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Download Elements Elements (cont.) Elements (cont.) Dalton`s Atomic Theory
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Elements • Over 112 known: 88 found in nature, others are man made. Chapter 4 Chemical Foundations: Elements, Atoms, and Ions • Each element has a unique one- or two-letter symbol Copyright © Houghton Mifflin Company. All rights reserved. Elements (cont.) Copyright © Houghton Mifflin Company. All rights reserved. 4|3 Elements (cont.) 4|4 Dalton’s Atomic Theory 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. • Atoms of different elements combine to form compounds. – 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 Copyright © Houghton Mifflin Company. All rights reserved. 4|7 1 Dalton’s Atomic Theory Formulas Describe Compounds • 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. • 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 • Cannot turn lead into gold by a chemical reaction Copyright © Houghton Mifflin Company. All rights reserved. 4|8 Molecular and Ionic Compounds Copyright © Houghton Mifflin Company. All rights reserved. 4|9 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 | 10 What Are Atoms Made Of? 4 | 11 The Electron • J.J. Thomson investigated a beam called a cathode ray. • Tiny, negatively charged particle • Very light compared to mass of atom – 1/1836th the mass of a H atom • He determined that the ray was made of tiny negatively charged particles we now call electrons. Copyright © Houghton Mifflin Company. All rights reserved. Copyright © Houghton Mifflin Company. All rights reserved. • Move very rapidly within the atom • Atoms of different elements all contain electrons • Discovered by J.J. Thomson 4 | 12 Copyright © Houghton Mifflin Company. All rights reserved. 4 | 13 2 The Proton Rutherford’s Gold Foil Expt • 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 | 14 Rutherford’s Nuclear Model Copyright © Houghton Mifflin Company. All rights reserved. 4 | 15 Components of an Atom • 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 | 16 The Modern Atom Copyright © Houghton Mifflin Company. All rights reserved. 4 | 17 The Modern Atom (cont.) • Atoms are composed of three main pieces: protons, neutrons, and electrons. • The nucleus consists of protons and neutrons. Copyright © Houghton Mifflin Company. All rights reserved. 4 | 18 Copyright © Houghton Mifflin Company. All rights reserved. 4 | 19 3