Chemical Bonding and Ions - Unit IV
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Questions and Answers

What is the name given to a positively charged ion?

Cation

What is the periodic property related to the gain and loss of electrons?

Gain & loss of electron

Atoms will gain or lose electrons to form ions that are less stable than their parent atoms.

False

What is the suffix used for anions?

<p>ide</p> Signup and view all the answers

What is the word added to the name of cations with only one ionic form?

<p>ion</p> Signup and view all the answers

What is the term used to indicate the charge of a cation with multiple ionic forms?

<p>Stock number</p> Signup and view all the answers

Ionic radius is not a periodic property.

<p>False</p> Signup and view all the answers

How does ionic charge affect ionic radius?

<p>Ionic charge affects the ionic radius, with a higher ionic charge resulting in a smaller ionic radius.</p> Signup and view all the answers

Which of the following statements is TRUE about ionic radius of transition elements?

<p>It is more variable than atomic radius.</p> Signup and view all the answers

What is the general trend for ionic radius as we move down a group?

<p>Ionic radius increases going down a group.</p> Signup and view all the answers

What is the general trend for ionic radius as we move across a period?

<p>Ionic radius generally decreases going across a period.</p> Signup and view all the answers

Which ion is the largest in size among Cs+, K+, F-, and Cl-

<p>Cs+</p> Signup and view all the answers

Ionic bonding involves the complete transfer of electrons from one atom to another.

<p>True</p> Signup and view all the answers

What type of attraction forms an ionic bond?

<p>Electrostatic attraction</p> Signup and view all the answers

What law describes the force between two charged particles?

<p>Coulomb's law</p> Signup and view all the answers

What is the value of the constant 'k' in Coulomb's law?

<p>9 × 10⁹ N• m²• C⁻²</p> Signup and view all the answers

A negative potential energy between two ions indicates repulsion.

<p>False</p> Signup and view all the answers

What is the tendency for atoms in the s- and p-blocks to combine in a way that each atom acquires eight electrons in its valence shell known as?

<p>Octet rule</p> Signup and view all the answers

What is the chemical formula of the ionic compound formed from the reaction between sodium and sulfur?

<p>Na₂S</p> Signup and view all the answers

Covalent bonding occurs between elements with similar electronegativity values.

<p>True</p> Signup and view all the answers

Covalent bonding involves the transfer of electrons.

<p>False</p> Signup and view all the answers

What is the type of covalent bond when two atoms share one electron pair?

<p>Single bond</p> Signup and view all the answers

Atoms with similar electronegativity values share the electrons ______, forming ______ covalent bonds.

<p>equally, non-polar</p> Signup and view all the answers

Atoms with different electronegativity values share electrons ______, forming ______ covalent bonds.

<p>unequally, polar</p> Signup and view all the answers

What is a molecule that has partial charges on opposite ends called?

<p>Dipole</p> Signup and view all the answers

What is the measure of the bond polarity?

<p>Dipole moment</p> Signup and view all the answers

The dipole moment is the product of the charge on either atom and the distance between them.

<p>True</p> Signup and view all the answers

What is the SI unit for a dipole moment?

<p>Coulomb-meter (Cm)</p> Signup and view all the answers

What is the name of a convenient unit used for covalent bond polarities?

<p>Debye (D)</p> Signup and view all the answers

What is the conversion factor between debye (D) and Coulomb-meter (Cm)?

<p>1D = 3.34 x 10⁻³⁰ Cm</p> Signup and view all the answers

According to the 'thumb rule', if the electronegativity difference between bonded atoms is greater than 0.4, the bond will behave as ______.

<p>polar</p> Signup and view all the answers

According to the 'thumb rule', if the electronegativity difference between bonded atoms is 0.4 or less, the bond will behave as ______.

<p>non-polar</p> Signup and view all the answers

What are polyatomic ions also known as?

<p>Molecular ions</p> Signup and view all the answers

Polyatomic ions have no charge.

