General Chemistry for Dentistry Students 2025 PDF

General Chemistry for Dentistry Students Prof. Dr. El-Zeiny Mousa Ebeid Professor of Physical Chemistry, Center of Basic Sciences, Misr University for Science and Technology (MUST) and...

General Chemistry for Dentistry Students Prof. Dr. El-Zeiny Mousa Ebeid Professor of Physical Chemistry, Center of Basic Sciences, Misr University for Science and Technology (MUST) and Dr. Mahmoud Abdel-samie Sakr Lecturer of Physical Chemistry, Center of Basic Sciences, Misr University for Science and Technology (MUST) 2025 Chapter One Chemical Bonding https://www.youtube.com/watch?v=vnvlM3S1Yb8 Theories of Chemical Bonding The Valence-Bond (VB) Theory This theory describes the covalent bond formation because of overlap between electrons in valence orbitals. The simplest model to demonstrate this overlap is the case of hydrogen molecule formation described by a potential energy diagram. In this potential energy diagram, d0 gives the mean bond distance and v denotes energy quantized vibrational energy levels. On the atomic scale in which all motions are quantized, a vibrating system can possess a series of vibrational frequencies, or states. These are depicted by the horizontal lines in the potential energy curve shown here. Notice that the very bottom of the curve does not correspond to an allowed state because at this point the positions of the atoms are precisely specified, which would violate the uncertainty principle. The lowest-allowed or ground vibrational state is the one denoted by 0, and it is normally the only state that is significantly populated in most molecules at room temperature. To jump to a higher state, the molecule must absorb a photon whose energy is equal to the energy difference between the two states. Vibrational energy levels in both ground and excited states are shown in Figure (1-1). 1  v =6 H H v =5 Potential separated v =4 atoms energy v =3 v =2 v =1 v =0 H2 molecule do Internuclear distance Fig. 1-1 Potential energy diagrams for H2 molecule, ground and excited states and the origin of fluorescence. 2 Caries detection using fluorescence. Fluorescence had been suggested for caries detection since 1980s where clinical application was performed for visual detection of green fluorescence of tooth tissue. The technique used a 488 nm excitation wavelength from an argon-ion laser to discriminate bright green fluorescing healthy tooth tissue from poorly fluorescing caries lesions. The observed green fluorescence loss is an indirect measure of mineral loss. Photo-images of this technique are given in Figure 1-2. Premolar before and after exposure, showing decalcified area Occlusal caries Figure 1-2 Green fluorescence of healthy teeth occurring argon ion laser 488 nm excitation. Around that time, a red fluorescence method emerged. The red fluorescence, excited either using long UV (350- 410 nm) or red (550-670 nm) wavelengths, was observed in advanced caries as well as plaque (‫)التسبات‬ ‫ ر‬and calculus on teeth. Opposite to the green fluorescence loss observed in caries, a substantial red fluorescence occurs between 650 and 800 nm in caries lesions that is much brighter than that of enamel or dentine as shown in Figure 1-3. (S. Parker, Low-level laser use in dentistry, British Dental Journal 2007; 202: DOI: 10.1038/sj.bdj.). [See photos below: Jonas A. Rodrigues; Isabel Hug; Klaus W. Neuhaus; Adrian Lussi, J. Biomed. Opt. 16(10), 107003 (October 03, 2011). doi:10.1117/1.3631796]. Figure 1-3 Red fluorescence occurring in caries lesions upon UV excitation. 3 Figure 1-4. Top, white light view of the teeth and oral structures during a dental examination. No unusual features can be seen. Bottom, the same field viewed under UVA 405nm fluorescence excitation with an orange filter. The presence of porcelain crowns (A), deposits of dental plaque and dental calculus on the teeth and near the gingival tissues (B), and a tooth-colored resin composite filling (C) are readily apparent, because of lack of fluorescence, red fluorescence, and bright yellow fluorescence, respectively. Images taken with a custom-built multi-wavelength fluorescence dental diagnostic camera (GC Corporation, Japan). Fluorescence imaging techniques have been used to detect oral cancer and its precursors. The fluorophore