Electronegativity & Ionic Bonds

Electronegativity in Chemical Bonds

• Electronegativity describes the tendency of atoms to attract electrons in a bond
• High electronegativity, usually found in non-metals, attracts electrons
• Low electronegativity, typically found in metals, loses electrons
• Nonpolar Covalent bonds exist with an electronegativity difference of 0 to 0.5
• Polar Covalent electronegativity differences extend from 0.5 to 1.7
• Ionic bonds are observed where the difference in electronegativity is greater than 1.7

Ionic Bonds

• Ionic bonds involve the transfer of electrons between atoms
• High electronegativity non metals attract electrons
• Low electronegative metals lose electrons
• Ionic bonds are strong and are formed when electrons are transferred from one atom to another
• This results in electrostatic attraction between oppositely charged ions, ranging from 1,100 to 20,000 kJ/mole in ionic crystals
• The transferring of electrons results in the formation of cations and anions
• Oppositely charged ions are strongly attracted to each other
• When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules
• Water forms a hydration shell around charge solutes

Charged Ions (Cation and Anion) in Ionic Bonds

• Neutral atoms have an equal number of protons and electrons
• Anions are negatively charged ions resulting from gaining electrons
• Cations are positively charged ions formed by losing electrons
• Non-metal atoms typically form anions
• Metal atoms typically form cations

Van der Waals Interactions

• Van der Waals bonds, ranging less than 4 kJ/mole, are weak forces between molecules
• They are observed in condensed phases like solid and liquid
• Van der Waals bonds are secondary bonds from uneven charge distribution
• Ionic and covalent bonds form the primary bonds
• Non-directional attraction of atoms or molecules from all directions
• Weaker than ionic and covalent chemical bonds
• Van der Waals bonds are effective only over a short range
• Plays roles such as stabilizing protein structure, polymer chains, cohesion of insert gases, and physical adorption of molecules on solid surfaces

Properties of Water

• The polarity and hydrogen bonding ability of water combine to create four very important properties of water
• These properties including Cohesion & Adhesion
• Cohesion & Adhesion is crucial for the transportation of water within organisms
• Water is an Universal Solvent: excellent solvent for various substances
• Water provides Moderation of temperature by resisting temperature changes
• Density of Solid vs. Liquid of water: ice is less dense than the liquid form

Dissociation of Water

• The autoionization of water is a rare but significant phenomenon in which water dissociates
• This is a reversible reaction where a water molecule donates a proton to another water molecule to form H3O+ and OH-
• Increased H3O+ results in lower pH
• Decreased H3O+ results in higher pH
• H3O+, also known as hydronium ion, is a water molecule that has gained an extra hydrogen ion (H+)

Acids and Bases

• Acids increase the concentration of H+ in solution which decreases the concentration of OH-
• H3O+ is the hydrated form of H+ ion
• Bases reduce the concentration of H+ in solution which increases the concentration of OH-
• OH- ions can combine with H3O+ ions to form water
• The Acid dissociation constant (Ka) and the Base dissociation constant (Kb) indicate the strength of an acid or base
• The pH scale ranges from 0 to 14, reflecting the degree of dissociation
• Acids donate H+ in aqueous solutions
• The addition of acids Increase the H+ concentration of a solution, acids are between 0-7
• Bases donate OH or accept H⁺ in aqueous solutions, bases are between 7-14
• Pure water acts both as an acid and a base

Calculating pH Formula

• pH is usually a positive number between 0 to 14
• In pure water: [H3O+] = [H+] = 1 x 10-7M (moles/liter)
• pH = -log[H3O+] = -log[H+]
• Most acidic solutions will have the highest [H+] concentration
• Least acidic solutions will have the lowest [H+] concentration
• Small changes in pH are very important

Blood pH

• Blood is normall around 7.4 pH .
• Change from 7.4 to 7.0, leads to death in minutes
• Results in a 2.5 times change
• Homeostatic Imbalances: Includes Acids and Bases
• Homeostatic Imbalances may result in Excessive acidity of the blood: which causes Acidosis
• Excessive alkaline (basic) of blood causes Alkalosis

Buffers

• Buffers minimize changes in concentrations of H⁺ and OH
• The body's buffering system stabilizes of blood pH levels
• The lowering of pH is a process where raising pH as more CO2 is made
• The purple arrows indicate the reverse process: the lowering of pH as more bicarbonate (HCO 3-) is created

Water

• An aqueous solution is one in which water is the solvent
• Hydrophilic substances are "water loving" and able to interact with water
• They are typically polar and/or charged (ions) molecules
• Hydrophobic substances are "water fearing" and do not interact with water
• They are typically nonpolar molecules
• Nonpolar molecules have no significant partial charges and symmetrical distribution of electrons
• Polar molecules Unequal distribution of electrons and includes a Partial positive and a partial negative charge results in asymmetrical molecules

Functional Groups and Carbon Chemistry

• Organic chemistry is important because it is the study of carbon-containing compounds and it is the basis of all life on Earth
• The human body is composed mainly of Oxygen 65.0%, Carbon 18.5%, Hydrogen 9.5% and Nitrogen 3.3% (96.3% total)
• Carbon can form 4 bonds, enabling it to form large, diverse, and complex molecules as well as a variety of carbon skeletons
• Molecular diversity arises from variations in length and shape of carbon chains

Hydrocarbons

• Hydrocarbons are organic chemical compounds composed only of carbon (C) and hydrogen (H) with little polarity
• Consequently they are usually hydrophobic and insoluble

Functional Groups

• Functional groups determine the characteristics and chemical reactivity of organic molecules such as the hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, phosphate, and methyl groups
• Functional groups are less stable than the carbon backbone and are more likely to participate in chemical reactions

Hydroxyl Group

• Alcohols have an R-OH structure and are polar and can involve hydrogen bonding
• They often participates in condensation reactions
• They are Required in side chain for phosphorylation of proteins

Carbonyl Group

• Aldehydes have at least one of the R-groups as a hydrogen
• Aldehydes are polar and are Very reactive
• Aldehydes are important participants in energy-releasing reactions and organic synthesis pathways

Carboxyl Group

• Carboxylic acids have an R-COOH structure
• Acids are Charged and acidic
• Acids lonizes in cells to form R-COO- and H+

Amino Group

• Amines charged and basic
• H+ is accepted to form R-NH3+ in cells
• Nucleic acids like DNA and RNA

Sulfhydryl Group

• Thiols are R-SH where R is organic
• Sulfur molecules Can form disulfide bridges
• Antioxidant properties help protect cells from oxidative damage

Phosphate Group

• Organic phosphates are a R-O-PO3
• Charged and acidic and form -O-PO32- in cells
• Phosphate contributes to Nucleic acids, cell membranes, and various proteins

Methyl Group

• Alkyl groups are H-CH3
• Have an Electronegativity: carbon ≈ hydrogen
• Electrons equally shared between atoms
• Methyls groups are nonpolar, with nonpolar covalent bonds
• Affects DNA methylation, affecting gene expression and regulation

Explore electronegativity's role in chemical bonds. Understand how differences in electronegativity lead to nonpolar covalent, polar covalent, and ionic bonds. Also, learn how electron transfer forms ions, creating strong electrostatic attractions in ionic crystals.