John E. McMurry Robert C. Fay C H E M I S T R Y Sixth Edition Chapter 2 Atoms, Molecules, and Ions

Conservation of Mass and the Law of Definite Proportions Law of Conservation of Mass: Mass is neither created nor destroyed in chemical reactions.

Conservation of Mass and the Law of Definite Proportions Hg I 2 (s) + 2KNO 3 (aq)Hg(NO 3 ) 2 (aq) + 2K I(aq) 4.55 g g = 6.57 g 3.25 g g = 6.57 g

Conservation of Mass and the Law of Definite Proportions Law of Definite Proportions: Different samples of a pure chemical substance always contain the same proportion of elements by mass. By mass, water is:88.8 % oxygen 11.2 % hydrogen

The Law of Multiple Proportions and Dalton’s Atomic Theory Law of Multiple Proportions: Elements can combine in different ways to form different substances, whose mass ratios are small whole-number multiples of each other. Insert Figure 2.2 p37 7 grams nitrogen per 8 grams oxygen 7 grams nitrogen per 16 grams oxygen nitrogen monoxide (NO): nitrogen dioxide (NO2):

The Law of Multiple Proportions and Dalton’s Atomic Theory Elements are made up of tiny particles called atoms. Each element is characterized by the mass of its atoms. Atoms of the same element have the same mass, but atoms of different elements have different masses. The chemical combination of elements to make different chemical compounds occurs when atoms join in small whole-number ratios. Chemical reactions only rearrange how atoms are combined in chemical compounds; the atoms themselves don’t change.

Atomic Structure: Electrons Cathode-Ray Tubes: J. J. Thomson ( ) proposed that cathode rays must consist of tiny negatively charged particles. We now call them electrons.

Atomic structure: Electrons The strength of deflecting magnetic electric field The size of the negative charge of electron The mass of the electron

Atomic Structure: Electrons Millikan’s oil drop experiment

Atomic Structure: Protons and Neutrons

Rutherford’s Gold Foil Experiment In Rutherford’s gold foil experiment ( ),positively charged particles were aimed at atoms of gold. mostly went straight through the atoms. were deflected only occasionally. Conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close. Rutherford proposed that the atom must consist mainly of empty space with the mass concentrated in a tiny central core—the nucleus

Atomic Structure: Protons and Neutrons The mass of the atom is primarily in the nucleus.

Atomic Structure: Protons and Neutrons The charge of the proton is opposite in sign but equal to that of the electron.

Atomic Numbers Atomic Number (Z): Number of protons in an atom’s nucleus. Equivalent to the number of electrons around an atom’s nucleus Mass Number (A): The sum of the number of protons and the number of neutrons in an atom’s nucleus Isotope: Atoms with identical atomic numbers but different mass numbers

Atomic Numbers

carbon-14 C 14 6 atomic number mass number carbon-12 C 12 6 atomic number mass number 6 protons 6 electrons 8 neutrons 6 protons 6 electrons 6 neutrons

Atomic Masses and the Mole The mass of 1 atom of carbon-12 is defined to be 12 amu. Atomic Mass: The weighted average of the isotopic masses of the element’s naturally occurring isotopes

An atom of zinc has a mass number of 65. A. How many protons are in this zinc atom? B. How many neutrons are in the zinc atom? C. What is the mass number of a zinc atom that has Examples

An atom has 14 protons and 20 neutrons. A. Its atomic number is B. Its mass number is C. The element is Examples

Example Write the atomic symbols for atoms with the following subatomic particles: A. 8 p +, 8 n, 8 e - ___________ B. 47p +, 60 n, 47 e - ___________

Atomic Masses and the Mole carbon-12:98.89 % natural abundance12 amu carbon-13:1.11 % natural abundance amu Why is the atomic mass of the element carbon amu? = amu mass of carbon = (12 amu)(0.9889) + ( amu)( ) = amu amu

Atomic Masses and the Mole Atomic mass unit (amu) is the mass in grams of a single atom Isotopic mass 1 amu = x g

Atomic Mass of Magnesium The atomic mass of Mg is due to all the Mg isotopes. is a weighted average. is not a whole number. 23

Calculating Atomic Mass The calculation for atomic mass requires the percent(%) abundance of each isotope. atomic mass of each isotope of that element. sum of the weighted averages. mass of isotope(1)x (%) + mass of isotope(2) x (%)

Calculating Atomic Mass for Cl 35 Cl has atomic mass amu (75.76%) and 37 C has atomic mass amu (24.24%). Use atomic mass and percent of each isotope to calculate the contribution of each isotope to the weighted average. Atomic mass 35 Cl x % abundance = Atomic mass 37 Cl x % abundance = Sum is atomic mass of Cl is 25

Learning Check Gallium is an element found in lasers used in compact disc players. In a sample of gallium, there is 60.10% of 69 Ga (atomic mass ) atoms and 39.90% of 71 Ga (atomic mass ) atoms. What is the atomic mass of gallium? Which isotope has more atoms? 26

Atomic Masses and the Mole Avogadro’s Number (N A ): One mole of any substance contains x formula units. Molar Mass: The mass in grams of one mole of any element. It is numerically equivalent to its atomic mass.

Molar Mass from Periodic Table Molar mass is the atomic mass expressed in grams mole of Ag 1 mole of C 1 mole of S = g = g = g Copyright © 2009 by Pearson Education, Inc.

