Atomic Structure Quiz

Electronic Structure of Atoms

• Atoms consist of a nucleus surrounded by electrons.
• The nucleus contains protons (positively charged) and neutrons (no charge).
• Electrons occupy specific regions of space called orbitals.
• The number of protons in a neutral atom is equal to the number of electrons.
• The sum of protons and neutrons determines the atomic mass of an element.
• The number of protons is called the atomic number.

Atomic Orbitals

• Atomic orbitals are described by four quantum numbers:
  • Principal quantum number (n): Defines the energy level of the electron. Higher values of n correspond to higher energy levels and greater distances from the nucleus.
  • Azimuthal quantum number (l): Represents the shape of the orbital. This determines the orbital's angular momentum.
    • l = 0 is an s orbital (spherical)
    • l = 1 is a p orbital (dumbbell shaped)
    • l = 2 is a d orbital
    • l = 3 is an f orbital
  • Magnetic quantum number (ml): Specifies the spatial orientation of the orbital.
  • Spin quantum number (ms): Represents the intrinsic angular momentum of the electron, which is quantized and can be either spin up (m_s = +1/2) or spin down (m_s = -1/2).

Electron Configuration

• The Aufbau principle states that electrons are added to orbitals in order of increasing energy.
• Pauli exclusion principle: no two electrons in an atom can have the same set of four quantum numbers.
  • A maximum of two electrons can occupy a single orbital, and they must have opposite spins.
• Hund's rules:
  • Lower energy orbitals are filled before higher energy orbitals.
  • Electrons will occupy degenerate orbitals individually with parallel spins before pairing up in the same orbital.
• Stable configurations can occur when d orbitals are half-filled or completely filled, such as in Chromium and Copper.
• Electron configurations can be written using the inert gas core as a shorthand, denoting the preceding noble gas configuration.

Ionization

• Ionization is the process of an atom losing one or more electrons.
• This results in a positively charged ion called a cation.
• The electrons lost are typically the most loosely held ones.
• The electronic structure of the ion may not reflect the level of electron loss, especially with transition metals.

Periodic Table

• The periodic table organizes chemical elements by increasing atomic number, electron configuration, and recurring chemical properties.
• Rows are called periods and columns are called groups.
• Some groups have specific names, such as halogens and noble gases.
• The filling of s and p orbitals corresponds to the eight main groups.
• Transitions metals occur between groups IIA and IIIA, during the filling of d orbitals.
• The lanthanides and actinides are located below the main table, corresponding to the filling of f orbitals.

Electronegativity

• Electronegativity measures an element's attraction for electrons.
• Electronegativity increases from left to right across a period and from bottom to top within a group (excluding Group VIIIA).
• Electropositivity is the opposite of electronegativity and varies in the opposite direction.

Electronic Structure of Molecules

• Three major forces govern molecular formation:
  • Coulombic attraction between electrons and nuclei
  • Number of valence electrons
  • Orbital distribution
• There are two main types of chemical bonds:
  • Covalent bonds: involve the sharing of electron pairs.
    • Nonpolar covalent bonds involve equal sharing between atoms.
    • Polar covalent bonds involve unequal sharing, where the electron density shifts towards the more electronegative atom.
  • Ionic bonds: formed by the transfer of electrons from an electropositive atom to an electronegative atom, resulting in electrostatic attraction between oppositely charged ions.

Orbital Hybridization

• Orbital hybridization involves mixing atomic orbitals to form new, degenerate hybrid orbitals that differ in spatial orientation and directional properties.
• The number of hybrid orbitals formed is equal to the number of atomic orbitals involved in the hybridization.
• There are three main types of hybrid orbitals:
  • sp: Linear geometry, forms two sp orbitals oriented at 180 degrees.
  • sp²: Trigonal planar geometry, forms three sp² orbitals oriented at 120 degrees.
  • sp³: Tetrahedral geometry, forms four sp³ orbitals oriented towards the corners of a tetrahedron.

Types of Bonding Interactions

• Ionic bonding: an electrostatic interaction between oppositely charged ions.
  • Many stable ions have inert gas valence shell structures (octet rule).
  • Typically occurs between electropositive metals and electronegative nonmetals.
• Covalent bonding: involves sharing of electron pairs between atoms.
  • Nonpolar covalent bonds involve equal sharing.
  • Polar covalent bonds involve unequal sharing, leading to partial charges.
• Coordinate covalent bonding: Both electrons in the bond originate from the same atom.
  • The donor atom provides the electron pair for the covalent bond.
  • The acceptor atom has an empty orbital that can overlap with the donor orbital.
• Hydrogen bonding: A weak secondary interaction between a partially positive hydrogen atom (bonded to a highly electronegative atom) and a nonbonding electron pair on a neighboring electronegative atom.
  • Plays a key role in many physical and chemical properties of water, such as its high boiling point.
• Van der Waals forces: Weak electrical dipole forces that arise due to temporary electron clouds distortions.
  • These are the only forces holding nonpolar molecules together.

Resonance

• Resonance describes delocalization of electrons, where a molecule can be represented by multiple resonance structures (canonical structures).
• The actual electron distribution is a hybrid of all contributing resonance structures.

Coordination Compounds and Complexation

• Metal cations can form coordination compounds by binding to additional anions or neutral molecules known as ligands.
• Ligands bond directly to the metal cation, following a specific coordination number that represents the maximum number of ligands a metal ion can accommodate.
• The arrangement of ligands around the metal ion gives the complex a specific geometry.

