Searching For an Organizing Principle

Name: Searching For an Organizing Principle
Uploaded: 2017-07-09T11:53:56+00:00
Duration: PTM23S37
Channel: Allan Barton
Description: Searching For an Organizing Principle

Searching For an Organizing Principle
6.1 Searching For an Organizing Principle Searching For an Organizing Principle How did chemists begin to organize the known elements?

6.1 Searching For an Organizing Principle Certain chemical properties are repeating - reactivity with water (Na, K, etc.) - reactivity with other elements, etc.

6.1 Searching For an Organizing Principle Chlorine, bromine, and iodine have very similar chemical properties. Chlorine, bromine, and iodine have very similar chemical properties. The numbers shown are the average atomic masses for these elements.

Mendeleev’s Periodic Table
6.1 Mendeleev’s Periodic Table Mendeleev - Arranged elements by properties and atomic mass. - First example of a Periodic Table of the Elements. - Mendeleev's approach allowed him to successfully predict the masses and properties of elements that were not known at the time he developed his table.

Mendeleev’s Periodic Table
6.1 Mendeleev’s Periodic Table An Early Version of Mendeleev’s Periodic Table In this early version of Mendeleev’s periodic table, the rows contain elements with similar properties. Observing A fourth element is grouped with chlorine (Cl), bromine (Br), and (I) iodine. What is this element’s symbol?

The Modern Periodic Table
Moseley - Mendeleev's arrangement was not completely uniform, some elements were apparently 'out of place'. Note the masses of Te and I in Mendeleev's table. - Moseley discovered that the nuclear charge increased for each increase of atomic mass. - This work provided experimental justification for the modern form of the Periodic Table. - This work also resulted in defining atomic number.

The Periodic Law Moseley's refinement of Mendeleev's table gave us the modern statement of the Periodic Law. Periodic Table of the Elements - Arrangement of elements by atomic number so that elements with similar properties fall in the same column. Periodic Law - physical and chemical properties of the elements are periodic functions of their atomic numbers. There have been a number of additions to Mendeleev's table since he first proposed it, but the underlying principle that elements could be arranged by properties is still the same.

6.1 The Periodic Law In the modern periodic table, elements are arranged in order of increasing atomic number. In the modern periodic table, the elements are arranged in order of increasing atomic number. Interpreting Diagrams How many elements are there in the second period?

6.1 The Periodic Law The periodic law: When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties. The properties of the elements within a period change as you move across a period from left to right. The pattern of properties within a period repeats as you move from one period to the next.

Metals, Nonmetals, and Metalloids
6.1 Metals, Nonmetals, and Metalloids Metals, Nonmetals, and Metalloids What are three broad classes of elements?

6.1 Metals, Nonmetals, and Metalloids Three classes of elements are metals, nonmetals, and metalloids. Across a period, the properties of elements become less metallic and more nonmetallic.

6.1 Metals, Nonmetals, and Metalloids Metals, Metalloids, and Nonmetals in the Periodic Table One way to classify elements in the periodic table is as metals, nonmetals, and metalloids. Inferring What is the purpose for the black stair-step line?

6.1 Metals, Nonmetals, and Metalloids Metals Metals are good conductors of heat and electric current. 80% of elements are metals. Metals have a high luster, are ductile, and are malleable.

6.1 Metals, Nonmetals, and Metalloids Uses of Iron, Copper, and Aluminum The metals iron, copper, and aluminum have many important uses. How each metal is used is determined by its properties.

6.1 Metals, Nonmetals, and Metalloids Nonmetals In general, nonmetals are poor conductors of heat and electric current. Most nonmetals are gases at room temperature. A few nonmetals are solids, such as sulfur and phosphorus. One nonmetal, bromine, is a dark-red liquid.

6.1 Metals, Nonmetals, and Metalloids Metalloids A metalloid generally has properties that are similar to those of metals and nonmetals. The behavior of a metalloid can be controlled by changing conditions.

6.1 Metals, Nonmetals, and Metalloids If a small amount of boron is mixed with silicon, the mixture is a good conductor of electric current. Silicon can be cut into wafers, and used to make computer chips.