may be due to cell constituents i.e., endogenous and the fluorescence is then termed autofluorescence imaging (AFI). Examples of intrinsic fluorophores are nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD). Pre-malignant lesions are associated with a loss of autofluorescence compared to benign oral mucosa and appear dark during imaging. Figure 1-5 Autofluorescence imaging (AFI) (A) A white light image of the ventral tongue of a patient with an oral premalignant lesion, which, when biopsied, was confirmed to be severe dysplasia and (B) a corresponding autofluorescence image obtained with the VELscope® (LED Dental Inc., BC, Canada). The arrow indicates the region of fluorescence visualization loss and biopsy location. 4  The other type of fluorescence imaging depends on exogenously added fluorophores such as 5- ALA that has been administered topically and intravenously for diagnostic purposes. A brain tumor showing fluorescence following uptake of 5- ALA. (Figure 1-6). Figure 1-6 A brain tumor giving fluorescence following uptake of 5-ALA. The technique was recently approved in USA. 5 The Molecular Orbital (MO) Theory In this theory, core electrons are considered. Atomic orbitals overlap if their wave functions are of the same sign and are antibonding if their wave functions have opposite signs. This results in bonding and anti-bonding molecular orbitals respectively. Another presentation is as follows: * 1s 1s  The overlap of were functions in p-orbitals is shown in Figure 1-7. The existence of antibonding orbitals is important to explain electronic transitions in molecules. For example, electrons in the  molecular level can transfer to the * antibonding level upon electronic excitation. This is denoted  → * transition. Similarly, electrons in the  molecular level can be excited to the * antibonding level and the transition is then termed  → * transition. In atoms where non-bonding (or lone pair) electrons exist, n → * and n → * transitions are possible where n denote the non-bonding level. For a molecule like formaldehyde, electronic transitions can occur as shown in Figure 1-8. In a saturated molecule like methane, only  → * transitions can occur due to the absence of  bonds (and consequently * orbitals). No n → * transition is also possible due to the absence of non-bonding electrons in methane. If the number of electrons in the overlapping atomic orbitals is large enough to fill the antibonding orbitals, this reduces the bonding ability of the bonding orbitals. This bonding ability is reduced to zero if the antibonding orbital contains several electrons that equal the number of electrons in the bonding orbital. 6  + + + + − − − -orbital In-phase overlap (A bonding orbital) + + + − _ − + − − -orbital * Out-of-phase overlap (An antibonding orbital) Fig. 1-7 Atomic overlap giving molecular orbitals. * Energy * (1) (2) (3) (4) n   Fig. 1-8 Electronic transitions in formaldehyde H.. C O: H (1)  → * (2)  → * (3) n → * (4) n → * 7 Bonding in O2 molecule: Molecular oxygen is an essential species in our life. Bonding in molecular oxygen is shown in Figure (1-9). The most effective bond in molecular oxygen is the  2pz bond. The inner 1s and 2s electrons are inner electrons and do not appear in the bonding process. Both electrons in the *x and *y antibonding orbitals partially cancel the bonding ability of the x and y molecular orbitals leaving these bonds as weak bonds. Electrons in the *2s cancel the bonding effect of the 2s molecular orbital and two electrons will appear as lone pair. Thus, bonding in molecular oxygen can be presented as follows: y :O x O:  2 s electrons 2pz The arrows indicate the two unpaired electrons in the *x and *y molecular orbitals. These two unpaired electrons cause the paramagnetic character of molecular oxygen. *2p *x *y z 2 p4 2 p4 x y  2p z *2 s 2s 2 2s 2  2s *1 s 1s 2 1s 2 1 s 8O O2 8O Fig. 1-9 Molecular orbitals in oxygen molecule as derived from atomic oxygen orbitals. 