Lecture 2 presented

Lecture 2 presented

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Unformatted text preview: Lecture 2: Atoms, molecules, biological molecules and reac7ons Chapters 2 and 3 1 A review of atomic structure Loca7ons of electrons in an atom are described by orbitals. • Orbital: region where electron is found at least 90% of the 7me. • Orbitals have characteris7c shapes and orienta7ons, and can be occupied by two electrons. • Orbitals are filled in a specific sequence. 2 Figure 2.4 Electron Shells and Orbitals 3 Figure 2.5 Electron Shells Determine the Reac7vity of Atoms 4 How Does Atomic Structure Explain the Proper7es of MaRer? The outermost electron shell (valence shell) determines how the atom behaves. If the outermost shell is full, the atom is stable; it won’t react with other atoms. Reac)ve atoms have unpaired electrons in their outermost shell. 5 6 Figure 2.6 Electrons Are Shared in Covalent Bonds 7 Figure 2.7 Covalent Bonding Can Form Compounds Carbon can form four covalent bonds. 8 9 2.2 How Do Atoms Bond to Form Molecules? Covalent bonds can be • Single—sharing 1 pair of electrons CH • Double—sharing 2 pairs of electrons CC • Triple—sharing 3 pairs of electrons NN 10 10 How Do Atoms Bond to Form Molecules? Sharing of electrons in a covalent bond is not always equal. Electronega.vity: the aRrac7ve force that an atomic nucleus exerts on electrons. It depends on the number of protons and...
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