<p>False</p> Signup and view all the answers

Atomic orbitals overlap to form molecular orbitals.

<p>True</p> Signup and view all the answers

Electrons in covalent bonds reside only in atomic orbitals.

<p>False</p> Signup and view all the answers

What is the relation between the total number of molecular orbitals and the total number of atomic orbitals involved in bonding?

<p>The total number of molecular orbitals is equal to the total number of atomic orbitals involved in bonding.</p> Signup and view all the answers

What is a molecular orbital that is lower in energy than the involved atomic orbitals called?

<p>Bonding molecular orbital</p> Signup and view all the answers

What is a molecular orbital that higher in energy that the involved atomic orbitals called?

<p>Anti-bonding molecular orbital</p> Signup and view all the answers

Electrons filling in a molecular orbital follow the Aufbau principle, the Pauli Exclusion Principle and Hund's Rule.

<p>True</p> Signup and view all the answers

Electrons in bonding orbitals ______ the molecule, while electrons in antibonding orbitals ______ the molecule.

<p>stabilize, destabilize</p> Signup and view all the answers

Filled antibonding orbitals decrease the electron density between the atoms.

<p>True</p> Signup and view all the answers

How is Anti-bonding molecular orbital formed?

<p>Anti-bonding molecular orbitals are formed by the out-of-phase combination of atomic orbitals.</p> Signup and view all the answers

What is the name of the allotrope of carbon that has 2-dimensional properties?

<p>Graphene</p> Signup and view all the answers

What is the hybridization state of carbon atoms in graphene?

<p>sp² hybridization</p> Signup and view all the answers

What is the length of a C-C bond in graphene?

<p>1.42 Å</p> Signup and view all the answers

The stability of graphene is attributed to the weak interactions between its carbon atoms.

<p>False</p> Signup and view all the answers

Graphene is chemically the least reactive form of carbon.

<p>False</p> Signup and view all the answers

Graphene burns at a very high temperature.

<p>False</p> Signup and view all the answers

Graphene is a good conductor of electricity.

<p>True</p> Signup and view all the answers

Electrons in graphene flow more easily than in copper.

<p>True</p> Signup and view all the answers

Graphene is a good thermal conductor.

<p>True</p> Signup and view all the answers

Graphene is the lightest material ever discovered.

<p>False</p> Signup and view all the answers

Graphene is brittle and easily breaks.

<p>True</p> Signup and view all the answers

Graphene is permeable to gases and allows them to pass through.

<p>False</p> Signup and view all the answers

Graphene can only transmit 50% of light.

<p>False</p> Signup and view all the answers

Carbon nanotubes (CNTs) are made by wrapping a graphene sheet.

<p>True</p> Signup and view all the answers

Carbon nanotubes have low thermal conductivity.

<p>False</p> Signup and view all the answers

What is the approximate elongation to failure for carbon nanotubes?

<p>~18%</p> Signup and view all the answers

Carbon nanotubes have low tensile strength.

<p>False</p> Signup and view all the answers

Carbon nanotubes are inflexible and cannot be bent.

<p>False</p> Signup and view all the answers

Carbon nanotubes have a high thermal expansion coefficient.

<p>False</p> Signup and view all the answers

Carbon nanotubes are not good electron field emitters.

<p>False</p> Signup and view all the answers

What is the process used to synthesize CNTs by striking an electric arc between two graphite electrodes?

<p>Electric arc discharge process</p> Signup and view all the answers

What is the typical size of the graphite electrodes used in the electric arc discharge process to produce CNTs?

<p>5-25mm</p> Signup and view all the answers

What is the typical gap between the electrodes during the electric arc discharge process?

<p>~1mm</p> Signup and view all the answers

What is the typical current applied during the electric arc discharge process?

<p>50-100 amp</p> Signup and view all the answers

What is the typical voltage used in the electric arc discharge process?

