Types of Bonds

Types of Bonds

Ionic Bonds

  • Ionic bonds are formed between metals and nonmetals.

  • Characteristics of Elements:

    • Nonmetals have high electronegativity values.

    • Metals have low electronegativity values.

Electron Transfer

  • There is a large difference in the electronegativity values of metals and nonmetals.

  • Electrons are transferred from the metal to the nonmetal:

    • The metal becomes a positive cation (e.g., Na+).

    • The nonmetal becomes a negative anion (e.g., Cl-).

Example Element Pairs

  • Sodium (Na) and Chlorine (Cl):

    • Na: Low Electronegativity (loses electron)

    • Cl: High Electronegativity (gains electron)

Crystal Lattice Formation

  • Ionic substances form large crystal lattices.

  • Characteristics of Ionic Substances:

    • Have very high melting points.

    • Exist as hard, brittle solids at room temperature.

    • Break easily due to lattice disruption:

    • When an external force is applied, similar charges repel, causing the crystal structure to crack.

Conductivity

  • Ionic substances do not conduct electricity as solids because the ions are locked in place.

  • Conductivity occurs when:

    • Molten (liquid form).

    • Dissolved in water (aqueous solution).

Electrolytes

  • Ionic substances that conduct electricity when dissolved are referred to as electrolytes.

Questions for Review on Ionic Bonds

  1. What types of elements bond to form ionic substances?

  2. Why are electrons transferred in ionic bonds?

  3. Why are ionic substances solid and brittle?

  4. Why do ionic substances only conduct electricity when molten or dissolved?

Covalent Bonds

  • Covalent bonds are formed between nonmetals.

  • Due to similar electronegativity values, electrons are shared between the bonding elements.

Bond Formation

  • The nuclei of each element attract the electron clouds of neighboring elements.

  • Covalent bonding occurs when the attractive forces equal the repulsive forces, resulting in overlapping electron clouds.

Molecular Substances

  • Substances that are covalently bonded are known as molecular substances.

    • Example: Table Salt as Ionic (NaCl).

    • Example: Sucrose (C12H22O11) as a molecular compound.

    • Other examples: Water (H2O), Propane (C3H8).

Melting and Boiling Points

  • Covalent substances generally have:

    • Low melting and boiling points.

    • Can exist as solids, liquids, or gases at room temperature.

Conductivity in Covalent Substances

  • Covalent substances do not conduct electricity and are termed nonelectrolytes.

  • Comparison:

    • Dissolved ions (e.g., NaCl) are electrolytes.

    • Dissolved molecules (e.g., sugar) are nonelectrolytes.

Questions for Review on Covalent Bonds

  1. What types of elements form covalent substances?

  2. Why are covalent substances called molecular substances?

  3. Explain how a covalent bond forms in terms of attractive and repulsive forces.

  4. Do covalent substances conduct electricity?

Polar and Nonpolar Covalent Bonds

  • Nonpolar Covalent Bond:

    • Elements have very similar electronegativity values.

    • Electrons are shared equally, resulting in an even distribution of charge.

    • Example: C-C bond.

  • Polar Covalent Bond:

    • There is a moderate electronegativity difference between the atoms.

    • Electrons are shared unequally, leading to an uneven distribution of charge:

    • δ+ indicates a partial positive charge.

    • δ- indicates a partial negative charge.

    • Example: O-H bond.

Comparison of Bonds

  • Nonpolar Covalent Bond vs. Polar Covalent Bond vs. Ionic Bond:

    • A continuum exists from ionic to nonpolar covalent substances.

Questions for Review on Polar vs. Nonpolar Bonds

  1. What is the difference between a polar and a nonpolar covalent bond?

  2. Which types have very similar electronegativity values?

Identifying Bond Types

  • Example Compounds:

    • KCl (Ionic or Covalent?)

    • Na2SO4 (Ionic or Covalent?)

    • O2 (Ionic or Covalent?)

    • CH4 (Ionic or Covalent?)

    • Consider if it is metal-nonmetal or nonmetal-nonmetal.

Covalent-Network Bonds

  • Covalent-Network Bonds are formed by elements such as carbon and silicon, which create a network of overlapping atoms.

    • Examples include diamond and graphite.

  • Allotropes:

    • Definition: Allotropes are two or more physical forms in which an element can exist.

    • Examples of Carbon Allotropes:

    • Diamond

    • Graphite

    • Fullerene

    • Soot

Metallic Bonds

  • Formed between metal atoms.

  • Metals form large crystals with many vacant outer orbitals that overlap:

    • This allows electrons to flow freely, creating a delocalized 'sea of electrons'.

Properties of Metals

  • All metals are solid at room temperature, except for mercury.

  • Metals are characterized as:

    • Malleable: Can be hammered into thin sheets.

    • Ductile: Can be drawn into wires.

Electrical and Thermal Conductivity

  • Metals conduct heat and electricity very well due to the delocalized electrons that can flow and carry current.

Appearance of Metals

  • Metals appear shiny because they absorb and emit a wide range of colors:

    • Electrons can absorb quantized energy and become excited; when they fall back, they release energy as light.

Questions for Review on Metallic Bonds

  1. Why do we say metals are nuclei floating in a “sea of electrons”?

  2. Why do metals conduct electricity as solids?

Comparison Chart for Bond Types

Bond Type

State at Room Temp

Conductivity

Other Properties

Ionic

Solid

Conducts in solutions or molten

Brittle, high melting point

Covalent

Mostly liquid or gas

Non-conductor

Low melting/boiling points

Metallic

Solid

Conductor

Malleable, ductile, shiny

Identifying Bond Types: Example Scenarios

  1. A shiny substance that is malleable and conducts electricity (likely metallic).

  2. A white, crystalline substance that does not conduct as a solid, but does conduct when dissolved in water (likely ionic).

  3. A white crystalline substance that does not conduct as a solid or when dissolved in water (likely covalent).

  4. A greenish gas that has a sharp smell (likely covalent).

Matching Properties to Bond Types

  1. Sea of electrons: c. Metallic substances

  2. Crystal lattice: a. Ionic substances

  3. Individual molecules: b. Covalent substances

  4. Conduct when solid: c. Metallic substances

  5. Conduct when dissolved in water: a. Ionic substances

  6. Never conduct: b. Covalent substances

  7. Carbon and silicon: d. Covalent-network substances