ap chem unit 2: chemical bonding

what are inter and intra molecular forces based upon?

coulombic attractions

what is the difference between inter and intra molecular forces?

inter: interactions between covalent molecules (typically weak) - hydrogen bonding, dipole-dipole, LDFs

intra: within compounds (both strong) - ionic and covalent

the ability of an atom within a covalent bond to attract electrons to itself

electronegativity

what happens if two covalently bonded atoms have the exact same electronegativity?

the electrons will be equally shared and distributed, making it a non-polar covalent bond

example: diatomic elements, elements that have similar electronegativities

what is the difference in electronegativities chart?

what happens in situations where one atom has a much higher electronegativity than the other (covalent bonding)?

electrons are attracted towards the more electronegative atom, leading to a re-distribution of the electron cloud. the molecule is then said to have a dipole and is classified as polar-covalent

example: HF

what do the chemical and physical properties of a compound rely upon?

the presence or absence of dipoles and the intermolecular coulombic attraction determine the type of intermolecular forces present. in turn, the type of intermolecular forces present can greatly influence the properties of the molecule

what is the difference between molecules and particles?

• molecules: covalently bonded compounds

  • particles: ions and ionicly bonded compounds

explain covalent bonding

• valence electrons shared to achieve full s and p valence sub shells (octet), forming molecules, typically between two nonmetalse

• one shared pair of electrons represent a single bond (longest and weakest)

• two shared pairs represent a double bond (shorter and stronger)

• three shared pairs of electrons represent a triple bond (shortest and strongest)

explain the leonard jones internuclear distance versus potential energy plot

• x axis is bond length

• y axis is bond strength and how much energy it requires to break it apart

  • the lower on the y-axis, the stronger the bond

explain ionic bonding

• the differences in electronegativities are so great that one atom can completely take an electron away from the other (transfer of electrons)

• all atoms are neutral. once they gain/lose electrons, they are charged particles (ions)

  • strong bond: higher melting and boiling points

explain how coulomb’s law applies to ionic bonding and give an example

the strongest ionic bonds are formed between ions that are small (because they can get closer to one another) and that have the highest magnitude charges

smaller+higher charge=stronger bond

example: BeO is stronger than FrI

when comparing sodium chloride and sodium bromide, which compound would be expected to have the strongest ionic bonds, i.e., the greatest Coulombic attraction? explain your answer

Sodium chloride (NaCl) has stronger ionic bonds (greater Coulombic attraction) than sodium bromide (NaBr) because the chloride ion is smaller than the bromide ion, resulting in a shorter distance between ions and thus a stronger coulombic attraction.

how are ions in ionic solids positioned?

in an ionic/crystal lattice held together by strong electrostatic forces, giving ionic solids high melting and boiling points

can ionic substances conduct electricity?

no, unless they are molten (liquid) or in solution (aqueous).e

explain what solvation does to an ionic solid

• solvation: act of dissolving

• polaw water molecules are attracted to oppositely charged ions, penetrating the lattice and attaching themselves to ions

  • ion to dipole

• process is called hydration

• ions conduct electricity in this state because ions are free to move

what are the solubility rules?

any ionic compound with Na⁺, K⁺, NH₄⁺, or NO₃^- will always dissolve

can non polar solvents dissolve polar bonds?

no

explain ionic substance with some covalent character

if the cation is small and highly charged, it will have the ability to distort the charge cloud around the anion. distortion will be at a maximum when the cation is small and highly charged and when the anion is large and highly charged (electrons more loosely held)

further away electronegativities

example: BeTe

• Be is small and highly charged; higher coulombic attraction to electrons, distorting/pulling the electron cloud of Te

• Te is large with a high charge

explain covalent substance with some ionic character (polar covalent)

if one atom in a covalent bond has a higher electronegativity than the other, then the electrons are attracted towards the more electronegative atom, leading to an electron could distortion and re-distribution of electron charge density

closer electronegativities

explain nonpolar/polar/and ionic based on periodic table

the closer the elements are on the periodic table, the more likely they are to be non polar covalent. the further away they are, they gain greater ionic character and polarity because of greater electronegativity differences

how do you make lewis structures?

1. count the number of valence electrons on each atom

2. put the least electronegative element in the center

3. bond until all atoms have a full octet

exceptions:

• H has a duet and can ONLY be an outside atom

  • elements in period 3 have expanded octets (10, 12)

what are dative/co-ordinate bonds? give an example

a covalent bond where one atom donates both of the shared electrons in a bond, unlike a normal covalent bond where each atom contributes one electron. an example is boron, which often does not have a complete octet (only has 6 electrons) but can make up the octet by forming bonds with other compounds that have a non-bonding pair such as NH₃

explain the chart for hybridization

explain single, double, and triple bonds in the terms of sigma and pi bonds

• single: 1 sigma bond

• double: 1 sigma, 1 pi

• triple: 1 sigma, 2 pi

pi bond is evidence of unhybridized orbital

what are the names of hydrocarbons based on single, double, and triple bonds

single bonds: alkane

double bonds: alkenes

triple bonds: alkynes

what are isomers?

same formula, different arrangement of atoms. to be isomers, it has to have another object to compare with

what are resonance structures?

a lewis structure that involves multiple bonds and therefore can be drawn in different ways; shows differing arrangements of electrons

how do you determine the best lewis structure if it is not equally likely?

use formal charge of individual atoms

1. formal charges of 0 is best

2. smallest total formal charge is second best (smallest: absolute value closest to 0)

3. negative numbered formal charge goes on the most electronegative element

what happens if all resonance structures are likely to occur on the same molecule?

