2 models of bondings and structure Flashcards
Formal charge
Formal charge (FC) is determined for each atom in a structure from:
FC = V – (½B + L)
where V = valence electrons, B = number of bonding electrons, L = number of one pair electrons
The most stable of several Lewis (electron dot) structures is the structure that has: the lowest formal charges, negative values for formal charge on the
more electronegative atoms.
Ionic bonding
Electrostatic attraction between oppostiely charged ions
Physical properties of ionic compound
- lattice structures ➪positively charged ions are packed as closely as possible to the negative
charged ions, while ions of the same charge are as far apart as possible ➪maximizes electrostatic attraction between the ions, while minimizing repulsion - surrounded by 6 other atoms
- low volatility
- Higher temperature (solid at room temperature)
- no conductivity, except at molten or aqeous state
- ionic compounds are soluble in polar solven ➪ partial charges of water is attracted to opposite charge in the lattice (eg: H2O)
Compare the conductvity of AlCl3 (s) and AlCl3(l)
- AlCl3 (s) : no conductivity at solid state ➪ no delocalized electrons at covalent
- AlCl3(l): covalent bonds but no delocalized electrons due to cordiante bonds to Al
Draw the ionic strucure between Na and Cl
a) state the electronegative value and the shape of pure covalent
- 0<x<0.5: non polar bond have equal sharing of bond electrons/dipole moment is cancled ➱temporailiy dipole ➱ they are symmetrical [F2, H2, and O2]
- 0.5<x<1.8: polar covalent are paritally ionic/partial tansfer of unequal sharing of electron➱ permanent dipole ➱ they are unsymmetrical
- 1.8<x: greatest electronegtaive difference➱complete transfer of electrons
Covalent bonds
- electrostatic attraction between a shared pair of electrons and the positively charged
- generally occur between non metals
- Most stable of similar ionization and affinity for electrons by sharing of electrons
- in a covalent strucure, shared electron are attracted to the nulceus of both atoms
- exists as london dispersion force, permanent dipole force, instaneous dipole force and hydrogen bond
Bond length
measure of the distance between the two bonded nuclei
Bond strength
described in terms of bond enthalpy, and is effectively a measure of the energy required to break the bond
Lattice enthalpy
a) write an equation for lattice enthalpy NaCl
energy needed to seperates the ions and the entahlprt change is positive
Describe the relationship between bond strength and length
- bond length increases down the group
- Bond length decreases as the number of electron pair increases because there will be a greater attractive force between
the two nuclei - bond strength increase up the group
- Bond strength increases as the number of electron pair increases as more energy is required to break them
Rules to Expanded octect
rules to drawing the lewis diagram
- (desired number of electrons - actual number)/2= # lone pairs
- draw the central atom by using the least electronegative electron
- complete the octect
desired number of hydrogen= 2
actual e= # valence electron
desired e= valence electrons + extra set of theoritical lone pair
rules for drawing polyatomic ion
- (desired number of electrons - actual number+charge number)/2= # lone pairs
- draw the central atom by using the least electronegative electron
- complete the octect
- check for resonance strucure
*indivisual charge -ve/extra e are distributed to the surrounding atoms to make full valence electrons. Cooridnate dative bond is from the central atom to make bondings with the surrounding atom.
*charge +ve/ electron are removed from sourrounding atoms, therefore central atom needs to donate an coordinate bond. You need to draw an arrow indicating where the coordinate bond came from.
2)Draw an resonance structure of sulfate SO42-
3)find its bond order
Draw
a) BeCl2
b) BF3
c)BF3NH3
- incomplete octect, they are electron deficient and have tendency to accept electron pair from NH2 or H20
Coordinate bond
- dative bond, covalent bond in which both the shared electrons are provided by one of the atoms.
Drawing expanded octect
1) number of valence electrons in the central atom is the number of bonds/surrounding atoms attached
find the bond order of C~O bond in CH3CO2-
- resonance strucure with bond order of 1.5
- shorter than single bond and longer than double bond
(#bond involved in coordinate bond)-(# atoms bonded)/2
Draw
a)NO2
No is an electron deficient central atom, 0.5 bond mean the central atom has radical.
