Unit 5 The Structure of Matter

Chapter 17 The Elements and The Periodic Table

17A – A Brief History of the Elements

• Objectives:– Summarize the historical development of the idea of a

chemical element– Describe the role of alchemy in the discovery of chemical

elements– Explain how the historical problem of element symbols

was solved– Identify the naturally monatomic and diatomic elements– Recognize and correctly use modern chemical symbols

for elements• Assignments: Outline, Worksheet, and Section Review

page 415

Introduction

Earliest Known Elements

• Native minerals – Solid elements, like gold and silver that

naturally occur in their pure form– Around since Bible times

• Facet page 411

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

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

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

Berzelius’s Element Notation

• Jons Jakob 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

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 418-419, the periodic table…START TO MEMORIZE!

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