Chemical Bonding (without Giant molecular and simple molecular structures) Flashcards
Define a metallic bond
Metallic bond refers to the electrostatic attraction between a lattice of positive ions and a sea of delocalised electrons.
What are the factors that affect the strength of metallic bonds?
Number delocalised electrons:
More delocalised electrons released by the metal, stronger their electrostatic forces of attraction.
Charge density of metal cation (Charge/density):
Cations with larger charge will attract electrons more strongly. In addition if the cationic radius of the metal cation is smaller, the delocalised electrons will be closer to the nucleus, and are more strongly attracted. Hence metal cation with higher charge density will exert a greater electrostatic attraction to the sea of delocalised electrons, resulting in stronger metallic bond.
Describe the structure of ionic compounds and define an ionic bond.
Ionic compound have a giant ionic lattice structure consisting of oppositely charged ions that are arranged in a regular lattice. Ionic bond is defined as the electrostatic attraction between oppositely charged ions.
Physical properties of Metals
Good conductors of electricity in both solid and molten states as the mobile delocalised electrons act as charge carriers.
Ductile and malleable as layer of cations can glide over another readily without breaking the metallic bond to maintain electrostatic forces of attraction between metal cations and sea of delocalised electrons.
What are the factors affecting the strength of ionic bonds?
Strength of ionic bond is related to the related lattice energy of the ionic compound and hence depends on Charge and ionic radius of ions.
Lattice energy is the energy released when 1 mole of solid ionic compound is formed from its constituent gaseous ions.
Lattice energy = (charge cation x charge anion)/(Ionic radius of cation + Ionic radius of anion)
Charge factor is more important factor than size factor.
What are the physical properties of Ionic compounds?
High melting/boiling point
Conducts electricity in the molten and aqueous state but not in solid state as in molten and aqueous state oppositely charged ions are free to move hence act as charge carriers to conduct electricity.
Hard but brittle. Hard as ions are held together by strong forces of attraction between oppositely charged ions hence a lot of energy is required to overcome the electrostatic attractions. Brittle as ions are arranged in an orderly lattice of layered ions and thus it is possible to displace one layer of ions relative to the other layer, causing layers of similar charged ions to come together resulting in repulsion of like-charges.
Define a covalent bond
It is defined as the electrostatic attraction between the shared paid of electrons and the positively charged nuclei.
Describe how covalent bonds are formed.
Covalent bonds are formed when one or more pairs of electrons are shared between atoms, resulting in the formation of molecules and when 2 atoms move close enough together, interaction occurs between the valence electrons and the nuclei of the atoms resulting in sharing of electrons to achieve stable octet electronic configuration.
How is a sigma bond formed?
When 2 orbital overlap head-on.
How is pie bond formed?
When p orbitals of 2 atoms overlap sideways and can only be formed after a sigma bond is formed.
Is a pie or sigma bond stronger and why?
Sigma bond is stronger. Head-on overlapping of orbitals in sigma bond during the formation of a sigma bond is more effective than sideways overlapping of orbitals in a pie bond.
What is a Dative covalent bond?
It is a covalent bond whereby the shared paid of electrons is provided by only one of the bonding atoms. Represented by an ‘–>’.
How is dative covalent bond formed?
One atom must have a lone pair of electrons for donation while another atom must have an empty energetically accessible orbital to accept the pair of electrons.
Define bond energy of a covalent bond.
Strength of covalent bond is measured by its bond energy which is defined as the energy required to break 1 mole of of that covalent bond between 2 atoms in the gaseous state under standard conditions.
What are the factors affecting the strength of a covalent bond?
Number of bonds between atoms (as a whole):
An increase in numbers of bonds increases the number of shared electrons between two atoms.
Effectiveness of overlap of orbitals:
Larger orbitals are more diffuse so overlap is less effective resulting in weaker electrostatic attraction between shared pair of electrons and 2 positive nuclei resulting in weaker covalent bonds. Thus larger atoms tend to form weaker covalent bonds.
