Topic 4: Bonding Flashcards
isoelectronic ions
two atoms, ions, or molecules with the same electronic structure and same number of ve-
what are the two exceptions for electron config.
cr and cu
what is the structure of an ionic bond
lattice structure
characteristics of a lattice structure
high bp/mp
conducts electricity when molten or in solution
brittle
soluble in water
white crystalline solids
hard bc of the high mp/bp
what does the strength of an ionic bond depend on
charge of the ion - higher charge = stronger ionic bond (e.g. 2+ > 1+) bc they exert greater attractive forces between each other
size of ion - smaller sized ion = stronger ionic bond (bc more tightly packed in the lattice and there is a shorter distance between oppositely charge ions)
what is an ionic bond held together by
electrostatic attraction between oppositely charged ions
why does an ionic lattice require a lot of energy to be overcome
contains a large number of ions, so a lot of energy is needed to overcome the ionic bonding
soluble ionic compounds
salts of group 1 ions and ammonium ion (NH4+)
salts containing the nitrate ion and ethanoate ion (CH3CO2-)
salts containing chloride ion, bromide ion, and iodide ion, except when combined with Ag+, Pb2+, Cu2+, and Hg2 2+
salts containing sulfate ion except when combined with Ca2+, Sr2+, Ba2+, Ag+, and Pb2+
insoluble ionic compounds
hydroxides, and sulfates are insoluble except when combined with group 1 ions, ammonium ion, and Ca2+, Sr2+, Ba2+
carbonates, phosphates, except when combined with group 1 ions and ammonium ion
why are ionic compounds brittle
the strong bonds between the positive and negative ions creates a crystal lattice and applying pressure shifts the alignment of ions, causing them to repel, leaving the structure broken
why ionic compounds can conduct e- when molten or dissolved but not when solid
the crystal lattice must be broken apart for the ions to be able to move and carry charge. when solid, the ions cannot move which prevents the flow of charged particles
how can total bond length be calculated
atomic radius of one atom plus the atomic radius of another
why are the bonds between n2 longer than the bonds between the o2
more bonds (triple bonds) are shorter than the longer bonds (double bonds) and are therefore stronger
define a covalent bond
the electrostatic attraction between positively charged nuclei and shared pairs of bonding electrons
when does a coordinate (dative) covalent bond form
when both electrons in a bond pair come from the same atom
define electronegativity
attraction of an atom for a bonding pair of electrons measured on the pauling scale
how is a sigma bond formed
direct head-on (axial) overlap of atomic orbitals
can be between: p and s, p and p, s and s
it is a single bond
free rotation of atoms
electron density concentrated between the nuclei of bonding atoms
how is a pi bond formed
sideways overlap of p-orbitals
double bond and is only formed in the presence of a sigma bond
no free rotation around pi bondelectron density is concentrated above and below the plane of the nuclei of bonding atoms
which atom goes at the center of the molecule
the least electronegative (unless it is H)
what does a triple bond consist of
two pi bonds and one sigma bond
what is a resonance hybrid structure
average of two resonance structures, neither one nor the other, bond order is somewhere in between
how can i calculate the bond order
total number of bonds/number of sigma bonds
how to work out the hybridization of an atom
count the number of sigma molecules and lone pairs around the atom (e.g. 3 sigma bonds and 1 lone pair = sp3)
what must a molecule have in order for it to conduct electricity
charged particles e.g. ions or electrons, the charged particles can move
explain the characteristics of graphite
high mp/bp - there are many strong covalent bonds that must be broken (surrounded by 3 sigma bonds - sp2)
conducts electricity - delocalized inhavit the unhybridized p orbitals (there are spare unhybridized p orbitals in every layer)
slipper - the weak IMF between the layers breaks easily
explain the characteristics of diamond
high mp/bp - many strong covalent bonds (sp3)
electrical insulator - no charged particles
very hard - lots of strong covalent bonds
explain characteristics of sio2
high mp/bp
electrical insulator
very hard
sp3 silicon (4sigma bonds)
sp3 oxygen (2 sigma, 2 pi)
which ion is larger, Na+ or F-
although Na+ and F- have the same electron configuration, sodium has two more protons than f-, meaning there is a stronger force of attraction between the nucleus and electrons in the Na+ than the F- resulting in a smaller atomic radius
why is the electrical conductivity of solid potassium bromide poor, but the aqueous solution of potassium bromide is a good electrical conductor
When potassium bromide is a solid, the ions are not free to move around and therefore cannot conduct electricity. however, when dissolved in solution, the potassium bromide dissociates into potassium ions and bromide ions, which are free to move and conduct electricity
what does bond polarity result from
difference in electronegativities of bonded atoms
characteristics of metallic bond
layers slide - malleable
positive metal ions and sea of delocalized e- can conduct electricity bc the e- can carry a current
high bp/mp bc of strong electrostatic attraction between the ions and dl e-
as size of the ion increases
the metallic bond becomes weaker and mp decreases
explain how a molecule can contain polar bonds but still be a nonpolar molecule
Although individual bonds may be polar, a molecule may be non-polar overall if, because of the symmetry of the molecule, the dipole moments of the individual bonds cancel out.
