The Periodic TableSection 1 Section 2: A Guided Tour of the Periodic Table Preview Key Ideas Bellringer Recognizing a Pattern Changing the Arrangement.

The Periodic Table Section 1

Section 2: A Guided Tour of the Periodic TablePreview• Key Ideas • Bellringer• Recognizing a Pattern• Changing the Arrangement• The Periodic Table of the Elements


Key Ideas

〉How did Mendeleev arrange the elements in his periodic table?

〉How are elements arranged in the modern periodic table?


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 Homeopathic Medicine Modern HousekeepingComputer World Sports and Scores Easy Car RepairsBeautiful Homes Calling All Boys The Health NewsletterAuto Racing All About Computing Football StoriesThe Healthy Man Home Decorating Read Aloud StoriesSporting Times Classic Cars Building a Web SiteChild’s Play The Healthy Woman Home Makers MagazineFamily Computing Golf for Everyone The Sports Car StoryBeautiful Homes Nursery Rhymes Good NutritionCar Trends How to Use the Internet Tennis Tips


Bellringer, continued1. 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 Homeopathic Medicine Modern HousekeepingComputer World Sports and Scores Easy Car RepairsBeautiful Homes Calling All Boys The Health NewsletterAuto Racing All About Computing Football StoriesThe Healthy Man Home Decorating Read Aloud StoriesSporting Times Classic Cars Building a Web SiteChild’s Play The Healthy Woman Home Makers MagazineFamily Computing Golf for Everyone The Sports Car StoryBeautiful Homes Nursery Rhymes Good NutritionCar Trends How to Use the Internet Tennis Tips


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.


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.


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.


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 of the Elements


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


Visual Concept: Periodic Table Overview

Click the button below to watch the Visual Concept.


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 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.


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.


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.


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.


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


Atomic Number and Mass Number, continued


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.


Isotopes, continued


Isotopes, continued• The number of neutrons can be calculated.

– number of neutrons = mass number – atomic number


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)


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.

The Periodic TableSection 1 Section 2: A Guided Tour of the Periodic Table Preview Key Ideas Bellringer Recognizing a Pattern Changing the Arrangement.

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