Properties of Ligands

• Ligands are generally anions or neutral molecules, not atoms.
• They possess at least one nonbonded electron pair for forming coordinate covalent bonds with the metal ion.
• The stability of complexes depends on the ligand type. More basic ligands generally form more stable complexes.
• Ligands can be classified by the number of positions they can coordinate with a metal (monodentate, bidentate, etc.).

Chelation

• When polydentate ligands coordinate with a metal ion, they form a ring structure called a chelate.
• Chelates with five-, six-, or seven-membered rings are generally the most stable.

Bonding in Complexes

• The metal's (n-1)d, ns, and np orbitals can hybridize to form six bonding orbitals that point towards the ligands.
• The geometry of the complex is determined by the hybridization and coordination number.

Complex Formation and Chelating Agents

• Complexes are formed when a central metal ion is surrounded by ligands, which are molecules or ions that have a lone pair of electrons.
• The coordination number is the number of ligands that are directly attached to the metal ion.
• In complexes with six ligands, metal ions with three or less electrons in their d orbitals will form d2sp3 hybrid orbitals. This leads to six equivalent hybrid orbitals that bond with the six ligands, forming octahedral complexes with examples like [Cr(CN)6] -3.
• Metal ions with more than 3 d electrons will undergo a configuration change to achieve a lower spin configuration. This can be measured experimentally by analyzing the magnetic moment of the complex, which is the result of unpaired electrons.
• The d2sp3 hybridization is called "inner orbital hybridization" when 3d orbitals are involved, while the hybridization involving 4d orbitals (4d,4s, 4p) is referred to as "outer orbital hybridization."
• Chelating agents are organic compounds that bind to metal ions, forming stable complexes.
• Chelating agents have applications in:
  • Analytical chemistry: used to determine metal concentrations by titration.
  • Solubilization of metal ions: increase solubility and stabilize the oxidation state.
  • Pharmaceutical chemistry: used as preservatives in preparations containing hydrogen peroxide, and for treating heavy metal poisonings and metabolic disorders.

Chelating Agents

• Calcium Disodium Edetate (EDTA)

  • A white crystalline granule used primarily for lead poisoning treatment.
  • Forms an insoluble complex with lead that is excreted by the kidneys.
  • EDTA has a strong affinity for calcium, therefore, the disodium calcium form is preferred to avoid hypocalcemia.
  • Also used for poisoning due to copper, nickel, cadmium, zinc, chromium, and manganese.
  • Poorly absorbed orally, given intravenously.
  • Intramuscular administration is used for diagnosing metal poisonings.

• Disodium Edetate:

  • White crystalline powder soluble in water.
  • Chelates the same metals as the calcium disodium form.
  • Limited by the risk of hypocalcemia.
  • Used in hypercalcemic states (high serum calcium).
  • Can be helpful for occlusive vascular disease and cardiac arrhythmias associated with high blood calcium levels.
  • Not effective in dissolving urinary calculi.
  • Administered intravenously.

• Dimercaprol (BAL)

  • A colorless or almost colorless liquid with a disagreeable odor.
  • Used to treat heavy metal poisoning (primarily arsenic, mercury, and gold) by competing with enzymes for these metals, forming less toxic complexes that can be excreted.
  • Contraindicated in poisonings due to iron, cadmium, or selenium because the resulting complexes are more toxic.
  • Dimercaprol-metal chelates dissociate in acidic media, therefore, urine needs to be alkalinized to prevent free metal release.
  • Administered intramuscularly.

• Penicillamine:

  • A white or off-white crystalline powder that chelates copper, iron, mercury, lead, gold, and other metals.
  • Primarily used to improve copper excretion in patients with Wilson’s disease.
  • Resistant to metabolic inactivation by amino acid oxidase.
  • Used in treatment of gold dermatitis for patients on chronic gold therapy.
  • Administered orally.

• Deferoxamine Mesylate:

  • A white crystalline lyophilized powder soluble in water.
  • Produced naturally by Streptomyces pilosus as a ferric [Fe(III)]complex.
  • Has a particular affinity for ferric ions, forming stable water-soluble octahedral complexes.
  • Weak affinity for ferrous ions and other divalent metal ions.
  • Used with other drugs and procedures for treating acute iron toxicity.
  • Administered intramuscularly or intravenously.

Gastrointestinal Protectives, Adsorbents, and Cathartics

• Gastrointestinal agents used to treat mild diarrhea.
• Diarrhea is a symptom of impaired digestion or absorption leading to increased intestinal bulk, increased peristalsis, and expulsion of intestinal contents.
• Diarrhea can be acute or chronic.
• Acute diarrhea can be caused by bacteria, chemicals, drugs, allergies, and disease.
• Chronic diarrhea can result from surgery, carcinomas, inflammatory conditions, and absorptive defects.
• Dehydration and electrolyte imbalances are serious complications of diarrhea, particularly in young children and elderly individuals.
• Antidiarrheal agents treat the symptoms and sometimes the cause, but not the complications.
• Most antidiarrheal products combine adsorbent-protectives, antispasmodics, and sometimes antibacterial agents.
• The ideal antispasmodic agent should act directly on the smooth muscles of the gut to reduce peristalsis and increase segmentation.
• Antibacterials are only effective if there's an actual infection or during outbreaks caused by known microorganisms.

