Flashcards in General Chemistry- Bonding and Chemical Interactions Deck (180):
Most atoms can form what?
What atoms are the exception to forming molecules?
The noble gases
How are the atoms in molecules held together?
What are chemical bonds?
Strong attractive forces
How are chemical bonds formed?
The interaction of the valence electrons of the combining atoms.
Compounds usually have similar or different chemical and physical properties as the elements that make them up?
For many molecules, the atoms combine based on what rule?
What is the octet rule?
An atom tends to bond with other atoms so that it has eight electrons in its outermost shell, thereby forming a stable electron configuration similar to that of the noble gases
Why is the octet rule on a rule of thumb?
There are more elements that can be exceptions to the rule than those that follow the rule.
Which elements are exceptions to the octet rule?
All elements in period 3 and greater
Which elements are stable with fewer than 8 electrons?
Which elements are stable with an expanded octet?
Elements in period 3 or greater
What elements are another example of an exception to the octet rule?
An molecule with an odd number of valence electrons cannot distribute those electrons to give eight to each atom.
What is an example of an odd number molecule?
Nitric Oxide (NO)- (11)
What are the common elements that almost always abide by the octet rule?
What are the two types of chemical bonds?
What occurs during ionic bonding?
One or more electrons from an atom with a low ionization energy, typically a metal, are transferred to an atom with a high electron affinity, typically a nonmetal.
What holds the ionic bonds togethere?
Electrostatic attraction between opposite charges
The electrostatic attraction in ionic bonds creates what?
Lattice structures consisting of repeating rows of cations and anions, rather than individual molecular bonds
What occurs in covalent bonding?
An electron pair is shared between two atoms, typically nonmetals, that have relatively similar values of electronegativity.
What determines the polarity in a covalent bond?
The degree to which the pair of electrons is shared equally or unequally between the two atoms
If the electron pair is shared equally in a covalent bond, it is _________?
If the electron pair is shared unequally, the bond is ________________?
When is a bond called coordinate covalent?
If both of the shared electrons are contributed by only one of the two atoms
What is an example of nonpolar covalent bonding?
What do covalent compounds consist of?
Individually bonded molecules
Ionic bonds form between atoms that have ___________ ________.
Significantly different electronegativities
The atoms become what in ionic bonding?
cations and anions
The ionic bond is the result of ___________?
Electrostatic force of attraction between the opposite charges of these ions.
What are not shared in ionic bonds?
What must occur before ionic bonding takes place?
The difference in elecctronegativity must be gre3ater than 1.7 on the pauling scale.
Ionic bonds are usually formed between what type of atoms?
Metals and nonmetals
How can you determine whether a compound will form an ionic bond, equation wise?
Difference in electronegativity values (/\EN)
What are three ionic bond examples?
What are the common ionic compound characteristic physical properties?
High melting and boiling points
Dissolve in water and other polar solvents
In the molten or aqueous state good conductors of electricity
Form crystalline lattice with repeating positive and negative ions
Why does the formation of ionic compounds create such attractive force?
The attractive forces between the oppositely charged ions are maximized
Repulsive forces between ions of like charge are minimized
What type of atoms form covalent bonds?
Atoms with similar electronegativities
Why don't atoms with similar electronegativities form ions when bonded?
The energy required to form ions through the complete transfer of one or more electrons is greater than the energy that would be released upon the formation of an ionic bond. So it is energetically unfavorable to create ions.
What do covalent bonds contain?
Discrete molecular units with relatively weak intermolecular interactions.
Covalent bonds tend to have what?
Lower melting and boiling points
Covalent bonds are ________________ because ____________?
Poor conductors of electricity in the liquid state because they do not break down constituent ions.
What is it called when atoms share one, two, or three electrons?
Triple covalent bonds
What is the bond order?
The number of shared elecctron pairs between two atoms
What is the bond order for a single, double and triple bond?
What are the three characteristics of a covalent bond?
What is bond length?
The average distance between the two nuclei of atoms in a bond.
As the nuber of electron pairs increases, bond length _______.
Decreases due to the two atoms being pulled closer together
What is bond energy?
The energy required to break a bond by separating its components into their isolated, gaseous atomic states.
The greather the number of pairs of electrons the ________ energy required to break them.
Which has a greater bond energy: single ro triple bond?
When does polarity occur?
When two atoms have a relative difference in electronegativities
Atoms with higher electronegativity get _______ share of __________.
Larger share of the electron density
What must be negotiated in a covalent bond?
Atoms must negotiate the degree to which the electron pairs are shared
What does a polar bond create?