8 For N2 molecule: Similarly, one can work out bonding in N2 (showing its inertness) and NO molecules. For nitric oxide (NO), we have resonance between the two forms:...... N O.. N O.. This resonance causes stability of the NO molecule. This relationship between a single electron and the lone pair is sometimes called a three-electron bond and the NO molecule would then be described as having its atoms joined by a double bond plus a three-electron bond. When an electron is added to O2 molecule, a very reactive species known as superoxide anion O2 - is obtained of the following molecular orbital structure: Superoxide anion O2 - is an important species in medicine since it belongs to reactive oxygen species (ROS) which cause aging according to some theories. Similarly, one can work out bonding in N2 (showing its inertness) and NO molecules. For nitric oxide (NO), we have resonance between the two forms: *x *y  *x *y...... N O.. N O.. This resonance causes stability of the NO molecule. In is known that the multiplicity of electronic states (M) is given as: 1 1 S= + + =1 2 2 M = 2S + 1 9  where S is the numerical sum of the total spin quantum numbers in the system under investigation. Thus, for molecular oxygen, all the electrons are paired except two electrons. The spins of paired electrons cancel each other, and we are left with the spins of the unpaired electrons only. Then for molecular oxygen: 1 1 S= + + =1 2 2 The determinant sign means that we disregard the sign of the total sum of the spin. M=21+1=3 We therefore say that molecular oxygen exists in the triplet state. This triplet state is denoted T and since this is a ground state (not excited one), it is written To. We might ask this question: what would happen to the electrons in molecular oxygen upon electronic excitation i.e., when these electrons absorb energy by one means or another? One of the ways the molecule acquires this energy is through the change in spin of one of the * electrons giving the following configuration of the first excited state in O2 molecule: The total spin of molecular oxygen in this case is then given as: 1 1 S= + − = Zero 2 2 and the multiplicity of molecular oxygen is given as J=20+1=1 The electronic state is then termed a singlet state and molecular oxygen is said to be in the singlet electronic state. We mentioned earlier that singlet oxygen is widely applied in photo-dynamic therapy. Photo-toxic drugs Some drugs act as sensitizers to singlet oxygen inside the human body leading to the phenomenon of photo-toxicity. The tuberculosis antibiotic doxycycline is a potent photosensitizer of human skin. The anti-inflammatory drug benoxaprofen also exhibits photo-toxic properties via singlet oxygen generation. A list of ca. 400 drugs of photo-toxic properties is currently available in literature. A patient under treatment by any of these drugs should not be subjected to direct sunlight to avoid generation of singlet oxygen that attacks skin tissues causing skin burns or skin disorder. 10 11 Photodynamic Therapy (PDT) Photodynamic therapy is a field of photomedicine in which light is used to activate certain compounds, known as photosensitizers, for purposes of therapy. These photosensitizers are selectively retained in malignant tumors then upon appropriate laser irradiation they cause destruction of the tumor. PDT begins with the intravenous injection of the photosensitizer into the patient. Within a time- span of typically 48-72 hours, the photosensitizer selectively deposits in the malignant tissue and is cleared from normal tissue. The photosensitizer is activated by red laser light (  630 nm) to produce singlet oxygen 1 * O2 which kills the cancerous tissue. The production of singlet oxygen occurs according to the following scheme: h M* M ⎯⎯→ Energy transfere M* + O2 ⎯⎯⎯⎯⎯⎯⎯ → M + 1 O*2 1O* + tissue ⎯⎯ → necrosis 2 (Destruction of malignant tissue) There are several properties the sensitizer should possess. Foremost is the selective deposition in the cancerous tissue. It is also beneficial if the sensitizer is a fluorescent compound because one can then ensure, by fluorescence measurement, that the sensitizer has indeed deposited in the tissue of interest and not elsewhere. Finally, of course, it is necessary that the sensitizer be nontoxic. The photosensitizers commonly employed are levulinic acid and hematoporphyrin derivatives. Argon laser-pumped dye lasers are currently the choice for PDT, with the light delivered by fiber optics to the tissue to be destroyed. Fiber optics is also used in fluorescence measurement to ensure, via fluorescence detection, that the tissue selectivity has been achieved. PDT has primarily been used in the treatment of bladder and lung cancers. Aminolevulinic acid is used for Blue Light Therapy. Its trade name is Levulan ™. Methyl aminolevulinate is used for Red Light Therapy). Its trade name is Metvix™. Aminolevulinic acid Methyl aminolevulinate (for Blue Light Therapy) (for Red Light Therapy). 