Chapter 2: Bonding Flashcards
What are the 3 types of IMF in increasing strength?
van der Waals (weakest)
dipole-dipole
hydrogen bonding
What are van der Waal forces?
- they exist in ALL molecules
- force of attraction
How do van der Waal forces work?
- at any point, more electrons on one side of atom than the other, so electron density is higher on one side
- this creates a temporary dipole which causes attraction between mol.
- the dipoles are temp. because electrons are always moving so dipoles can flip at any time
- this causes an overall effect of attraction
How do van der Waals and mp/bp change with size of molecule?
the larger the mol. = more electrons = stronger vdw forces, therefore, more energy is required to overcome the forces, so larger mol, have higher mp/bp
What state is butter at room temperature?
solid, made of saturated fats, straight chains
can pack more tightly together, stronger vdw
higher mp/bp
What state is olive oil at room temperature?
liquid, made of unsaturated fats, branched chains, do not lie close together, weaker vdw forces, less energy required to overcome, lower mp/bp
When do dipole-dipole forces occur?
When partial charges (delta +, delta -) are always present, due to the difference in electronegativities
forces of ATTRACTION between opp. charged ends of a dipole
When does hydrogen bonding occur?
attraction between lone pair of an O, N or F atom and δ + hydrogen
H must be bonded to O, N or F
ONF are electronegative, but H isn’t, so causes a polar bond
Why does water expand when frozen?
when undergoing freezing, more hydrogen bonds are being formed which leads to a regular, LATTICE structure which means water mol. are more spread out so it expands and has lower density than water
What is the trend of mp down group 6/7 when bonded to hydrogen?
H₂O and HF have H bonding so high mp as forces are very strong
then there’s a large drop because no hydrogen bonding is present
but then there is an increase, because down the group, the size of the mol. increases so stronger vdw forces
Suggest the strongest type of IMF between CCl₂F₂?
vdw - yes
dipole-dipole - yes
H bonding - no
answer: dipole-dipole
State the strongest IMF between methane?
no ONF so no hydrogen bonding
no halogens so no large diff. in electronegativities so no dipole-dipole
answer: dipole-dipole
Although phosphine mol. contain hydrogen atoms, there is no hydrogen bonding, suggest why?
H
H - P- H
Phosphorus is not very electronegative so not big enough of a difference of electronegativities between P and H for hydrogen bonding to occur
Do metals/nonmetals have large/small electronegativities?
metals typically have low electronegativity
non-metals typically have high electronegativites
What is ionic bonding?
bonds between metals and non-metals
it is the electrostatic attraction between oppositely charged ions acting in all directions,
forms a giant, ionic crystal lattice
What are the properties of ionic compounds?
- high mp/bp because lots of energy required to break strong electrostatic forces of attraction
- conducts electricity when molten, because ions become free to move and carry charge
- brittle- layers cannot slide over each other
What is covalent bonding?
the sharing of one or more pairs of electrons between non-metals
macromolecular
simple molecular
How does diamond bond?
each carbon of atom is covalently bonded to 4 other C atoms
How does graphite bond and what are its properties?
each C atom is covalently bonded to 3 C atoms, 1 delocalised electron per atom of C. arranged in LAYERS
-slippery- weak van der Waal forces between layers
Why do macromolecular substances have high mp/bp?
MANY. STRONG covalent bonds between all atoms
Do macromolecular substances conduct electricity?
no because there are no free electrons or mobile ions carry charge
What is the A-level rule for covalent bonding?
central atoms can promote electrons between orbitals in the same principal energy level
but this promotion requires energy
How can you tell how many covalent bonds the central atom will make?
number of unpaired e⁻ = number of bonds that atom can make
What is metallic bonding?
electrostatic attraction between positive central ions and negative delocalised e⁻
arranged in a regular lattice structure
What is a dative covalent bond/coordinate bond?
-when the shared pair of electrons in the covalent bond
come from only one of the bonding atoms
When is ionic bonding stronger?
when the ions are smaller and/ or have higher
charges
What is electronegativity?
the power of an atom to attract the shared pair of electrons in a covalent bond
How does metallic bond strength increase?
greater the charge of the ion, the stronger the metallic bonds because the ion is stronger so the electrostatic attraction to the delocalised electrons is stronger so more energy is required to overcome the forces of attraction
NHF₂ + BF₃ ——-> F₂HNBF₃
State the type of bond formed between N and B in F₂HNBF₃
Explain how this bond is formed?
dative covalent bond
lone pair from N is donated to B to form a dative covalent bond
Deduce when the bonding in nitrogen oxide is covalent rather that ionic?
this is because there is a small difference in electronegativity
Suggest why titanium can be hammered into different shapes and why these objects with different shapes have similar strengths
layers of ions can slide over each other
they have similar strengths because they have the same metallic bond
Explain why the mp of Al is higher than mp of Na?
Al has a greater charge and more delocalised e⁻ than Na therefore, it has a stronger force of attraction between the + ion and e⁻, requires more energy to break
