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Introduction to Chemical Bonding and Chemical Formulas

Introduction to Chemical Bonding and Chemical Formulas. Ch. 6, Sec. 1 Ch. 7, Sec. 1. Valence Electrons are…?. The electrons responsible for the chemical properties of atoms, and are those in the outer energy level. Valence electrons - The s and p electrons in the outer energy level

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Introduction to Chemical Bonding and Chemical Formulas

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  1. Introduction to Chemical Bonding and Chemical Formulas Ch. 6, Sec. 1 Ch. 7, Sec. 1

  2. Valence Electrons are…? • The electrons responsible for the chemical properties of atoms, and are those in the outer energy level. • Valence electrons - The s and p electrons in the outer energy level • the highest occupied energy level • Core electrons– are those in the energy levels below.

  3. Introduction to Bonding • Chemical bond: mutual electric attraction between nuclei and valence electrons of differing atoms that “hold” them together as a compound. • Results in a reduction of the potential energy of the system, thereby becoming more stable • Major types: ionicand covalent • The bond type depends on the atoms’ electronegativities

  4. Major Bond Types • Ionic bond- electrons are transferred between atoms; cations attract anions. • Covalent bond: electrons are shared between two atoms • Nonpolar= atoms shared equally (mostly) • Polar= atoms shared unequally

  5. Ionic vs. Covalent

  6. Electronegativies Figure 20 on page 161

  7. More • Subtract the electronegativities to determine the nature of the bond • If the difference is greater than 1.7, the bond is ionic • ΔEN of 1.7 is about 50% ionic character • If the difference is from 0 to 0.3, the bond is non-polar covalent. • If the difference is from 0.3 to 1.7, the bond is polar covalent.

  8. Character of BondsFigure 2 on page 176 About 50% ionic character

  9. Nonpolar-Polar-IonicFigure 3 on page 177

  10. Summary • If the atoms have very differentelectronegativities, then ionic bonding occurs ( Metal and Nonmetal) • If they both have high electronegativities, then covalent bonding occurs (Two nonmetals) • If they both have low electronegativities, then metallic bonding occurs (Two metals)

  11. Practice: What kind of bond? • Na and Cl • Sr and O • C and O • Ni and Fe • N and O • Br and Br • Ti and Cr • ionic • ionic • polar covalent • metallic • polar covalent • non-polar covalent • metallic

  12. Keeping Track of Electrons • Atoms in the same group have the same outer electronic structure and therefore the same number of valence electrons. • The number of valence electrons is easily determined. It is the group number for groups 1 and 2 • Group 1: H, Li, Na, K, etc. have 1 valence e- • Group 2: Be, Mg, Ca, etc. have 2 valence e-

  13. More about Keeping Track • For elements in groups 13-17: • Subtract 10 from the group number • This is the number of valence electrons

  14. Chemical Formulas • A unit of matter composed of two or more nonmetal atoms is a molecule. • A chemical formulais an expression of the number of atoms of each element in a compound. • The chemical formula of sulfuric acid is H2SO4.

  15. Writing Chemical Formulas • The number of each type of atom in a molecule is indicated with a subscript in a chemical formula. • If there is only one atom of a certain type, no “1” is used. • A molecule of vitamin B3 has 6 carbon atoms, 6 hydrogen atoms, 2 nitrogen atoms, and 1 oxygen atom. What is the chemical formula? C6H6N2O

  16. Interpreting Chemical Formulas • Some chemical formulas use parentheses to clarify atomic composition. • Ethylene glycol, a component of some antifreezes, has a chemical formula of C2H4(OH)2. It contains 2 carbon atoms, 4 hydrogen atoms, and 2 OH units, for a total of 6 hydrogen atoms and 2 oxygen atoms. How many total atoms are in ethylene glycol? • Ethylene glycol has a total of 10 atoms.

  17. Formulas • How many atoms of carbon are in NaCH3COO • 2 • How many atoms of nitrogen are in NH4NO3? • 2 • How many calcium atoms are in C12H22O11? • 0 • How many oxygen atoms are in Co(NO3)2? • 6 • How many atoms are in Al2(SO4)3? • 17

  18. Using Formulas • How many oxygen atoms in the following? CaCO3 Al2(SO4)3 • How many ions in the following? CaCl2 NaOH Al2(SO4)3 3 atoms of oxygen 12 (3 x 4) atoms of oxygen 3 total ions (1 Ca2+ ion and 2 Cl1- ions) 2 total ions (1 Na1+ ion and 1 OH1- ion) 5 total ions (2 Al3+ + 3 SO42- ions)

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