• electrons and bonds move around

  • actual measurements of bonds are an average of the lengths of all bonds because the bond is split between all atoms

what are the rules of polarity?

for a molecule to be polar, 2 things must be true:

• molecules must contain at least one bond dipole

• bond dipoles must not cancel out due to symmetry (make sure to check ALL angles of symmetry because if you can find evidence for asymmetry, then it is polar)

what are the bond angles, electron geometry, and molecular geometry of a molecule that has 2 bonds and no lone pairs around the central atom? what does it look like?

• 2 bonds, no lone pairs

• bond angles: 180 degrees

• electron geometry: linear

• molecular geometry: linear

what are the bond angles, electron geometry, and molecular geometry of a molecule that has 3 bonds and no lone pairs around the central atom? what does it look like?

• 3 bonds, no lone pairs

• bond angles: 120 degrees

• electron geometry: trigonal planar

• molecular geometry: trigonal planar

what are the bond angles, electron geometry, and molecular geometry of a molecule that has 2 bonds and 1 lone pairs around the central atom? what does it look like?

• 2 bonds, 1 lone pair

• bond angles: slightly less than 120 degrees

• electron geometry: trigonal planar

• molecular geometry: bent or v shaped

what are the bond angles, electron geometry, and molecular geometry of a molecule that has 4 bonds and no lone pairs around the central atom? what does it look like?

• 4 bonds, no lone pairs 

• bond angles: 109.5 degrees

• electron geometry: tetrahedral

• molecular geometry: tetrahedral

what are the bond angles, electron geometry, and molecular geometry of a molecule that has 3 bonds and 1 lone pairs around the central atom? what does it look like?

• 3 bonds, 1 lone pair

• bond angles: 107.5 degrees

• electron geometry: tetrahedral

• molecular geometry: trigonal pyramidal

what are the bond angles, electron geometry, and molecular geometry of a molecule that has 2 bonds and 2 lone pairs around the central atom? what does it look like?

• 2 bonds, 2 lone pairs

• bond angles: 104.5 degrees

• electron geometry: tetrahedral

• molecular geometry: bent or v shaped

what are the bond angles, electron geometry, and molecular geometry of a molecule that has 5 bonds and no lone pairs around the central atom? what does it look like?

• 5 bonds, no lone pairs

• bond angles: 120 degrees in plane, 90 degrees perpendicular to plane

• electron geometry: trigonal bipyramidal

• molecular geometry: trigonal bipyramidal

what are the bond angles, electron geometry, and molecular geometry of a molecule that has 4 bonds and 1 lone pairs around the central atom? what does it look like?

• 4 bonds, 1 lone pair

• bond angles: complex

• electron geometry: trigonal bipyramidal

• molecular geometry: seesaw

what are the bond angles, electron geometry, and molecular geometry of a molecule that has 3 bonds and 2 lone pairs around the central atom? what does it look like?

• 3 bonds, 2 lone pairs

• bond angles: about 90 degrees

• electron geometry: trigonal bipyramidal

• molecular geometry: t shaped

what are the bond angles, electron geometry, and molecular geometry of a molecule that has 2 bonds and 3 lone pairs around the central atom? what does it look like?

• 2 bonds, 3 lone pairs

• bond angles: 180 degrees

• electron geometry: trigonal bipyramidal

• molecular geometry: linear

what are the bond angles, electron geometry, and molecular geometry of a molecule that has 6 bonds and no lone pairs around the central atom? what does it look like?

• 6 bonds, no lone pairs

• bond angles: 90 degrees

• electron geometry: octahedral

• molecular geometry: octahedral

what are the bond angles, electron geometry, and molecular geometry of a molecule that has 5 bonds and 1 lone pairs around the central atom? what does it look like?

• 5 bonds, 1 lone pair

• bond angles: about 90 degrees

• electron geometry: octahedral

• molecular geometry: square pyramidal

what are the bond angles, electron geometry, and molecular geometry of a molecule that has 4 bonds and 2 lone pairs around the central atom? what does it look like?

• 4 bonds, 2 lone pairs

• bond angles: 90 degrees

• electron geometry: octahedral

• molecular geometry: square planar

what is a special property of metals and what other properties does that cause?

• metals have a sea of delocalized electrons that surrounds the positively charged cations

• makes metals good conductors of heat and electricity

  • causes malleability/ductilitywh

what is an alloy?

a mixture between multiple metals or a metal and nonmetal

• NO chemical bonding occurring because it is a mixture

what is an interstitial alloy? give an example

• smaller atoms fill the spaces between larger atoms

• happens when there is a large difference in atomic radii

• typically formed between elements of different periods

• typically stronger than metallic counterpart

• example: steel (iron and carbon)

what is a substitutional alloy? give an example

• atoms of one metal are replaced by the atoms of another metal, like they’re mixed together basically

• happens when atomic radii are similar

• typically formed between elements of the same period

• example: brass (copper and zinc)

what are the similarities between alloys and metals?

• generally good conductors of electricity

• sometimes the surface will have different properties from the core

  • outside can react with oxygen and form an oxide, which has different properties from the inside portion which hasn’t reacted