C2.2 Structure and properties Flashcards
What type of force holds ions together?
electrostatic forces between the atoms
Why do ionic compounds have high melting and boiling points?
there are strong bonds-strong electrostatic forces and lots of energy is required to overcome these
Why can ionic compounds conduct electricity when molten or dissolved in water?
because their ions (individually charged particles) are free to move around and can carry a charge through the liquid, in a solid they are in a fixed position
How strong are the forces between covalent molecules?
How does this affect their melting and boiling points?
the forces between simple molecules are weak
they have low melting and boiling points
Can substances made of simple molecules conduct electricity?
No - simple molecules have no overall charge, so they cannot carry electrical charge
Which covalently bonded substances have high melting and boiling points
substances with giant covalent structures
How strong are the forces between atoms in a covalent bond?
covalent bonds within a simple molecule are very strong
Why is graphite slippery and conducts electricity?
There are no covalent bonds between the layers allowing the layers to slide over each other
It conducts electricity because of the delocalised electrons along its layers
Why is diamond not soft and slippery?
the atoms in diamond have a different structure because all its carbon atoms form four strong covalent bonds
the atoms cannot slide and this makes diamond a very hard substance
What are delocalised electrons?
they are the outermost electrons in atoms that can roam away from where they cam, leaving an ion (in metals mainly)
Why do metals conduct electricity?
the delocalised electrons mean that electricity can pass through them quickly and easily-carrying a charge
Why can metals be bent and shaped?
we can bend and shape metals because the layers of atoms (or ions) in giant metallic structures/lattices can slide over each other
What is a shape memory alloy and a use for it?
S.M.As return to their original shaped when heated, after being deformed
Dentists use them in braces and doctors use them to hold bones in place while they heal
How are polymers classified?
Thermosetting and Thermosoftening
Describe thermosetting polymers
strong covalent bonds between chains, which form cross links
will not soften but will eventually char if heated very strongly
