CHEM BONDING Flashcards
Describe the structure of an ionic compound
A giant lattice structure consisting of oppositely-charged ions arranged in a regular pattern
Describe an ionic bond ITO (In terms of) EFOA (Electrostatic forces of attraction)
The electrostatic force of attraction between oppositely-charged ions
Factors affecting strength of ionic bond
(i) Magnitude of charge > (ii) interionic distance
Why are ionic compounds hard but brittle
A strong force is needed to overcome EFOA between oppositely-charged ions.
As oppositely-charged ions are arranged in regular pattern, displacing a layer of ions relative to another causes ions of similar charge to come together, losing EFOA.
Why are ionic compounds soluble in polar solvent but insoluble in non-polar solvents.
Ion-dipole interactions formed in polar solvents release sufficient energy to overcome forces of attraction between polar solvent molecules and ionic bonds.
Opposite is true in non-polar solvents.
What classes of covalent substances are there
(i) Giant molecular substancr
(ii) Simple molecular substance
Describe covalent bond ITO EFOA
A covalent bond is the strong EFOA between 2 positive nuclei and a shared pair of electrons
Describe structure of a giant molecular substance
It consists of atoms held by strong EFOA between their positively-charged nuclei and shared pair of electrons arranged in a 3-dimensional network
Why are simple molecules soluble in non polar solvents
IMF formed with molecules of non-polar solvents release enough energy to overcome IMF of solvent molecules and the molecules
What does bond length refer to
Distance between the 2 positive nuclei in a covalent bond
What is a sigma bond
A sigma bond refers to a covalent bond formed due to head-on orbital overlap
What is a pie bond
A pie bond refers to a covalent bond formed due to sideways-orbital overlap, which can only be formed after the atoms involved have formed a sigma bond
What is a dative bond
A dative bond is a covalent bond formed when an atom donates an available lone pair of electrons to an atom with an accessible empty orbital
What is a dimer
A dimer refers to a molecule consisting of a molecule bonded to an identical molecule
What is a transition metal complex ion
A transition metal complex ion is a transition metal ion able to be bonded to ligands due to the vacant low-lying d-orbitals in the transition metal ions
What are the factors determining covalent bond strength
(i) number of bonds
(ii) effectiveness of orbital overlap
Why do longer bond lengths lead to weaker covalent bonds
Longer bond length leads to more diffuse orbitals, which leads to less effective orbital overlap, and thus a weaker EFOA between positive nuclei
What are the 5 steps in making a ‘dot-and-cross’ diagram
- Find central atom
- Find out number of valence electrons present in the atoms involved
- Find out number of bonds needed for each atom to achieve stable conf.
- Draw out the lone pairs of electrons in central and surrounding atoms
- Ensure all atoms achieve octet configuration (or duet for hydrogen)
How do you find out which atom is the central atom in a ‘d-n-c’ diagram
The least electronegative atom
What are the exceptions of the octet configuration (aside from hydrogen)
(i) electron-deficient
(ii) radicals
(iii) expanded shells
What is the first postulate of VESPR theory
The first postulate states that the electron pairs arround the central atom are arranged as far apart as possible, in space to minimise repulsive forces between electron pairs
What is the second postulate of the VESPR theory
The second postulate states that the repulsion between lone-pair - lone-pair electrons are greater than in lone-pair - bond-pair electrons which is in turn greater than in bond-pair - bond-pair electrons.
What is the third postulate of the VESPR theory
The third postulate is that repulsion between bond-pair of electrons increases with an increase in the electronegativity of the central atom
What does the first postulate tell us about the basic shape of a molecule or ion
The first postulate tells us that the number of electron-pairs surrounding the central atom determines the basic shape of the molecule or ion. Additionally, the electrons in a multiple bonds are regarded as a single region of electron cloud as the electrons are localised between the atoms involved in the covalent bond.
What does the second postulate of VESPR tell us about the bond angles
The second postulate tells us that when a lone pair is present, the greater repulsive force exerted on adjacent bond-pairs would in turn cause a compression of bond angle
What does third postulate of VESPR theory tell us about bond angles
The third postulate tells us that when a more electronegative central atom is present, the electron cloud would be pulled in towards the atom to a greater extent, and hence result in a greater repulsive force experienced between bond-pairs as they are closer to each other. Hence bond angle is higher.
