Liaison chimique Flashcards
Define metallic bonds
Strong electrostatic forces of attract n btw cations and sea of delocalised electrons in giant metallic lattice structure
Explain the strength of metallic bonds
Generally strong and large amt energy needed to break such bonds
Strength of metallic bond is directly proportional to:
- no of valence e- contributed per atom
- charge density (charge of cation divided by radius of cation) of metal cation
Define giant metallic lattice structures
Such structures consist of cations in a sea of delocalised electrons held tgt by strong electrostatic forces of attract n
Name and expound on properties of giant metallic substances
- High mp, bp
bcos large amt energy required to overcome strong electrostatic forces of attract n btw cation and sea of delocalised e- - Good electrical/thermal conductor
bcos delocalised e- act as free mobile carriers to conduct electricity/heat - Malleable (hammer to sheets), ductile (drawn into wires)
Bcos when force is applied, layers of ions can easily slide over each other w/o breaking metallic bond.
Metallic bonds easily reformed & lattice can b restored
Name a use of metals
alloy formation
- metal tensile strength is increased due to presence of diff size of cations in metallic lattice inhibiting sliding
eg bronze made of copper & zinc
Define Ionic Bonds
strong electrostatic forces of attract n btw oppositely charged ions in giant ionic lattice structure
When drawing dot-and-cross diagrams, what is and is not required?
- Oni show valence e-
- Legend not needed
- alternate dot and cross for diff adjacent atoms/atom types
What is the relationship between magnitude of lattice energy and strength of ionic bond?
the greater magnitude lattice energy, stronger ionic bond within compound
magnitude of lattice energy is proportional to?
(q+ x q-)/(r+ + r-)
where,
+ is cation & - is anion
q is charge, r is radius
Strength of ionic bond is … to charge of ion and …ionic radius of ion?
directly proportional to charge of ion,
inversely proportional to ionic radius of ion
Define giant ionic lattice structures
such structures consist of oppositely charged ions held tgt by strong electrostatic forces of attract n
Explain physical properties of giant ionic lattice compounds
- High mp, bp
bcos large amt energy needed to overcome strong electrostatic attract n btw oppositely charged ions - Gd conductor of electricity in molten, aq state but non-conductor in solid state
bcos in molten, aq state, presence of free mobile ions conduct electricity
in solid state, ions can oni vibrate abt fixed positions, so no free mobile ions to conduct electricity - Generally soluble in polar solvents eg water, insoluble in non-polar solvents
eg
- soluble in water means,
energy released in forming strong ion-dipole interact n btw ions & water enough to overcome ionic bonding btw cations and anions in crystal lattice
- insoluble in non-polar solvent means,
due to absence of strong solute-solvent interact n, inadequate release of energy to overcome strong ionic bonding in crystal lattice - Hard and brittle
Hard:
bcos, as ionic solid, oppositely charged ions held tgt by strong electrostatic forces of attract n
Brittle:
bcos stress applied on ionic lattice cause sliding of layers of ions. So, ions of similar charges come tgt and resultant repulsion shatters ionic structure
Name a use of ionic compound
used a refractories able to withstand high temp due to high mp and chemical inertness
Define covalent bond
electrostatic attract n btw shared pair of e- and +vely charged nuclei
What are the types of covalent bonds? Describe them
sigma and pi bonds
sigma bond
formed when 2 orbital overlap head-on. e- density of sigma bond is concentrated btw nuclei of bonding atoms
pi bonds
- formed when two p orbitals overlap side-on. e- density in pi bond is concentrated above & below internuclear axis
- pi bond takes place when atoms form multiple bonds (double or triple bond), where one of these bonds must be sigma, the rest are pi bonds
What are types of sigma bonds?
- s-s overlap
eg H2
head-on overlap btw 2 1s orbitals of 2 H atoms - p-p overlap
eg F2
head-on overlap btw 2px orbitals of 2 F atoms - s-p overlap
eg HCl
head-on overlap btw 1s orbital of H atom and 3px orbital of Cl atom
What are types of pi bonds?
- Double bond (1 pi, 1 sigma)
eg O2 with p-p orbital side-on overlap between 2py orbitals - Triple bond (2pi, 1 sigma)
eg N2 with p-p orbital side-on overlap
of 2py and 2pz orbitals of 2 N atoms respectively
How to count no. of sigma and pi bond?
All single covalent bond oni hv 1 sigma bond. Double bonds and triple bonds form pi bonds after 1 sigma bond formed
Strength of covalent bond directly proportional to …?
Smaller atoms have …?
Larger orbitals …?
extent of orbital overlap,
greater extent of overlap btw orbitals,
r more diffused -> lower accumulation of e- density
Stronger covalent bond, …. bond energy
so bond … during chemical rxn
larger,
less easily breaks