2. Bonding and structure ( METALLIC) Flashcards
What is metallic bonding
The strong electrostatic force of attraction between positive metal ions (cation) and the delocalised electrons
What is a cation
a positive ion
–> metals will always loose electrons (never gain) to form a full outer shell
What is an anion
a negative ion
What structure do metals with metallic bonding form
A giant metallic lattice structure
Give and explain the 4 properties of metals
1) high melting points - strong electrostatic forces between ions and electrons
2) can conduct electricity due to sea of delocalised electrons as they are free to move and carry a charge through the structure. Good conductors of thermal energy as well
3) malleable - positive ions are identical and so layers can slide over each other without disrupting electrostatic attraction
4) Ductile, insoluable
Give the 2 main properties that affect the strength of metallic bonds so therefore melting points of metals
1) Size of charge - greater charge, greater number of delocalised electrons per atom
more charge = stronger due to attraction of nucleus and delocalised electrons
2) size of ion
smaller = stronger. Smaller ions are packed more closely together
What determines the number of delocalised electrons in a metal? and what determines the number of delocalised electrons per ion?
The number of electrons it has on its outer shell determines the number of delocalised electrons
The charge number = the number of delocalised electrons per ion. Eg: Ca 2+ has 2 delocalised electrons per cation
What is the weakest part of a metal
The gaps between the boundaries of the crystals
What happens when the crystals in metals are heated then cooled quickly
The size of the crystals decreases leading to big gaps between them. This causes the metal to be brittle and break when bended
What happens when the crystals in metals are heated and cooled slowly
The size of the crystals increases so smaller gaps and closer fitting boundaries. The metal only bends not breaks
What is bond enthalpy linked to
The length of a bond
Give the relationship between bond length and bond enthalpy
shorter bond length = larger bond enthalpy
What is bond length
The distance between the nucleis where the attractive and repulsive forces balance
Give the relationship between electron density and bond length
HIGHER electron density means more electrons in the bond so stronger attractive forces between electrons and nucelus. This means there is a SHORTER bond length as atoms are pulled closer together.
Describe the bond enthalpy of C-C compared to C=C
C=C has a double covalent bond so greater electron density. This means there is a shorter bond length so higher bond enthalpy then C-C