<p>15-25 volts</p> Signup and view all the answers

What is the typical environment used in the electric arc discharge process?

<p>He gas (100-500 torr pressure for CNTs &amp; below 100 torr for fullerenes)</p> Signup and view all the answers

What is the chemical method used to synthesize CNTs by cracking a hydrocarbon gas?

<p>Chemical Vapor Deposition</p> Signup and view all the answers

What are some of the common gases used in the chemical vapor deposition process to synthesize CNTs?

<p>Benzene, Hexane, or Methane</p> Signup and view all the answers

What is the typical pressure range used in the chemical vapor deposition process?

<p>0.1 to 1 torr</p> Signup and view all the answers

What are some common catalysts used in the CVD process for CNT synthesis?

<p>Fe/Co/Ni/Pt</p> Signup and view all the answers

What is the typical furnace temperature used in the CVD process?

<p>~1000°C</p> Signup and view all the answers

Fullerenes are similar in structure to graphene.

<p>True</p> Signup and view all the answers

What is the hybridization state of carbon atoms in fullerenes?

<p>sp² hybridization</p> Signup and view all the answers

Fullerenes consist of only hexagonal rings.

<p>False</p> Signup and view all the answers

Fullerenes have only one bond length.

<p>False</p> Signup and view all the answers

Study Notes

Unit IV: Chemical Bonding - The Formation of Materials

  • This unit covers chemical bonding and its effect on the chemical properties of elements.
  • Ionic and covalent bonding are compared based on the octet rule and valence bond theory.
  • Polar and non-polar covalent bonds are discussed.
  • Molecular orbital theory is introduced to explain magnetism, bond order, and hybridization, which is helpful in Carbon chemistry.
  • Intermolecular forces, including hydrogen bonding, are examined.
  • A case study focuses on the special properties of water.

Atoms and Ions

  • Cations are positively charged ions.
  • Anions are negatively charged ions.
  • Periodic property: Gain and loss of electrons.
  • Atoms gain or lose electrons to form ions with more stable electronic configurations than their parent atoms.
  • This stability is achieved by achieving a closed valence shell.

Periodic Table and Common Ions

  • A periodic table is shown, representing the common ions formed by elements in each group.
  • Some elements have more than one ionic form, indicated by an asterisk (*).
  • A table lists elements with multiple ionic forms, their groups, and associated ionic forms.

Variability in Ionic Forms

  • Transition metals require significant energy to remove all valence electrons to reach a noble gas configuration.
  • Achieving additional ionic forms is more energy-efficient by losing fewer electrons.
  • The resulting electronic configuration remains more stable than the parent atom's configuration.

Determining Electronic Configuration of Ions

  • The electronic configuration of O²⁻ is [He]2s²2p⁶.
  • Electronic configurations for Ni(II) and Fe(II) are also needed.

Naming Ions

  • Anions are named by adding "-ide" to the root of the parent element's name (e.g., chloride, nitride).
  • Cations with one ionic form are named by adding "ion" to the element's name (e.g., sodium ion, zinc ion).
  • Cations with multiple ionic forms are named using a Roman numeral in parentheses to indicate the charge (e.g., iron(II), iron(III)).

Ionic Radius

  • Ionic radius is a periodic property.
  • The graph displays atomic radius (blue) and ionic radius (green) in picometers as a function of atomic number.
  • Anions have a larger ionic radius than their parent atoms.
  • Cations have a smaller ionic radius than their parent atoms.
  • The ionic radius of transition metals is variable compared to neutral atoms because ionic charge affects the ionic radius.
  • A higher ionic charge leads to a stronger nuclear attraction and a smaller ionic radius.
  • A summary lists that cations are smaller than their parent atoms, anions are larger, and increasing charge decreases ionic radius.

