Mendeleev’s Periodic Table This arrangement was the forerunner of today’s periodic table....

Mendeleev’s Periodic Table

• This arrangement was the forerunner of today’s periodic table.

Periodic TablePeriodic TablePeriodic TablePeriodic Table

• One of the tests of a scientific theory is the ability to use it to make successful predictions.


• Mendeleev correctly predicted the properties of several undiscovered elements.

• In order to group elements with similar properties in the same columns, Mendeleev had to leave some blank spaces in his table.

• He suggested that these spaces represented undiscovered elements.


• Mendeleev was so confident of the periodicity of the elements that he placed some elements in groups with others of similar properties even though arranging them strictly by atomic mass would have resulted in a different arrangement.



Relationship of the Periodic Table to Atomic Structure

• Elements are ordered in the periodic table by atomic number, which is related to the number of electrons they have.

• As you move from one element to the next across Periods 2 and 3, the number of valence electrons increases by one.

• Group 18 elements have the maximum number of eight valence electrons in their outermost energy level.



• STANDARD – Students know how to use the periodic table to determine the number of electrons available for bonding.


Atomic Structure of Elements Within a Period

• The period number of an element is the same as the number of its outermost energy level, so the valence electrons of an element in the second period, for example, are in the second energy level.

• A Period 3 element such as aluminum has its valence electrons in the third energy level.


Atomic Structure of Elements Within a Group

• Because elements in the same group have the same number of valence electrons, they have similar properties.

• Sodium is in Group 1 because it has one valence electron.

• Because other elements in Group 1 also have one valence electron, they have similar chemical properties.



• Four groups have commonly used names: the alkali metals in Group 1, the alkaline earth metals in Group 2, the halogens in Group 17, and the noble gases in Group 18.



• The word halogen is from the Greek words for “salt former” so named because the compounds that halogens form with metals are saltlike.

• The elements in Group 18 are called noble gases because they are much less reactive than most of the other elements.


Electrons in Energy Levels—Group 16


Physical States and Classes of the Elements

• Nonmetals occupy the upper-right-hand corner.

• Metalloids are located along the boundary between metals and nonmetals.

• The majority of the elements are metals. They occupy the entire left side and center of the periodic table.


Atomic radius

• STANDARD - Students know how to use the periodic table to identify metals, semimetals, nonmetals, and halogens.

• STANDARD - Students know how to use the periodic table to identify alkali metals, alkaline earth metals and transition metals, trends in ionization energy, electronegativity, and the relative sizes of ions and atoms.


Metals

• All metals except mercury are solids at room temperature; in fact, most have extremely high melting points.

• The periodic table shows that most of the metals (coded blue) are not main group elements.


Metals

• The elements in Groups 3 through 12 of the periodic table are called the transition elements.

• All transition elements are metals.


Nonmetals

• Although the majority of the elements in the periodic table are metals, many nonmetals are abundant in nature

• The nonmetals oxygen and nitrogen make up 99 percent of Earth’s atmosphere.


Nonmetals

• Carbon, another nonmetal, is found in more compounds than all the other elements combined.

• The many compounds of carbon, nitrogen, and oxygen are important in a wide variety of applications.


Nonmetals• Most nonmetals don’t conduct electricity,

are much poorer conductors of heat than metals, and are brittle when solid.

• Many are gases at room temperature; those that are solids lack the luster of metals.

• Their melting points tend to be lower than those of metals.

• With the exception of carbon, nonmetals have five, six, seven, or eight valence electrons.


• Metalloids have some chemical and physical properties of metals and other properties of nonmetals.

• In the periodic table, the metalloids lie along the border between metals and nonmetals.


Metalloids

• The ability of a semiconductor to conduct an electrical current can be increased by adding a small amount of certain other elements.

• Silicon’s semiconducting properties made the computer revolution possible.

• A semiconductor is an element that does not conduct electricity as well as a metal, but does conduct slightly better than a nonmetal.


Atomic radius

• Research shows that atoms tend to decrease in size across a period because the nuclei are increasing in positive charge while electrons are being added to sublevels that are very close in energy.

• As a result, the increased nuclear charge pulls the outermost electrons closer to the nucleus, making the atom smaller.


Atomic radius

• Moving down through a group, atomic radii increase.

• Even though the positive charge of the nucleus increases, each successive element has electrons in the next higher energy level.


Atomic radius

• Electrons in these higher energy levels are located farther from the nucleus than those in lower energy levels.

• The increased size of higher energy level outweighs the increased nuclear charge.

• Therefore, the atoms increase in size.


Mendeleev’s Periodic Table This arrangement was the forerunner of today’s periodic table....

Documents

Transcript of Mendeleev’s Periodic Table This arrangement was the forerunner of today’s periodic table....