Mechanism of Adsorption

• Adsorption is a process where a substance (adsorbate) adheres to the surface of another substance (adsorbent).

• In gastrointestinal protectives and adsorbents, substances like activated charcoal, kaolin, and certain clays act as adsorbents that bind toxins, gases, and bacteria in the gut.

• Types of Adsorption:*

• Physical Adsorption: Based on weak, non-specific Van der Waals forces. Reversible and doesn't involve chemical bonding.

• Chemical Adsorption: Involves stronger chemical bonds. Can be irreversible and involves electron exchange or sharing.

• Factors Affecting Adsorption:*

• Surface Area and Porosity: Adsorbents with high surface areas and porous structures, like activated charcoal, adsorb more substances.

• Polarity: Adsorption is more effective when the adsorbent and adsorbate have similar polarities.

• pH Sensitivity: The surrounding pH can affect the efficiency of adsorption, as some adsorbents become soluble depending on the pH level.

Bismuth-Containing Products

• Bismuth salts are used as antidiarrheals and antacids.

• Bismuth subcarbonate has been used as an antacid.

• Soluble bismuth cation exerts a mild astringent and antiseptic action.

• Bismuth salts react with intestinal hydrogen sulfide to form bismuth sulfide, resulting in black stools.

• They provide dual action: adsorbing toxins and bacteria & forming a protective barrier in the intestines.

• Bi3+ + 3H2S → Bi2S3 (black precipitate) + 6H+

• 1. Bismuth Subnitrate, N.F.XIII ([Bi(OH)2NO3]4·BiO(OH))*

• A white, slightly hygroscopic powder with an acid reaction.

• Insoluble in water and alcohol, soluble in hydrochloric or nitric acid.

• Assayed in terms of bismuth trioxide (Bi2O3).

• Incompatible with tragacanth, but the difficulty can be overcome by using sodium or trisodium phosphates.

• Can inhibit pepsin.

• Used as a component of Milk of Bismuth.

Milk of Bismuth

• Contains bismuth hydroxide and bismuth sub carbonate in suspension in water.

• Classified as an astringent and antacid.

• 2. Bismuth Subcarbonate, U.S.P.XVIII ([BiO) CO ] ·H O) ₂ ₃ ₂ ₂*

• A white or pale yellowish white odorless, tasteless powder.

• Stable in air but affected by light.

• Insoluble in water and alcohol, soluble in nitric acid and hydrochloric acid with effervescence.

• Assayed in terms of bismuth trioxide (Bi2O3).

Nonofficial Bismuth Compounds

• Bismuth Subgallate
• Bismuth Subsalicylate
• Bismuth Ammonium Citrate

Activated Clays and Other Adsorbents

• Used for industrial adsorption and clinically for mild short-duration diarrhea.

• 1. Kaolin*

• A native hydrated aluminum silicate powder.

• Binds toxins and bacteria through both physical and chemical adsorption.

• Insoluble in water, cold diluted acids, and alkali hydroxide solutions.

• Typically combined with pectin, forming Kaopectate® and Kao-Con®.

• Can interfere with the absorption of lincomycin.

• 2. Activated Charcoal*

• Used as an adsorbent for diarrhea and as an antidote in certain poisoning.

• Works primarily through physical adsorption.

• Highly porous and effective in binding large organic molecules like bacterial toxins, chemicals, and drugs.

Saline Cathartics

• Agents that increase intestinal evacuation.
• Laxatives are mild cathartics.
• Properly used for:
  • Easing defecation in patients with hemorrhoids or rectal disorders.
  • Avoiding blood pressure increases during defecation for patients with hypertension.
  • Relief of acute constipation.
  • Removing solid material from the intestinal tract for x-ray studies.
• Prolonged use can lead to dependence and disruption of bowel rhythm.
• Constipation is infrequent or difficult defecation, caused by various factors including diet, drugs, and intestinal dysfunction.

Types of Laxatives

• Stimulant laxatives:

  • Act by irritating the intestinal tract to increase peristalsis.
  • Examples: phenolphthalein, aloin, cascara extract, rhubarb extract, senna extract, podophyllin, castor oil, 1,8-dihydroxyanthraquinone (danthron), oxyphenisatin, bisacodyl, and calomel.

• Bulk-forming laxatives:

  • Made from cellulose and other nondigestible polysaccharides.
  • Swell when wet to stimulate peristalsis.
  • Examples: psyllium seed, methyl cellulose, sodium carboxymethylcellulose, and karaya gum.

• Emollient laxatives:

  • Act as lubricants or stool softeners to facilitate passage of compacted fecal material.
  • Examples: Mineral oil (lubricant) and d-octyl sodium sulfosuccinate (stool softener).

• Saline cathartics:

  • Increase the osmotic load of the gastrointestinal tract.
  • Made of poorly absorbed anions and sometimes cations.
  • Increased osmotic pressure draws fluids into the intestines, increasing bulk and stimulating peristalsis.
  • Examples of poorly absorbed anions: biphosphate (H2PO4-), phosphate (HPO4 2-), sulfate, and tartrate.
  • Saline cathartics must be taken with large amounts of water to avoid dehydration and excessive hypertonicity in the stomach.
  • Relatively free of side effects when used for short periods.