What's the Ionic Radius Trend in Transition Elements

  • The ionic radius of the transition metals exhibits more variability than the atomic radius of the neutral atoms.
  • Ionic charge impacts the ionic radius.
  • Higher ionic charge results in stronger nuclear attraction and a smaller ionic radius.

Octet Rule

  • Atoms in the s- and p-blocks tend to combine in ways that achieve eight valence electrons. Example: NaCl.

Determining Chemical Formula

  • Calculate the formula for a compound formed from the ionic reaction of sodium and sulfur.
  • Identify the electronic configurations and electron dot representations for the neutral atoms.
  • Determine the combination of atoms that result in a closed valence shell (eight electrons).
  • Write out the chemical formula.

Covalent Bonding

  • Covalent bonding involves elements with similar electronegativities.
  • A closed valence shell is achieved by sharing electrons (e.g., H₂ and Cl₂).

Covalent Bond Types

  • Single bond: Sharing one electron pair.
  • Double bond: Sharing two electron pairs.
  • Triple bond: Sharing three electron pairs.
  • Non-polar covalent bonds: Equal sharing of electrons between atoms with similar electronegativities.
  • Polar covalent bonds: Unequal sharing of electrons between atoms with different electronegativities.
  • Dipole: A bond or molecule with a partial positive charge on one end and a partial negative charge on the other end.
  • Dipole moment: A measure of bond polarity

Dipole Moment

  • The bond dipole is modeled as two partial opposite charges (δ+ and δ−) separated by a distance.
  • The dipole moment (µ) is calculated as the product of the charge magnitude (δ) and the bond length (d).
  • SI units for dipole moment are coulomb-meters (Cm), while a convenient unit for covalent bond polarities is debye (D).

Pauling Scale

  • The Pauling scale provides electronegativity values for elements.

"Thumb Rule" for Bond Behavior

  • Electronegativity difference > 0.4: Polar bond
  • Electronegativity difference ≤ 0.4: Non-polar bond
  • Electronegativity difference > 2: Ionic bond

Mixed Covalent/Ionic Bonding

  • Polyatomic ions (molecular ions) are ions composed of multiple atoms covalently bonded to behave as a single unit.
  • Polyatomic ions have a charge because the group of atoms gains or loses electrons

Molecular Orbitals

  • Atomic orbitals overlap to form molecular orbitals.
  • Electrons in covalent bonds are not confined to atomic orbitals but occupy molecular orbitals.
  • The number of molecular orbitals equals the number of atomic orbitals involved in bonding.
  • Bonding molecular orbital (lower energy than atomic orbitals).
  • Anti-bonding molecular orbital (higher energy than atomic orbitals).

MO for Helium (molecule)

  • A molecular orbital diagram for the H₂ molecule is displayed.

MO Shapes

  • The shapes of bonding and anti-bonding molecular orbitals are illustrated, showing atomic orbital and molecular orbital shapes for bonding and anti-bonding molecular orbitals.

Bond Order

  • Single covalent bonds comprise one sigma molecular orbital (σ).
  • Double covalent bonds comprise one sigma molecular orbital (σ) and one pi molecular orbital (π).
  • Triple covalent bonds comprise one sigma molecular orbital (σ) and two pi molecular orbitals (π).
  • Bond order is the number of bonds between two atoms. The bond order is determined from a molecular orbital diagram.

MO for Oxygen Molecule

  • A molecular orbital diagram for the oxygen molecule is demonstrated.

MO for Nitrogen Molecule

  • A molecular orbital diagram for the nitrogen molecule is shown

Electronic Configurations

  • A table showing electronic configurations, bond order, bond energy, bond lengths, and unpaired electrons for diatomic molecules formed from elements in the second period of the periodic table.

Engineering Materials - Nano materials

  • Materials that have at least one dimension in the range of 1 to 100 nm are considered nanomaterials.
  • Mechanical, thermal, optical, electrical, and magnetic properties of materials change when the particles have nanometer dimensions.

