Unit 1: Section 3 - Bonding
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What is ionic bonding?
Strong electrostatic forces of attraction between oppositely charged ions held in a lattice
How high are ionically bonded substances’ bp and mp? Why?
High - takes alot 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 (doesn’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 are used in bonding and aren’t free to move
Do simple molecular substances have a high/low mpt and bpt? 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 mpt and bpts? Why?
High - it takes alot 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 - macromolecular covalent - but each C 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 carry charge - conducts electricity
Describe metallic bonding
Lattice of positive metal ions strongly bonded to a sea of delocalised electrons Layers can slide over each other - malleable
Do metallic compounds have high/low bpt and mpts? Why?
High - 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 charge
How does the strength of metallic bonds change across the periodic table? Why?
Increases * Higher melting and boiling points * Higher charge on metal ions * More delocalised electrons per ion * Stronger force of attraction between them
What is the definition of electronegativity?
The ability of an atom to attract the pair of electrons (the electron density) in a covalent bond
What 3 things affect electronegativity?
• Nuclear charge • Atomic radius • Electron shielding
What is the most electronegative element?
Fluorine - 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 intermolecular force?
Hydrogen bonding
Describe van der Waals’ forces of attraction
Temporary dipoles are created by the random movement of electrons -> induces dipole in neighbouring molecules -> temporary induced dipole-dipole attraction aka van der Waals forces of attraction
What is the weakest type of intermolecular force?
van der Waals forces