Saline Cathartics

• Sodium Biphosphate, Sodium Phosphate, Sodium Sulfate, and Potassium Sodium Tartrate are saline cathartics.
• Patients on low-sodium diets should avoid these.
• Sodium Biphosphate is a urinary acidifier with a neutral pH.
• Sodium Phosphate is frequently employed as a saline cathartic in Fleet Enema and Phospho-Soda.
• Dried Sodium Phosphate is a nearly anhydrous white powder that readily absorbs moisture.
• It is used as a saline cathartic in Effervescent Sodium Phosphate, a mixture of sodium bicarbonate, tartaric acid, and citric acid.

Topical Agents

• Topical compounds are applied to body surfaces to protect areas from irritation, particularly of mechanical origin.
• Protectives are substances used for this purpose.
• They are generally insoluble and inert to prevent absorption through the skin and interactions with tissue.

Talc

• Talc is a hydrous magnesium silicate commonly used as a lubricating and protective dusting powder.
• It can be used to prevent irritation due to friction, and to protect areas from further irritation.
• It is unctuous, adheres readily to the skin, and is free from grittiness.
• It is the softest mineral known.
• It is odorless, tasteless, and insoluble in water, dilute acids, and dilute bases.

Zinc Oxide

• Zinc Oxide is a very fine, odorless, amorphous, white or yellowish white powder.
• It is insoluble in water and alcohol, but reacts with dilute acids and ammonium compounds to form water-soluble products.
• It acts as a mild astringent and a weak antimicrobial compound, reducing skin irritation and providing a protective barrier.

Calamine

• Calamine is zinc oxide with a small proportion of ferric oxide, giving it a pink color.
• It is insoluble in water but soluble in mineral acids.
• It is used in dusting powders, ointments, and lotions for its soothing, absorbent, and protective properties.

Antimicrobial Agents

• Antimicrobial agents are used for the prevention and/or reduction of infection caused by microorganisms.
• Antiseptics are used on living tissues to prevent infection.
• Germicides directly kill microorganisms, e.g., bactericides, fungicides, amebicides.
• -stat agents inhibit the growth of microorganisms without killing them.
• Disinfectants kill microorganisms on inanimate objects but are not safe for use on living tissue.

Hydrogen Peroxide Solution

• It is a clear, colorless liquid that can decompose on standing or when exposed to light or heated.
• It acts as a mild oxidizing antiseptic, decomposing into water and oxygen in the presence of the enzyme catalase.
• It is commonly used as a gargle or mouthwash for bacterial infections of the throat and mouth, and in diluted form, as a vaginal douche.

Sodium Hypochlorite Solution

• It is a clear, pale greenish-yellow liquid with a chlorine odor.
• It is a strong oxidizing agent and acts as a disinfectant and laundry bleach.
• Diluted Sodium Hypochlorite Solution, N.F.XIII, is approved for use as an antibacterial agent on tissues.

Iodine Solution

• Iodine Solution and Iodine Tincture contain the same concentrations of ingredients but differ in the solvent (water for the solution, alcohol for the tincture).
• They are both reddish-brown solutions with a characteristic iodine odor.
• Iodine is a mild oxidizing agent, forming hypoiodous acid in water.
• It is effective against many microorganisms, with Iodine Tincture being potentially more effective as the alcohol aids penetration.
• Iodine Solution is preferred for open wounds due to the irritating nature of alcohol.

Silver Nitrate

• Silver Nitrate exists as colorless or white crystals that darken upon exposure to light in the presence of organic matter.
• Solutions of silver nitrate function as antibacterial agents, primarily due to the activity of the silver ion.
• Silver ion acts as a protein precipitant, reacting with both bacterial and human proteins.
• Overuse of silver preparations can lead to argyria, a condition characterized by a darkening of the skin due to the deposition of silver.

Silver Nitrate Uses

• Silver nitrate is used as an antibacterial agent in solutions ranging from 0.01% to 10%. Higher concentrations can cause irritation.
• A 1% solution of Silver Nitrate Ophthalmic Solution is used to prevent ophthalmia neonatorum (infection in newborn eyes).
• Silver nitrate is effective against gonococcal organisms.
• A 0.5% aqueous solution of silver nitrate is used as a wet dressing for third-degree burns.

Astringent Agents

• Astringent agents cause protein precipitation on cell surfaces, leading to protein coagulation and tissue constriction.
• Astringents act on small blood vessels (smooth muscle) and are applied topically.
• Astringents have a mild antimicrobial effect, restrict blood flow, and do not kill cells.
• Common astringent products include aluminum, zinc, and zirconium salts.

Aluminum Chloride (AlCl₃ ·6H₂O)

• It acts as a Lewis acid and is soluble in water, alcohol, and glycerin, creating an acidic solution.
• Used as an astringent and mild antiseptic in solutions ranging from 10% to 25%.
• Can cause tissue irritation due to hydrolysis forming hydrochloric acid (HCl).
• Initially used as an antiperspirant, but its irritating nature led to its replacement.

Aluminum Hydroxy Chloride

• Refers to monohydroxy chloride and dihydroxy chloride.
• These compounds are acidic and less soluble in water than aluminum chloride.
• Less irritating than aluminum chloride, making them suitable for antiperspirants.
• Used in deodorant sprays, creams, and solutions around 20% concentration.