12 Antimicrobial photodynamic therapy (aPDT) Bacterial, fungal, and viral infections can be treated by PDT. The major clinical applications include disinfection of root canals, periodontal pockets, deep carious lesions, and sites of peri-implants without thermal effects. Argon laser-pumped dye lasers are currently the choice for PDT, with the light delivered by fiber optics to the tissue to be destroyed. Fiber optics is also used in fluorescence measurement to ensure, via fluorescence detection, that the tissue selectivity has been achieved. Sequential photos showing complete tumor elimination. The patient had other lesions elsewhere in the body. Application of PDT in dentistry: Photoactivated dye disinfection using laser radiation. This technique is effective in killing bacteria in complex biofilms such as subgingival plaque and carious lesions, since visible red light transmits well across dentin. The photo-activated dye technique can be undertaken with a range of visible red and near infrared lasers and systems using low- power (0.1 W) He-Ne or visible red semiconductor diode lasers. The photo-activated toluidine blue dye is used to increase the above- mentioned laser radiation absorption. Toluidine blue dye This procedure can be applied effectively for killing bacteria, fungi, and viruses. The major clinical applications include disinfection of root canals, periodontal pockets, deep carious lesions, and sites of peri-implants without thermal effects. The dye – tolonium chloride – can also be used in high concentrations for screening patients for malignancies of the oral mucosa and oropharynx (‫)البلعوم‬. 13  Photo-activated disinfection of Cavity decontamination prepared cavity, upper first molar Presentation of a true-positive staining on a red and white homogenous patch on the right buccal mucosa. (A) The lesion presented clinically as a red and white homogenous patch. (B) Vital staining with methylene blue showed deep and focal staining of the lesion. (C) The final pathology revealed severe dysplasia. (H &E, 40×). [Akhtar Riaz, Balasundari Shreedhar, Mala Kamboj* and S Natarajan, Methylene blue as an early diagnostic marker for oral precancer and cancer, SpringerPlus 2013, 2:95 http://www.springerplus.com/content/2/1/95] Thus, Photodynamic Therapy (PDT) is a medical treatment that uses a combination of light and photosensitizing agents to selectively destroy or eliminate target cells or microorganisms. In dentistry, PDT has found several applications, primarily in the treatment of oral infections and oral cancer. It offers a minimally invasive and potentially less harmful alternative to traditional treatments. Here are some more applications of PDT in dentistry along with examples of materials used: 14 1. Treatment of Periodontal Disease: PDT can be used to treat periodontal (gum) disease by targeting and killing the bacteria responsible for the infection. Photosensitizing agents like methylene blue or toluidine blue O are applied to the infected gum tissue. When exposed to a specific wavelength of laser or LED light, these agents produce singlet oxygen that destroys bacteria. Activation of photosensitizer (1% methylene blue) with diode laser 2. Management of Oral Lesions and Precancerous Conditions: PDT can be applied to manage various oral lesions and potentially precancerous conditions like leukoplakia. By selectively targeting abnormal cells, PDT can help prevent the progression of these conditions to oral cancer. 3. Disinfection of Root Canals: In endodontics, PDT can be used to disinfect root canals during root canal therapy. Photosensitizers are applied, and a laser is used to eliminate bacteria and infected tissue from the root canal, improving the success rate of the procedure. According to the American Association of Endodontists (AAE), millions of teeth are treated and more importantly saved every year with root canal treatment, which becomes necessary when the dental pulp, the living tissue deep inside the tooth, becomes inflamed and/or infected. 