Ionic and Molecular Compounds Flashcards
how do chemical bonds form?
when atoms lose gain or share valence electrons to acquire a close shell of valence electrons
ionic bonds
when valence electrons of a metal atom are transferred to the atom of a nonmetal and the resulting ions attract each other
covalent bonds
occur when nonmetal atoms share electrons to attain a noble gas arrangement
Na + ion
principle cation outside the cell: highest concentration outside the cell
K+ ion
principle cation inside teh cell
Ca2+ ion
cation found in bones
Mg2+ ion
cation found in bones
ionic compounds
consist of positive or negative charges held together by strong electrical attractions between oppositely charged ions
when do ionic compounds form
if the overall energy of the system decreases: we can obtain this through the born-haber cycle
allows us to understand if a compound will form spontaneously or not
the crystalline state
it is characterized by the arrangement of the ions in the 14 Bravais lattices
which transition metals cannot form 2 or more positive ions
Zn2+ , Cd2+ and Ag+
nomenclature used for metals with variable charge
- the ion with the lower oxidation state gains the suffix -ous
- the ion with the higher oxidation state gains the suffix -ic
which is the only polyatomic ion that does not have a negative charge
NH4 +
how are polyatomic ions derived?
from the loss of hydrogen ions by a molecule with an acid character
how to tell if a compound is ionic or covalent
ionic: if the first element in the formula is a metal or the ammonium ion
covalent: the first element in the formula is a nonmetal
describe how the covalent bond of a hydrogen molecules is formed
-forms as the atoms move closer and the positive charge of the nucleus attracts the electron of the other atom
-has a shared pair of electrons, a covalent bond, to give a noble gas arrangement of He to each H atom
- forms, when the molecule formed, is more stable than the 2 individual H atoms
which elements do not form octets
hydrogen and boron
which is the central atom in Lewis structure
the least electronegative
what is the importance of molecule structures?
molecules like drugs can be designed based on Lewis’s Theory eg thalidomide
why is the octet rule not right?
- hydrogen requires just 2e to form a noble gas arrangement
- nonmetals P, S, Cl, Br and I can form compounds with 10 or 12 valence electrons
- sulfur in SF6 are 12 valence electrons: 6 bonds
- in BCl3 the B atom has only 3 valence electrons to share.
electronegativity
ability to attract shared electrons by the nucleus
describe the changes of electronegativity along a period
increases from left to right: increasing the positive charge of the nucleus therefore stronger attraction for electrons
describe the changes of electronegativity down a group
increases from top to bottom as there is a decreasing distance of the valence electrons from the nucleus
why is the polarity of the bonds important
because polarity affects reactivity and solubility
what can be used to predict the polarity of a bond?
the difference in electronegativity of bonding atoms can be used
nonpolar covalent bond
occurs between nonmetals: it is an equal or almost equal sharing of electrons by the 2 bonding atoms and has a very small electronegativity difference between atoms
polar covalent bond
occurs between nonmetal atoms: it is an unequal sharing of electrons and has a moderate electronegativity difference
dipole
segregation of charges in a polar bond
electronegativity difference between 0 and 0.4
nonpolar covalent bond
electronegativity difference between 0.5 and 1.8
polar covalent bond
electronegativity difference greater than 1.8
bond is ionic and the electrons are considered transferred
polar molecules
one end of the molecule is more negatively charged than the other. the polar bonds in the molecule do not cancel each other out. the electrons are shared unequally in the polar covalent bond
describe resonance structures
delocalised electrons: a single bond length is detected that is intermediate between single and double bonds.
what does it mean when energy wise when several resonance forms can be drawn?
the actual energy of the molecule is lower than the energy of the individual structure because of higher entropy
metallic bonding
lattice of metal ions bathed in a shared electron cloud
alloys
the atoms of the added metals replace some positions in the array, leading to the same or different lattice with modulated properties
perturbation theory
application of a quantum mechanics approximation
what happens as 2 atoms approach each other?
it leads to an overlap between the orbitals: interaction between the nucleus of one atom and the electron of the other
when do bonds form
when the interactions lead to a decrease in energy. the interaction is stabilised when 2 semi-occupied orbitals of similar sizes overlap
when does the bond not form
when fully occupied orbitals overlap, the interaction leads to repulsion and the bond does not form
hybridization
shuffling between differrent sublevel orbitals to give isoenergetic hybrid orbitals
it increases the electron probability density in a single lobe allowing better superposition with other orbitals; 4 hybrid isoenergetic sp3 orbitals are obtained
why can carbon form 4 bonds
because 4 hybrid isoenergetic sp3 orbitals are obtained
sp2 hybridisation
double bond
1s and 2p orbitals
3 sp2 orbitals
trigonal planar shape 120 degrees
type of bonds: 3 sigma + 1 pi
sp hybridisation
triple bonds
1s and 1p orbital
2sp orbitals
linear shape 180 degrees
type of bond: 2 sigma + 2 pi
sp3 hybridisation
single bonds
tetrahedral 109.5 degrees
types of bonds: 4 sigma
pi bond
half filled py or pz orbital + half filled py or pz orbital
formed by the side-to-side overlap of p orbitals
sigma bond
half fillled px orbital + half filled px orbital
head on overlap of atomic orbitals along the bond axis
BF3
boron has an e configuration 1s2 2s2 2p1: sp2 hybridisation therefore 3 bonds and 1 unoccupied p orbital
SF6
sulfur electron configuration: 1s2 2s2 2p6 3s2 3p4: it can form 6 sp3d2 hybrid orbitals
VSEPR
electron groups are arranged as far apart as possible around the central atom to minimise charge repulsion
dipole- dipole attractions
intermolecular force between 2 dipoles
hydrogen bonds
strong dipole attractions when a hydrogen atom is bonded to F, O, or N
van der waals
weak attractions between nonpolar molecules: caused by temporary dipoles that develop when molecules bump into each other
intermolecular forces
forces between molecules
intramolecular force
forces within a molecule
list in increasing strength intermolecular and intramolecular bonds
dispersion forces
dipole-dipole attraction
hydrogen bond
covalent bond
ionic bond
what affects the melting points of compounds
it is related to the strength of the attractive forces between molecules and compounds
where is the melting point the highest
in ionic compounds due to the strong attractive forces between ions in the compound
how are proteins stabilized
hydrogen bonds stabilise their structure
how are nucleic acids stabilized
hydrogen bonds between complementary bases
what stabilizes the conformation of macromolecules such as proteins and nucleic acids?
the sum of several weak forces: portions of the molecule that are several bonds get close to each other in space and attract weakly
describe the structure of ethanol
ethanol has both a hydrophilic and a hydrophobic component.
hand sanitisers
at 70% ethanol, the interactions between proteins and water are replaced by interactions with ethanol. these weak forces destabilize the structure of the structure of the proteins that lose their function
what can ethanol disrupt?
hydrophobic interactions between nonpolar aa residues in proteins
draw the molecular orbital diagram for when Zavg is less than 8
see notes
draw the molecular orbital diagram for when Zavg is greater or equal to 8
see notes
bond order
bond order = (electrons in bonding orbitals - electrons in antibonding orbitals)/ 2
bonding molecular orbital
the sum of the wave function: a region where it is more likely to find an electron
antibonding molecular orbital
subtraction of the wave function: does not favor the formation of a molecule
paramagnetism
unpaired electrons: attracted to the magnetic field
diamagnetism
paired electrons: repelled by a magnetic field
bond order 1
single bond
bond order 2
double bond
why are antibonding orbitals at higher energy?
bc of the presence of nodal planes