Classifying the Elements
6.2 Classifying the Elements A coin may contain much information in a small space—its value, the year it was minted, and its country of origin. Each square in a periodic table also contains information. You will learn what types of information are usually listed in a periodic table.

Squares in the Periodic Table
6.2 Squares in the Periodic Table Squares in the Periodic Table What type of information can be displayed in a periodic table?

6.2 Squares in the Periodic Table The periodic table displays the symbols and names of the elements, along with information about the structure of their atoms. This is the element square for sodium from the periodic table. Interpreting Diagrams What does the data in the square tell you about the structure of sodium atoms?

6.2 Squares in the Periodic Table The background colors in the squares are used to distinguish groups of elements. The Group 1A elements are called alkali metals. The Group 2A elements are called alkaline earth metals. The nonmetals of Group 7A are called halogens.

6.2 Squares in the Periodic Table In this periodic table, the colors of the boxes are used to classify representative elements and transition elements.

Electron Configurations in Groups
6.2 Electron Configurations in Groups Electron Configurations in Groups How can elements be classified based on their electron configurations?

6.2 Electron Configurations in Groups Elements can be sorted into noble gases, representative elements, transition metals, or inner transition metals based on their electron configurations.

6.2 Electron Configurations in Groups The blimp contains helium, one of the noble gases. This blimp contains helium, one of the noble gases. Applying Concepts What does the ability of a helium-filled blimp to rise in air tell you about the density of helium?

6.2 Electron Configurations in Groups The Noble Gases The noble gases are the elements in Group 8A of the periodic table. The electron configurations for the first four noble gases in Group 8A are listed below.

6.2 Electron Configurations in Groups The Representative Elements Elements in groups 1A through 7A are often referred to as representative elements because they display a wide range of physical and chemical properties. The s and p sublevels of the highest occupied energy level are not filled. The group number equals the number of electrons in the highest occupied energy level.

6.2 Electron Configurations in Groups In atoms of the Group 1A elements below, there is only one electron in the highest occupied energy level.

6.2 Electron Configurations in Groups In atoms of the Group 4A elements below, there are four electrons in the highest occupied energy level.

Representative Elements
6.2 Representative Elements Representative Elements Some of the representative elements exist in nature as elements. Others are found only in compounds.

6.2 Transition Elements Transition Elements There are two types of transition elements— transition metals and inner transition metals. They are classified based on their electron configurations.

6.2 Transition Elements In atoms of a transition metal, the highest occupied s sublevel and a nearby d sublevel contain electrons. In atoms of an inner transition metal, the highest occupied s sublevel and a nearby f sublevel generally contain electrons.

Blocks of Elements 6.2 Transition Elements
This diagram classifies elements into blocks according to sublevels that are filled or filling with electrons. Interpreting Diagrams In the highest occupied energy level of a halogen atom, how many electrons are in the p sublevel?

6.3 Trends in Atomic Size Trends in Atomic Size What are the trends among the elements for atomic size?

6.3 Trends in Atomic Size The atomic radius is one half of the distance between the nuclei of two atoms of the same element when the atoms are joined. This diagram lists the atomic radii of seven nonmetals. An atomic radius is half the distance between the nuclei of two atoms of the same element when the atoms are joined.

Group and Periodic Trends in Atomic Size
6.3 Trends in Atomic Size Group and Periodic Trends in Atomic Size In general, atomic size increases from top to bottom within a group and decreases from left to right across a period.

6.3 Trends in Atomic Size This graph plots atomic radius versus atomic number for 55 elements. INTERPRETING GRAPHS a. Analyzing Data Which alkali metal has an atomic radius of 238 pm? b. Drawing Conclusions Based on the data for alkali metals and noble gases, how does atomic size change within a group? c. Predicting Is an atom of barium, atomic number 56, smaller or larger than an atom of cesium (Cs)?

6.3 Trends in Atomic Size The size of atoms tends to decrease from left to right across a period and increase from top to bottom within a group. Predicting If a halogen and an alkali metal are in the same period, which one will have the larger radius?

Atomic radius Defined as one-half the distance between nuclei of identical atoms joined in a molecule. Across period - as Z increases, n remains the same. Increased attraction of electrons in same n. Remember n gives some indication of location of electrons from nucleus. Down group - Z increases, so does n. Electrons are farther away from positive nucleus, attractive force for valence electrons decreases.

