Bonding Flashcards
What determines the physical properties of molecules-intermolecular forces or intramolecular forces?
Intermolecular forces
Why is the formation of covalent bonds energetically unfavorable compared to that of ionic bonds?
Atoms of the covalent bonds have similar electronegativities, requiring more input of energy to form the bonds than the energy release upon their formation
What is the strength of the intermolecular forces of ionic bonded molecules and covalently bonded molecules? What effect does this have on their physical properties?
Ionic bonds have strong intermolecular forces due to electrostatic attraction between the ions. This confers a high melting and boiling point. In contrast, covalently bonded molecules have weak intermolecular forces resulting in low melting and boiling points
Can both ionic bonded and covalently bonded molecules conduct electricity?
Only ionic bonded molecules can conduct electricity. This can be done ONLY in the liquid and aqueous states.
Bond Order
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Why do atoms form covalent bonds?
To complete their valence shell with 8 electrons
What differentiates between polar-covalent (partially ionic) and covalent?
Electronegativity differences between the two atoms. If the the difference is less than 1.5, its covalent. If its between 1.5 and 2.0 (greater than 2.0 is ionic) then it is polar covalent.
What are the two types of covalent bonds? Where is their electron density located?
Sigma bond’s electron density is located in the internuclear region. Pi bond electron density are located above and below the internuclear region
What effect do bonding orbitals have on bond length?
Each atom undergoes hybridization of their valence electron orbitals to form a bond with another atom. The more s character that orbital has, the shorter the bonding orbital. The amount of s character is determined by now many bonding orbitals is required of the atom. The more atoms to which that atom is attached to, the less s-character it has since it must utilize the p-orbitals, extending the bond orbital due to the p-orbital dumbbell shape. Therefore, bond length is dependent on the orbital hybridization of the two atoms.
What must be true of the spin of electrons in order for electron densities to overlap during bonding?
The spins of the electrons must be the same
How does sharing of electrons confer bond length and strength?
The more electrons that are shared between atoms, the stronger the bond, and the closer the atoms are pulled together, resulting in decreased bond length. The rule is ENTIRELY depending on electron density.
How does subtstitution of one atom change bond strength between two atoms?
A substituted atom will create bond of lesser strength because of inductive effects, decreasing the electron density between the two atoms. Because bond strength is directly proportional to electron density, the less electron density confers a weaker bond
When drawing a lewis structure, what is characteristic about the central atom? What are the remaining steps to drawing a lewis structure
- The central atom is the least electronegative atom
- Count the number of valence electrons of all the atoms, for all of these will be involved in creating the overall molecular structure
- Draw the single (sigma) bonds between the atoms. Sigma bonds are always the first bonds created (provides the molecular foundation)
- Calculate the remaining valence electrons. Add the remaining electrons to the outer atoms - the outer atoms are more electronegative (see #1)
- If the central atom does not meet octet rule, create double or triple bonds
What is the formal charge and how is it calculated?
Formal charge is the notation given to an atom that has more or less than the number of valence electrons it has during its isolated state.
Formal charge is calculated by subtracting the number of bonding and nonbonding electrons from the # valence electrons in its isolated state.
What is bond dissociation energy and what role does it play in determining bond stability and strength?
Bond dissociation energy is the energy required to to cleave a bond in a homolytic fashion. As bonds break and reform, energy is released. If the energy released upon the formation of new bonds is greater than the energy required to break the bonds, it is said that the molecule is more stable and stronger. A more stable and stronger bond will require more energy input to break in (greater bond dissociation energy).