Zinc Chloride

• Forms an acidic solution due to hydrolysis, producing hydrochloric acid (HCl) and basic zinc chloride.
• Solutions should be filtered through asbestos or glass wool as they can dissolve materials like paper and cotton.
• Forms zinc oxychloride when mixed with zinc oxide, which is used in dental cements.

Uses of Zinc Chloride

• Acts as a strong astringent and mild antiseptic due to its protein precipitation properties.
• Functions as an escharotic, aiding in tissue sloughing and scar tissue formation.
• Used in low concentrations (0.5 to 2%) as nasal sprays or applied to mucous membranes for sinus drainage.
• A 10% solution is used as a dentin desensitizer for teeth.

Atomic Structure

• Atoms consist of a central nucleus surrounded by electrons.
• The nucleus contains protons, which have a positive charge and a mass of 1.672 x 10^-24 g, and neutrons, which are uncharged and have a mass of 1.675 x 10^-24 g.
• Electrons possess a negative charge of one electrostatic unit (e.s.u.) and a mass of 9.107 x 10^-28 g.
• The number of protons in an atom is equal to the number of electrons in the neutral atom.
• The number of protons determines the atomic number of the element.
• The sum of the masses of the protons and neutrons in an atom accounts for the atom's atomic mass.
• The region of space around the nucleus where electrons are likely to be found is described by atomic orbitals.

Quantum Numbers

• The principal quantum number (n) determines the energy level of an electron. As n increases, the energy level rises.
• The suborbital quantum number (l) describes the shape and size of an electron's orbital.
  • l = 0 corresponds to an s orbital, which is spherical.
  • l = 1 corresponds to a p orbital, which is dumbbell-shaped.
  • l = 2 corresponds to a d orbital, which has a more complex shape.
  • l = 3 corresponds to an f orbital, which has an even more complex shape.
• The magnetic quantum number (ml) specifies the spatial orientation of an orbital.
• The spin quantum number (ms) represents the intrinsic angular momentum of an electron, which is oriented either spin up (+1/2) or spin down (-1/2).

Filling Atomic Orbitals

• The Aufbau principle states that electrons are added to orbitals in order of increasing energy.
• The Pauli exclusion principle states that no two electrons in an atom can have the same set of quantum numbers. Therefore, a maximum of two electrons can occupy a single orbital, and they must have opposite spins.
• Hund's rules state:
  • Lower energy orbitals are filled before higher energy orbitals.
  • Electrons occupy degenerate orbitals singly, with parallel spin, as long as possible.

Ionization

• Ionization is the process of an atom losing one or more electrons, resulting in a cation (positive ion).
• The outermost electrons are typically the ones lost during ionization.
• The electronic structure of an ion might not reveal the exact level from which the electron was removed.
• Transition elements can ionize to form cations with electrons remaining in the d orbitals.
• Elements in Groups VIA and VIIA tend to gain electrons to form anions (negative ions).

Periodic Table

• The periodic table organizes elements based on their atomic number, electron configuration, and recurring chemical properties.
• Elements are arranged in rows (periods) and columns (groups).
• Groups I-VIIIA correspond to the filling of s and p orbitals.
• Transition elements (Groups IB - VIIIB) result from the filling of d orbitals.
• The lanthanides and actinides are located below the main body of the table and involve the filling of f orbitals.
• Electronegativity increases from left to right across a period and from bottom to top within a group (except for Group VIIIA).

Bonding in Molecules

• The formation of molecules involves three primary forces:
  • Coulombic attraction between electrons and nuclei.
  • Number of electrons in valence orbitals.
  • Distribution of valence orbitals.
• There are two main types of bonds:
  • Covalent bonds involve the sharing of electron pairs between atoms (polar or nonpolar).
  • Ionic bonds involve the transfer of electrons from an electropositive atom to an electronegative atom.
• Orbital hybridization is the mixing of atomic orbitals to form new, degenerate orbitals with distinct spatial orientations and directional properties.
• The number of hybrid orbitals formed equals the number of atomic orbitals involved in hybridization.

Types of Hybrid Orbitals

• sp orbitals: Two sp orbitals, oriented 180° apart, are formed by the combination of one s and one p orbital.
• sp2 orbitals: Three sp2 orbitals, arranged in a triangular planar geometry (120° apart), result from the combination of one s and two p orbitals.
• sp3 orbitals: Four sp3 orbitals, oriented towards the corners of a tetrahedron (109.5° apart), are formed by the combination of one s and three p orbitals.

Types of Bonding Interactions

• Ionic Bonding: Electrostatic attraction between oppositely charged ions.
• Covalent Bonding: Sharing of electron pairs between atoms (nonpolar or polar).
  • Sigma bonds: Molecular orbitals that are symmetrical about the bond axis.
  • Pi bonds: Molecular orbitals located on both sides of the bond axis, perpendicular to a plane passing through the bond axis.
• Coordinate Covalent Bonding: Both electrons in the bond come from a single atom (donor).
• Hydrogen Bonding: Weak interaction between a partially positive hydrogen atom and a lone pair of electrons on an electronegative atom in a neighboring molecule.
• Van der Waals Forces (London Forces): Weak electrical forces between molecules due to temporary dipoles.

