1. Atoms, Molecules, and Ions Warm Up A measured mass of an unreactive metal was dropped into a small graduated cylinder half filled with water. The following measurements were made. Mass of metal = 19.611 grams Volume of water before addition of metal = 12.4 milliliters Volume of water after addition of metal = 14.9 milliliters The density of the metal should be reported as (A) 7.8444 grams per mL (B) 7.844 grams per mL (C) 7.84 grams per mL (D) 7.8 grams per mL (E) 8 grams per mL

2. Atoms, Molecules, and Ions Chapter 2 Atoms, Molecules, and Ions John D. Bookstaver St. Charles Community College Cottleville, MO © 2009, Prentice-Hall, Inc.

3. Atoms, Molecules, and Ions Subatomic Particles  Protons and electrons are the only particles that have a charge.  Protons and neutrons have essentially the same mass.  The mass of an electron is so small we ignore it. © 2009, Prentice-Hall, Inc.

4. Atoms, Molecules, and Ions Symbols of Elements Elements are symbolized by one or two letters. © 2009, Prentice-Hall, Inc.

5. Atoms, Molecules, and Ions Atomic Number All atoms of the same element have the same number of protons: The atomic number (Z) © 2009, Prentice-Hall, Inc.

6. Atoms, Molecules, and Ions Atomic Mass The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom. © 2009, Prentice-Hall, Inc.

7. Atoms, Molecules, and Ions Isotopes  Isotopes are atoms of the same element with different masses.  Isotopes have different numbers of neutrons. © 2009, Prentice-Hall, Inc. 11 6 C 12 6 C 13 6 C 14 6 C Same number of protonsDifferent masses

8. Atoms, Molecules, and Ions Average Mass  Because in the real world we use large amounts of atoms and molecules, we use average masses in calculations.  Average mass is calculated from the isotopes of an element weighted by their relative abundances. © 2009, Prentice-Hall, Inc. Average mass is shown on periodic table

9. Atoms, Molecules, and Ions Check for Understanding  How many protons, neutrons and electrons are there in an atom of oxygen-17 ( )?  8 protons (equal to atomic number)  9 neutrons (mass number – number of protons, 17 – 8 = 9  8 electrons (equal to number of protons in a neutral atom)  Use your periodic table to determine the number of protons, neutrons, and electrons in a potassium (K) atom.  19 protons, 20 neutrons (39 – 19 = 20), 19 electrons © 2009, Prentice-Hall, Inc.

10. Atoms, Molecules, and Ions Metals and Nonmetals  Metals are on right side of periodic table (with the exception of hydrogen)  Nonmetals are on the right.  Metalloids are in the middle. © 2009, Prentice-Hall, Inc.

11. Atoms, Molecules, and Ions Chemical Formulas The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound. © 2009, Prentice-Hall, Inc.

12. Atoms, Molecules, and Ions Chemical Formulas Molecular compounds are composed of covalently bonded atoms and contain only nonmetals. © 2009, Prentice-Hall, Inc.

13. Atoms, Molecules, and Ions Diatomic Molecules These seven elements occur naturally as molecules containing two atoms. © 2009, Prentice-Hall, Inc. So if someone says we need oxygen to survive, that oxygen is really O 2 not just O. Single oxygen atoms are not found alone in the air.

14. Atoms, Molecules, and Ions Ions  When atoms lose or gain electrons, they become ions.  Cations are positive and are formed when atoms lose electrons.  Anions are negative and are formed when atoms gain electrons. © 2009, Prentice-Hall, Inc.

15. Atoms, Molecules, and Ions Ionic Bonds Ionic compounds (such as NaCl) are generally formed between metals and nonmetals. © 2009, Prentice-Hall, Inc.

16. Atoms, Molecules, and Ions Check for understanding  Are the following molecular compounds or ionic compounds?  KF  CH 4  FeSO 4  Explanation: Both KF and FeSO 4 contain a metal ion, K + and Fe 2+, and thus are ionic compounds.  CH 4 contains only nonmetals so it is molecular. © 2009, Prentice-Hall, Inc. Ionic Molecular Ionic

17. Atoms, Molecules, and Ions Common Cations © 2009, Prentice-Hall, Inc.

18. Atoms, Molecules, and Ions Common Anions © 2009, Prentice-Hall, Inc.

19. Atoms, Molecules, and Ions Writing Formulas  Because compounds are electrically neutral, one can determine the formula of a compound this way:  The charge on the cation becomes the subscript on the anion.  The charge on the anion becomes the subscript on the cation.  If these subscripts are not in the lowest whole- number ratio, divide them by the greatest common factor. © 2009, Prentice-Hall, Inc.

20. Atoms, Molecules, and Ions Polyatomic Ions  Polyatomic ions are “many atom” ions, OR charged compounds.  Examples:  SO 4 2- (sulfate)  NH 4 + (ammonium)  CH 3 COO - (acetate)  To write formulas follow the same procedure as before.  For magnesium sulfate we have Mg 2+ and SO 4 2- giving us: MgSO 4  Notice the subscript on the polyatomic ion remains.  If you use more than one polyatomic ion, as in magnesium acetate, you must put parentheses around the polyatomic ion: Mg(CH 3 COO) 2 © 2009, Prentice-Hall, Inc.

21. Atoms, Molecules, and Ions Inorganic Nomenclature  Write the name of the cation.  If the anion is an element, change its ending to -ide; if the anion is a polyatomic ion, simply write the name of the polyatomic ion.  If the cation can have more than one possible charge, write the charge as a Roman numeral in parentheses. © 2009, Prentice-Hall, Inc.

22. Atoms, Molecules, and Ions Examples  Write the formulas for the following ions:  Calcium hydroxide  Iron (III) chloride  Potassium carbonate  Ca(OH) 2  FeCl 3  K 2 CO 3  Name the following:  Pb(NO 3 ) 2  Na 2 S  Mg 3 (PO 4 ) 2  lead (II) nitrate  sodium sulfide  magnesium phosphate © 2009, Prentice-Hall, Inc.