4. Treatment of Denture Stomatitis: PDT can be used to treat denture stomatitis, a fungal infection that affects the oral mucosa beneath dentures. Photosensitizing agents are applied to the affected area, and exposure to light helps eliminate fungal infection. 5. Decontamination of Dental Implants: PDT can be used to decontaminate dental implant surfaces before placement to reduce the risk of post-implant infections. This is particularly important in cases where there is a risk of bacterial contamination. Materials used in PDT in dentistry include photosensitizing agents and light sources: 15 Photosensitizing Agents: Examples of photosensitizers used in dentistry include methylene blue, toluidine blue O, 5-aminolevulinic acid (5-ALA), and Photofrin. These compounds are chosen based on their ability to target specific tissues or microorganisms. Light Sources: Various light sources can be used in PDT, such as lasers and light- emitting diodes (LEDs). The choice of light source depends on the specific application and the photosensitizer used. PDT in dentistry offers a non-invasive, targeted, and potentially less damaging approach to treating oral infections and certain oral conditions. However, its use may be limited to specific cases, and it should be administered by trained dental professionals. Molecular orbital theory (MO theory) is thus a fundamental concept in chemistry that describes how electrons are distributed in molecular orbitals formed by the combination of atomic orbitals of individual atoms within a molecule. There are two major uses of orbital pictures and energies generated from MO theory. One is to predict reactivity, and the other is to predict spectral properties in the UV-Visible regions. While not directly applied in everyday dental procedures, MO theory has some indirect applications in dentistry: 1. Drug Design and Pharmacology: MO theory can help in understanding the electronic structure of drugs and their interactions with target molecules in the oral cavity. This knowledge is valuable for designing effective pharmaceuticals for dental applications, such as pain management, local anesthesia, or antibiotics. 2. Dental Materials: Dental materials often involve the interaction of electrons between different elements and compounds. Understanding the molecular orbitals of these materials can aid in the development of new dental materials with desirable properties, such as dental adhesives, restorative materials, and ceramics. 3. Biochemistry and Enzyme Function: MO theory can be used to study the electronic structure and reactivity of enzymes involved in oral health and digestion. Understanding the electronic aspects of enzymatic reactions is crucial for developing treatments for conditions like periodontal disease. 16 4. Oral Pathology and Diagnostic Techniques: In some cases, molecular orbital theory principles may be applied indirectly to understand the electronic properties of molecules involved in oral diseases or diagnostic techniques like spectroscopy, which can help in the early detection of dental and oral pathologies. 5. Materials Testing and Analysis: Researchers and dental materials scientists may use MO theory as part of their analytical toolkit to study the properties of dental materials, such as the electronic behavior of materials used in dental implants, orthodontic appliances, or prosthetic devices. While MO theory may not be directly utilized by dentists in their day-to-day clinical practice, it serves as a foundational concept in the development and understanding of various dental materials, pharmaceuticals, and the underlying chemistry of oral health and disease. Researchers and materials scientists in the field of dentistry may apply MO theory principles in their work to create better dental materials and treatments. The structure of iodine water according to MO theory The familiar iodine solutions used as antiseptics often contain triiodide ion ( I- → I2 ). Iodine 127 10 2 5 53 I has the electronic configuration: [Kr] 4d 5s 5p. The triiodide ion is formed as follows: ⎯→ I-3 I2(s) + I-(aq) ⎯ (aq) Kc = 710 at 25°C A coordination bond is formed in which I- acts as a Lewis base (electron donor) and I2 acts as a Lewis acid (electron acceptor). The