Allotropes of Carbon:

  • Graphene, diamond, fullerene, and carbon nanotubes are displayed.
  • These are allotropes of carbon, having different crystal structures.

Structure Of Graphene

  • Graphene is a crystalline allotrope of carbon with 2-dimensional properties.
  • Carbon atoms are sp² hybridized.
  • Each carbon atom forms one sigma bond and one pi bond with each of its three nearest neighbours.
  • C-C bond length in graphene is 1.42 Å.
  • The structure's stability stems from the tightly packed carbon atoms and their sp² orbital hybridization, forming sigma bonds and pi bonds.

Properties of Graphene

  • Graphene is chemically very reactive.
  • Graphene burns at a low temperature.
  • Graphene displays high electron mobility.
  • Graphene is a good conductor of electricity and perfect thermal conductor with exceptionally high strength per unit weight.

Applications of Graphene

  • Bio-medical advancements, including DNA sequencing.
  • Integrated circuits and high-performance processors.
  • Optical electronics and displays like touchscreens, liquid crystal displays, and organic photovoltaics.
  • Energy Storage Devices: Supercapacitors
  • Nano-ribbon Filters, and Chemical Sensors
  • Piezoelectric, energy harvesting and composite materials
  • Liquid Cells for Electron Microscopy, and thermal management
  • Optical Modulators

Types of Carbon Nanotubes

  • Single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), armchair, zigzag, and chiral configurations are demonstrated.

Properties of Carbon Nanotubes

  • High thermal conductivity
  • High electrical conductivity
  • High tensile strength
  • Very elastic with considerable bending ability
  • Low thermal expansion coefficient.
  • Good electron field emitters

Synthesis of Carbon Nanotubes (CNTs)

  • Electric arc discharge method (two graphite electrodes under specific conditions).
  • Chemical Vapor Deposition (CVD) method (using hydrocarbons at specified pressure and temperatures).

Applications of Carbon Nanotubes

  • Field emission, thermal conductivity, energy storage, conductive properties, conductive adhesives, and thermal materials are among the applications of Carbon Nanotubes.
  • Molecular electronics, structural applications such as fibers and fabrics, and biomedical use.
  • CNTs are beneficial in air and water filtration.

Fullerene Structure

  • Fullerenes have a structure similar to graphite, with linked hexagonal rings and have a football-like shape called Bucky ball.
  • Fullerenes exhibit sp² hybridization and have a trigonal planar shape, consisting of 20 hexagons and 12 pentagons.
  • Each carbon atom is attached to three other carbon atoms and has sp² hybridization.
  • The C60 molecule's structure features two bond lengths: 6:6 bonds (like double bonds) and 6:5 bonds. C60 contains 30 double bonds.

Applications of Fullerene (C60)

  • Antioxidants, antiviral agents, photosensitizers for photodynamic therapy (PDT).
  • Solar cells, protective eye wear, and hydrogen gas storage.

Polymers

  • Polymers are large molecules (macromolecules) formed from repeating subunits.
  • Synthetic plastics (polystyrene) and natural biopolymers (DNA, proteins) are examples.

Monomers

  • Monomers are the small molecules that make up polymers.

Polymerization

  • Polymerization is the process of joining monomers chemically to form polymer chains or three-dimensional networks.

Polymerization Reactions: Addition Polymerization

  • Monomers add to each other through a catalyst.
  • Examples include alkenes like ethene and propene, which contain double bonds.
  • Polyethylene formation via addition polymerization is illustrated

Polymerization Reactions: Condensation Polymerization

  • Monomers join to form polymers, releasing a small molecule as a byproduct (e.g., water, carbon dioxide, ammonia).
  • Two different monomers usually react alternately. Example nylon-66 formation

Degree of Polymerization (DP)

  • DP is the number of repeating monomer units in a polymer chain.

Functionality of Polymers

  • Functionality of a monomer is the number of bonds that a monomer's repeating unit forms with other monomers.
  • Mono-, di-, and tri-functional molecules are defined.