properties of diamond
- giant covalent (macromolecular structure): no individual molecules 3D, continuing in one structure
- each carbon is joined to 4 other carbons (tetrahedral array) with covalent bonds
- high mp/bp bc a lot of E must be supplied to break covalent bonds when diamond is melted
- does not conduct electricity because the e- are held in strong covalent bonds and are not free to move around (no delocalized electrons that can move)
- not soluble bc there are no attractions between the solvent molecules and diamond that could occur to outweigh the attractions between the covalently bonded carbon atoms
properties of graphite
- giant covalent structure
- layer structure
- each c is bonded to 3 others in a trigonal planar array
- covalent bonds between the carbons, but only weak London forces between layers which is why it is a good lubricant bc not much force is required to separate the layers
- high mp/bp because the covalent bonds within the layers must be broken when it is melted or boiled
- not soluble because of strong covalent bonds between atoms
- conducts elec. because there are delocalized e- that can move between the layers
explain how graphite can conduct electricity
- one pi orbital contains one electron in carbon that is perpendicular to the plane of the layers, which can overlap sideways to give a “pi delocalized system” extending over the layer, allowing it to conduct e-
graphene
- high mp and tensile strnegth
- strong covalent bonds - must be broken to break the sheet
- good electrical and thermal conductor
buckminsterfullerene
- insoluble in water; soluble in organic solvents e.g. benzene
- individual C60 molecules (molecular structure)
- cannot conduct e- because although there is a delocalization of e- over the molecule, the molecular structures means that electrons cannot move between molecules
sio2
- giant covalent
- each oxygen is sp - bonded to two si
- due to lone pairs on each O atom, shape is bent
- each si is sp3 - bonded to 4 o
- covalent bonds between atoms must be broken in order to met it - requires lots of E
briefly explain how london forces arise
- temporary dipole-induced dipole interactions
- electrons in an atom are constantly in motion, and at any one time, they will not be symmetrically distributed about the nucleus resulting in a temporary dipole, inducing an opposite dipole in the neighboring atom
- the dipoles attract each other so there is an attractive force between the atoms
- constantly reappearing and disappearing
what can increase the strength of London forces
more electrons means that the temporary dipoles will be larger with more electrons moving around. the larger atoms in the molecule means the outer e- will be less strongly hed, so the molecule is more polarizable and the induced dipoles will be larger
hydrogen bonds
occur between molecules when a very electronegative atom (N,O,F) is joined to a hydrogen atom in the molecule, polarizing the bond, so there is a strong interaction between the delta + and delta -
what is broken when covalent molecular substances are melted/boiled
IMF not covalent bonds
rule for solubility
a substance will dissolve in a solvent if the IMF in the solute and solvent are similar
delocalization
sharing of a pair of e- between 3 or more atoms
exceptions to the octet rule
incomplete octet (BeCl2, BCl3, BF3)
expanded octet (SO4)2- , (PO4)3-,
expanded octets must be in period 3 or beyond
why can the octet be expanded
the max number of e- in the second shell is 8
but period 3 elements have access to the 3d subshell, which is still in the same principal quantum number, and so requires little energy to promote an electron
what is the order of repulsion of bonds
lone pair - lone pair; lone pair - bonding pair; bonding pair - bonding pair
why are lone pair lone pair interactions exhibit the greatest repulsive force
lone pairs are held closer to the nucleus and occupy more space in the electron cloud because they are only held by one nucleus. By contrast, the bonding pairs are further from the nucleus but more localized (i.e. cannot move around as much)
