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Chapter 6

Chapter 6. Sections 1,2 and 3. Key Terms. Only a few atoms exist as isolated atoms – Noble Gases Molecule Smallest electrically neutral unit of a substance that still has the properties of the substance. Made up of two or more atoms that behave as a unit. Some are diatomic (appear as pairs)

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Chapter 6

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  1. Chapter 6 Sections 1,2 and 3

  2. Key Terms • Only a few atoms exist as isolated atoms – Noble Gases • Molecule • Smallest electrically neutral unit of a substance that still has the properties of the substance. • Made up of two or more atoms that behave as a unit. • Some are diatomic (appear as pairs) • Br2I2N2Cl2H2O2F2

  3. Molecular Compounds • Atoms of different elements combine chemically • Compounds composed of molecules are called molecular compounds. • Some general characteristics: • Low melting and boiling points • Most are liquids or gases • Composed of two or more non-metals

  4. Ionic Compounds • Ions – atoms or groups of atoms that have positive or negative charges (that means the # of p+ does not equal the # of e-) • Metallic elements tend to form cations (positive charges) • The protons outnumber the electrons • The charge is usually written after the symbol and to the upper right (Na+) • Cations are named the same as the element. • Ions behave very differently than the atoms they came from.

  5. Anions • Non-metals usually form anions. • Negative (electrons outnumber the protons). • Happens when elements gain electrons • The name of a typical monatomic anion (1 atom that is negative) ends in –ide Example: Cl- = chloride

  6. Compounds composed of cations and anions are called ionic compounds. • Usually made of metals with non-metals • Ionic compounds are electrically neutral • Usually solids at room temperature and melt at extremely high temperatures.

  7. Chemical Formulas • Shows the kinds and number of atoms in the smallest representative unit of the substance. • Use elemental symbols • Subscripts show haw many of each atom are present. • Example: oxygen = O2

  8. Molecular Formula • Chemical formula for a molecular compound. • Tells nothing about structure or arrangement of atoms. • Example = carbon dioxide = CO2 One carbon atom and two oxygen atoms tightly bound to each other.

  9. Formula Unit • Used for ionic compounds • Ionic compounds are not molecules • It is the lowest whole number ration of ions in a compound. • Example: NaCl (sodium chloride or table salt) is made of one sodium ion and one chloride ion. Thus, the ratio is 1:1 (sodium = +1 charge and chloride = -1 charge) • Example #2: MgCl2 (magnesium chloride) is made of one magnesium cation (+2 charge) and two chloride anions (-1 each) thus the ratio is 1:2

  10. Laws • Law of multiple proportions • If two or more compounds made of the same elements exist they are a whole ratio of each others composition. • Law of definite proportions • Samples of the same compound have the elements present in the same ratio.

  11. Monatomic Ions • Ions consisting of only one atom • Table 6.2 (p143) • Can be predicted from group on the periodic table.

  12. Roman Numeral is the charge! Transition Metals • Most can have multiple charges • Exceptions = Silver (Ag+), Zinc (Zn+2) and Cadmium (Cd+2) • Roman Numeral is used to show the charge on the cation • Example: Copper (I) = Cu+1

  13. Table 6.3 Page 144

  14. Polyatomic Ions • Tightly bound groups of atoms that behave as a unit and carry a charge. • Change the prefix and suffix to show a change in the number of oxygen present. • Exceptions = Cyanide, Hydroxide and ammonium • Practice with the common ion sheet

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