Chapter 3: 3.1 Ionic and Covalent Bonding Flashcards
True or False:
Only core electrons participate in bonding
False, only valence electrons participate in bonding
Elements of low electronegativity typically form:
Ionic bonds
Elements of moderate electronegativity typically form:
Covalent bonds
Elements of higher electronegativity can form:
Covalent or Ionic bonds
True or False:
In an ionic bond, the two atoms share electrons equally
False, this is due to the large difference in negativity between the two atoms
When is a bond considered ionic?
When there is a complete transfer of an electron from the atom of lower electronegativity to the atom with the higher electronegativity
At what difference in electronegativity do ionic bonds occur?
Greater than 1.9
Compounds that have ionic bonds have what properties?
High melting points
Crystal lattices
What can Coulomb’s law determine?
The magnitude of the attractive force between anions and cations
Scenario:
When ions get bigger, what will happen?
Spacing between ions gets bigger
Weaker force of attraction (changes melting points etc.)
Covalent bonds involve _______ of electrons
Sharing
True or False:
The electrons in covalent bonds are always shared equally
False
At what difference in electronegativity is the sharing of electrons in covalent bonding deemed unequal?
Less than 1.9, greater than 0.5
What are covalent bonds with unequal sharing of electrons known as?
Polar covalent bonds (Polar bond, for short)
What do polar bonds give rise to?
Dipole moment
The greater the difference in electronegativity, the ______ the magnitude of the dipole moment
Larger
Dipole moment should be drawn:
Either way, as long as you are consistent
Positive to negative (electron pull)
Negative to positive (IUPAC)
What is used to show dipole moment?
Electrostatic Potential Maps
What do the colors on an Electrostatic Potential Map represent?
Red: Negative
Blue: Positive
What are covalent bonds with approximately equal sharing of electrons known as?
Nonpolar covalent bonds
At what difference in electronegativity do nonpolar covalent bonds occur?
0.5 or less
Why are bonds with an electronegativity difference of 0.5 or lower called “nonpolar covalent bonds”?
They have virtually no permanent dipole movements
Define:
Lewis structure
A diagram showing the atoms, the covalent bonds, the lone electron pairs, and any charges that may be present on the atoms
True or False:
Lewis structures show the molecular shape of a molecule
False, Lewis structures are not intended to show or imply molecular shape
Define:
Formal Charge
The difference between the number of electrons “owned’ by that atom in the Lewis structure and the number of valence electrons in a free atom of the same element in its neutral state
What is the number of electrons “owned” by an atom?
The nonbonding electrons, along with half the electrons in the covalent bonds formed by the atom
Define:
Octet Rule
If there are enough valence electrons in the molecule, then all of the second-row (2nd row p-block elements) atoms C, N, O, F, Ne must have 8 valence electrons
Does the Octet Rule apply to Li and Be? How about B?
Li and Be usually do not form covalent bonds, so the Lewis theory is rarely applied to them
Boron-containing compounds usually do not have enough valence electrons for B atoms to satisfy the octet rule
True or False:
Atoms in the second row sometimes have more than 8 electrons in a Lewis Structure
False, C, N, O, F, and Ne atoms can never have more than 8 electrons in a Lewis structure
Lewis Structure Procedure:
Step 1
Count total number of valence electrons in molecule by adding valence electrons of each neutral atom
Add one for each negative charge, subtract one for each positive charge
Lewis Structure Procedure:
Step 2
Draw a skeleton structure, joining atoms together by single bond
Usually element with lowest electronegativity is the central atom
Lewis Structure Procedure:
Step 3
Count the number of single bonds drawn and calculate the number of valence electrons in the bonds
Lewis Structure Procedure:
Step 4
Distribute the remaining valence electrons among the atoms
Lewis Structure Procedure:
Step 5
Assign formal charges to all atoms and check their sum
How do we choose the best Lewis structure?
The best is normally the structure in which the formal charges are the smallest and consistent with the relative electronegativities of the atoms
Define:
Resonance structures
Multiple correct Lewis structures that differ only in the positions of the electrons and multiple bonds
How are resonance structures best represented?
Resonance hybrids
Define:
Average bond order
Average number of bonds between specific atoms
Line Diagrams, True or False:
Each solid line represents an ionic bond
False, each solid line represents a covalent bond
Line Diagrams, True or False:
If no atom is draw at the intersection of two lines, it is assumed to be a carbon atom
True
If no atom is drawn at the end of a line, what is it assumed to be?
A carbon atom
Line Diagrams, True or False:
Hydrogen atoms bonded to carbons are shown
False
Line Diagrams, True or False:
All non-carbon atoms must be drawn along with hydrogens that are attached to them
True
