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Chapter 4 Atomic Structure. Early Models of the Atom. This is the Greek philosopher Democritus who began the search for a description of matter more than 2400 years ago.
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This is the Greek philosopher Democritus who began the search for a description of matter more than 2400 years ago. • He asked: Could matter be divided into smaller and smaller pieces forever, or was there a limit to the number of times a piece of matter could be divided?
Atomos • His theory: Matter could not be divided into smaller and smaller pieces forever, eventually the smallest possible piece would be obtained. • This piece would be indivisible. • He named the smallest piece of matter “atomos,” meaning “not to be cut.”
This theory was ignored and forgotten for more than 2000 years!
4.1 Dalton’s Atomic Theory • All elements are composed of tiny indivisible particles called atoms.
4.1 Dalton’s Atomic Theory • Atoms of the same element are identical. The atoms of any one element are different from those of any other element.
4.1 Dalton’s Atomic Theory • Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.
4.1 Dalton’s Atomic Theory • Chemical reactions occur when atoms are separated, joined, or rearranged.
Nobel Laureates Heinrich Rohrer and Gerd Binnig and a scanning tunneling microscope • Blue NickelThe unreconstructed surface of Nickel.
Cathode Ray Tube • U-tube video • http://www.cleanvideosearch.com/media/action/yt/watch?videoId=XBqHkraf8iE • http://www.cleanvideosearch.com/media/action/yt/watch?videoId=c-HPFaBtwvI
4.3 Atomic Mass • The atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element. • A weighted average mass reflects both the mass and the relative abundance of the isotopes as they occur in nature.
4.3 Atomic Mass • To calculate the atomic mass of an element, multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products.
4.3 Atomic Mass • For example, carbon has two stable isotopes: • Carbon-12, which has a natural abundance of 98.89%, and • Carbon-13, which has a natural abundance of 1.11%.
Practice Problem 23 • The element copper has naturally occurring isotopes with mass numbers of 63 and 65. The relative abundance and atomic masses are 69.2% for mass = 62.93 amu, and 30.8% for mass = 64.93 amu. Calculate the average atomic mass for copper.
4.3 The Periodic Table—A Preview • A periodic table is an arrangement of elements in which the elements are separated into groups based on a set of repeating properties. • A periodic table allows you to easily compare the properties of one element (or a group of elements) to another element (or group of elements).
4.3 The Periodic Table—A Preview • Each horizontal row of the periodic table is called a period. • Within a given period, the properties of the elements vary as you move across it from element to element.
4.3 The Periodic Table—A Preview • Each vertical column of the periodic table is called a group, or family. • Elements within a group have similar chemical and physical properties.