Conducting Polymers

  • Conductive polymers conduct electricity and are either intrinsic or extrinsic.
  • Some polymers become conductive by doping with electron donors or acceptors (e g. Polyaniline). Example structures of conducting polymers are shown.

Doping

  • Doping increases conductivity by adding or removing electrons from a polymer.
  • Different doping techniques are described, including oxidative doping (p-type), reductive doping (n-type), and protonic doping.
  • Doping with oxidizing and reducing agents are shown with mechanisms.

Electroluminescent Polymers

  • Electroluminescence is the property of a material to emit light when stimulated electrically.
  • Electroluminescent polymers are used to create light–emitting devices.

Construction and Working – Electroluminescent device

  • Describe layered structure in the electroluminescent Polymer device.
  • Explain the injection of holes and electrons through the anode and cathode.
  • Explain the mechanisms of light emission.

PPV Polymer

  • Precursor polymer of poly(p-phenylene vinylene) (PPV) is a preparation method using precursor and its heating to form PPV.

Biomaterials

  • Biomaterials are intended to interface with biological systems, such as tissues and organs, for evaluation, treatment, enhancement, or replacement.
  • Bioceramics, metallic biomaterials, biocomposites, biologically based biomaterials, and polymeric biomaterials are discussed.

Biocompatibility

  • Biocompatibility is the ability of a material to perform in a system with an appropriate biological response.
  • Host response is the biological reaction to the material's presence.

Polymeric Biomaterials, Advantages & Disadvantages

  • Polymeric biomaterials are easy to shape, have customizable properties, and facilitate surface modification and cell immobilization. They have biodegradability strengths, but difficulties arise in sterilization, and they can absorb water and proteins, leading to surface contamination, wear, and breakdown.

Examples of Polymeric Biomaterials

  • Some examples are PMMA (polymethyl methacrylate), PVC (polyvinyl chloride), PLA/PGA (polylactic/polyglycolic acid), PE (polyethylene), PP (polypropylene), PA (polyamide), PTFE (polytetrafluoroethylene), PET (polyethylene terephthalate), PUR (polyurethane), and silicones.

Bioceramics: Advantages and Disadvantages

  • Bioceramics exhibit high compression strength, wear resistance, polish ability and bioactivity/inertness. However, bioceramics have high modulus, low strength in tension, low fracture toughness, and fabrication difficulties.

Examples of Bioceramics

  • Examples include Alumina, Zirconia (partially stabilized), Silicate glass, Calcium phosphate (apatite), and Calcium carbonate.

Metallic Biomaterials: Advantages and Disadvantages

  • Metallic biomaterials offer high strength, fatigue resistance, wear resistance, ease of fabrication and sterilization, and shape memory. Drawbacks include high modulus, corrosion, metal ion sensitivity/toxicity, and their metallic appearance.

Examples of Metallic Biomaterials

  • Stainless steel (316L), Co-Cr alloys, Ti6Al4V, Au-Ag-Cu-Pd alloys, Amalgam (AgSnCuZnHg), Ni-Ti, and Titanium.

General Criteria for Materials Selection

  • Mechanical and chemical properties
  • Undesirable biological effects (non-toxic, non-allergenic, etc.)
  • Processability, reproducibility, and sterilization
  • Cost-effectiveness.

Biomaterials Applications

  • Various applications, including dental implants, tooth fillings, vascular implants, drug delivery, bone fixation, bone defect fillings, hip joint prostheses, tissue engineering scaffolds, and contact lenses.

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Unit IV Chemical Bonding: PDF

Description

This quiz explores the concepts of chemical bonding, including ionic and covalent bonds, and their impact on the properties of elements. It covers periodic trends in ion formation, intermolecular forces, and introduces molecular orbital theory. The significance of the periodic table and common ions is also examined, providing a comprehensive understanding of materials' formation.

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