Determine which molecule has the strongest bond: ethane, ethyne and ethyne
Electrogentive value for central atom
F>O>CL>N
Rules to drawing coordiante covalent bond
a) (NH4)+1
b)(H3O)+
c)CO
d)CH3OOH
e)HCOOH
6) CH3CH2COOH
- try using the HONC rule first
- if Honk rule dosent work then that means there is coorindate bond
- put electrons away from each other
- look at the functional group to identigy the structure, eg:COOH, OH
- make sure to put lone pairs of electron in atoms that does not meet the desired number of electrons
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electron domain
Describes the number of electrons in the valence shell. They may be occupied by lone pairs, single, doubleor triple bonds. Includes number of bonding pairs and non-bonding pairs surrounding the central molecule
Draw
a) Mgcl2
b)AlCl3
Al2O3
VSEPR theory
lone pair – lone pair > lone pair – bonding pair > bonding pair – bonding pair
draw
a) XeF4
b)XeF2
intermolecular force
Van der waals
- lone disperion force: all molecules, weak attraction between non-polar electron
- Dipole-induced force: induces non polar to become temporary dipole
- Dipole-dipole force: permanent dipole/polar molecules
- hydrogen bond:F,O,N——H
- intermoleulcar force depends on electronegativity difference.
What factor that increases the strength of intermolecular force
- down the group, larger number of electrons, decreases electron density (larger), stronger london dispersion force➱ higher boiling/melting point/lower volatility
- increased molar mass/size
- extent of polarity within the molecule
What causes increases in bond polarity?
Electronegativity (larger difference between partial charges) across period/up the group: higher nuclear charge but same sheilding or less electron shell therefore high electron affinity, shared electrons with stronger attraction to the nucleus of the opposite atom, increased electronegativity/dipole moment, will cause unsymmetrical shape and show ionic
Benzene
*C6H6
* delocalized pi electron spread equally through the ring.
* carbon-carbon bond have intemediate bond strength and length between single and double bond
* resonance structure that provides stabillity, unreactive
1)draw ozone resonance strucure
2) describe the strength and length bonds of ozone
3) what makes causes double bonds in ozone
- resonance hydride have delocalized elecrron to be shared in more than on bonding position to make double bond.
- It has intermediate bond strength and length between single and double bond
- The double bond is composed of a sigma (σ) bond from the overlap of
hybrid orbitals, and a pi (π) bond from the overlap of unhybridized p orbitals. The electrons in the pi bond are less tightly held so become delocalized through the structure, giving rise to the resonance forms
allotropes of carbon
different form of an elemet in the same physical state
State the type of intermolecular force involved in CH3OCH3 and C3H8
melting and boiling points of polar compounds to be higher than those of non-polar substances of comparable molecular mass.
Hydrogen bonding
- attatched to fluorine, nitrogen, or oxygen causes large electronegativity difference
- small size no shielding, the hydrogen now exerts a strong attractive force on a lone pair in the electronegative atom of a neighbouring molecule
- two hydrogen atoms in each molecule and the two lone pairs on the oxygen atom, each H2O can form up to four hydrogen bonds with neighbouring molecules
Solubility of molecular compoud
- Non-polar substances are generally able to dissolve in non-polar solvents by the formation of London dispersion forces between solute and solvent
- Polar covalent compounds are generally soluble in water by dipole interactions and hydrogen bonding
- ionic: must become molten state
- molecular: depends on polarity/electronegativity difference
- Giant covalent: insoluble
Fill out the physical properties of ionic compound and covalent compounds
Explain the bonding strucure of sillicion dioxide
- tetrahedral in giant lattice strucure that involved all four sillicon valence electrons
- each si atom is covalently bonded to four O atoms and each O to two Si atoms
What are the physical properties of sillixion
- strong
- insoluble in water
- high melting point
- non-conductor of electricity.
