1.3 - Bonding Flashcards
What ionic bonding?
Strong electrostatic forces of attraction between oppositely charged ions held in a lattice.
An example of an ionically bonded substance.
NaCl (sodium chloride - salt)
How high are ionically bonded substances’ bp and mp? Why?
High - takes lots of energy to break strong electrostatic forces of attraction between oppositely charged ions.
Do ionic compounds conduct electricity? Why?
Yes, when molten or in solution as the ions are free to move and carry charge but they don’t when they are solid.
What is simple molecular covalent bonding?
Strong covalent bonds between atoms, weak Van Der Waals forces of attraction between the molecules.
Are there any lone electrons in simple covalent bonding?
No - all involved in bonding.
Can simple molecular covalent molecules conduct electricity? Why?
No - all electrons are used in bonding so there aren’t any free electrons to move around.
Do simple molecular substances have a high/low MP and BP? Why?
Low - weak Van der Waals forces of attraction between molecules that don’t take much energy to overcome (these are overcome rather than covalent bonds).
Describe the macromolecular covalent binding.
Lattice of many atoms held together by strong covalent bonds.
Do substances with macromolecular covalent bonds have high/low MP and BP? Why?
High - it takes a lot of energy to overcome many strong covalent forces.
Do substances with macromolecular covalent bonds conduct electricity?
Most of them don’t as all the electrons are used in bonding.
Describet the structure of graphite.
- Similar to diamond - maromolecular covalent - but each C atom is only bonded to 3 others, so its in layers.
- Weak Van der Waals forced of attractions between layers which allows it to slide over each other -> soft, slippery.
- One electron from each carbon is delocalised and can carry charge -> conducts electricity.
Describe the structure of diamond.
3D tetrahedral structure of C atoms, with each C atom bonded to four others.
Define electronegativity.
The ability of an atom to attract the pair of electrons (electron density) in a covalent bond.
How does the strength of metallic bonds change across the periodic table? Why?
- It increases due to higher MP and BP.
- Its stronger.
- Higher charge on metal ions.
- More delocalised electrons per ions.
- Stronger forces of attractions between them.
What effects electronegativity? (3)
- Nuclear charge
- Atomic radius
- Electron shielding
DO metallic compounds conduct electricity? Why?
Yes as delocalised electrons can move throughout the metal to carry charge.
Describe metallic bonding.
Lattice of positive metal ions strongly attracted to a sea of delocalised electrons. Layers can slide over each other - malleable (can be formed into different shapes).
Do metallic compounds have high/low MP and BP? Why?
Both are high as strong forces of attraction between positive metal ions and negatively charged sea of delocalised electrons.
What id the most electronegative element?
Flourine - largest nuclear charge for its electron shielding, small atomic radius.
How do you get non-polar bonds?
Both bonding elements have the same electronegativities.
When do you get polar bonds?
When the bonding atoms have different electronegativities.
What is the strongest type of IMF?
Hydrogen bonding.
What is the weakest IMF?
Van der Waals.
Describe the Van der Waals forces of attraction.
Temporary dipoles are created by the random movement of electrons -> induces dipole in neighbouring molecule -> temporary induced dipole-dipole attraction aka van der waals forces of attraction.
Are Van der Waals forces stronger in smaller or larger molecules?
Larger - more electrons.
Describe permanent dipole-dipole attraction.
Some molecules with polar bonds have permanent dipoles -> forces of attraction between those dipoles and those of neighbouring molecules.
What conditions are needed for hydrogen bonding to occur?
- O-H, N-H or F-H, lone pair of electrons on O, F, N.
- Becaouse O, N and F are highly electronegative, H nucleus is left exposed.
- Strong force of attraction between H nucleus and lone oair of electrons on O, N, F.
Why is ice less dense than liquid water?
- In liquid water, hydrogen bonds constantly break and reform as molecules move about.
- In ice, the hydrogen bonds hold the molecules in fised positions; this makes them slightly further apart than in liquid water.
What is dative/ co-ordinate covalent bond? When is it formed?
Formed when an electron deficient atom/ion/ accepts a lone pair of electrons from an atom/ion with a lone pair of electons.
What does the shape of molecules depend on?
- Number of electrons in the valence shell of the central atom
- Number of these electrons which are bonded or lone pairs.
What does teh ‘Electron Pair Repulsion Theory’ state?
That electron pairs will take up positions as far away from each other as possible, to minimise the repulsive forces between them.
Which experience the most repulsion?
LP-LP
LP-BP
BP-BP
LP-LP: strongest repulsion.
LP-BP: middle repulsion.
BP-BP: Weakest repulsion.
