Ch 3 - Bonding and Chemical Interactions

Question 1

What are the 2 types of chemical bonds?

Answer 1

covalent and ionic

Question 2

What are elements trying to attain by bonding?

Answer 2

a noble gas-like electron configuration

Question 3

What is the octet rule?

Answer 3

• states that elements will be most stable with 8 valence electrons

Question 4

What are the exceptions to the octet rule?

Answer 4

• elements with an incomplete octet are stable with fewer than 8 electrons and include H, He, Li, Be, and B
• elements with an expanded octet are stable with more than 8 electrons and include all elements in period 3 or greater
• compounds with an odd number of electrons cannot have 8 electrons on each element

Question 5

How are ionic bonds formed?

Answer 5

• formed via the transfer of one or more electrons from an element with a relatively low ionization energy to an element with a relatively high electron affinity

Question 6

What elements usually form ionic bonds?

Answer 6

ionic bonds occur between elements with large differences in electronegativity (EN > 1.7), usually between metals and nonmetals

Question 7

What is the difference between a cation and an anion?

Answer 7

• cation: positively charged ion

- anion: negatively charged ion

Question 8

What causes ions to remain in close proximity?

Answer 8

the resulting electrostatic attraction between anions and cations, forming an ionic bond

Question 9

What do ionic compounds form?

Answer 9

• crystalline lattices, large organized arrays of ions

Question 10

What are the unique physical and chemical properties of ionic compounds?

Answer 10

• tend to dissociate in water and other polar solvents
• ionic solids tend to have high melting points
• good conductors of heat and electricity
• crystal lattice arrangement to minimize repulsive forces
• large difference in EN between ions

Question 11

How are covalent bonds formed?

Answer 11

via the sharing of electrons between 2 elements of similar electronegativities

Question 12

What is bond order and how does it correlate with bond strength, energy, and length?

Answer 12

• bond order refers to whether a covalent bond is a single, double, or triple bond
• as bond order increases, bond strength and energy increase and bond length decrease

Question 13

How can covalent bonds be categorized?

Answer 13

• non polar bonds: result in molecules in which both atoms have exactly the same electronegativity; some bonds are considered non polar when there is a very small difference in EN between atoms (<0.5), even though they technically are slightly polar
• polar bonds: form when there is a significant difference in EN (0.5-1.7), but not enough to transfer electrons to form an ionic bond (higher EN element has partial negative charge and lower EN element has partial positive charge)

Question 14

When do coordinate covalent bonds form?

Answer 14

• when a single atom provides both bonding electrons while the other atom does not contribute any
• coordinate covalent bonds are most often found in Lewis acid-base chemistry

Question 15

What are Lewis dot symbols?

Answer 15

• a chemical representation of an atom’s valence electrons
• drawing a complete Lewis dot structure requires a balance of valence, bonding, and non bonding electrons in a molecule or ion

Question 16

What are formal charges?

Answer 16

• exist when an atom is surrounded by more or fewer valence electrons than it has in its neutral state
  = valence electrons - dots - sticks

Question 17

What are resonance structures?

Answer 17

• for any molecule with pi system of electrons, resonance exists
• they represent all of the possible configurations of electrons (stable and unstable) that contribute to overall structure

Question 18

What does the VSEPR theory predict?

Answer 18

• the 3D molecular geometry of covalently bonded molecules
• electrons (whether bonding or non bonding) arrange themselves to be as far apart as possible from each other in 3D space, leading to characteristic geometries

Question 19

Which bonded electrons exert more repulsion?

Answer 19

non bonding electrons exert more repulsion than bonding electrons because they reside closer to the nucleus

Question 20

What is the difference between electronic and molecular geometry?

Answer 20

• ele: the position of all electrons in a molecule, whether bonding or non bonding
• mol: the position of only the bonding pairs of electrons in a molecule

Question 21

What does the polarity of a molecule depend on?

Answer 21

• the dipole moment of each bond and the sum of the dipole moments in a molecular structure

Question 22

What is the difference between the type of bonds in polar and non polar molecules?

Answer 22

• all polar molecules contain polar bonds

- non polar molecules may contain non polar bonds or polar bonds with dipole moments that cancel each other

Question 23

What do sigma and pi bonds result from and what do they describe?

Answer 23

• they describe the patterns of overlap observed when molecular bonds are formed
• sigma results of head to head overlap
• pi results of the overlap of 2 parallel electron cloud densities

Question 24

What are intermolecular forces?

Answer 24

electrostatic attractions between molecules

- significantly weaker than covalent bonds (which are weaker than ionic bonds)

Question 25

What are the types of intermolecular forces?

Answer 25

• london dispersion: the weakest interaction, but are present in all atoms and molecules (as the size of the atom or structure increases, so does the corresponding London dispersion force)
• dipole dipole: occur between the oppositely charged ends of polar molecules, are stronger than London forces (evident in solid and liquid phases but negligible in the gas phase due to the distance between particles)
• Hydrogen bond: specialized subset of dipole dipole interactions involved in intra- and intermolecular attraction (occur when H is bonded to F, O, or N)

Question 26

What is bond length?

Answer 26

• the average distance between the 2 nuclei of atoms in a bond
• single bonds are the longest, though they are the weakest

Question 27

What are the 7 diatomic elements?

Answer 27

H, N, O, F, Cl, Br, I

Question 28

What are the geometric shapes of compounds given their electron clouds?

Answer 28

• 2: linear
• 3: trigonal planar
• 4: tetrahedral
• 5: trigonal bipyramidal
• 6: octahedral

Question 29

What are the values of deltaEN for a polar, nonpolar, or ionic bond?

Answer 29

• non polar <0.5
• polar 0.5-1.7
• ionic >1.7