empty molecular orbital in I2 being the σ*5pz 17 Lewis Theory The Lewis Theory of bonding was essential in understanding how elements bonded; it provided a visual representation for them. These Lewis dot structures are a simplistic way of representing the electrons in molecules. This theory also helped to define resonance and formal charge. Resonance Resonance is the existence in more than one electronic structure. The phenomenon implies no mass transfer. It differs from another phenomenon known as tautomerism in which more than one chemical structure exists and mass transfer of atoms occurs. In acetic acid, no resonance occurs. Therefore, the two carbon – oxygen distances are different whereas in acetate ion, resonance exists and the two carbon – oxygen distances become the same. Acetic acid No resonance. The two carbon – oxygen distances are different Acetate ion Resonance exists. The two carbon – oxygen distances are the same. 18 Resonance in benzene derivatives affects their properties. Some examples are given as follows: Lewis’s theory and the octet rule Write out some structures for carbon monoxide CO 4 6 4 6 4 6 3 3 2 2 1 1 2 2 2 4 2 6 -1 +1 0 0 +1 -1  The octet The octet Predominates rule does not rule does not as it satisfies apply to C apply to C the octet rule atom that is atom that is for both C surrounded surrounded and O atoms. by 6 by 4 electrons. electrons. The presence of a negative formal charge on carbon in CO molecule makes it a stronger ligand compared with O2. Therefore, CO possesses an affinity for hemoglobin that is 300 times greater than that of O2 and this is the origin of carbon monoxide poisoning. Hemoglobin 19 Revision Questions on Theories of Chemical Bonding - Equations describing photo-toxicity in drugs are as follows: ………………………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………… -Draw and label each of the following: (a) The potential energy curves for bond formation according to Valence Bond (VB) Theory showing the origin of fluorescence. (b) Bonding in O2 molecule according to (d) Bonding in triiodide ion ( I- ) 3 molecular orbital (MO) theory (You have according to the molecular orbital 8O). (MO) theory given iodine has 5p5. (e) The resonating structures of the (f) The structure of hemoglobin following species leading to inhibition of polymerization in dental acrylate resins 20  Choose from the right  column * the statement that suits the left column below: 2pz x* y * N2 molecule 6- A- given 7N Superoxide 7- *x *y  *x 2 p4 *y B anion O2 - O2 ground 8- C x y state  2p NO 9- z D molecule. *2 s 2s 2 10- E Singlet O2  2s *1 s The electronic transitions in ammonia molecule NH3 : A- ( → *) B- (n → *) 1s 2 C- (n → *) D- Both A and C are true 1 s The electronic O 2 transitions in in ammonium ion NH4+: 8O 8O A- ( → *) B- (n → *) C- (n → *) D- Both A and C are true For the two compounds pyridine and aniline: + Pyridine Aniline The electronic transition that is present in pyridine but absent in aniline is: A- ( → *) B- (n → *) C- (n → *) D- ( → *) 21  Singlet oxygen 1O2* is diamagnetic (A) True (B) False CO binds to hemoglobin through its oxygen atom. A- True B- False According to molecular orbital theory and given 7N and 8O, resonance exists in: A- O2 B- NO C- N2 D- None of them According to molecular orbital theory, the molecule of least chemical reactivity is: A- O2 B- NO C- N2 D- 1 O*2 Upon photolysis of H2 molecules into H atoms according to the following equation, H-H ⎯⎯ → 2 H. The electronic transition that disappears is: A- ( → *) B- (n → *) C- (n → *) D- ( → *) Iodine water is important disinfecting substance. It is formed of the triiodide ion ( I- - - 3 ) of the structure (I →I2), then the bond between I and I2 is a coordination bond. A- True B- False Iodine water is important disinfecting substance. It is formed of the triiodide ion ( I- - 3 ) of the structure (I →I2), then I2 molecule acts as a Lewis base: A- True B- False 22  Iodine water is important disinfecting substance. It is formed of the triiodide ion ( I- - 3 ) of the structure (I →I2), then according to the molecular orbital (MO) theory and given iodine has 5p5 as the outermost bonding orbit then, the empty orbital in I2 molecule is: A- 5pz B- *5pz C- 5pz D- *5pz The photo-toxicity of drugs is attributed to the generation of: A- O atoms