Learning Check Give the molar mass for each A. 1 mole of K atoms =________ B. 1 mole of Sn atoms =________ 29

Collection Terms A collection term states a specific number of items. 1 dozen donuts = 12 donuts 1 ream of paper = 500 sheets 1 case = 24 cans 2 Copyright © 2009 by Pearson Education, Inc.

A Mole of Atoms A mole is a collection that contains the same number of particles as there are carbon atoms in 12.0 g of carbon x atoms of an element (Avogadro’s number). 1 mole element Number of Atoms 1 mole C = 6.02 x C atoms 1 mole Na = 6.02 x Na atoms 1 mole Au= 6.02 x Au atoms 3

Samples of 1 Mole Quantities 1 mole of C atoms= 6.02 x C atoms 1 mole of Al atoms= 6.02 x Al atoms 1 mole of S atoms= 6.02 x S atoms 5

Avogadro’s Number and the Mole Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 3/33 Avogadro’s Number (N A ): One mole of any substance contains x formula units. One mole of any substance is equivalent to its molar mass. 1 mole = g C:C: x molecules = g 1 mole = 1.08 g x molecules = 1.08 g H

Avogadro’s Number Avogadro’s number, 6.02 x 10 23, can be written as an equality and two conversion factors. Equality: 1 mole = 6.02 x particles Conversion Factors: 6.02 x particles and 1 mole 1 mole6.02 x particles 6

Learning Check 1. The number of atoms in 2.0 g of Al atoms is 2. The number of moles of S in 1.8 x atoms of S 10

Compounds and Mixtures Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 2/36 Same compositionVariable composition

Compounds and Mixtures Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 2/37 Variable properties Similar properties The same number of protons Cannot be separated physically

Molecules and Covalent Bonds Covalent Bond: Results when two atoms share several (usually two) electrons. Typically a nonmetal bonded to a nonmetal

Molecules and Covalent Bonds Covalent Bond: Results when two atoms share several (usually two) electrons. Typically a nonmetal bonded to a nonmetal Molecule: The unit of matter that results when two or more atoms are joined by covalent bonds.

Molecules and Covalent Bonds Insert Figure 2.12 p56

Ions and Ionic Bonds Ionic Bond: A transfer of one or more electrons from one atom to another. A strong electrical attraction between charged particles. Typically a metal bonded to a nonmetal. Ion: A charged particle Cation: A positively charged particle. Metals tend to form cations. Anion: A negatively charged particle. Nonmetals tend to form anions.

Molecules, Ions, and Chemical Bonds Na 1+ + Cl 1- Na + Cl 11 protons 10 electrons 17 protons 18 electrons 11 protons 11 electrons 17 protons 17 electrons In the formation of sodium chloride, one electron is transferred from the sodium atom to the chlorine atom.

Naming Chemical Compounds Cation Charges for Typical Main-Group Ions

Naming Chemical Compounds © 2012 Pearson Education, Inc. Chapter 2/44 1- Anion Charges for Typical Main-Group Ions 3-2-

Naming Chemical Compounds Ionic Compound: A neutral compound in which the total number of positive charges must equal the total number of negative charges. aluminum sulfide:Al 2 S 3 Al 3+ S 2- sodium chloride:NaClNa + Cl - magnesium oxide:MgOMg 2+ O 2- Binary Ionic Compounds

Naming Chemical Compounds Some transition metals form more than one cation

Naming Chemical Compounds Use Roman numerals in parentheses to indicate the charge on metals that form more than one kind of cation. lead(II) fluoride:PbF 2 Pb 2+ F-F- iron(III) oxide:Fe 2 O 3 Fe 3+ O 2- tin(II) chloride:SnCl 2 Sn 2+ Cl - Binary Ionic Compounds

Naming Ionic Compounds To name a compound that contains two elements, identify the cation and anion. name the cation first, followed by the name of the anion with an – ide ending. 48

Example Write the formula and names of the following compounds: 1) K + and Br - 2) Ca 2+ and O 2- 3) Pb 4+ and S 2- 4) Cu 2+ and F - 49

Naming Chemical Compounds Because nonmetals often combine with one another in different proportions to form different compounds, numerical prefixes are usually included in the names of binary molecular compounds. Binary Molecular Compounds

Naming Chemical Compounds Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 2/51 N2F4N2F4 The second element listed is more anionlike and takes the name of the element with an “ide” modification to the ending. The first element listed is more cationlike and takes the name of the element. The prefix is added to the front of each to indicate the number of each atom. dinitrogen tetrafluoride

Naming Chemical Compounds Binary Molecular Compounds dinitrogen tetroxideN2O4N2O4 carbon monoxideCO Whenever the prefix for the first element is “mono,” drop it. Whenever the prefix ends in “a” or “o” and the element name begins with a vowel, drop the “a” or “o” in the prefix. carbon dioxideCO 2

Learning Check Write the name of each covalent compound. P 2 O 5 _____________________ SiCl 4 _____________________ CCl 4 _____________________ N 2 O_____________________ 53

Naming Chemical Compounds

Polyatomic Ionic Compounds sodium carbonate:Na 2 CO 3 Na + CO 3 2- iron(II) hydroxide:Fe(OH) 2 Fe 2+ OH - magnesium carbonate:MgCO 3 Mg 2+ CO 3 2- sodium hydroxide:NaOHNa + OH -

Learning Check Write formula and name of the following compounds: A.Mg 2+ and NO 3 - B.Al 3+ and BrO 3 - C.Fe 2+ and SO 4 2- D.Ba 2+ and PO

Examples Write the correct formula for each. A. aluminum nitrate B. copper(II) nitrate C. iron(III) hydrogen sulfite D. tin(IV) hydroxide 57