Ionic Molecular Bonding Flashcards
What is the Aufbau Principle?
That each electron in ground states occupy orbitals in order of increasing energy level
Explain the Pauli Exclusion Principle:
An orbital cannot hold more than two electrons and electrons occupying orbital must have opposite spins
Explain Hund’s rule:
Orbitals in a subshell must be occupied signly with parallel spins before they can be occupied in pairs
Why does atomic radii increase down the group?
As number of protons increase, effective nuclear charge increases. Down the group, increases by one electron shell, thus shielding effect increases. Shielding effect increases more than effective nuclear charge, resulting in nucleus exerting weaker pull on valence electrons
Why does atomic radii decrease across a period?
Nuclear charge increases due to increase in number of protons, resulting in stronger electrostatic forces of attraction between nucleus and valence electrons, while shielding effect remains relatively constant. Outermost electrons pulled closer to the nucleus
What are physical properties of ionic compounds?
High melting and boiling points, soluble in water, conducts electricity in molten and aqueous state and is hard, rigid and brittle
What is the formula for lattice energy?
Product of charges / Sum of ionic radii
Explain why ionic molecules are soluble in water:
Each ion on the crystal’s surface attract oppositely charged poles of polar water molecules. Ion dipole interactions result in the ions being hydrated, which releases energy, and results in ionic crystal structure breaking down and solid dissolving
Why do ionic compounds not conduct electricity in their solid states?
The ions are fixed in positions and aren’t free to move in molten and aqueous solutions. In molten and aqueous solutions, ions are mobile acting as charge carriers
Why are ionic compounds brittle?
When sufficient pressure is applied, ions of like charge are brought next to each other, and the repulsive forces crack the salt suddenly
Describe metallic bonding:
Has a giant metallic lattice containing array of ions, with sea of delocalised electrons that are bonded to the cation.
Why do metals conduct electricity?
Delocalised electrons in the metallic lattice act as charge carriers to conduct electricity
Why are metals good conductors of heat?
The delocalised electrons in metal disperse the heat quickly from region of higher temperature to lower. More energetic electrons collide and speed up the slower less energetic molecules
Why are metals malleable and ductile?
When external force applied, layers of metal ions slide past one another. Although shape changes, metal does not break because sea of electrons prevents repulsions among cations
Why are alloys harder?
Alloying makes metals harder as atoms of added metal have different size, which will disrupt the orderly arrangement of metal atoms that can no longer slide over each other.
What is band length?
Distance between 2 nuclei when the covalent bond is formed
What are the different types of bonds in covalent bonds and their shapes?
Sigma and Pi bonds. Sigma bonds (only p or d orbitals) is round and head on overlap, whereas bonds are shaped like a hourglass and have side on overlap
Define Electronegativity.
Relative ability of atom to attract the shared electrons in a covalent bond
What are the criteria for electron-deficient molecules or expansion of octet?
Only central atom is allowed to have fewer or more than 8 electrons (ie. peripheral atoms must have full octet). Only atoms with period 3 onwards can have expansion of octet, as they have vacant d-orbitals.
What are radicals/odd electron species and their characteristics?
They are molecules that contain an odd number of valence electrons, and extremely reactive. Usually have group 5 or 7 as the central atom. Examples: ClO2, NO2
What are dative/coordinate bonds?
They are bonds formed when one atom donates a lone pair to another atom with a vacant orbital. Denoted by arrow in Lewis Structure. Usually formed between electron deficient species and molecule with lone pair
What are the names for bonds between 2, 3 and 4 electron groups without lone pair?
2 electron groups: Linear (eg. CO2)
3 electron groups: Trigonal Planar (eg. CO3)
4 electron groups: Tetrahedral (eg. CH4)
What are the names for bonds between 2, 3 and 4 electron groups with lone pair?
2 bonds/1-2 lone pair: Bent/V shaped (eg. SO2, H2O)
3 bonds/1-2 lone pair: Trigonal Pyramidal (eg. NH3)
What is delta minus and delta plus?
Delta minus denotes a partial negative charge due to the build up of electron density around the more electronegative atom, whereas delta plus acquires a partial positive charge.
What are non-polar and polar bonds?
In non-polar bonds, electrons are shared equally (eg. Cl2), with net-dipole charge of 0. Whereas in polar bond, there is unequal sharing of bonding electrons due to differences in electronegativity of atoms (eg. HCl)
Which covalent molecules have partial ionic character?
A polar covalent bond is said to have partial ionic character.
What are ionic bonds with covalent character?
These molecules are ones with have large different in polarising power. The attraction on the anion’s electron cloud may be strong enough to distort it such that there is partial sharing of electrons from the covalent bond
What is polarity?
Polarity is the separation of positive and negative charge
What is Fajan’s Rules?
- Bonding tends to be covalent if the charges on both cation and anion are large.
- Bonding tends to be covalent if the cation is small and the anion is large.
What intermolecular forces exist between polar molecules?
Hydrogen Bonds (strongest, 5% covalent bond), permanent dipole permanent dipole (pdpd) interactions (1% covalent bond)
What intermolecular forces exist between non-polar molecules?
Dispersion Forces
What factor affects PDPD interactions?
- Dipole moment (greater the dipole moment, stronger the pdpd interactions)
What are the criteria for hydrogen bonding?
- Hydrogen atom bonded to either N, O or F molecules
2. Lone pair present
Describe the formation of dispersion forces:
In an atom, since the electrons are constantly moving, it sometimes results in an instantaneous (temporary) dipole as electron cloud becomes distorted. This can induce a dipole in neighboring molecule, and the electrostatic forces of attraction between the fluctuating dipoles are called dispersion forces
What are the factors affecting dispersion forces?
- Size of electron cloud (measure of the ease which electron cloud can be polarized, thus the greater electron cloud size, stronger the dispersion forces)
- Molecular Shape (when a molecule has higher surface area, it allows for more points of contact for polarizability, allowing for stronger forces)
What are covalent molecules soluble in?
Covalent molecules are soluble in organic solvents such as propanone, benzene. Only some are soluble in water.
Describe the covalent bonding in Diamond:
- Giant molecular structure, 3D covalent network
2. Each C atom tetrahedrally bonded to 4 other C atoms
Describe the covalent bonding in Graphite:
- Giant molecular structure, 3D covalent network
- Made of individual flat layers of carbon atoms arranged hexagonally
- Each carbon atom is bonded to 3 other carbon atoms
- Fourth valence electron delocalised throughout the layer, overlapping with each other sideways to form pi bonding throughout sheet of atoms
- Dispersion forces between the layers