The ________ end of the dipole at the _________ and _____________ end at the __________.
Positive end of the dipole at the less electronegative atom and the negative end at the more electronegative atom
What is a non-polar covalent bond?
Atoms that have identical or nearly identical electronegativities and share electron pairs. They do so with equal distribution of the electrons.
There is no ________ in a non polar covalent bond?
Separation of charge across the bond
Only bond between _____________ will have exactly the same ___________.
Atoms of the same element willl have the exact same electronegativity
What are the seven common diatonic molecules?
When are bonds basically nonpolar?
Difference in electronegativity less than 0.5
Atoms that differ moderately in their electronegativities will result in ____________.
Polar covalent bonds
What is the range of difference in electronegatvities that result in polar covalent bonds?
The more electronegative the element the more ____________, taking on a ____________ charge.
Greater portion of the electron density taking on a partial negative charge.
The less electronegative the ___________, taking on a ________ charge.
Smaller portion of the electron density taking on a partial positive charge
How do you indicate the differece in charge?
An arrow crossed at its tail end and pointing toward the negative end.
What is the dipole moment?
A vector quantity give by the equation: p=qd
What do the letters represent in the dipole moment equation?
p: the dipole moment
q: magnitude of charge
d: the displacement vector separating the two partial charges
How is the dipole moment vector measured?
Debye units (Coulomb-meters)
What is a coordinate covalent bond?
Both of the shared electrons originated on the same atom.
What does it generally mean to have a coordinate covalent bond?
A lone pair of one atom attacked another atom with an unhybridized p-orbital to form a bond.
A distinction between where a coordinate bond comes from is only helpful, how?
For keeping track of the valence electrons and formal charges.
Where are coordinate covalent bonds typically found?
In Lewis acid-base reactions
What is a Lewis acid?
Any compound that will accept a lone pair of electrons
What is Lewis base?
Any compound that will donate a pair of electrons to form a covalent bond
What are bonding electrons?
The electrons involved in a covalent bond are in the valence shell
What are nonbonding electrons?
Electrons in the valence shell that are not involved in covalent bonds.
What are lone pairs?
Unshared electron pairs
Why are they called lone pairs?
because they are associated only with one atomic nucleus
Why was the Lewis structure developed?
To keep track of the bonded and nonbonded electron pairs
Is the valence electrons in a neutral atom the same as valence electrons in an atom in the Lewis structure?
Why is there a formal charage for an atom in a Lewis structure?
To note the difference in number of valence electrons in a neutral atom and a Lewis structure atom.
Can more than one Lewis strcutre be drawn for a molecule?
What happens if Lewis structures differ in their bond connectivity or arrangement?
Then the Lewis structures represent different possible compounds.
When does the Lewis strcture show different resonance forms?
If Lewis structures show the same bond connectivity and differ only in the arrangement of the electron pairs
Do Lewis structures respresent the actual geometry of a real compound?
How can you check the likelihood of each arrangement using the Lewis structure?
Checking the formal charges on the atoms in each arrangement.
How can you tell the stability of an arrangement based on the Lewis structure and formal charge?
The arrangement that minimizes the number and magnitude of formal charages is the most stable arrangement
What is another name for Lewis structure?
Lewis dot diagram
How is the Lewis structure drawn?
The chemical symbol of an element surrounded by dots, each representing one of the s or p valence electrons of the atom
Can a Lewis structure also show the valence electrons of molecules?
Which atom is the central atom in a Lewis structure?
The atom with the least electronegativity
Which atoms usually occupy a terminal position in a Lewis diagram?
Which atom ALWAYS occupies a terminal position?
What are the steps for drawing a Lewis structure?
Draw skeletal structure
Count valence electrons
Draw single bond
Draw remaining valence electrons of attached atoms
Complete octet of central atom by making multiple bonds if need be.
How can you count the valence electrons of a molecule?
Sum of the valence electrons of all atoms present
How do you draw electrons in a Lewis diagram?
How are bonded electron pairs drawn in a Lewis structure?
A line: Which represents a pair of electrons
How do you determine if a Lewis structure is a representation of an actual arrangement of atoms in a compound?
One must calculate the formal charge of each atom.
What should be assumed when calculating formal charage in a Lewis structure?
Assume that each electron pair is split evently betweeen the two nuclei in the bond.
What is the equation to calculate formal charge?
Formal Charage=V-(Nnonbonding)- 1/2 (Nbonding)
What do the letters represent in the equation to calculate formal charge?
V: normal number of electrons in the atom's valence shell
(Nnonbonding): # of nonbonding electrons
(Nbonding): # of bonding electrons
What is the difference between formal charge and oxidation number?