Coordination Compounds and Complexation

• Coordination compounds form when a metal cation bonds to additional ligands (anions or neutral molecules) beyond its normal valence requirements.
• The maximum number of ligands a metal ion can bond to is called the coordination number.
• Ligands are typically anions or neutral molecules with nonbonded electron pairs.
• Chelate complexes are formed when polydentate ligands bond to a metal ion, creating a ring structure.
• Chelating agents are polydentate ligands that can improve metal ion solubility and stability.

Bonding in Complexes

• The (n-1)d, ns, and np orbitals can hybridize to form six bonding orbitals directed towards the ligands.

Coordination Complexes and Chelating Agents

• Cr(III) forms a complex with six CN- ligands, [Cr(CN)6]-3.
• Cr(III) has 3d3 configuration, leaving two d orbitals, one s, and three p orbitals empty for bonding.
• Fe(III) with six water molecules in a complex shows a magnetic moment (MM) of 6, indicating 5 unpaired electrons. - This suggests an outer orbital hybridization involving 4d, 4s, and 4p orbitals.
• Replacing water with six CN- ligands in the Fe(III) complex results in an MM of 2, indicating one unpaired electron.
• The strong negative field of CN- ligands forces pairing of electrons in the d orbitals of Fe(III), resulting in a low spin configuration.
• Chelating agents play a role in analytical chemistry by determining metal concentrations through titration.
• Chelating agents solubilize and stabilize metal ions in analytical solutions, enhancing their reactivity.
• Benedict’s and Fehling’s solutions, used for reducing substance detection, employ chelating agents like citric acid and tartaric acid to complex copper(II) ions.
• Chelating agents act as preservatives, preventing decomposition due to trace metal quantities.
• Chelating agents are effective in treating heavy metal poisoning by forming stable, excretable complexes.
• Calcium disodium edetate (EDTA) is used to treat lead poisoning by forming insoluble complexes excreted by kidneys.
• EDTA has a strong affinity for calcium, and the disodium calcium form is used to avoid hypocalcemic states.
• EDTA is also effective against other metals like copper, nickel, cadmium, zinc, chromium, and manganese but not mercury, arsenic, or gold.
• EDTA is poorly absorbed from the gastrointestinal tract and is administered intravenously.
• Disodium edetate is used in conditions dealing with hypercalcemic states.
• Dimercaprol (BAL) is a chelating agent used in arsenic, mercury, and gold poisoning.
• BAL forms complexes with heavy metals, disrupting their interaction with essential enzymes.
• BAL is contraindicated in iron, cadmium, and selenium poisoning due to the toxicity of the resulting complexes.
• BAL is administered intramuscularly due to its poor gastrointestinal absorption.
• Penicillamine chelates copper, iron, mercury, lead, gold, and other metals.
• Penicillamine is used to improve copper excretion in patients with Wilson’s disease.
• Penicillamine is effective due to its resistance to metabolic inactivation by amino acid oxidase.
• Penicillamine is used for treating gold dermatitis in patients receiving chronic gold therapy.
• Deferoxamine mesylate is a chelating agent with a high affinity for ferric ions (Fe(III)).
• Deferoxamine mesylate forms stable, water-soluble complexes with ferric ions.
• Deferoxamine mesylate is used for the treatment of acute iron toxicity.
• Deferoxamine mesylate is administered intramuscularly or intravenously due to poor gastrointestinal absorption.

Gastrointestinal Protectives, Adsorbents, and Cathartics

• Diarrhea is a symptom characterized by increased intestinal bulk stimulating peristalsis, leading to frequent defecation.
• Acute diarrhea can be caused by bacterial toxins, chemical poisons, drugs, allergy, and disease.
• Chronic diarrhea arises from conditions like gastrointestinal surgery, carcinomas, inflammatory conditions, and absorptive defects.
• Antidiarrheal agents aim at treating the symptoms and potentially the cause of diarrhea but not its complications.
• Antidiarrheal products often contain adsorbent-protectives, antispasmodics, and antibacterial agents.
• Adsorbent-protectives bind toxins, bacteria, and viruses in the gastrointestinal tract and provide a protective barrier to the intestinal mucosa.
• Adsorbents bind substances through physical or chemical adsorption.
• Physical adsorption involves weak, nonspecific forces like Van der Waals forces, while chemical adsorption entails stronger chemical bonding.
• Activated charcoal acts as an adsorbent with a high surface area and porous structure, effectively binding various substances.
• Clay adsorbs toxins and bacteria through both physical and chemical adsorption.
• Bismuth salts exert a mild astringent and antiseptic action and form bismuth sulfide, visible as black stools.
• Bismuth subnitrate (N.F.XIII) is practically insoluble in water and alcohol, but dissolves in acids.
• Bismuth subnitrate has a well-known incompatibility with tragacanth but can be overcome using sodium biphosphate or trisodium phosphate.
• Bismuth subnitrate is a component of Milk of Bismuth, acting as a mild astringent-protective.
• Bismuth subcarbonate (U.S.P.XVIII) is practically insoluble in water and alcohol, but dissolves in hydrochloric or nitric acid with effervescence.
• Kaolin is a hydrated aluminum silicate that binds toxins and bacteria through both physical and chemical adsorption.
• Kaolin is insoluble in water, diluted acids, and alkali hydroxides.
• Activated charcoal works primarily through physical adsorption due to its highly porous structure, effectively binding large organic molecules.
• Saline cathartics act by increasing the osmotic load in the gastrointestinal tract, drawing fluids into the intestines and stimulating peristalsis.
• Saline cathartics are salts of poorly absorbable anions like biphosphate, phosphate, sulfate, and tartrate.
• Saline cathartics are water-soluble and should be taken with water to prevent dehydration and minimize nausea and vomiting.
• Saline cathartics are generally safe for short-term use, but prolonged use can lead to dependence.
• Constipation can be caused by various factors like resisting the urge to defecate, intestinal atony, spasm, emotions, drugs, and diet.
• Stimulant laxatives act by locally irritating the intestinal tract, stimulating peristalsis.
• Bulk-forming laxatives swell with water, increasing intestinal bulk and stimulating peristalsis.
• Emollient laxatives function as lubricants or stool softeners, facilitating the passage of compacted fecal material.

