Chemical Bonding Flashcards
What are chemical bonds?
Electrostatic forces of attraction that exist between particles
What is electronegativity?
Electronegativity of an atom is a measure of its ability to attract electrons in a bonds
How do electronegativity generally change across a period?
Increases across a period
How do electronegativity generally change down a group?
Decreases down a group
What bonds do large difference in electronegativity form?
ionic bonds
What bonds do small or no difference in electronegativity form?
covalent bonds (electronegative) or metallic bonds (electropositive)
What are metallic bonds?
Strong electrostatic forces of attraction between a lattice of positive metal cation and a sea of delocalised mobile valence electrons
What is the structure that has metallic bonds?
Giant metallic lattice structure
What is the nature of metallic bonds?
Non-directional
What are the factors that affect the strength of metallic bonds?
- charge and ionic radius of metal cation
- number of valence electrons metal atom has
How does charge and ionic radius affect the strength of metallic bonds?
- the greater the charge and the smaller the size of metal cation (greater the charge density)
- stroger the electrostatic forces of attraction between metal cation and delocalised mobile valence electrons
How does the number of valence electrons affect the strength of metallic bonds?
the larger the mass of valence electrons in the metal atom, the greater the charge of the resultant metal cation and the larger the number of declocalised valence electrons contributed into the sea of delocalised mobile valence electrons
What are ionic bonds?
strong electrostatic forces of attraction between cations and anions
What structure has ionic bonds?
Giant ionic lattice structure
What is the nature of ionic bonds?
Non-directional
What is coordinate number?
The number of oppositely charged ions surrounding an ion
What can ionic bond strength be deduced from?
lattice energy of an ionic compound
What is lattice energy?
Energy released when one mole of solid ionic compound is formed from its constitutent gaseous ions under standard conditions
What affects the magnitude of lattice energy?
- charges of cation and anion
- ionic radii of cation and anion
What is the formula for lattice energy?
LE ∝ |Z⁺ × Z⁻ / r⁺ + r⁻|
What are covalent bonds?
strong electrostatic forces of attraction between nuclei of each atom for the shared pair of electrons
What is separation between atoms a fine balance of?
- attraction of nuclei for shared electrons
- repulsion between electrons on each atom
- repulsion between positively charged nuclei of each atom
What is bond length?
distance between the nuclei of atoms involved in a covalent bond
How are covalent bonds formed?
- electrons involved are both unpaired electrons and located in higher energy orbitals
- electrons are shared such that each atom will attain noble gas configuration
What are the exceptions to duplet and octet rule?
- Molecules with central atom that has fewer than 8 electrons in its valence shell, central atom is electron deficient
- Molecules with central atom that has mroe than 8 electrons in its valence shell
Why can some atoms accomodate more than 8 electrons in its valence shell?
- expansion of octet occurs due to the presence of vacant, energetically accessible d orbitals
- in excited state electrons gain energy and is promoted to a higher energy orbital
What is a sigma bond?
Head-on overlap
What is a pi bond?
Sideways overlap
Is a sigma bond stronger or a pi bond stronger and what are the implications?
- sigma bond is stronger than pi bond due to more extensive overlap of orbitals in a sigma bond compared to a pi bond
- it is harder to break a single bond compared to one of bonds in double or triple bond
What are dative bonds?
Covalent bonds formed when an atom donates a lone pair of electrons into an empty orbital of an electron deficient atom for sharing
What happens to two molecules of AlCl₃ in gaseous state?
AlCl₃ monomers form co-ordinate bonds with each other to give rise to dimer Al₂Cl₂
What can the strength of covalent bond be deduced by?
bond dissociation energy
What is bond dissociation energy?
Enthalpy change when one mole of a particular covalent bond between atoms in a gaseous molecule is broken
What is the relationship between strength of covalent bond and bond dissociation energy?
The stronger the covalent bond, the greater the bond dissociation energy
What are the factors that affect the strength of covalent bond?
- effectiveness of orbital overlap
- bond multiplicity/order
- polarity of the bond
How does effectiveness of orbital overlap affect strength of covalent bond?
the larger the size of bonding atoms, the larger and more diffused the valence orbitals, the less effective the overlap of orbitals and the weaker the covalent bonds
How does bond multiplicity/order affect strength of covalent bond?
single bond < double bond < triple bond
When does a polar bond arise?
When the atoms contributing electrons to the covalent bond have a difference in electronegativities
Usually when will a covalent bond formed be polar?
When the covalent bond is formed between two different atoms with the exception of C and H, S and P, P and H, S and H (Please Have Common Sense)
How does polarity of the bond affect the strength of covalent bond?
- dipole moment results in ionic character in covalent bond
- it may increase or weaken the strength of bonds
What is giant covalent structure?
Atoms extensively bound together by strong covalent bonds
What are some examples of giant covalent structure?
Diamond (C), Si, SiO2, Graphite (C)
What is the bonding and structure like in graphite?
- In graphite, each carbon atom in the layer is bonded to 3 other carbon atoms via strong covalent bonds to form a hexagonal arrangement of carbon atoms
- The 4th valence electron of each carbon atom is delocalised between the layers of carbon atoms
- The layers are held together by weak instantaneous dipole-induced dipole forces
What are elements or compounds with simple covalent structure like?
- They consist of discrete molecules (covalent molecule with weak IMF)
- These molecules are held together by intermolecular forces that exist between them
- Within the molecules, the atoms of these discrete molecules are held together by strong covalent bonds
What is bond angle?
Angle between two bond pairs