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The Periodic Table Section 1 Section 2: A Guided Tour of the Periodic Table Preview • Key Ideas • Bellringer • Recognizing a Pattern • Changing the Arrangement • The Periodic Table of the Elements The Periodic Table Section 1 Key Ideas 〉How did Mendeleev arrange the elements in his periodic table? 〉How are elements arranged in the modern periodic table? The Periodic Table Section 1 Bellringer One way to organize a large group of objects is to arrange them into groups of similar objects. This is how scientists organize all of the many elements. Practice the skill of categorizing by arranging the magazines listed below into similar groups. Calling All Girls Computer World Beautiful Homes Auto Racing The Healthy Man Sporting Times Child’s Play Family Computing Beautiful Homes Car Trends Homeopathic Medicine Sports and Scores Calling All Boys All About Computing Home Decorating Classic Cars The Healthy Woman Golf for Everyone Nursery Rhymes How to Use the Internet Modern Housekeeping Easy Car Repairs The Health Newsletter Football Stories Read Aloud Stories Building a Web Site Home Makers Magazine The Sports Car Story Good Nutrition Tennis Tips The Periodic Table Section 1 Bellringer, continued 1. Arrange the magazines into similar groups. 2. What criteria did you use for grouping the magazines? 3. Once you arrange the magazines into groups, could you sort the material further to make it even more organized? Calling All Girls Computer World Beautiful Homes Auto Racing The Healthy Man Sporting Times Child’s Play Family Computing Beautiful Homes Car Trends Homeopathic Medicine Sports and Scores Calling All Boys All About Computing Home Decorating Classic Cars The Healthy Woman Golf for Everyone Nursery Rhymes How to Use the Internet Modern Housekeeping Easy Car Repairs The Health Newsletter Football Stories Read Aloud Stories Building a Web Site Home Makers Magazine The Sports Car Story Good Nutrition Tennis Tips The Periodic Table Section 1 Recognizing a Pattern 〉How did Mendeleev arrange the elements in his periodic table? 〉In his periodic table, Mendeleev arranged elements in rows by increasing atomic mass. The Periodic Table Section 1 Recognizing a Pattern, continued • Mendeleev was able to predict new elements. – Mendeleev left spaces in his table to make the pattern fit. – He used the spaces to successfully predict the existence and properties of elements not yet discovered. • A few elements did not fit the pattern. The Periodic Table Section 1 Changing the Arrangement 〉How are elements arranged in the modern periodic table? 〉The modern periodic table organizes elements by atomic number. When the elements are arranged in this way, elements that have similar properties appear at regular intervals. The Periodic Table Section 1 Changing the Arrangement, continued • As scientists learned more about the structure of the atom, they improved Mendeleev’s table. • Arranging the table by atomic number (number of protons) rather than by atomic mass fixed the discrepancies in Mendeleev’s table. • periodic law: the law that states that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements The Periodic Table Section 1 The Periodic Table of the Elements The Periodic Table Section 1 Changing the Arrangement, continued • Elements become less metallic across each period. – period: a horizontal row of elements in the periodic table • Elements in a group have similar properties. – group: a vertical column of elements in the periodic table; elements in a group share chemical properties The Periodic Table Section 1 Visual Concept: Periodic Table Overview Click the button below to watch the Visual Concept. The Periodic Table Section 1 The Role of Electrons 〉Why do elements within a group of the periodic table have similar chemical properties? 〉The periodic trends in the periodic table are the result of electron arrangement. The Periodic Table Section 1 The Role of Electrons, continued • Valence electrons account for similar properties. • An element’s location in the periodic table is related to electron arrangement. – Example: Lithium and sodium, in Group 1, each have one valence electron. The Periodic Table Section 1 Ion Formation 〉What happens to an atom that gains or loses electrons? 〉If an atom gains or loses electrons, it no longer has an equal number of electrons and protons. Because the charges do not cancel completely, the atom has a net electric charge. The Periodic Table Section 1 Ion Formation, continued • Group 1 elements form positive ions. – The single valence electron is easily removed. • Group 17 elements form negative ions. – The addition of one valence electron fills the outer energy level. The Periodic Table Section 1 Atomic Number and Mass Number 〉What do atoms of an element have in common with other atoms of the same element? 〉Atoms of each element have the same number of protons, but they can have different numbers of neutrons. The Periodic Table Section 1 Atomic Number and Mass Number, continued • The atomic number equals the number of protons. – atomic number: the number of protons in the nucleus of an atom • The mass number equals the total number of subatomic particles in the nucleus. – mass number: the sum of the numbers of protons and neutrons in the nucleus of an atom The Periodic Table Section 1 Atomic Number and Mass Number, continued The Periodic Table Section 1 Isotopes 〉Why do isotopes of the same element have different atomic masses? 〉Isotopes of an element vary in mass because their numbers of neutrons differ. The Periodic Table Isotopes, continued Section 1 The Periodic Table Section 1 Isotopes, continued • The number of neutrons can be calculated. – number of neutrons = mass number – atomic number The Periodic Table Section 1 Atomic Masses 〉What unit is used to express atomic mass? 〉Because working with such tiny masses is difficult, atomic masses are usually expressed in unified atomic mass units. • unified atomic mass unit: a unit of mass that describes the mass of an atom or molecule; it is exactly 1/12 the mass of a carbon atom with mass number 12 (symbol, u) The Periodic Table Section 1 Atomic Masses, continued • Average atomic mass is a weighted average. – Isotope abundance determines the average atomic mass. – Example: Chlorine-35 is more abundant than chlorine-37, so chlorine’s average atomic mass (35.453 u) is closer to 35 than to 37.