Organic Chemistry I - Review of General Chemistry - Quick Guides | Chemistry

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Study GuideOrganic Chemistry I–Review of General Chemistry1.Ionic BondingWhat Is Ionic Bonding?Ionic bonding happens whenelectrons are transferredfrom one atom to another. This transfercreatesions—atoms with an electrical charge.•An atom thatloseselectrons becomes apositively charged ion (cation).•An atom thatgainselectrons becomes anegatively charged ion (anion).Thestrong attraction between opposite charges(positive and negative) is what holds the ionstogether. This attraction is the core of anionic bond.Why Do Atoms Form Ionic Bonds?Atoms form ionic bonds to becomemore stable. Most atoms are most stable when their outer shellhaseight electrons. This is called anoctet.An octet is typical of thenoble gases, which are very stable elements because their outermostenergy level is full.1.1Example: Sodium and ChlorineLet’s look at a common example—sodium (Na)andchlorine (Cl).•Sodiumhas one electron in its outer shell. It becomes stable bylosing that electron.oAfter losing one electron, sodium becomes aNa⁺ion.oIt now has the same electron arrangement as the noble gasneon. This is calledbeingisoelectronic(having the same number and arrangement of electrons).

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Study Guide•Chlorinehas seven electrons in its outer shell. It becomes stable bygaining one electron.oAfter gaining an electron, chlorine becomes aCl⁻ion.oIt now has the same electron arrangement as the noble gasargon, so it is alsoisoelectronic.1.2How the Ionic Bond FormsOnce sodium becomes positive and chlorine becomes negative, theyattract each other. Thiselectrostatic attractionbetween the ions forms anionic bond, creating a stable compound.Where Ionic Bonds Usually OccurIonic bonds usually form between:•MetalsinGroup IA and IIA(such as sodium or calcium), and•NonmetalsinGroup VIA and VIIA(such as oxygen or chlorine) of the periodic table.These groups are more likely to lose or gain electrons, making ionic bonding common between them.Key TakeawaysIonic bonding is all aboutelectron transfer,opposite charges, andstability. By losing or gainingelectrons, atoms achieve a full outer shell and stick together through strong electrostatic attraction.2. Covalent Bonding and ElectronegativityWhat Is Covalent Bonding?Covalent bonding happens whenatoms share electronsinstead of transferring them. By sharingelectrons, each atom can fill its outer shell and becomemore stable.This type of bonding is very common inmolecules, especially in organic compounds.

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Study GuideExample: Methane (CH₄)A good example of covalent bonding ismethane (CH₄), the simplest organic compound.•Carbonhasfour valence electronsand needs four more to complete its outer shell (anoctet).•Hydrogenhasone valence electronand becomes stable when it hastwo electrons(this iscalled aduet).In methane, carbon shares one electron with each of four hydrogen atoms.•Carbon ends up witheight electronsin its outer shell.•Each hydrogen ends up withtwo electrons, making itisoelectronic with helium, which hasa full shell.As a result, all the atoms involved become more stable.2.1Pure Covalent BondsIn apure covalent bond, the shared electrons areequally sharedbetween the atoms.This only happens when the two bonded atoms arethe same element, because they attractelectrons equally.•A classic example is thehydrogen molecule (H₂).•Each hydrogen atom pulls on the shared electrons equally, so the bond is completelynonpolar.2.2Unequal Sharing and Bond PolarityMost covalent bonds arenotpure. In many cases, one atom attracts the shared electronsmorestronglythan the other.

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Study GuideWhen this happens:•The electrons move closer to the more attractive atom.•That atom becomes slightlynegative (partial negative charge).•The other atom becomes slightlypositive (partial positive charge).This uneven distribution of electrons makes the bondpolar, meaning the molecule has apositiveend and a negative end.What Is Electronegativity?Electronegativityis the ability of an atom toattract electronsin a chemical bond.It depends on two related properties:•Electron affinity: the energy released when an atom gains an electron.•Ionization energy: the energy required to remove the most loosely held electron from anatom.Atoms with high electronegativity attract electrons strongly.2.3The Pauling Electronegativity ScaleElectronegativity is measured using thePauling scale, developed byLinus Pauling.•Fluorineis the most electronegative element, with a value of4.0.•Highly electronegative elements includehalogens,oxygen,nitrogen, andsulfur.•Thealkali metalsandalkaline earth metalshave low electronegativity.oCesiumandfranciumare among the least electronegative, with values around0.7.Electronegativity and Type of BondThedifference in electronegativitybetween two atoms helps predict the type of bond they will form:•Large difference (2 or more)→Ionic bond•Smaller difference (less than 2)→Covalent bond•No difference (same atoms)→Pure covalent bond

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Study GuideThe smaller the electronegativity difference, theless polarthe bond is. As the difference approacheszero, the bond becomes more purely covalent.Carbon and Bond PolarityCarbon, with an electronegativity of2.5, is very versatile. It can form:•Low-polarity covalent bonds, and•High-polarity covalent bonds,depending on the atom it is bonded to. This flexibility is one reason carbon is so important in organicchemistry.Common Electronegativity ValuesKey TakeawaysCovalent bonding is aboutsharing electrons, while electronegativity explainshow evenlythoseelectrons are shared. Understanding electronegativity helps predict whether a bond will bepurecovalent,polar covalent, orionic—a key idea for mastering chemistry.

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Study Guide3.Brønsted–Lowry Theory of Acids and Bases3.1Early Ideas: Arrhenius TheoryIn the early 1900s,Svante Arrheniusexplained acids and bases in a simple way:•Anacidis a substance that releaseshydrogen ions (H⁺)in water.•Abaseis a substance that releaseshydroxide ions (OH⁻)in water.According to this theory,neutralizationhappens when a hydrogen ion reacts with a hydroxide ion toformwater (H₂O).This model works well—but only for reactions that happenin water.Why a New Theory Was NeededThe main limitation of the Arrhenius theory is that it appliesonly to aqueous (water-based)solutions. Chemists needed a broader explanation that could describe acid–base reactions in moresituations.This led to theBrønsted–Lowry theory, developed a few decades later.3.2Brønsted–Lowry Theory: The Big IdeaThe Brønsted–Lowry theory defines acids and bases based onproton (H⁺) transfer:•ABrønsted–Lowry acidis any substance that candonate a proton.•ABrønsted–Lowry baseis any substance that canaccept a proton.This definition is much more general and works in many different environments—not just in water.

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