Introductory Chemistry: A Foundation, 6 th Ed. Introductory Chemistry, 6 th Ed. Basic Chemistry, 6 th Ed. by Steven S. Zumdahl & Donald J. DeCoste University of Illinois

Chapter 4 Chemical Foundations: Elements, Atoms, and Ions

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 3 Elements Over 112 known: 88 found in nature, others are man made. Each element has a unique one- or two-letter symbol

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 4 Elements (cont.)

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 5 Elements (cont.)

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 6 Dalton’s Atomic Theory Elements are composed of tiny particles called atoms. All atoms of a given element are identical. –All carbon atoms have the same chemical and physical properties. Atoms of a given element are different from those of any other element. –Carbon atoms have different chemical and physical properties than sulfur atoms.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 7 Dalton’s Atomic Theory Atoms of different elements combine to form compounds.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 8 Dalton’s Atomic Theory Law of Constant Composition: all samples of a compound contain the same proportions (by mass) of the elements that form the compound. Atoms are indivisible by chemical processes. –All atoms present at beginning are present at the end. –Atoms are not created or destroyed, just rearranged in chemical reactions. –Atoms of one element cannot change into atoms of another element. Cannot turn lead into gold by a chemical reaction

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 9 Formulas Describe Compounds A compound is a distinct substance that is composed of atoms of two or more elements. Compounds are identified by the number and type of each atom in the simplest unit of the compound. –Molecules or ions

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 10 Molecular and Ionic Compounds

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 11 Writing Formulas of Compounds Each element is represented by its symbol. The number of each type of atom is indicated by a subscript written to the right of the element symbol. If only one atom is present, do not include a subscript. If polyatomic groups are present in the molecule, they are written inside parentheses if more than one group is present. Examples: H 2 O, NaCl, KNO 3, Mg(NO 3 ) 2

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 12 What Are Atoms Made Of? J.J. Thomson investigated a beam called a cathode ray. He determined that the ray was made of tiny negatively charged particles we now call electrons.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 13 What Are Atoms Made Of?

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 14 The Electron Tiny, negatively charged particle Very light compared to mass of atom –1/1836 th the mass of a H atom Move very rapidly within the atom Atoms of different elements all produce electrons; therefore electrons are a fundamental unit of atoms.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 15 The Proton If negative electrons exist, must also have positive particles to balance the charge and make the atom electrically neutral Assume “Plum Pudding Model” - electrons suspended in a positively charged electric field

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 16 Rutherford’s Gold Foil Expt

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 17 Rutherford’s Nuclear Model The atom contains a tiny dense center called the nucleus. –The volume is about 1/10 trillionth the volume of the atom. The nucleus is essentially the entire mass of the atom. The nucleus is positively charged. –The amount of positive charge of the nucleus balances the negative charge of the electrons. The electrons move around in the empty space of the atom surrounding the nucleus.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 18 Components of an Atom

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 19 The Modern Atom Atoms are composed of three main pieces: protons, neutrons, and electrons. The nucleus contains protons and neutrons.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 20 The Modern Atom (cont.)

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 21 Isotopes All atoms of an element have the same number of protons. The number of protons in an atom of a given element is the same as the atomic number. –Found on the periodic table Atoms of an element with different numbers of neutrons are called isotopes.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 22 Isotopes (cont.) All isotopes of an element are chemically identical. –Undergo the exact same chemical reactions Isotopes of an element have different masses. Isotopes are identified by their mass numbers. –Mass number = # protons + # neutrons

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 23 Isotopes of Carbon 12 C has 6 protons (atomic number ) and 6 neutrons (atomic mass number = = 12) 13 C has 6 protons and 7 neutrons (atomic mass number = = 13) 14 C has 6 protons and 8 neutrons (atomic mass number = = 14)

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 24 Elements Arranged in a pattern called the periodic table Position on the table allows us to predict properties of the element

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 25 Elements (cont.) Metals –About 75% of all the elements –Lustrous, malleable, ductile, conduct heat and electricity Nonmetals –Dull, brittle, insulators Metalloids –Also know as semi-metals –Some properties of both metals & nonmetals

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 26 The Modern Periodic Table Elements with similar chemical and physical properties are in the same column. Groups (Families) and Periods

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 27 The Modern Periodic Table (cont.)

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 28 The Modern Periodic Table (cont.) Main group = representative elements –“A” columns Transition elements –All metals Bottom rows = inner transition elements = rare earth elements –Metals –Lanthanides and actinides

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 29 Natural States of Elements Gases: monatomic gases such as noble gases and diatomic gases such as O 2 Liquids such as Hg or Br 2 Solids such as metals or allotropes of carbon

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 30 Natural States of Elements (cont.)

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 31 Ions Cations: ions that have a positive charge –Form when an atom loses electrons Anions: ions that have a negative charge –Form when an atom gains electrons Ions with opposite charges attract –Therefore cations and anions attract each other

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 32 Ions (cont.) Moving ions conduct electricity. Compound must have no total charge, therefore we must balance the numbers of cations and anions in a compound to get 0 total charge.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 33 Atomic Structures of Ions Metals form cations. For each positive charge the ion has 1 less electron than the neutral atom. –Na = 11 e -, Na + = 10 e - –Ca = 20 e -, Ca +2 = 18 e - Cations are named the same as the metal sodiumNa  Na + + 1e - sodium ion calciumCa  Ca e - calcium ion

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 34 Atomic Structures of Ions (cont.) Nonmetals form anions. For each negative charge the ion has 1 more electron than the neutral atom. –F = 9 e -, F - = 10 e - –P = 15 e -, P 3- = 18 e - Anions are named by changing the ending of the name to -ide –FluorineF + 1e -  F - fluoride ion –OxygenO + 2e -  O 2- oxide ion

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 35 Ionic Charges and Compounds Charges on the ions of some elements can be predicted from the periodic table. Cations and anions usually form simultaneously to yield an ionic compound.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 36 Ionic Charges and Compounds (cont.)

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 37 Formulas of Ionic Compounds The formula of an ionic compound can be determined by balancing the positive charge of the cation(s) with the negative charge of the anion(s) to yield a net charge of zero.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 38 Formation of Ionic Compounds