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Questions and Answers
Which element's octet rule is considered most important when drawing Lewis structures?
Which element's octet rule is considered most important when drawing Lewis structures?
- Chlorine
- Carbon (correct)
- Potassium
- Helium
What is the main consideration when determining the appropriate Lewis structure for molecules with elements outside the first two periods?
What is the main consideration when determining the appropriate Lewis structure for molecules with elements outside the first two periods?
- Minimizing formal charges (correct)
- Using only single bonds
- Maximizing the number of lone pairs
- Satisfying only the octet rule
How does electronegativity influence Lewis structures?
How does electronegativity influence Lewis structures?
- It affects the arrangement of electrons but not bond types.
- It has no impact on Lewis structure representation.
- It influences which atom will carry a formal charge. (correct)
- It determines the bond strength in single bonds only.
In Lewis structures, an expanded octet typically involves which of the following elements?
In Lewis structures, an expanded octet typically involves which of the following elements?
What type of bonding is primarily represented by Lewis structures?
What type of bonding is primarily represented by Lewis structures?
What is the primary characteristic of ionic bonding?
What is the primary characteristic of ionic bonding?
Which statement correctly defines a polar covalent bond?
Which statement correctly defines a polar covalent bond?
What does the concept of electronegativity refer to?
What does the concept of electronegativity refer to?
Which element has the highest electronegativity according to the Pauling scale?
Which element has the highest electronegativity according to the Pauling scale?
When drawing a Lewis structure, which conditions must be satisfied for a complete octet?
When drawing a Lewis structure, which conditions must be satisfied for a complete octet?
Under which condition can elements in periods 3 and beyond have expanded octets?
Under which condition can elements in periods 3 and beyond have expanded octets?
Which of the following statements about formal charges is inaccurate?
Which of the following statements about formal charges is inaccurate?
In a Lewis structure for chlorine gas (Cl2), how many total valence electrons are present?
In a Lewis structure for chlorine gas (Cl2), how many total valence electrons are present?
What is the typical difference in electronegativity (ΔEN) for a polar covalent bond?
What is the typical difference in electronegativity (ΔEN) for a polar covalent bond?
Which type of bonding is exhibited by sodium chloride (NaCl)?
Which type of bonding is exhibited by sodium chloride (NaCl)?
What is the average formal charge on an oxygen atom in the PO43- ion?
What is the average formal charge on an oxygen atom in the PO43- ion?
What is the average bond order for the P-O bonds in PO43-?
What is the average bond order for the P-O bonds in PO43-?
Which molecule has the highest average terminal C-O bond order among HCO3−, CO2, and CO32−?
Which molecule has the highest average terminal C-O bond order among HCO3−, CO2, and CO32−?
As bond order increases, what happens to bond length?
As bond order increases, what happens to bond length?
What is the relationship between bond length and bond dissociation energy?
What is the relationship between bond length and bond dissociation energy?
How many equivalent resonance structures exist for the PO43- ion?
How many equivalent resonance structures exist for the PO43- ion?
In terms of formal charge, rank HCO3−, CO2, and CO32− from the least negative to the most negative average charge on terminal oxygens.
In terms of formal charge, rank HCO3−, CO2, and CO32− from the least negative to the most negative average charge on terminal oxygens.
What do resonance structures allow for in a molecule?
What do resonance structures allow for in a molecule?
What theory helps predict molecular shape based on electron pair repulsion?
What theory helps predict molecular shape based on electron pair repulsion?
What happens to the bond energy as the bond order increases?
What happens to the bond energy as the bond order increases?
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Study Notes
Bonding
- Involves either the sharing or transfer of outer electrons
- Goal is for atoms to achieve a stable configuration
- Usually accomplished by following the octet rule, which states that atoms strive to have eight valence electrons
Ionic Bonding
- Involves the transfer of electrons
- Usually between a metal and a non-metal
- Example: Sodium Chloride (NaCl)
- Sodium ([Ne]3s1) becomes Na+ ([Ne]) by losing an electron
- Chlorine ([Ne]3s23p5) becomes Cl- ([Ar]) by gaining an electron
Covalent Bonding
- Involves the sharing of electrons
- Usually between two non-metals
- Often used to gain an octet of electrons
- Lewis structures show all electrons as equivalent
- Bonds are often depicted as lines
Electronegativity (EN)
- An atom's ability to attract electrons in a bond
- Trend:EN increases across a period and up a group
- Pauling scale: Fluorine has the highest electronegativity at 4.0
Bond Polarity
- Polar covalent bonds are characterized by unequal sharing of electrons
- Dipole moment: The difference in electronegativity between atoms dictates the polarity of a covalent bond
- Large difference (>1.9): Ionic bond
- Intermediate difference (0.5 - 1.9): Polar Covalent Bond
- Small difference (< 0.5): Nonpolar covalent bond
Electrostatic Potential Maps
- Visual representations of electron density within a molecule
- Red regions indicate high electron density (negative)
- Blue regions indicate low electron density (positive)
Lewis Structures
- Show all bonding and non-bonding electrons
- Formal charges are also indicated
- Complete shells are usually achieved by combining bonding and non-bonding electrons
- Hydrogen is content with 1 electron pair
- Beryllium is content with 2 electron pairs
- Boron and Aluminum are content with 3 electron pairs
- Elements in periods 3 and beyond can have expanded octets if they are the central atom
- Bonding electrons can participate in single, double, or triple bonds
Drawing Lewis Structures
- Count the total number of valence electrons
- Choose the central atom: The least electronegative atom becomes the central atom
- Arrange surrounding atoms
- Fill in the outer atoms with electrons to achieve octets
- Fill in the central atom with electrons to achieve an octet
- If you run out of electrons, make double or triple bonds
Resonance Structures
- Resonance Structures represent alternative Lewis structures for a molecule that share the same connectivity but have different electron distributions.
- These structures are connected by double headed arrows
- The resonance hybrid is an average of all possible resonance structures
- They help explain the delocalization of electrons within a molecule
- Bond lengths, orders, and charges are averages of all resonance structures
- Most polyatomic anions have resonance structures
Bond Order, Length & Energy
- Covalent bond length: The approximate distance between two nuclei involved in a covalent bond
- Bond dissociation energy (homolysis): The energy required to break 1 mole of bonds in the gas phase
- Bond order, length, and energy are related:
- As bond order increases, bond length decreases
- As bond length decreases, bond energy increases
Molecular Shape
- VSEPR Theory/Gillespie-Nyholm theory proposes: Electron pairs around a central atom repel each other and try to maximize their separation
Special Cases
- The octet rule is more important for C, N, O, F
- Minimizing formal charges is more important for other elements on the periodic table
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