Formal charge underestimates the effect of electronegativity differences, wheras oxidation numbers overestimate the effect of electronegativity differences.
What is the resounance structures?
Two or more Lewis structures that demonstrate the same arrangement of atoms but that differ in the specific placement of the electrons
How are resonance structures represented?
With a Double-headed arrow between them
What is resonance hybrid?
The actual structure of the compound
What contributes more to the resonance hybrid?
The more stable the structure, the more it contributes to the character of the resonance hybrid.
What are the guidelines for determining the stability of resonance structures?
A Lewis structure with small or no formal charges is preferred over a Lewis structure with large formal charges
A Lewis structure with less separation between opposite charages is preferred over a Lewis structure with a large separation of opposite charges
A Lewist structure in which negative formal charges are placed on more electronegative atoms is more stable than one in which the negative formal charges are placed on less electronegative atoms
On test day, what should not be discounted in regards to Lewis structures/
Lewis structure with a central atom that has more than four bonds.
What is the valence shell electron pair repulsion theory?
What does VSEPR do?
Uses Lewis dot structures to predict the molecular geometry of covalently bonded molecules.
What does the VSEPR theory state?
The three-dimensional arrangement of atoms surrounding a central atom is determined by the repulsions between bonding and nonbonding electron pairs in the valence shell of the central atom.
What are the steps for predicting the geometrical structure of a molecule?
Draw the Lewis dot structure of the molecule.
Count the total number of bonding and nonbonding electron pairs in the valence shell of the central atom.
Arrange the electron pairs around the central atom so that they are as far apart as possible.
What are the 5 most common shapes of configuration of molecules that do not have charge or lone pair of electrons around the central atom according to the VSEPR theory?
What are the angles of the 5 most common shapes of configuration of molecules that do not have charge or lone pair of electrons around the central atom according to the VSEPR theory?
Linear: 180 degrees
Tigonal Planar: 120 degrees
Tetrahedral: 109.5 degrees
Trigonal bipyramidal: 90 degrees, 120 degrees, 180 degrees
Octahedral: 90 degrees, 180 degrees
What are the regions of the electron density of the 5 most common shapes of configuration of molecules that do not have charge or lone pair of electrons around the central atom according to the VSEPR theory?
Trigonal planar: 3
Trigonal bipyramidal: 5
What are examples of molecules that follow the 5 most common shapes of configuration of molecules that do not have charge or lone pair of electrons around the central atom according to the VSEPR theory?
Trigonal Planar: BH3
Trigonal Bipyramidal: PCL5
What is the difference between electronic geometry and molecular geometry?
Electronic geometry describes the spatial arrangement of all pairs of electrons around the central atom, including both the bonding and the lone pairs.
Molecular geometry describes the spatial arrangement of only the bonding pairs of electrons.
What is one important implication of electronic geometry?
The determination of the ideal bond angle.
What will the MCAT primarily focus on: molecular geometry or electronic geometry?
Why is the ideal bond angle important in electronic geometry?
Nonbonding pairs are able exert more repulsion than bonding pairs because these electrons reside closer to the nucleus.
What is molecular dipole?
An overall separation of charge across the molecule
Does the presence of bond dipoles result in a molecular dipole?
No the presence of bond dipoles does not necessarily result in a molecular dipole
How do you determine molecular dipole?
The molecular geometry and the vector addition of the bond dipoles based upon the molecular geometry.
Does a compound with nonpolar bond ever have a polar molecular dipole?
No, it is always nonpolar
Does a compound with polar bond ever have a polar molecular dipole?
May be polar or nonpolar
What determines molecular dipole in a molecule with polar bonds?
The spatial orientation of the polar bonds in the molecule
What type of geometry results in a nonpolar compound?
Molecular geometry such that the bond dipole moments cancel each other out, then the result is a nonpolar compound
What type of geometry results in a net dipole moment?
Molecular geometry is arranged such that the bond dipoles do not cancel each other out, the molecule will have a net dipole moment and will therefore be polar
What do the 4 quantum nummbers describe?
The energy and position of an electrong in an atom.
What does the principle quantum number indicate?
The average energy level of the shell
What does the azimuthal quantum number describe?
The subshells within each principal energy level
What is the shape of the s subshell which has one orbital?
What is the shape of the p subhsell, and what axes are they on? What angles do they make with each other?
Barbells along the x, y, z axes at right angles to each other
When two atoms bond to form a compound, what interaction occurs?
The atomic orbitals interact to form a molecular orbital
What does the molecuar oribtal describe?
