Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Introductory Chemistry: A Foundation, 6th Ed. Introductory Chemistry, 6th Ed. Basic Chemistry, 6th Ed. by Steven S. Zumdahl & Donald J. DeCoste University of Illinois Chapter 4 Chemical Foundations: Elements, Atoms, and Ions 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|3 Elements (cont.) Copyright © Houghton Mifflin Company. All rights reserved. 4|4 Elements (cont.) Copyright © Houghton Mifflin Company. All rights reserved. 4|5 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|6 Dalton’s Atomic Theory • Atoms of different elements combine to form compounds. Copyright © Houghton Mifflin Company. All rights reserved. 4|7 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|8 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|9 Molecular and Ionic Compounds Copyright © Houghton Mifflin Company. All rights reserved. 4 | 10 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: H2O, NaCl, KNO3, Mg(NO3)2 Copyright © Houghton Mifflin Company. All rights reserved. 4 | 11 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 | 12 What Are Atoms Made Of? Copyright © Houghton Mifflin Company. All rights reserved. 4 | 13 The Electron • Tiny, negatively charged particle • Very light compared to mass of atom – 1/1836th 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 | 14 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 | 15 Rutherford’s Gold Foil Expt Copyright © Houghton Mifflin Company. All rights reserved. 4 | 16 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 | 17 Components of an Atom Copyright © Houghton Mifflin Company. All rights reserved. 4 | 18 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 | 19 The Modern Atom (cont.) Copyright © Houghton Mifflin Company. All rights reserved. 4 | 20 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 | 21 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 | 22 Isotopes of Carbon • 12C • 13C • 14C has 6 protons (atomic number ) and 6 neutrons (atomic mass number = 6 + 6 = 12) has 6 protons and 7 neutrons (atomic mass number = 6 + 7 = 13) has 6 protons and 8 neutrons (atomic mass number = 6 + 8 = 14) Copyright © Houghton Mifflin Company. All rights reserved. 4 | 23 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 | 24 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 | 25 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 | 26 The Modern Periodic Table (cont.) Copyright © Houghton Mifflin Company. All rights reserved. 4 | 27 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 | 28 Natural States of Elements • Gases: monatomic gases such as noble gases and diatomic gases such as O2 • Liquids such as Hg or Br2 • Solids such as metals or allotropes of carbon Copyright © Houghton Mifflin Company. All rights reserved. 4 | 29 Natural States of Elements (cont.) Copyright © Houghton Mifflin Company. All rights reserved. 4 | 30 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 | 31 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 | 32 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 sodium Na Na+ + 1e- sodium ion calcium Ca Ca+2 + 2e- calcium ion Copyright © Houghton Mifflin Company. All rights reserved. 4 | 33 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-, P3- = 18 e- • Anions are named by changing the ending of the name to -ide – Fluorine – Oxygen F + 1e- FO + 2e- O2- Copyright © Houghton Mifflin Company. All rights reserved. fluoride ion oxide ion 4 | 34 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 | 35 Ionic Charges and Compounds (cont.) Copyright © Houghton Mifflin Company. All rights reserved. 4 | 36 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 | 37 Formation of Ionic Compounds Copyright © Houghton Mifflin Company. All rights reserved. 4 | 38