Bonding Flashcards
Define electronegativity:
power of an atom to attract the bonding pair of electrons towards itself in a covalent bond.
Describe the:
* bonding
* structure
of: NaCl and ice. In each case draw a diagram showing how each structure can be represented. Explain, by reference to the types of bonding present, why the melting point of these two compounds is very different. (12)
- NaCl is ionic
- giant ionic lattice
- ions placed correctly
- electrostatic attraction between ions
… - covalent bonds between atoms in water
- hydrogen bonding between water molecules
- tetrahedral representation showing two covalent and two hydrogen bonds
- 2 hydrogen bonds per molecule
… - attraction between NaCl ions is very strong
- covalent bonds are very strong
- hydrogen bonds between water molecules in ice are much weaker
… - consequently, less energy required to break hydrogen bonds in ice to form seperate water molecules than to break ionic bonds in NaCl and make seperate ions
Explain the low melting and boiling point of simple molecular substances (halogens):
- non polar molecules because of same electronegativity
- only have Van der Waals forces acting between molecules
- weak attraction easily broken
Explain the shape of a PCl3 molecule:
- 4 areas of electron density
- 3 bonding pairs, 1 lone pair
- electrons repel e/o to be as far apart as possible to minimise repulsion, lone pairs repel more than bonding pairs
- trigonal pyramidal shape
- 107 bond angle
Factors that affect strength of metallic bonding:
- Number of protons/ Strength of nuclear attraction.
The more protons the stronger the bond - Number of delocalised electrons per atom (the outer shell electrons are delocalised)
The more delocalised electrons the stronger the bond - Size of ion. The smaller the ion, the stronger the bond.
Properties of giant ionic lattices:
- High mp and bp: strong electrostatic forces of attraction between oppositely charged ions require a lot of energy to overcome. The higher the charge the stronger the attraction
- Soluble in water ➜ when ionic compound dissolved in water, a polar molecule, it surrounds the ions and can overcome the elec.stat. forces of attraction.
this is why many ionic compounds can dissolve in polar solvents. - when the charge increases, solubility decreases bcs polar water molecules can’t overcome attraction
- don’t conduct elec. when solid ➜ ions locked in place by attraction, not free to carry charge
What is Dative Covalent bonding:
A dative covalent bond forms when the shared pair of electrons in the covalent bond come from only one of the bonding atoms.
explain how the strongest type of IMF in liquid HF arises
- large difference in electronegativity betw/ H & F
- F most electronegative
- H+ — F- dipole created
- attraction formed betw H+ & lone pair of electrons of F
- (draw diagram of two molecules)
VdW only applies to
simple covalent molecules
electronegativity only applies to
covalent bonding
VdW =
induced dipole-dipole
For small molecules with the …………., permanent dipoles are ………… dipoles
For small molecules with the same number of electrons, permanent dipoles are stronger than induced dipoles
intramolecular
forces acting within a molecule
Hydrogen bonding is a type of
permanent dipole – dipole bonding
explain how h bonding in liquid HF arises
- large difference in electronegativity between H and F
- H+ and F- dipole created
- attraction formed between H+ and lone pair of F-
VdW increases with
increasing atomic mass (Mr)
explain why MgO has higher boiling point than MgCl2 and Mg
- Mg -> has metallic bonding, giant metallic lattice structure
- electrostatic forces of attraction betw/ +ve ions and sea of delocalised electrons
- MgO & MgCl2 -> has ionic bonding, giant ionic lattice structure
- many strong electrostatic forces of attraction betw/ oppositely charged ions
- ionic bonds stronger than metallic bonds
- ionic bond require more energy to overcome than metallic bonds
- ionic bonds in MgO stronger than in MgCl2
- because O2- ions have greater charge density than Cl- ions
- so stronger attraction betw/ Mg2+ and O2- than Mg2+ and Cl-
trigonal pyramidal bond angle
107
define relative atomic mass
the average mass of an atom of an element relative to one twelfth of the mass of an atom of carbon-12
define relative molecular mass
the average mass of a molecule relative to one twelfth of the mass of an atom of carbon-12
Because alcohols form hydrogen bonds with water, they tend to be relatively soluble in water.
The hydroxyl group is referred to as a hydrophilic (“water-loving”) group, because it forms hydrogen bonds with water and enhances the solubility of an alcohol in water.
The second ionization energy is always larger than the first ionization energy,
because it requires even more energy to remove an electron from a cation than it is from a neutral atom.
How does molecular weight affect boiling point?
In the ABSENCE of other intermolecular force, the higher the molecular mass the greater the boiling point.
intermolecular forces
which molecule has the highest boiling point?
* HI
* HCl
* HF
* HBr
- HI has highest molecular weight
- HOWEVER, HF has hydrogen bonding present, strongest intermolecular force means highest boiling point
VdW forces exist betw/ all molecules. Why? (3)
- as electrons are always moving, at any moment in time a temporary dipole dipole could occur
- this can induce a dipole in a neighbouring molecule
- these partial +ve and -ve charges attract each other
why does graphite have such a high boiling point?
- layers of C atoms
- connected by covalent bonds within each layer
- vdW betw/ layers
- many strong covalent bonds need to be broken
Bromine (Br2), strontium chloride (SrCl2) and iodine monochloride (ICl) all have similar Mr values.
Suggest, with reasons, the order of melting points for these three substances. (6)
- SrCl2> ICl > Br
- SrCl2 strong ionic bonds / (strong electrostatic attraction between opposite ions)
- Lattice so many strong bonds to overcome
- ICl has dipole-dipole between molecules – weaker than ionic bonds
- Br2 has van der Waals forces between molecules – much weaker
Phosphorus exists as;
P4
Silicon tetrafluoride (SiF4) is a tetrahedral molecule.
Deduce the type of intermolecular forces in SiF4
Explain how this type of intermolecular force arises and why no other type of intermolecular force exists in a sample of SiF4: (3)
- Van der Waals forces
- (Uneven distribution of electrons in) one molecule induces dipole in neighbouring/another/nearby molecule
- symmetrical molecule / dipoles cancel
State the trend in melting points of the elements down G2 from Mg to Ba. (3)
- Trend: decreases
- Explanation: Metallic bonds weaker
OR weaker attraction between ions (or nuclei) & delocalised electrons - Atoms (ions) larger
Describe the bonding in metals. (2)
- Lattice of metal / +ve ions/ cations / atoms (1)
- (Surrounded by) delocalised electrons (1)
Which element has highest melting point in Period 3 (4)
- Si
- forms giant covalent, macromolecular structure
- covalent bonds
- many strong covalent bonds need lots of energy to break
