MCD4390_Lectures_Week 3

MCD4390_Lectures_Week 3 - Blackman Chapter 5 Week 3 From...

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1 Atoms and Atomic Structure 1 Week 3 - From Atoms to Molecules Blackman Chapter 5 Week 3: From Atoms To Molecules 3.1 The Simplest Molecule: H2 3.2 Basic Properties 3.3 Diatomics 3.4 Electronegativity 3.5 Ionic Bonding 3.6 Lewis Structures 3.7 Resonance 3.8 Geometry 3.9 VSEPR Theory Atoms and Atomic Structure 2 Learning objectives (3.1-3.6) Blackman 5.1 Discuss the phenomenom of electrostatic energy Identify the electrostatic interaction in H 2 . Define bond length and bond energy. Define and illustrate sigma ( s ) bonds. Explore two additional diatomics, F 2 & HF. Introduce the concepts of polarity, dipole moments & electronegativity Discuss ionic bonding. Apply the octet rule to draw Lewis structures for polyatomics, including resonance structures when appropriate.
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2 Atoms and Atomic Structure 3 Fundamentals of Bonding Molecular compounds Electrons are shared between atoms (covalent bonds) Ionic compounds Electrons are transferred between atoms to form +ve and -ve ions (ionic bonds) These are over-simplified descriptions Across the next three weeks we will explore several different models of bonding. Blackman 5.1 Atoms and Atomic Structure 4 3.1 The Simplest Molecule: H 2 Molecules contain two or more nuclei and two or more e - s. We need to consider ALL of the electrostatic interactions! Blackman 5.1 The most stable arrangement of atoms occurs when the potential energy is an absolute minimum. We view the electrons as being shared between the nuclei and call this shared electron density a covalent bond. H H
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3 Atoms and Atomic Structure 5 3.1 The Simplest Molecule: H 2 H 2 potential energy diagram (a Morse potential). At 74 pm, we obtain the best possible balance between the attractive and repulsive forces in the molecule. Blackman 5.1 Atoms and Atomic Structure 6 3.2 Basic Properties - Bond Length The separation distance at which the molecule has the maximum energetic advantage over the separated atoms (74 pm for H 2 ) is known as the bond length . Yet experimental studies of molecular motion reveal that nuclei within molecules move continuously, oscillating about their lowest energy separation distance like two balls attached to opposite ends of a spring. H H 74 pm Blackman 5.1
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