Saline Cathartics

• Sodium Biphosphate, Sodium Phosphate, Sodium Sulfate, and Potassium Sodium Tartrate are saline cathartics containing sodium.
• Magnesium salts should be avoided for patients with renal impairment because some magnesium is absorbed and it has a central nervous system depressant effect.
• Sodium Biphosphate is a colorless or white powder that is slightly deliquescent and acid to litmus.
• Sodium Biphosphate dissociates into ions when dissolved in water: NaH2PO4 → Na+ + H2PO4⁻
• It is used as a cathartic in Phospho-Soda, Vacuetts, and Sal Hepatica.
• Sodium Phosphate is a colorless or white granular salt with an alkaline solution.
• Sodium Phosphate dissociates into ions when dissolved in water: Na2HPO4 → 2Na+ + HPO4²⁻
• It is used as a saline cathartic in Fleet Enema and Phospho-Soda.
• Dried Sodium Phosphate is a nearly anhydrous white powder that readily absorbs moisture.
• Dried Sodium Phosphate is used in Effervescent Sodium Phosphate which is a mixture of Sodium Bicarbonate, Tartaric Acid, and Citric Acid.

Topical Agents

• Topical drugs are applied to body surfaces and primarily act at the surface of application.
• Some topical drugs can penetrate deeper tissues and lead to systemic effects such as toxicity or allergic reactions.
• Topical agents can be categorized into three types: protective agents, antimicrobial agents, and astringent compounds.

Protective Agents

• Protectives are applied to the skin to protect certain areas from irritation.
• Protective agents should be insoluble and chemically inert.
• Protective agents are biologically inactive and should not be absorbed by the skin.
• Many protectives act as adsorbents and absorb moisture from the skin's surface.
• Protectives are commonly used as powders, ointments, or suspensions.

Talc

• Talc is a hydrous magnesium silicate that is a very fine, white or grayish white powder.
• Talc is unctuous, adheres readily to the skin, and is free from grittiness.
• It is odorless, tasteless, and insoluble in water, dilute acids, and dilute bases.
• Talc has low adsorptive properties.
• Talc can be synthesized through reacting magnesium oxide or a magnesium salt with silica at elevated temperatures and pressures.
• It is used as a lubricating, protective dusting powder to prevent irritation due to friction.
• It is used in preparations that may be perfumed for cosmetic purposes or medicated with antimicrobial agents.

Zinc Oxide

• Zinc Oxide is a very fine, odorless, amorphous, white or yellowish white powder.
• It is insoluble in water and alcohol and will gradually absorb carbon dioxide from the air to form basic zinc carbonate.
• Zinc Oxide reacts with dilute acids and aqueous solutions of ammonium compounds to form water-soluble products.
• Zinc Oxide is used as a mild astringent and a weak antimicrobial compound due to the release of a small amount of zinc ion from hydrolysis in the acidic moisture on the skin.
• It is used as an astringent and topical protective in ointments in the treatment of skin ulcerations and other dermatological problems.
• Zinc Oxide is the primary ingredient in Calamine.

Calamine

• Calamine is zinc oxide with a small proportion of ferric oxide.
• The presence of ferric oxide gives Calamine a pink color.
• Calamine is insoluble in water and soluble in mineral acids.
• Calamine is a topical protective and is used in dusting powders, ointments, and lotions for its soothing, absorbent, and protective properties.

Antimicrobial Agents

• Antimicrobial agents are chemicals used to prevent and/or reduce infection caused by microorganisms.
• The term antimicrobial agent includes antiseptics, germicides, and disinfectants as well as -stat agents.
• Antiseptic: A substance that kills or inhibits the growth of microorganisms, usually applied to living tissues (e.g., skin) to prevent infection.
• Germicide: A substance that kills microorganisms outright.
• -stat: Refers to agents that do not kill microorganisms, but inhibit their growth.
• Disinfectant: A chemical used to kill microorganisms on inanimate objects, such as instruments or surfaces.
• Sterilization: A process that completely removes or kills all microorganisms from an object.
• The mechanisms of action of inorganic antimicrobial agents can be divided into three general categories: oxidation, halogenation, and protein precipitation.

Oxidation

• The effective oxidative action of oxidizing compounds involves the reducing groups present in most proteins, e.g., the sulfhydryl (-SH) group in cysteine.
• Oxidizing antiseptics form disulfide bridges in proteins, altering their confirmation and function.

Halogenation

• Halogenation occurs with antiseptics of the hypohalite type and hypochlorite, OCl⁻.
• Halogenation can result in the substitution of chlorine atoms for hydrogen atoms, which changes the forces responsible for the proper conformation of the protein molecule.

