Bonds & Crystals
3-D array of alternating positive and negative ions in an ionic compound
What is a crystal lattice?
Measure of the "pull" an atom has to attract a pair of bonding electrons.
What is electronegativity?
Draw the Lewis diagram for NaCl.
Teacher will correct.
Describe what a momentary dipole is and the intermolecular force it causes
A moment when electrons are dispersed unequally, causing a temporary dipole in a molecule. Responsible for London Forces
Intermolecular forces that exist in all molecules
What are london forces?
Two electrons side by side in a Lewis dot diagram represent:
What is a lone pair?
Which molecule is polar: NH3, BF3 or NH4?
NH3
Draw the VSEPR diagram for PH3 and state the name of the shape.
Teacher will check drawing. Shape is trigonal pyramidal.
List the 3 intermolecular forces in order from weakest to strongest.
Dipole dipole, london dispersion, hydrogen bonding
Describe how intermolecular forces influence melting and boiling points
More forces present = needs more energy to break bonds = higher melting or boiling point.
The difference between a covalent bond and an ionic bond
Covalent bonds share electrons between two nonmetals, ionic bonds transfer electrons between a metal and a nonmetal.
Which of the following is a polar molecule and why?
SiF4, XeF4, Cl2O, SF4
Cl2O, electrons are shared unequally and a molecular dipole exists
Which of the following is a polar molecule and why?
SiF4, XeF4, BF3, SF4
BF3, electrons are shared unequally and a molecular dipole exists
What intermolecular forces are present in PH3
London dispersion and dipole-dipole forces
What intermolecular forces are present between CH3OH molecules?
London forces, dipole dipole, and hydrogen bonds
3-D arrangement of atoms continuously linked throughout the crystal by strong covalent bonds
What is a covalent network?
Why is HCl a polar molecule?
Chlorine has a higher electronegativity than hydrogen. Electrons want to spend more time around chlorine than around hydrogen, there is an unequal sharing of electrons, making HCl a polar molecule.
When a clear molecular dipole doesn't exist in a molecule, the molecule is said to be...
What is nonpolar?
Intermolecular forces that only exist between polar molecules
What are dipole-dipole forces?
2 conditions needed for hydrogen bonds to form
1. Hydrogen atom must be covalently bonded to another very electronegative atom (N, O, or F)
2. There must be at least one lone pair of electrons on the atom bonded to the hydrogen.
The difference between nonpolar covalent bonds and polar covalent bonds.
Nonpolar covalent bonds equally share electrons, polar covalent bonds share electrons unequally
Describe one electronegativity trend on the periodic table.
- More protons in the nucleus = greater attraction to the nucleus and harder for electrons to get taken = higher electronegativity
- More energy levels/farther from nucleus = electrons are not attracted to nucleus as much (nucleus is shielded) so electrons are easier to take (lower electronegativity)
What are the VSEPR shapes present in methanol?
Tetrahedral and bent
Put the following chemicals in order from lowest to highest melting points: Ethane, Butanol, Propane, Methane, Butane.
Methane, Ethane, Propane, Butane, Butanol
One factor which influences the strength of London dispersion forces
What is
- Amount of electrons in a molecule (more e- means easier LD force will form, and the stronger the force will be)
- Distance (farther away molecules are, the weaker the force)