B- O*2 C- Singlet oxygen. D- Both B and C are true. The possible electronic transitions in a nitrile compound.. R C N A-  → * ,  → * ,  → * , n → * B-  → * and  → * only C-  → * ,  → * , n → * , n → * D- Both A and C are true. The following electronic structure is not correct 1s1 1s 2 1s 2 1s 2 H He He He (a) (b) 1s1 1s 1 1s 2 1s1 H H He + He (c) (d) A- Figure (a) B- Figure (b) C- Figure (c) D- Figure (d) 23  Use the following table to mark in column (B) the electronic transition that will disappear following each chemical process mentioned in column (A) in the table: (A) Chemical process (B) Underline the disappearing electronic transition Protonation of ammonia ( → *)/(n → *)/(n → *)/ NH + H+ ⎯⎯ → NH4+ ( → *). 3 Polymerization of ethylene: ( → *)/(n → *)/(n → *)/ ( → *). Hydrogenation of benzene into cyclohexane ( → *)/(n → *)/(n → *)/ ( → *). Photolysis of H2 molecules into H atoms H-H ( → *)/(n → *)/(n → *)/ ⎯⎯ → 2 H. ( → *). For carbon monoxide CO molecule, the number of valence electrons on C is (2 / 4/ 6). The number of bonds in CO molecule is (1 / 2 / 3). The number of electrons as lone pair on carbon is (0 / 1 / 2 / 3). The charge on carbon is (+1 / -1). Upon CO poisoning action, CO binds to hemoglobin through (carbon / oxygen) atoms. This bonding is (stronger / weaker) than bonding with oxygen molecule. UV or red laser gives bright red emission with caries A- True B- False The first excited singlet state of oxygen is diamagnetic A. True B. False CO binds to hemoglobin through its carbon atom. A- True B- False In hemoglobin molecule, iron is present as Fe2+ and not as Fe A- True B- False The electronic transition (n → *) occurs at longer wavelength λ compared with the ( → *) transition A- True B- False 24  Argon ion laser of wavelength 488 nm gives green emission with healthy teeth. A- True B- False The possible electronic transitions in water are: A-  → *,  → *,  → * and n → * B-  → * and  → * only C-  → * and n → * D- Both A and C are true. Iodine water is an important disinfecting substance. It is formed of the triiodide ion ( I- - - 3 ) of the structure (I →I2), then the bond between I and I2 is a coordination bond. A- True B- False Iodine water is an important disinfecting substance. It is formed of the triiodide ion ( I- - 3 ) of the structure (I →I2), then I2 molecule acts as a Lewis base: A- True B- False Iodine water is an important disinfecting substance. It is formed of the triiodide ion ( I- - 3 ) of the structure (I →I2), then according to the molecular orbital (MO) theory and given iodine has 5p5 as the outermost bonding orbit then, the empty orbital in I2 molecule is: A- 5pz B- *5pz C- 5pz D- *5pz The possible electronic transitions in a nitrile compound.. R C N A-  → * ,  → * ,  → * , n → * B-  → * and  → * only C-  → * ,  → * , n → * , n → * D- Both A and C are true. 25  CO binds to hemoglobin more strongly than O2 molecule. This is because of: A- The absence of lone pair electrons on O2 molecule. B- The absence of lone pair electrons on carbon atoms in CO molecule C- A negative charge on carbon atoms in CO molecule D- A negative charge on oxygen atoms in CO molecule In the polymerization of ethylene: Polymerization of ethylene: A- The polymerization is exothermic B- The ( → *) disappears. C- Ethylene absorbs at longer wavelength compared with polyethylene. D- All A, B and C are true. CO binds to hemoglobin more strongly than O2 molecule. This is because of: A- The absence of lone pair electrons on O2 molecule. B- The absence of lone pair electrons on carbon atoms in CO molecule C- A negative charge on carbon atoms in CO molecule D- A negative charge on oxygen atoms in CO molecule According to molecular orbital theory and given 7N, then N2 molecule is a diamagnetic inert gas. A- True B- False Given nitrogen atom as 7N, then the number of valence electrons on N is 4. A- True B- False According to molecular orbital theory and given 7N, then N2 molecule is a diamagnetic inert gas. A- True B- False Iodine water is an important disinfecting substance. It is formed of the triiodide ion ( I- - 3 ) of the structure (I →I2), then: A. I2 molecule acts as a Lewis base B. I2 molecule undergoes oxidation in the bonding process. C. The empty orbital in I2 molecule is the *5pz molecular orbital. D. All A, B and C are true. 26