Protein Precipitation

• Protein precipitation involves the interaction of proteins with metallic ions having large charge/radius ratios or strong electrostatic fields.
• The interaction of metal ions with protein is nonspecific and at sufficient concentration will react with host as well as microbial protein.
• The presence of the metal "ties up" important functional groups at the active site on the enzyme

Hydrogen Peroxide

• Hydrogen Peroxide is a clear, colorless liquid which may have an odor resembling that of ozone.
• It is unstable and decomposes upon standing or agitation.
• Hydrogen Peroxide is unstable on prolonged exposure to light.
• Hydrogen Peroxide solutions may be stabilized with acids, complexing agents, or adsorbents.
• Hydrogen Peroxide is an oxidizing agent and decomposes into two oxide ions, O²⁻.
• The primary use of Hydrogen Peroxide Solution is as a mild oxidizing antiseptic.
• It can be used as a gargle or mouthwash for the treatment of bacterial infections of the throat and mouth.

Sodium Hypochlorite

• Sodium Hypochlorite is clear, pale greenish-yellow liquid having an odor of chlorine.
• It is affected by light.
• The Diluted Sodium Hypochlorite Solution is prepared by diluting the original sodium hypochlorite solution and adjusting the pH to 8.3 or lower.
• Sodium Hypochlorite solutions are strong oxidizing agents.
• Diluted Sodium Hypochlorite solution is used as an antibacterial agent for tissues.
• It can be used as a foot bath in the prevention of various fungal infections.
• Its antibacterial effectiveness can be increased by acidifying the solution.

Iodine Solution

• Iodine Solutions are transparent, reddish-brown liquids with a characteristic odor of iodine.
• Iodine Solutions contain the same concentrations of ingredients, with only the solvent being different.
• Both Iodine Solution and Iodine Tincture are prepared with purified water.
• Both formulations contain approximately 50% alcohol as the final solvent.
• Iodine Solution is preferred for application to wounds because the alcohol in the Tincture is very irritating to open tissue.
• Povidone-Iodine is a complex of iodine with carrier organic molecules serving as a solubilizing agent.
• Iodophors slowly liberate iodine in solution and have less tissue irritation, making them useful for sensitive areas and mucous membranes.

Silver Nitrate

• Silver Nitrate occurs as colorless or white crystals which become gray or grayish-black on exposure to light in the presence of organic matter.
• It is very soluble in water, sparingly soluble in alcohol, and freely soluble in boiling alcohol.
• Silver Nitrate is used as an antibacterial agent.
• The chemistry and pharmacological action of Silver Nitrate is related to the silver ion.
• The protein precipitant action of Silver Nitrate is not selective and will precipitate both bacterial and human protein.
• Extended use of silver preparations may cause a darkening of the skin due to the deposition of free silver below the epidermis. This condition is termed argyria and is essentially irreversible.

Silver Nitrate Uses

• Silver nitrate is used as an antibacterial agent in solutions ranging from 0.01% to 10%.
• Higher concentrations of silver nitrate can be astringent and irritant to tissues.
• A 1% solution of silver nitrate is used in the eyes of newborns to prevent ophthalmia neonatorum, an infection caused by gonococcal organisms.
• A 0.5% aqueous solution of silver nitrate is used as a wet dressing on third-degree burns.

Astringents

• Astringents are compounds that cause protein precipitation on cell surfaces, leading to coagulation of proteins and tissue constriction.
• They typically act on small blood vessels and are applied topically.
• Astringents have limited penetration, resulting in mild antimicrobial effects and restricted blood flow, but they do not cause cell death.

Uses of Astringents

• Styptic action: Stop bleeding from small cuts by promoting blood coagulation and constricting capillaries.
• Antiperspirant: Decrease sweat secretion.
• Constrict mucous membranes: Reduce inflammation by limiting blood flow to the surface.
• Topical actions: Remove unwanted tissue or restrict protein action. Higher concentrations can be corrosive.

Aluminum Chloride

• It is a Lewis acid, highly soluble in water, alcohol, and glycerin.
• It is used in aqueous solutions (10% to 25%) as an astringent and mild antiseptic.
• Can cause tissue irritation due to hydrolysis, which forms hydrochloric acid (HCl).
• Initially used as an antiperspirant but was too irritating and damaged clothing.

Aluminum Hydroxy Chloride

• Two forms exist: monohydroxy chloride and dihydroxy chloride.
• Both forms are acidic but less soluble in water than aluminum chloride.
• Less irritating and commonly used in commercial antiperspirants.
• Used in deodorants, creams, and solutions at approximately 20% concentration.

Zinc Chloride

• Solutions are acidic due to hydrolysis forming hydrochloric acid (HCl) and basic zinc chloride.
• Must be filtered through asbestos or glass wool to prevent dissolving substances like paper and cotton.
• Forms zinc oxychloride when mixed with zinc oxide, creating a hard mass used in some dental cements.

Uses of Zinc Chloride

• Astringent & antiseptic: Strong protein precipitant, acting as a strong astringent and mild antiseptic.
• Escharotic action: Aids in tissue sloughing and scar tissue formation, promoting healing.
• Nasal spray & sinus treatment: In low concentrations (0.5 to 2%), applied to mucous membranes or used as nasal sprays to aid sinus drainage.
• Dentin desensitizer: 10% solution applied to teeth to desensitize dentin.

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