Chemistry Covalent Compounds Quiz

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Questions and Answers

What occurs when an atom has a high electronegativity value in a covalent bond?

  • Attraction of the shared electrons towards itself (correct)
  • Decreased bond strength
  • Formation of a nonpolar bond
  • Increased electron sharing

Which electronegativity value range is indicative of a polar covalent bond?

  • 1.7 to 2.5
  • Greater than 2.5
  • 0.4 to 1.7 (correct)
  • 0.0 to 0.4

What is a primary reason that covalent substances typically do not conduct electricity?

  • They have too many ions
  • They are always solids at room temperature
  • They lack free-moving electrons (correct)
  • They form ionic bonds instead

What is the expected effect of impurities on the melting point of recrystallized benzoic acid?

<p>It lowers the melting point and widens the range (C)</p> Signup and view all the answers

What type of bond would form with an electronegativity difference greater than 1.7?

<p>Ionic bond (C)</p> Signup and view all the answers

What phenomenon occurs when soluble impurities are dissolved during recrystallization?

<p>They remain in solution (D)</p> Signup and view all the answers

Why is it essential to keep all equipment hot during the recrystallization of benzoic acid?

<p>To prevent crystallization of benzoic acid in solution (B)</p> Signup and view all the answers

In the test for nitrates, what result indicates a positive outcome with Iron II sulfate and concentrated sulfuric acid?

<p>A brown ring forms at the bottom (C)</p> Signup and view all the answers

What happens when ammonia is added to a solution containing chloride ions?

<p>The precipitate dissolves (C)</p> Signup and view all the answers

What is formed when magnesium sulfate is added to a solution containing carbonate ions?

<p>A white precipitate is formed (D)</p> Signup and view all the answers

What characteristic of covalent bonds distinguishes them from ionic bonds?

<p>They involve the sharing of electrons. (C)</p> Signup and view all the answers

What is the primary reason that molecular compounds typically do not conduct electricity?

<p>They do not dissociate into ions. (C)</p> Signup and view all the answers

What defines the difference between a sigma bond and a pi bond?

<p>A sigma bond is stronger than a pi bond. (C), A sigma bond forms before a pi bond (B)</p> Signup and view all the answers

Which statement best describes the characteristic of polar covalent bonds?

<p>Electrons are shared unequally between two atoms. (A)</p> Signup and view all the answers

How does the Octet Rule influence the behavior of atoms during bonding?

<p>Atoms aim to have eight valence electrons by sharing or transferring electrons. (A)</p> Signup and view all the answers

How does valency impact the formation of a compound?

<p>Valency indicates the number of bonds an atom can form based on its outer electrons. (A)</p> Signup and view all the answers

What distinguishes lone pairs from bond pairs in covalent bonding?

<p>Bond pairs share electrons while lone pairs do not. (A)</p> Signup and view all the answers

What characteristic is responsible for the high melting and boiling points of ionic compounds?

<p>Strong electrostatic forces between charged ions. (B)</p> Signup and view all the answers

What is the primary difference between an atom and an ion?

<p>An atom has a neutral charge, while an ion has a charge due to loss or gain of electrons. (B)</p> Signup and view all the answers

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Study Notes

Covalent and Ionic Compounds

  • Covalent compounds do not conduct electricity in molten state or solutions because they do not dissociate into ions.
  • Ionic compounds exhibit high melting and boiling points due to strong electrostatic forces between oppositely charged ions.

Bonding Types

  • A σ (sigma) bond results from end-on overlapping of orbitals, while a Ï€ (pi) bond forms from the sideways overlap of p-orbitals.
  • Electrons involved in a covalent bond are known as bond pairs; non-bonding electrons are called lone pairs.
  • Covalent compounds are characterized by electron sharing, in contrast to ionic compounds where charge transfer occurs.

Molecular Characteristics

  • Polar covalent bonds are defined by unequal electron sharing between two atoms, leading to partial charges.
  • The Octet Rule dictates that atoms prefer to have eight electrons in their outer energy level during chemical bonding.
  • Atoms are neutral, while ions carry charge, with ionic bonding involving the attraction of oppositely charged ions.

Valency and Electronegativity

  • Valency indicates the number of bonds an atom can form, essential for achieving stable electronic configurations in compounds.
  • Electronegativity measures an atom's attraction to shared electrons in a covalent bond, influencing the bond's polarity.

Predicting Bond Types

  • The type of bond can be predicted based on electronegativity differences:
    • Nonpolar covalent when difference is less than 0.4
    • Polar covalent when between 0.4 and 1.7
    • Ionic when greater than 1.7

Physical Properties of Covalent Substances

  • Covalent substances typically possess low melting and boiling points.

Experimental Techniques

  • Recrystallization is employed to purify benzoic acid by removing impurities.
  • Keeping equipment hot during this process prevents recrystallization of benzoic acid in solution.
  • Soluble impurities are washed away while the pure compound solidifies.
  • Melting point measurement of recrystallized benzoic acid indicates purity; the presence of impurities lowers the melting point and broadens the range.

Chemical Tests

  • A brown ring at the bottom of a test tube indicates the presence of nitrates when Iron II sulfate and sulfuric acid are added.
  • The precipitate formed from chloride ions dissolves upon the addition of ammonia.
  • Adding magnesium sulfate to a solution containing carbonate ions results in the formation of a white precipitate.

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