EXAM 2: 07 Molecular Structure Flashcards
Are electrons in covalent bonds always shared equally
No
Which electron gives up its electron and which atom accepts one in ionic bonding
Gives up - from the left side of the periodic table
Accepts - right side of the periodic table
Does electrostatic attraction increase or decrease the energy of a system
It lowers the energy or a system
In covalent bonding is the energy of the system increased or decreased
Decreased as the shared electron pairs bonded to both nuclei lowers it
What is polarity
Separation of electric charges leading to a molecule or its chemical groups having an electric dipole moment
What is electronegativity
The tendency of an atom to attract electron density in the bond toward itself
- the tendency of an atom to donate or accept electron density within chemical bonds
High electronegative atoms
Readily accept electron density, form negative ions
Low electronegative atoms
Sometimes called electropositive, readily donate electron density and form positive ions
What is a molecular compound
Made up of individual molecules that contain 2 or more atoms connected by a covalent bond
Characteristics of molecular compounds
Low melting points and poor conductivity ( two nonmetals )
What is a dipole moment
Experimental measure of the polarization of electron density in molecules
What is polarity
Separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment
What is a dipole
A molecule with one end having a partial negative charge and the other end having a partial positive charge; polar molecule
What determines if the bonds are polar covalent, covalent or ionic
The electronegativity differences between bonded atoms
What is a polar covalent bond
A covalent bond between atoms w/ different electronegativities; bonding electrons are shared unequally
What bonds represent the extremes of bonding possibilities
Purely ionic bonds and nonpolar covalent bonds
If the change in electronegativity is greater than 1.8
Full or almost full electron transfer, ionic solids
If the change in electronegativity is less than 0.4
Nonpolar covalent
As change in electronegativity increases…
So does polarity
If the change in polarity is equal to 0
Nonpolar covalent
Any molecule in which the enters of positive and negative charges do not coincide is a…
Polar molecule
What are dipole-dipole interactions
Attractive forces that act between polar molecules
Are dipole-dipole interactions stronger or weaker than ion-ion interactions
Weaker
What is a nonpolar covalent bond
Equal sharing of electrons between two nuclei
- ex: diatomic elements (H-H)(Cl-Cl) also C-H
What are polar covalent bonds
Unequal sharing of electrons between nuclei
- one nuclei is tugging on the electron density in the bond more than the other
- example: H-F, more electron density at F (partially negative) (C-O, O-H, N-H)
What makes a bond polar, nonpolar or ionic
It comes down to electronegativity
What is the difference between electronegativity and electron affinity
Electronegativity is the ability to attract electrons to itself in a chemical bond which electron affinityy is where an electron has been gained by an individual ion
What do Lewis structures show
Atom connectivity and apportionment of all bonding and nonbonding electrons to individual atoms in molecules
What is the central atom
The first atom listed, or the least electronegative
What does it mean to be hypervalent
Exceed the valence rules, more than 8 electrons around them
- must be from the 3rd period of the periodic table or below, and be large
The lewis structures that best describe electron distribution in molecules have the _______ formal charges possible
Smallest
What is the formula for formal charge
FC = Number of valence electrons - number of unpaired electrons and bonds
What are the guidelines used in selecting the dominant structure (when comparing different Lewis structures)
- the dominant structure has the smallest charge separation, preferably with zero formal charges or the smallest possible formal charges
- the positioning of the formal charges in the dominant structure is consistent with the relative electronegativities of atoms; the dominant structure should have negative formal charges on the most electronegative atoms, and positive charges on the least electronegative atoms
What are delocalized electrons
Electrons that are spread over a number of atoms in a molecule, rather than localized between a pair of atoms
What is a resonance structure
Two or more equally valid Lewis structures for a single molecule that differ only in the apportionment of electrons; must have the same arrangement of atomic nuclei
What does localized mean
Describes electrons that are limited to motions in limited space
- ex: residing in a small orbital or shared between two specific atoms
What is delocalized bonding
A type of bonding in which a bonding pair of electrons is spread over a number of atoms rather than localized between two
Cyclic delocalization of bonding electrons may lead to _______ stability
Increased
What are the three categories off octet rule expectations
- Molecules or polyatomic ions with an odd number of electrons
- Molecules or polyatomic ions with atoms that have fewer than an octet of valence electrons
- Molecules or polyatomic ions in which atoms have more than an octet of valence electrons
What are radicals
A chemical species, an atom or an ion with an odd number of electrons
- generally very reactive
