large moleucles are more easily polarizable
Dipole-Dipole
polar molecules orient themselves so oppositely charged ends are lose to one another
attractive electrostatic forces
present in solid and liquid phases but not gases due to distance of particles
higher mp and bp
Hydrogen bonds
strong form of dipole dipole that may be intra or inter moelcular
H bonded to an highly electronegative atom (O, N, F), it carries a positive charge to interact with partial negative charges of nearby electronegative atoms
very high boiling points due to high energy required to break H bonds
