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
How high are ionically bonded substances mp and bp? 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 conduct when solid)
What is simple molecular covalent bonding?
Strong covalent bonds between atoms, weak Van de 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 mpt and bpt? Why?
Low - weak van de 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 mpt and bpt ? 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 the structure of diamond
3D tetrahedral structure of C atoms with each C atom bonded to 4 others
Describe the structure of graphite
Similar to diamond but each atom is only bonded to 3 others so it is in layers
Weak van de Waals forces of attraction between layers allow them to Slide Over each other —> soft and slippery
One electron of each carbon is delocalised and can carry charge —> can conduct electricity
Describe metallic bonding
Lattice of positive metals ions strongly attracted to a sea of delocalised electrons. Layers slide over each other - malleable
Do metallic compounds have high mpt / bpt ? Why ?
High as strong forces of attraction between positive metal ions and negatively charged sea of delocalised electrons
Do metallic compounds conduct electricity ? Why?
Yes as delocalised electrons can move throughout the metal to carry charges
How does the strength of metallic bonding change across the periodic table? Why?
Increases - higher mpt and bpt, stronger
Higher charge on metal ions
More delocalised electrons per metal ion
Stronger forces of attraction between
Define electronegativity
The ability of an atom to attract a pair of electrons in a covalent bond
What affects electronegativity ? (3)
Atomic radius
Nuclear charge
Electron shielding
What is the most electronegative element?
Fluorine (F) - 4.0 on paulings scale
Largest nuclear charge for its electron shielding, smallest atomic radius
How do you get a non-polar bond?
Both bonding elements have the same electronegativity
When do you get a polar bond?
When both bonding atoms have different electronegativity
What is the strongest form of inter-molecular force?
Hydrogen bonding
What is the weakest form of intermolecular force?
Van de Waals forces
Describe Van de Waals forces of attraction
Temporary dipole is created by random movement of electrons —> induces dipole in neighbouring molecule —> temporary induced dipole dipole attraction aka Van de Waals forces of attraction
Are Van de Waals forces greater or smaller in 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 the dipoles 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, F and N are highly electronegative, H nucleus is left exposed
Strong force of attraction between H nucleus and lone pair of electrons on O, F or N of a neighbouring molecule
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 positions; this makes them slightly further apart than in water, making ice less dense than water
What is a dative/ coordinate covalent bond? When is it formed?
Formed when an electron deficient atom/ion accepts a lone pair of electrons from an atom with a lone pair of electrons (not used in bonding)
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 in lone pairs
What does the electron pair repulsion theory state?
That electrons will take up positions as far away from each other as possible, to minimise the repulsive forces between them
Which experience the strongest repulsion
Lone pair - lone pair
Lone pair - bonded pair
Bonded pair - bonded pair
LP-LP strongest repulsion
LP-BP middle repulsion
BP-BP weakest repulsion
What is the shape, diagram and bond angle in a shape with 2 bonded pairs and 0 lone pairs?
Linear
180 degrees
•—•—•
What is the shape, diagram and bond angle in a shape with 3 bonded pairs and 0 lone pairs
Trigonal planar
120 degrees
What is the shape, diagram and bond angle in a shape with 4 bonded pairs and 0 lone pairs?
Tetrahedral
109.5 degrees
What is the shape diagram and bond angle in a shape with 5 bonded pairs and 0 lone pairs
Trigonal bipyramid
90 and 120 degrees
What is the shape diagram and bond angle in a shape with 6 bonded pairs and 0 lone pairs
Octahedral
90 degrees
