3.1.3 Bonding Flashcards
What is ionic bonding?
Strong electrostatic forces of attraction between oppositely charged ions held in a lattice
Give an example of an ionically bonded substance
NaCl (sodium chloride - salt)
How high are ionically bonded substances’ boiling points and melting points? 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/in solution as the ions are free to move and carry charge (don’t when solid)
What is simple molecular covalent bonding?
Strong covalent bonds between atoms, weak van der Waals forces of attraction between 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 used in bonding and aren’t free to move.
Do simple molecular substances have a high/low melting point and boiling point? 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 macromolecular covalent bonding.
Lattice of many atoms held together by strong covalent bonds.
Do substances with macromolecular covalent bonds have high/low melting point and boiling points? Why?
High, as it takes a lot of energy to overcome many strong covalent bonds
Do substances with macromolecular covalent bonds conduct electricity?
Most don’t as all electrons are used in bonding.
Describe structure of diamond.
3D tetrahedral structure of C atoms, with each C atom bonded to four others.
Describe the structure of graphite.
- Similar to diamond - macromolecular covalent - but each carbon atom is only bonded to 3 others, so it is in layers
- Weak van der Waals forces of attraction between layers mean they can slide over each other -> soft, slippery
- one electron from each carbon is delocalised and can carry charge -> conducts electricity
Describe metallic bonding.
Lattice of positive metal ions strongly attracted to a sea of delocalised electrons.
Layers can slide over each other - malleable
Do metallic compounds have high/low boiling points and melting points? Why?
High as strong forces of attraction between positive metal ions and negatively changed sea of delocalised electrons.
Do metallic compounds conduct electricity? Why?
Yes as delocalised electrons can move throughout the metal to carry charge.
How does the strength of metallic bonds change across the periodic table? Why?
Increases -> higher melting and boiling points, stronger
- Higher charge on metal ions
- More delocalised electrons per ion
- Stronger force of attraction between them
Define electronegativity.
The ability of an atom to attract the pair of electrons (the electron density) in a covalent bond.
What affects electronegativity? (3)
- nuclear charge
- atomic radius
- electron shielding
What is the most electronegative element?
Fluorine (4.0 on Pauling’s scale) -> largest nuclear charge for its electron shielding, small atomic radius
How do you get a non-polar bond?
Both bonding elements have the same electronegativities.
When do you get a polar bond?
Bonding atoms have different electronegativities.
What is the strongest type of inter-molecular force?
Hydrogen bonding
What is the weakest type of inter-molecular force?
van der Waals forces
Describe 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 greater 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 bond, lone pair of electrons on O, F, N
- Because O, N and F are highly electronegative, H nucleus is left exposed
- Strong force of attraction between H nucleus and lone pair of electrons on O, N, F
Draw a diagram of hydrogen bonding.
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 fixed position making them slightly further apart than in liquid water.
What is a 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 electrons
Draw the formation of a dative covalent bond in ammonia.
What does the shape of molecules depend on?
Number of electrons in the valence shell of the central atom.
What does the 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?
Lone pair-lone pair
Lone pair-bonded pair
Bonded pair-bonded pair
LP-LP repulsion strongest
LP-BP repulsion middle
BP-BP repulsion weakest
What is the shape and bond angle in a shape with 2 bonded pairs and 0 lone pairs?
Linear
180°
What is the shape and the bond angle in a shape with 3 bonding pairs and 0 lone pairs?
Trigonal planar
120°
What is the shape and bond angle in a shape with 4 bonded pairs and 0 lone pairs?
Tetrahedral
109.5°
What is the shape and bond angle in a shape with 5 bonded pairs and 0 lone pairs?
Trigonal bipyramid
90° and 120°
What is the shape and bond angle in a shape with 6 bonded pairs and 0 lone pairs?
Octahedral
90°
