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Molecules and Bonding

Molecules and Bonding. Daniels Sims Fayola. How are molecules represented?. Chemical formula = symbols for the elements are used to indicate the types of atoms present and subscripts are used to indicate the relative numbers of atoms. EXAMPLE : CO2

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Molecules and Bonding

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  1. Molecules and Bonding Daniels Sims Fayola

  2. How are molecules represented? • Chemical formula = symbols for the elements are used to indicate the types of atoms present and subscripts are used to indicate the relative numbers of atoms. EXAMPLE: CO2 • Structural formula = individual bonds are shown indicated by lines. EXAMPLE: H-O-H

  3. The forces that hold atoms together in compounds. MUST follow the octet rule!!! Types of Bonds… Ionic Metallic Covalent Polar Covalent Non-polar Covalent (this one is like a covalent bond) What are Chemical Bonds?

  4. Ionic Bonds… • Closely packed, oppositely charged ions. (+) ion = cation and (-) ion = anion • Makes the compound electrically neutral and joined by electrostatic forces. • Formed when an atom that loses electrons easily (metals) reacts with an atom that has a whole lot of electrons (non-metals). • The most stable and strongest bond! • EXAMPLES… (NaCl, MgCl2, Na2O)

  5. Properties of Ionic Compounds… • Most are 3-D crystalline solids • Each ion is strongly attracted to each other • Conduct electrical current in a molten state

  6. Metallic Bonds… • Metals consist of closely packed cations (+ charges) • Cations are surrounded by mobile moving valence electrons • Consist of an attraction of free-floating valence electrons to the positively charges metal ions • Examples are Cu, Fe, Mg and precious metals

  7. Lets Practice… • Write the symbols for each element • Draw an arrow to show the transfer of electrons from one atom to the other (lewis structures) • Determine the charge for each ion and write the chemical formula • 1) Potassium + Fluorine • 2) Magnesium + Iodide • 3) Sodium + Oxygen • 4) Sodium + Chlorine • 5) Calcium + Chlorine • 6) Aluminum + Chlorine

  8. Covalent Bonds… • Electrons are shared by the 2 nuclei of the atoms. • Often non-metals form these bonds. • All organic molecules are covalent. • MOST COMMON BOND!!! • But there are 2 types of covalent bonds.

  9. Polar Covalent Bonds… • Unequal sharing of electrons because 2 different atoms (different electronegativities) • Makes one atom look more (+) and the other atom look more (-) (dipole moments) • Any molecules that are different can show some polarity. • EXAMPLES… (H2O, ClF, CCl4, HF)

  10. Non-Polar Covalent Bonds… • When atoms are shared equally because they are identical atoms. • Pretty much the same as regular covalent. • Doesn’t make one atom more + or more - • EXAMPLES…(H2, O2, N2, Cl2)

  11. VSEPR Theory… • The Valence-Shell Electron-Pair Repulsion Theory • Because electron pairs repel the molecules adjust their shapes so that the valence-electron pairs are as far apart as possible. (why H2O is bent) • Molecular shapes: linear, trigonal planar, bent, pyramidal, tetrahedral, bypyrimidal

  12. Covalent Bonding & Lewis Strucutes… • Single bonds: H2O, NH3, CH4, NF3 • Double bonds: CO2, CH3COOH (acetic acid) • Triple bonds: N2 • There can be some exceptions to the rules, but we won’t get into these

  13. Let’s Practice… • Write the symbols for each element • Rearrange the electrons to pair up or “fit like a puzzle” (use different colors for each atom) AKA make the lewis structure • Draw circles to show the sharing of electrons • Write the chemical formula for each molecule • 1) Hydrogen + Hydrogen • 2) Hydrogen + Oxygen • 3) Chlorine + Chlorine • 4) Carbon + Oxygen • 5) Carbon + Hydrogen

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