Chemical Bonding: Lewis Diagrams, VSEPR Theory - PDF
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Biotechnology High School
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This document provides educational notes on chemical bonding, covering topics such as ionic and covalent bonds, Lewis diagrams, polyatomic ions, VSEPR theory, and molecular geometry. It explores the octet rule, resonance structures, and exceptions to the rule, aiming to explain how molecules and ions behave. Key concepts include electron pair repulsion and the determination of molecular shapes.
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Chemical Bonding Bonds:Atoms bond because they become morestablewhen they havefull outer shells. ★ Donating, receiving, or sharingelectronsallows themto achieve stability. ★ TheOctet Rulemeans that there is a maximum numberfor 8 electrons in t...
Chemical Bonding Bonds:Atoms bond because they become morestablewhen they havefull outer shells. ★ Donating, receiving, or sharingelectronsallows themto achieve stability. ★ TheOctet Rulemeans that there is a maximum numberfor 8 electrons in the outer shell. Ions:Anionis an atom that haslostorgainedanelectron. Ionic bonding:Ionic bondingoccurs when ametalatomdonates one or more electrons to anon–metalatom. ★ Themetalbecomes morepositive(cation) and the non-metal becomes morenegative(anion) ○ In other words, the non-metal transfers its electron(s) to the metal. Covalent bonding:Covalent bondingoccurs when atomsshare pairs of electronsinstead of giving and receiving. ★ The pair is included in the outer shell of both atoms. Covalent bondingoccurs between atoms of nonmetals. Metallic bonds:Metallic bondsoccur when atoms ofmetalsgive up electrons,forming an electron sea. ★ The positively charged atoms are bonded through their attraction to the negatively charged electrons. Drawing Lewis Diagrams: ★ Find total number of valence e- ★ Arrange atoms - singular atom is usually in the middle ★ Form bonds between atoms (2 e-) ★ Distribute remaining e- to give each atom an octet ★ If there aren’t enough e- to go around, form double or triple bonds Polyatomic ions:Polyatomic ionsare charged entities composed of two or more atoms that are covalently bonded together, which collectively carry a positive or negative charge. Resonance Structures: ★ Molecules that can’t be correctly represented by a single Lewis diagram ★ Actual structure is an average of all possibilities ★ Show possible structures separated by a double-headed arrow Exceptions to the Octet Rule:It is impossible to write a good Lewis structure for molecules with odd numbers of electrons, yet some of these molecules exist in nature. ★ A significant exception of the octet rule is boron, which tends to form compounds with only 6 electrons around B, rather than 8. ★ Some molecules have more than 8 electrons around a central atom in their Lewis Structure. ○ These are referred to asexpanded octets VSEPR Theory:Valence Shell Electron Pair Repulsion ★ This theory explains how molecules and ions behave. ○ E.g. it explains why water molecules are so good at dissolving ionic substances even though water does not have an ionic bond. ★ Basic procedure: ○ Determine the central atom (lowest subscript and/or the atom capable of forming the most bonds) ○ Draw the electron dot structure and bar diagram ○ Determine the molecular geometry using ALL electron pairs AND atoms around the central atom ○ Modify the geometry to determine the molecular shape if non-bonding electron pairs exist by ignoring them, BUT LEAVE THE ATOMS OF BONDED PARIS WHERE THEY ARE. This is done because even if the electrons have no atom attached, these unbonded electron pairs still affect the shape of the structure ★ Bonded pairs/groupsare the atoms attached to the central atom ★ Lone pairs/groupsare the pairs of valence electrons attached to the lone pair, not bonded to a different atom. ★ Electron groupsare the bonding pairs and lone pairs added together. ★ A molecular structure issymmetricalif you can draw a plane in the middle and it is the same on both sides. ★ It ispolarif it’s nonsymmetrical, andnonpolarif it’s symmetrical. ○ This is because one side would have a different charge than the other if the molecule is nonsymmetrical. ★ Abentmolecule occurs when there’s 1 lone pair and 2 bonded pairs. VSEPR Theory video(link) ➔ Thebonding groupsandlone pairscan determine themolecular geometry,or the way atoms are arranged, in a molecule. ➔ Depending on the arrangement, there is a specificangleat which the atoms are apart. ★ A solid ismolecularif it is onlynonmetalsbonded together. ★ It isatomicif it only contains asingle element. ★ It isionicif it ismetalsandnonmetalstogether.
