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 = 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) grams per mL (B) grams per mL (C) 7.84 grams per mL (D) 7.8 grams per mL (E) 8 grams per mL

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

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.

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

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.

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.

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 C 12 6 C 13 6 C 14 6 C Same number of protonsDifferent masses

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

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.

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.

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.

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

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.

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.

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

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

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

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

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.

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.

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.

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.