Chem Quiz - chemical bonding and structures
Driving force for each atom is....
to gain a noble gas electron configuration
Ionic bonds
Electrostatic attraction between oppositely charged ions
Ionic compound structure
Lattice. Made of repeating units of positive and negative ions called unit cells. Their formulas are ratios of ions in their smallest ratio (empirical formula) and are known as the formula unit (ex. NaCl)
Loses an electron
Oxidized (metals)
Gains an electron
Reduced (non-metals)
Metals vs Non-metals noble gas configuration
Metals want to achieve the configuration of the noble gas in the period above
Non-metals want to achieve the configuration of the noble gas in its period
NH₄⁺
Ammonium
OH⁻
Hydroxide
NO₃⁻
Nitrate
HCO₃⁻
Hydrogencarbonate (bicarbonate)
CO₃²⁻
Carbonate
SO₄²⁻
Sulfate
PO₄³⁻
Phosphate
Intramolecular force
The force that holds the atoms in a molecule or ionic compound together (forces between atoms or ions). Electrostatic attraction +/-
Lattice Enthalpy
Energy needed to sperate ions represented by a positive number (energy used). Same amount of energy that is released when two ions combine. Higher enthalpy, stronger bond
Factors that affect lattice enthalpy
- increase in ionic charge increases lattice enthalpy
- increase in ionic radius of one ion decreases lattice enthalpy
- larger charge density greater lattice enthalpy
Melting/Boiling point
decreases as the atomic radius decreases. molecules need a very large amount of kinetic energy to break away from each other. The higher the charges, the higher the melting/boiling point. All ionic compounds have a high one
Volatility
The tendency of a substance to vaporize. Higher melting/boiling point, lower volatility.
Solubility
Maximum amount of solute that can dissolve in a given amount of solvent (water) to form a solution
Polarity
Occurs when two atoms have large differences in electronegativity
Ionic compounds in water
Very polar so they dissolve. The partial charges of water pull ions away from their lattice positions. They become surrounded by water and therefore hydrated. If the solvent isn't water we can use the term solvated.
Brittle Ionic Lattices
If you move a layer of ions, you'll get ions of the same charge next to each other. The layers repel each other and the crystal breaks up
Electrical Conductivity
Movement of electrons. Substance can only conduct electricity if charges can move independently of one another.
Solid ionic compounds do not conduct electricity cause they are strong together.
Molten ionic compounds do conduct electricity cause they have more freedom in a liquid
Solutions of ionic compounds in water do conduct electricity because the water breaks up the structure so that the ions are free to move around.
Ionic character
Cesium and fluorine show the most ionic character because cesium has the lowest Zeff and fluorine the highest. Ionic character with an anion decreases as you go across period 3. Eventually, the compound will become molecular.
Ionic character and electronegativity
The larger the difference in electronegativities between two bonded atoms, the more polar the bond. Ionic bond is when electrons completely attractive to one atom.
Percent Ionic character
- CsF is the most ionic compound and will have the largest electronegativity difference (3.2).
- % ionic character = difference in electronegativity / 3.2.
- Ionic: electronegativity difference > 1.8
- Covalent: electronegativity difference << 1.8
- Polar covalent compounds: 0 < electronegativity difference < 1.8
Bond strength
More bonds = Stronger bond
More bonds = Shorter bond
Determining polarity of a compounds
Electronegativity = X
△E = X higher - X lower
Polar covalent
Unequal sharing of electrons
Central Atom =
Least electronegative
Polar arrows
facing towards more electronegative ion/atom
Symmetry and polarity
if the dipole moments are symmetrical, then the vectors cancel out.
Polar:
Net dipole moments present, polarities don't cancel each other out and there is an unsymmetrical distribution of charge
Non-Polar
Not net dipole moment present, bond polarities do cancel each other out and there is a symmetrical distribution of charge.
Polar/Non-Polar Shapes
AB₃ = non-polar
AB₄ = non-polar
AB₂E = polar
AB₂E₂ = polar
AB₃E = polar
linear molecule (when more than two atoms) = non-polar
Bond polarity
Electronegativity difference between two atoms sharing electrons
Molecular polarity
Overall dipole moments
Allotropes
Different structural modifications of the same element
Graphite
Atoms covalently bonded and weak London dispersion forces (attraction of nuclei to electrons of other atoms)
Diamond
Each carbon bonded to four others. Tetrahedral geometry. Forms covalent network solid (lattice-like structure).
Graphene
Single planar sheet of carbon atoms in a hexagonal arrangement (only one atom thick).
Crystalline vs Amorphous
Crystalline Solids – Particles are arranged in a repeating pattern. They have a regular and ordered arrangement resulting in a definite shape.
Amorphous Solids – Particles are arranged randomly. They do not have an ordered arrangement resulting in irregular shapes.