Chapter 9 (part one): Chemical Bonding I: Lewis Theory Flashcards
Define Lewis theory
A simple model of chemical bonding using diagrams the represent bonds between atoms as lines or pairs of dots. In this theory, atoms bond together to obtain octets (eight valance electrons)
Define Lewis structure (Lewis dot structures)
A drawing that represents bonds between atoms as shared or transferred electrons; the valence electrons of atoms are represented as dots
Chemical bonds occur because…?
They lower the potential energy between the charged particles that compose atoms
Which law states that when atoms approach each other, the electrons of one atom are attracted to the nucleus of the other and vice versa
Coulumbs law
What are the three main types of bonding?
Ionic bonding
Covalent bonding
Metallic bonding
When a metal bonds with a non metal what occurs?
One or more electrons is transferred from the metal to the nonmetal
(Because metals have low ionizations energies and non metals have high electron affinities)
Oppositely charged ions _____ one another, ____ their overall potential energy as described by Coulomb’s law. The resulting bond is called…?
Attract
Lowering
An Ionic bond
Because nonmetals have _____ ionization energies, when a nonmetal bonds with a nonmetal neither atom transfers electrons instead they ______ electrons
High
Share
Nonmetals share electrons, the shared electrons interact with the nuclei of both of the bonding atoms, lowering their potential energy in accordance with _____ ______. The resulting bond is a _______ bond
Coulomb’s law
Covalent
The most stable arrangement for a covalent bond is the one with the ______ potential energy
Lowest
Define bonding theories
Models that predict how atoms bond together to form molecules
Metals have ____ ionization energies and so when metallic bonding occurs the ____ ____ model is used and it shows…?
Low
Electron sea
That all of the atoms in a metal lattic pool their valance electrons. These pooled electrons aren’t localized to a single atoms but are delocalized over the entire metal. The positively charged metal atoms are then attracted to the sea of electrons, holding the metal together
Define chemical bond
The sharing or transfer of electrons to attain stable electron configurations for the bonding atoms
If electrons are transferred, as between a metal and a nonmetal, the bond is _____
Ionic
If the electrons are shared, as occurs between two nonmetals, the bond is _____
Covalent
Define octet rule
The tendency for most bonded atoms to possess or share eight electrons in their outer shell to obtain stable electron configurations and lower their potential energy
Define lattice energy
The energy associated with forming a crystalline lattice from gaseous ions
The formation of an ionic compound is exothermic, why?
Because when the positively and negatively charged ions come together the potential energy decreases and the energy is emitted as heat
Define Born-Haber cycle
A hypothetical series of steps based on Hess’s law that represents the formation of an ionic compound from its constituent elements
As the ionic radii ______ as we move down the column, the ions cannot get as close to each other and therefore ____ release as much energy when the lattice forms
Increases
Don’t
Lattice energies become _____ exothermic (_____ negative) with increasing ionic radius
Less
Less
Lattice energies become _____ exothermic (_____ negative) with increasing magnitude of ionic charge
More
More
Define bonding pair
A pair of electrons shared between two atoms
Define lone pair
A pair of electrons associated with only one atom
Define nonbonding electrons
Lone pair electrons (A pair of electrons associated with only one atom)
Name the 4 steps for drawing a Lewis structure
- Find the total number electrons that will be used (# of valence electrons)
- Create a skeletal structure by putting a bond between each set of bonding atoms
- Put the remaining electrons around the atoms
- Make sure all the non hydrogen atoms have a full octet. If not, adjust accordingly
Molecular compounds have _____ bonds within the molecules but _____ intermolecular forces between molecules. This results in molecular bonds having _____ melting points and boiling points than ionic compounds
Strong
Weak
Lower
What do you do to show the structures are resonance structures
Put a double headed arrow between the two diagrams
Define resonance structures
Two or more valid Lewis structures that are shown with double-headed arrows between them to indicate that the actual structure of the molecules is intermediate between them
Define resonance hybrid
The actual structure of a molecule that is intermediate between two or more resonance structures
Which structure is the structure that actually exists? Resonance structure or resonance hybrid structure?
Resonance hybrid structure
Define formal charge
The charge that an atom In a Lewis structure would have if all the bonding electrons were shared equally between the bonded atoms
What is the formal charge equal to?
of valence electrons - (# of nonbonding electrons + 1/2 # of bonding electrons)
The sum of the formal charges in molecules or ions must equal…?
The overall charge of the ion or molecule
What are two guidelines to follow in terms of formal charge when drawing Lewis structures?
- smaller formal charges on individual atoms are better than larger ones
- when formal charges cannot be avoided, negative formal charges reside on the most electronegative atom
Main group elements in the third row of the periodic table and beyond often exhibit ______ which means…?
Hypercoordination
They are bonded to more than four other atoms or appear to have more than 4 pairs of electrons (an octet) around the central atom
Hypercoordinate compounds are said to have _____ _____ because it looks like their are more than eight electrons around the central atom in the Lewis structure
Expanded octet
define ionic bond
a chemical bond formed between two oppositely charge ions, generally a metallic cation and a nonmetalic anion, that are attracted to one another byt electrostatic forces
define covalent bond
a chemical bond in which two atoms two atoms share electrons that interact with both nuclei , lowering the potential energy of each atom through electrostatic interactions
define octect
eight electrons in a valence shell of an atom
why are bond energies always positive?
because it takes energy to break a bond
