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Questions and Answers
A nonpolar covalent bond occurs when the difference in electronegativity between two atoms is greater than 0.5.
False
Atoms generally form bonds to increase the energy of the system.
False
Ionic bonds are formed between atoms with similar electronegativities.
False
The Pauling scale is used to measure ionization energy.
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Polar covalent bonds occur when the difference in electronegativity is between 0.5 and 2.0.
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Metallic bonds involve the sharing of electrons between individual atoms.
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Hydrogen bonds constitute a form of ionic bonding.
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The electronegativity value for carbon is lower than that for chlorine.
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The vector length indicates the polarity of a bond.
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C2H2Cl2 is shown to be a non-polar molecule in all representations.
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The direction of the vector points toward the less polar atom.
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The parallelogram method can be used to determine the direction of the molecular polarity vector.
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In the analysis of C2H2Cl2, the polarities are indicated with Greek letters δ+ and δ–.
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Ionic bonds result from the complete transfer of one or more valence electrons between two atoms.
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Atoms with partial charges are referred to as being delta negative (δ–).
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The electronegativity difference required for ionic bonding is greater than 1.5.
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Ionic compounds tend to be gases at normal temperatures and pressures.
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The electronegativity of hydrogen is greater than that of carbon.
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Water (H2O) is covalently bonded due to the equal sharing of electrons.
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Ionic compounds typically form between metallic and non-metallic elements.
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A bond with an electronegativity difference of 0.8 would be classified as ionic.
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The compound acetone (C3H6O) contains ionic bonds.
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Elements towards the left of the periodic table tend to lose electrons easily, promoting the formation of ionic bonds.
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Cations become smaller and more highly charged from right to left across a period.
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Anions become larger and more polarisable down a group.
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The polarising power of diagonal neighbours in cations is significantly different.
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Anions become less polarisable as the associated cation becomes more positively charged.
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In ionic compounds, cations have no effect on the distortion of anion electron clouds.
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The electric dipole moment is a measurement of the magnitude of the dipole.
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When comparing Li+ and Na+, Li+ is generally more polarising due to its size and charge.
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Anions become smaller and less charged from left to right across a period.
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Polarisation leads to a more distorted electron cloud in negatively charged ions.
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The sizes of atoms and ions are commonly measured in micrometers (µm).
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HF has a dipole moment of 1.91.
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The molecule CH4 has a non-zero electric dipole moment.
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NaCl is a polar molecule with a dipole moment of 9.00.
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CO2 is considered a polar molecule due to its linear structure.
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CCl4 has a dipole moment of 1.04.
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NH3 has a dipole moment value of 1.47.
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Polar bonds can result in a nonpolar molecule if their dipoles cancel out.
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O3 has a dipole moment of 0.53.
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Dichloromethane (CH2Cl2) has a dipole moment of 1.55.
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HCl has a dipole moment of 1.08, making it a nonpolar molecule.
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Study Notes
Electronegativity
- A measure of an element's tendency to attract electron pairs.
- The Pauling scale is used to measure electronegativity.
Bonding
- A chemical bond forms when the combined atoms' energy is lower than the separate atoms' energy.
- Atoms strive for stability by completing or filling their outermost valence shells.
- Electronegativity plays a crucial role in bond formation.
- Various bond types exist, including:
- Nonpolar covalent
- Polar covalent
- Ionic
- Hydrogen bonding
- Coordinate bonds
- Metallic bonds
- Bonds can be single, double, or triple.
- Bonds can be classified as σ-bonds or π-bonds.
Nonpolar Covalent Bonds
- Atoms share an electron pair, resulting in no or minimal partial charges on the atoms.
- Form molecular compounds.
- Exist as solids, liquids, or gases at normal temperatures and pressures.
- Formed between elements with similar electronegativities.
- Electronegativity difference in nonpolar covalent bonds is less than 0.5.
Polar Covalent Bonds
- Electrons are shared unequally between two atoms.
- Solids, liquids, or gases at normal temperatures and pressures.
- Partial charges exist on atoms.
- Electronegativity difference in polar covalent bonds is between 0.5 and 2.0.
Ionic Bonds
- A complete transfer of valence electrons occurs from one atom to another.
- Full charges exist on resulting ions.
- High aqueous solubility.
- Attraction between cations and anions.
- Form ionic compounds.
- Solids at normal temperatures and pressures.
- Formed between elements with significant electronegativity differences.
- Ionic compounds are formed between metallic and nonmetallic elements typically.
- Electronegativity difference is greater than 2.0.
Polarisation - Cations
- In ionic compounds, the anion's spherical electron cloud distorts due to cation attraction.
- Smaller, more highly charged cations are more strongly polarizing, moving left to right across a period (Be2+ vs. Li+, Mg2+ vs. Na+, Al3+ vs. Mg2+).
- Cations become larger and less polarizing down a group (K+ vs. Na+ vs. Li+).
- Diagonal neighbors have similar polarizing power (Li+ ≈ Mg2+, Be2+ ≈ Al3+).
Polarisation - Anions
- Anions become smaller, less highly charged, and less polarizable (electron cloud becomes less distorted) from left to right across a period (O2- vs. F-).
- Anions become more polarizable as the associated cation becomes more positively charged (NaCl vs. MgCl2 vs. AlCl3).
- Anions become larger and more polarizable (electron cloud becomes more distorted) down a group (F- vs. Cl- vs. Br- vs. I-).
Dipoles and Partial Charges
- Partial charges result from small shifts in electron distribution.
- An electric dipole describes a positive charge next to an equal but opposite negative charge.
- Electric dipole moment (μ, debye) indicates the dipole's magnitude.
Polar Bonds vs. Polar Molecules
- A polar bond describes a covalent bond between atoms with partial charges.
- A polar molecule has a non-zero electric dipole moment.
- A molecule may have polar bonds but be nonpolar overall due to its shape, where the individual bond dipoles cancel each other.
Testing Molecular Polarity Using Vectors
- Vectors are used to determine a molecule's overall polarity.
- Vectors have length and direction and can be added or subtracted.
- A vector can represent a polar bond.
- The vector direction points towards the more polar atom along the bond axis.
- The vector length signifies the bond's polarity.
Testing Molecular Polarity Using Vectors - Examples
- C2H2Cl2 (1,2-Dichloroethene) can be polar or nonpolar depending on the chlorine atom positions. When chlorine atoms are on the same side of the molecule, it's polar. When on opposite sides, it's nonpolar.
- Vector analysis can be used to predict the overall polarity of the molecule.
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Description
This quiz covers the concepts of electronegativity and its significance in chemical bonding. You'll explore various types of bonds, including nonpolar covalent, polar covalent, ionic, and more, along with the role of electronegativity in bond formation. Test your understanding of key terms and principles in chemistry.
