The Evolving Understanding of Elements and the Periodic Table

1. Unit 5 The Structure of Matter Chapter 17 The Elements and The Periodic Table

2. 17A – A Brief History of the Elements

3. Introduction

4. Earliest Known Elements • Native minerals • Solid elements, like gold and silver that naturally occur in their pure form • Around since Bible times • Facet page 384

5. Earliest Known Elements • Ancient Greeks were the first to define elements as the basic building blocks of matter • Aristotle believed that all matter was composed of four “elements” • Air, fire, earth, and water • This model was accepted for thousands of years • Alchemy • Included aspects of chemistry, philosophy, religion, metallurgy, medicine and art • Acquired mystical and magical characteristics that often resulted in disreputable and harmful activities • Alchemists • Viewed as dishonest, shifty, greedy, or deluded because, for many of them, their main objective was to find ways to turn valueless materials like lead into gold • Many were serious • Discovered and purified man substances that were later understood to be chemical elements

6. Earliest Known Elements • Developed a complex system of symbols to describe their work • Different alchemist developed their own symbols often to hid their knowledge from other • This made sharing information very difficult

7. Studying Elements in the 17th and 18th Centuries • Alchemy was transformed into a real science in the 17th and 18th centuries by men like: • Isaac Newton • Did more for chemistry than physics; however, his work in physics immortalized him as one of the world’s greatest physicists • Robert Boyle • Known for Boyle’s law • Concluded that many substances could not be composed of Aristotle’s elements • Antoine Lavoisier • Dealt the death blow to Aristotle’s elements when he broke water down into hydrogen and oxygen • First to define an element as a simple chemical substance that could not be broken down into simpler substances by chemical analysis • They believed that scientific knowledge was gained by observing, experimenting, and reasoning • By the end of the 18th century 32 modern elements were known, but symbols were still difficult to memorize and use

8. Berzelius’s Element Notation • JonsJakob Berzelius • Swedish chemist and educator • Firmly established Dalton’s atomic theory • Introduced the modern system of element notation • Used the first one or two letters of an element’s Latin name • Quickly accepted by most European scientists • Essentially the same as the one used today • Discovered thorium, selenium, silicon, and cerium • When he died there were fifty-seven known elements

9. Modern Elements & Their Symbols • 117 elements exist today • The heaviest elements are all radioactive and have extremely short half-lives and are difficult to analyze before they decay to lighter elements • Represented by their chemical symbols • First letter is capitalized, second lowercase • PAGES 392-393, the periodic table…START TO MEMORIZE!

10. Modern Elements & Their Symbols • Most elements occur in nature combined in compounds, as masses of identical atoms, or in molecules of two or more atoms • Monatomic • Occur as single atoms • Only elements that exist naturally in this form are the noble (inert) gases • Diatomic • Naturally occur as molecules of two atoms • Seven: hydrogen, oxygen, nitrogen, flourine, chlorine, bromine, and iodine • Polyatomic • Molecules of elements that contain more than two atoms

11. 17B – The Periodic Table

12. Organizing the Elements • How would you like to memorize all the physical and chemical properties of every element? • After many attempts to organize the elements Mendeleev finally succeeded • The periodic table of the elements is one of the most useful tools of science • Knowing how it was developed will help you to see how it enables scientists (and students) to remember the chemical properties of elements

13. The Discovery of Periodicity • Johann Dobereiner • Found elements that had similarities and formed triads • De Chancourtois • The first scientist to test the theory of periodicity • Graphed the known elements in order of increasing atomic mass on paper • Rolled into a cylinder so that sixteen mass units marked off its circumference, every eighth element often had similar physical and chemical properties to the elements above and below it • John Newlands • Organized elements in order of increasing atomic masses and displayed them in seven columns • Every eighth element had similar properties • Called these repeating patterns octaves • Called his system the law of octaves • Worked better than Dobereiner’s, but most scientists were still unsatisfied • He was actually ridiculed for comparing a physical property of matter to a musical concept