1)Explain why H2O, HF and NH3 have higher boiling points
2) Explain why boiling point increases from peiroid 3
1) hydrogen bonds
2) increased number of electrons as you go down the group
Metallic bonding
electrostatic attraction between sea of delocalized electron and postive cations
What impacts the strength of metallic bonds
- number of delocalized electrons
- charge of the cation
- radius of the cation
a) Does Mg or Na have higher boiling point?
b) Does Na, K or Rb have higher melting poin?
a) Na (98ºC) < Mg (650ºC)
Mg has greater number of delocailized electron and smaller cations causing stronger metallic bond strength
b) Na (98ºC) > K (63ºC) > Rb (39ºC
decrease down a group as the size of the cation
increases, reducing the attraction between the delocalized electrons and the positive charges
Why does transitonal elements have strong metallic bonds?
e large number of
electrons that can become delocalized, from both 3d and 4s sub-shells
What are the physical properties of metallic bonding
Alloyes
- Contain more than one metal and have enhanced peroperties
- Alloys have non-directional nature of the delocalized electrons, and the lattice can accommodate ions of different size, harder for positive ions to slide ove each other preventing bending
- Alloys are often more chemically stable, stronger and more resistant to corrosion
Name the components to steel, stainless steel, brass and bronze
sigma bond (σ)
direct head-on/end-to-end overlap of atomic orbitals, resulting in electron density concentrated between the nuclei of the bonding atom
pi bonds
sideways overlap of atomic orbitals, resulting in electron density above and below the plane of the nuclei of the bonding atom
Exceptions to the octect rule
-small atoms like Be and B form stable molecules with fewer than an octet of
electrons.
- atoms of elements in Period 3 and below may expand their octet by using d
orbitals in their valence shel
Hydridization
mixing atomic orbitals to form new hybrid atomic orbitals of intermediate enrgy
1)Describe the hydrization of carbon
2)draw the hydrization electron configuration
A) Ecitation occurs in which an electron is promoted within the atom from the 2s orbital to the vacant 2p orbital. The atom now has four singly occupied electrons for bonding
SP3
- four hydrization between 1 s and 3 p oribtals
- forms four single bond
- 109.5 tetrahedra
- makes four sigma bonds
Double covalent bonds contain
one sigma bond and one pi bond. Triple covalent bonds contain one sigma bond and two pi bonds.
Sp2
- three hydridization between one s and 2 p electrons, one unhydrizied p oribtal
- 120 triangular planar
- 1 pi bond one sigma bonds
- shown in double bonds
Double covalent bonds contain
one sigma bond and one pi bond. Triple covalent bonds contain one sigma bond and two pi bonds.
SP
- two unhydridized p orbital, two sp hybrizied oritals
- 180 linear shape
- triple bonds
- two sigma bonds, 2 pi bonds
Kienetic energy formula of ionix compound
Describe the physical properties and bonding strucure of diamond, graphite, graphene and fullerene.
Fill out the bond angles
Explain the structure, electrical/thermal conductivity and physical properties of diamond
- Each C atom is sp3 hybrizied and covalently bonded to 4 other tetrhedrally arranged in a regular repetitive pattern with bond angels of 109.5
- no conductor as there are no delocalied eletrons as it is used for covalent bonds
- good thermal conductor
- hardest, and high melting point
- used for jewllery and cutting glass
Explain the structure, electrical/thermal conductivity and physical properties of fullerene
- C atom in sp2 hybridized and bondded in a sphere of 60 carbons (12pent, 20 hex) bonded to 3 other carbons (no fixed formula)
- poor electrical conductor as molecules have delocalized electrons, there is little electrons movement between molecules
- low thermal conductivity
- light and strong, makes reacts with K to make superconducting crystalline material with low melting point
- used for medical field and nanotubes
Explain the structure, electrical/thermal conductivity and physical properties of graphite
- each C atoms is sp2 hybrized and covaently bonded to 3 others forming hexagons with parrallel layers with bonded angle of 120. the valence electrons is delocalized and moves freely across the later. The layers london dispersion force allowing to slide over each other
- The covalent bonds within the layers are very strong, the LDF is weak between laters
- good conductor of electricity
- bad therm conductor as long as heat can be forced to conduct in a direction parrallel to the crystal later
- soft and slipperly, brittle, high melting point
- pencils, lubricants
Explain the structure, electrical/thermal conductivity and physical properties of graphene
why are metallic bonds mealiable
metallic bonds are non-directional. layer of cation can slide over each other and change shape without dirupting bonding