The probability of finding the bonding electrons in a given space.
How are molecular orbitals obtained?
Combining the wave functions of the atomic orbitals.
Qualitatively, how are molecular orbitals described?
The overlap of two atomic orbitals describes this molecular orbital
How is a bonding orbital formed?
If the wavelength signs of the two atomic orbitals are the same
How is an antibonding orbital formed?
If the wavelength signs of the two atomic orbitals are different
How many patterns of overlap are observed in the formation of molecular bonds?
What results in a sigma bond?
When orbitals overlap head-to-head
What do sigma bonds allow? Why?
For free rotation about their axes because the electron density of the bonding orbital is a single linear accumulation between the atomic nuclei.
What results in a pi bond formation?
When the orbitals overlap in such a way that there are two parallel electron cloud densities.
Pi bonds do not allow for what? Why?
For free rotation because the electrong densities of the oribitals are parallel and cannot be twisted in such a way that allows continuous overlapping of the clouds of electron densities.
The strength of ________ can impact _________ such as ________ and ____________.
These intermolecular forces can impact certain physical properties, such as meling and boiling points.
What is the weakest intermolecular interation?
What is another name for dispersion forces?
Which intermolecular interaction has intermediate strength?
Which intermolecular interation is the strongest?
Why is the hydrogen bond a misnomer?
There is no actual sharing or transfer of electrons
What do atoms and compounds participate in?
Weak electrostatic interactions.
Even the strongest intermolecular force, the ________, is not as strong as ___________.
The hydrogen bond, is not as strong as the covalent bond.
WHat percentage of strength does a hydrogen bond have compared to a covalent bond?
How much energy i required to overcome an electrostatic interaction?
Small or moderate amounts of energy
In a given moment, bonding electrons in nonpolar covalent bond, may be what?
unequally distributed between the two atoms
What is the result of bonding electrons in nonpolar covalent bonds with unequally distributed electron cloud?
A rapid polarization and counterpolarization of the electrong cloud and the formation of short-lived dipole moments.
The rapid polarization and counterpolariation of covalent bonds ineracts with what? Causing what?
The electron clouds of neighboring compounds, inducing the formation of more dipoles
What is the name of the attractive interactions of these short-lived and rapidly shifting dipoles?
London Dispersion forces
The London dispersion force is a type of what force?
Van der Waals force
London dispersion forces do not what? Therfore are what?
Do not extend over long distance and therefore are significant only when molecules are in close proximity
The strength of a London dispersion force depends on what?
The degree and ease by which the molecules can be polarized
Which type of molecules are easily polarized: Small or large molecules? Thus they have greater what?
Large molecules are more easily polarizable and thus possess greater dispersion forces
Which force is the only force that can cause noble gases to interact/liquify at any temperature?
Polar molecules orient themselves how, when they interact?
The oppositely charged ends of the respective molecular dipoles are closest to each other
What type of force is formed between two polar molecules that make up a compound?
An attractive electrostatic force
The dipole-dipole interaction is indicated how, when notating?
The attractive force is denoted by dashed lines in most molecular notations and indicates a temporary bonding interaction
Dipole-dipole interactions are present in what phases?
Solid and liquid phases
Why are Dipole-Dipole interactions not seen in the gas phase?
The significantly increased distance between gas particles
What is a result of dipole-dipole interactions compared to non-polar species of comparable molecular weight?
Polar species tend to have higher melting and boiling points than nonpolar species of comparable molecular weight due to these interactions
What is the similarty and difference of Dipole-dipole forces and Lond dispersion forces.
Both are electrostatic forces between opposite partial charges,
The difference is only in the transience or permanence of the molecular dipole
What is a hydrogen bond?
A specific, usually strong form of dipole-dipole interaction that may be intra-or intermolecular.
Hydrogen bonds are not _________, because __________.
Actually bonds, there is no sharing or transfer of electrons between atoms
What are the three highly electronegative atoms?
When hydrogen is bonded to a highly electronegative atom, it carries only ___________.
A small amount of the electron density in the covalent bond.
The hydrogen atom acts as what in a hydrogen bond?
A naked proton
Substances that display hydrogen bonding tend to have ___________ compared to _______________.
Unusually high boiling points compared to compounds of similar molecular weights that do not exhibit hydrogen bonding.
The high boiling point in substances with hydrogen bonds derives from what?
The energy required to break the hydrogen bonds.
Hydrogen bonding is particularly important in the behavior of what?
What has different regions that are stabilized by hydrogen bonding?
Many biochemical molecules, such as nucleotides