Single & Multiple Covalent Bonds

Covalent Bonds Single & Multiple Covalent Bonds: Octet rule states that most atoms want to have 8 electrons in their valence shell (PARTICULARLY important for C, N, O, and F) Boron commonly only forms 3 bonds, because it is a small molecule (6 electrons in valence shell) Ionic bonding is the complete donation of electrons (differences in electronegativity is so extreme that one rips off the electrons of the other) Covalent bonding is when two atoms share electrons with one another Polar covalent bonding occurs when one atom is more electronegative than the other and ends up hogging the electrons a little more while nonpolar covalent bonding occurs when both atoms have equal electronegativities and share the electrons equally Electronegativity & Bonding: Electronegativity is the power of an atom in a molecule to attract electrons to itself Pauling scale of electronegativity shows the electronegativity values for atoms (anything less than about 0.5 making the bond nonpolar, such as between carbon and hydrogen, and higher than 1.9 is generally thought of as ionic) Intramolecular & Intermolecular Forces: Intramolecular forces are forces that hold atoms together within a molecule 1. Ionic bonds are formed through the complete transfer of electrons between atoms (generates two oppositely charged ions → metal loses electrons and nonmetal gains electrons) 2. Covalent bonds are bonds formed between atoms of similar electronegativities, making them share them (polar and nonpolar has to do with differing electronegativities) 3. Metallic bonds occur specifically between atoms of metals where the valence electrons are free to move throughout the lattice (this is why current works) and are found in pure elemental metals (gold, aluminum, brass, etc.) Intermolecular forces are forces that exist between molecules (much weaker than intramolecular forces) 1. Dipole-dipole interactions are forces that occur when the partially positively charged part of a molecule interacts with the partially negatively charged part of the neighboring molecule (need partially charged ions) and are the stronger intermolecular force 2. Hydrogen-bonding is a special kind of dipole-dipole interaction that occurs specifically between a hydrogen atom bonded to either an oxygen, nitrogen, or fluorine atom (explains the higher melting points of H2O and HF) 3. London dispersion forces, under the category of Van der Waal forces are the weakest of the intermolecular forces and exist between all types of molecules. The more electrons a molecule has, the stronger its London dispersion forces are sp3 Hybridization: In order for electron configurations to make sense, you must hybridize the orbitals (take some from s and 3 from p and therefore get sp3) Sigma Bond (σ bonds) are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals (if it is only a single bond then it is a σ bond meaning that it is freely rotatable) Steric Number: Steric number is simply the # of σ bonds added to the # of lone pairs and tells us the number of hybridized orbitals that are present SN = 4 → sp3 | SN = 3 → sp2 | SN = 2 → sp Molecular Polarity: Dipole moment is quantity that describes two opposite charges separated by a distance signified by µ = Q*d Molecules, like CO2, have their dipole moments cancel out and therefore have no dipole moment (therefore nonpolar) and have a µ=0 sp2 Hybridization: sp2 typically occurs with planar molecules (such as carbon having only 3 species bound to it) and has 3 sp orbitals with an untouched π orbital A π (pi) bond is side by side overlap (not freely rotatable) Double bonds are shorter than single bonds, likely because of its increased s character Boron has only 3 valence electrons and an empty π shell, meaning that it can accept electrons and act as a Lewis acid sp Hybridization: sp typically occurs with triple bonds (50% s character and 50% p character), leading to the shortest bond out of the three options Forms two π bonds and one σ bond (not freely rotatable) sp hybridization will lead to linear geometry