14. Mendeleev and His Periodic Law • 3 years after Newlands • Arranged the elements in similar style according to increasing atomic mass • Did not believe that all elements repeated after every eight elements • Put elements together according to similar properties and left blank spaces when an element didn’t “fit” • Mendeleev called this principle that the properties of elements vary in a periodic or recurring pattern with their atomic masses the periodic law

15. Revising the Periodic Table • Mendeleev’s table had some problems • Iodine and Tellurium • Nickel and Cobalt • Henry Moseley • The properties of the elements vary with their atomic numbers in a periodic way • Facet • Page 391

16. 17C – Classes of Elements

17. Classes of Elements

18. Metals • Almost three fourths of the elements are metals • Common Characteristics of Metals • Clean surfaces of most metals have a silvery or metallic luster • All metals except mercury (Hg) are solids at room temperature • Most metals are malleable, or can be rolled or hammered into a shape • Most metals are ductile, or can be drawn into wire • Most metals are good conductors of electricity and heat • Metals tend to be reactive, easily forming bonds

19. Nonmetals • Common Characteristics of Nonmetals • Nonmetals exist as solids, liquids, and gases at room temperature; most are gases • Solid nonmetals exist as brittle crystals that shatter easily • Nonmetals are poor conductors of electricity and heat • Nonmetals have a variety of colors • Six nonmetals called the noble or inert gases do not readily react with other elements • Nonmetals other than the noble gases generally form bonds by sharing or taking electrons from other atoms

20. Metalloids • Also called semimetals • Straddle the stairstep line on the periodic table • Slightly conductive • Manufactured into semiconductors • Computers, portable music players, calculators, cell phones, or a host of other items using digital technology

21. Element Families • Each column on the periodic table is called a family or group • Have the same amount of valence electrons • Same properties • Numbered with 1A, 2A, etc in the US • Also numbered 1-18 for countries other than the US • This designation is preferred by the International Union of Pure and Applied Chemistry (IUPAC) • Be familiar with both!

22. Alkali Metals • Group 1A • 1 valence electron • Very reactive metals • Will combine with oxygen in the air so they need to be stored in a container of oil

23. Alkaline Earth Metals • Group 2A • 2 valence electrons • Slightly less reactive than alkali metals, but not stable enough to remain free in nature • Found in many common minerals

24. Transition Metals • Groups 1B-8B (3-12) • One or two valence electrons • Normally combined in alloys • Inner Transition Metals • Two rows below the periodic table

25. Miscellaneous Families • Boron Family • Group 3A • 3 valence electrons • Carbon Family • Group 4A • 4 valence electrons • Nitrogen Family • Group 5A • 5 valence electrons • Oxygen Family • Group 6A • 6 valence electrons

26. Halogens • Group 7A • 7 valence electrons • Very reactive • Exist as diatomic molecules • As atomic number increases the color darkens

27. Noble Gases • Group 8A • Also called Inert Gases • Very stable and nonreactive due to a full valence shell

28. Elemental Periods • Horizontal rows in the periodic table are called periods or series • Elements in the same period do not have similar properties • Numbered on the side of the table and tells you how many energy levels are in the atom • Facet • Page 403

29. 17D – Periodic Trends

30. Electron Structure & The Periodic Table • The number of valence electrons is important in determining the chemical and many physical properties of an element • Properties change with the increase of atomic number, and those changes reveal predictable trends across periods and within families • Electron dot notation • Illustrates the arrangement of valence electrons in an atom • Dots represent valence electrons • Elements group number determines how many dots surround its symbol

31. Electron Structure & The Periodic Table

32. Periodic Trends • Element properties repeat in a periodic way • Atomic Size • Increases down a family and decreases across a period • More trends discussed later: • Electronegativity • Electron affinity • Ionic size • Ionization energy