Some compounds are composed of particles called ions.
6.3 Ions Some compounds are composed of particles called ions. An ion is an atom or group of atoms that has a positive or negative charge. A cation is an ion with a positive charge. An anion is an ion with a negative charge.

6.3 Ions Ions How do ions form?

6.3 Ions Positive and negative ions form when electrons are transferred between atoms. When a sodium atom loses an electron, it becomes a positively charged ion. When a chlorine atom gains an electron, it becomes a negatively charged ion. Interpreting Diagrams What happens to the protons and neutrons during these changes?

Trends in Ionization Energy
6.3 Trends in Ionization Energy The energy required to remove an electron from an atom is called ionization energy. The energy required to remove the first electron from an atom is called the first ionization energy. The energy required to remove an electron from an ion with a 1+ charge is called the second ionization energy.

6.3 Trends in Ionization Energy Group and Periodic Trends in Ionization Energy First ionization energy tends to decrease from top to bottom within a group and increase from left to right across a period.

6.3 Trends in Ionization Energy

6.3 Trends in Ionization Energy First ionization energy tends to increase from left to right across a period and decrease from top to bottom within a group. Predicting Which element would have the larger first ionization energy—an alkali metal in period 2 or an alkali metal in period 4?

Ionization Energy (IE)
Defined as the amount of energy necessary to remove electrons from an element in the gaseous state. First Ionization A + energy → A+ + e- Across period - increasing Z, increasing IE, e - held 'tightly' Down group - increasing Z, decreasing IE, e - less tightly held Higher Ionization Energies A + energy → Ab+ + be- b - number of the ionization What is the reason for some of the other variations in ionization energies? Large jump between 1st and 2nd in Na Large jump between 2nd and 3rd in Mg Check out changes in electronic configurations.

6.3 Trends in Ionic Size Trends in Ionic Size During reactions between metals and nonmetals, metal atoms tend to lose electrons, and nonmetal atoms tend to gain electrons. The transfer has a predictable effect on the size of the ions that form.

6.3 Trends in Ionic Size Cations are always smaller than the atoms from which they form. Anions are always larger than the atoms from which they form.

Relative Sizes of Some Atoms and Ions
6.3 Trends in Ionic Size Relative Sizes of Some Atoms and Ions This diagram compares the relative sizes of atoms and ions for selected alkali metals and halogens. The data are given in picometers. Comparing and Contrasting What happens to the radius when an atom forms a cation? When an atom forms an anion?

Trends in Ionic Size 6.3 Size generally increases Trends in Ionic Size
The ionic radii for cations and anions decrease from left to right across periods and increase from top to bottom within groups.

Trends in Electronegativity
6.3 Trends in Electronegativity Trends in Electronegativity Electronegativity is the ability of an atom of an element to attract electrons when the atom is in a compound. In general, electronegativity values decrease from top to bottom within a group. For representative elements, the values tend to increase from left to right across a period.

Trends in Electronegativity
6.3 Trends in Electronegativity Representative Elements in Groups 1A through 7A

Electronegativity (Pauling Scale)
Measure of the ability of an atom to attract electrons This does not necessarily mean anything about reactivity under a given set of conditions. F - has the highest Fr - has the lowest Electronegativity also gives an indication of the tendency of atoms to form cations or anions. High electronegativity usually means an atom will favor forming anions. Atoms tend to form ions in an effort to attain a valence electronic configuration that is isoelectronic with a Noble gas.

Summary of Trends What is the underlying cause of periodic trends? 6.3

6.3 Summary of Trends The trends that exist among these properties can be explained by variations in atomic structure.

Nuclear Charge Electronegativity Size of anions Ionic size Shielding
6.3 Summary of Trends Nuclear Charge Electronegativity Size of anions Ionic size Shielding Ionization energy Size of cations Atomic Size Decreases Constant Increases Decreases Increases Properties that vary within groups and across periods include atomic size, ionic size, ionization energy, electronegativity, nuclear charge, and shielding effect. Interpreting Diagrams Which properties tend to decrease across a period?

Searching For an Organizing Principle

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