IBHL--Molecular_Models_Lab.doc - Molecular Models Lab REFERENCES Zumdahl Ch 8-9 With an understanding of electron configuration in atoms we can predict

IBHL--Molecular_Models_Lab.doc - Molecular Models Lab...

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Molecular Models Lab REFERENCES: Zumdahl, Ch. 8-9 With an understanding of electron configuration in atoms, we can predict how atoms bond together to form molecules. Lewis structures are diagrams that show exactly how atoms are bonded to one another. All valence electrons are shown in the Lewis structure, both shared and unshared. Shared pairs of electrons between two atoms form covalent bonds . These are represented with a dash. A single dash is one shared pair of electrons (single covalent bond), two dashes is two shared pairs of electrons (double covalent bond) and three dashes is three shared pairs of electrons (triple covalent bond). Unshared electrons exist in pairs and are called lone pairs . Single unshared electrons are rare and exist only in structures called radicals . The rules for drawing Lewis structures are as follows: Step 1: Count the total number of valence electrons Gp1-8 = Gp # Gp12-18 = Gp # - 10 anion: add e- cation: subtract e- Step 2: Draw the molecular skeleton Central atom usually lowest EN H never central All other atoms will bond to central Step 3: Connect atoms with single bonds Step 4: Place remaining valence e- on atoms as lone pairs to satisfy the octet rule (shares 8 e- ) H only shares 2 e- Be only shares 4 e- B only shares 6e- Step 5: For any atoms that don’t have enough for an octet, shift electron pairs around to form a double or triple bond. Try to keep the molecule symmetrical Step 6: If there are any extra electron pairs, place them on the central atom – even if it gives them more than an octet. Only elements in period three or higher can share more than an octet. They do so by using d orbitals Valence bond theory will explain this.
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The Lewis structure is the key to predicting many properties of our molecule. One of these is geometry. The Valence Shell Electron Pair Repulsion Theory (VSEPR) helps us with this.
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