Periodic TablePeriodic Tablefor beginnersfor beginners

Chapter 17-3Chapter 17-3

Organizing the ElementsOrganizing the ElementsBecause the pattern repeated, it was Because the pattern repeated, it was

considered to be periodic. Today, this considered to be periodic. Today, this arrangement is called a periodic table of arrangement is called a periodic table of elements. elements.

In the In the periodic tableperiodic table, the elements are , the elements are arranged by increasing atomic number arranged by increasing atomic number and by changes in physical and chemical and by changes in physical and chemical properties. properties.

Mendeleev's PredictionsMendeleev's Predictions Mendeleev had to leave blank spaces in Mendeleev had to leave blank spaces in

his periodic table to keep the elements his periodic table to keep the elements properly lined up according to their properly lined up according to their chemical properties. chemical properties.

He looked at the properties and atomic He looked at the properties and atomic masses of the elements surrounding these masses of the elements surrounding these blank spaces.blank spaces.

Mendeleev's PredictionsMendeleev's Predictions From this information, From this information,

he was able to predict he was able to predict the properties and the the properties and the mass numbers of new mass numbers of new elements that had not elements that had not yet been discovered.yet been discovered.

Mendeleev's PredictionsMendeleev's Predictions This table shows This table shows

Mendeleev's Mendeleev's predicted properties predicted properties for germanium, which for germanium, which he called ekasilicon. he called ekasilicon. His predictions His predictions proved to be proved to be accurate. accurate.

Improving the Periodic TableImproving the Periodic TableOn Mendeleev's table, the atomic mass On Mendeleev's table, the atomic mass

gradually increased from left to right. If gradually increased from left to right. If you look at the modern periodic table, you you look at the modern periodic table, you will see several examples, such as cobalt will see several examples, such as cobalt and nickel, where the mass decreases and nickel, where the mass decreases from left to right. from left to right.

Improving the Periodic TableImproving the Periodic Table

In 1913, the work of Henry G.J. Moseley, a In 1913, the work of Henry G.J. Moseley, a young English scientist, led to the young English scientist, led to the arrangement of elements based on their arrangement of elements based on their increasing atomic numbers instead of an increasing atomic numbers instead of an arrangement based on atomic masses. arrangement based on atomic masses.

The current periodic table uses Moseley's The current periodic table uses Moseley's arrangement of the elements. arrangement of the elements.

The Atom and the Periodic TableThe Atom and the Periodic TableThe vertical columns in the periodic table The vertical columns in the periodic table

are called are called groupsgroups, or families, and are , or families, and are numbered 1 through 18. numbered 1 through 18.

Elements in each group have similar Elements in each group have similar properties. properties.

Electron Cloud StructureElectron Cloud Structure In a neutral atom, the number of electrons In a neutral atom, the number of electrons

is equal to the number of protons.is equal to the number of protons.Therefore, a carbon atom, with an atomic Therefore, a carbon atom, with an atomic

number of six, has six protons and six number of six, has six protons and six electrons. electrons.

Rows on the TableRows on the Table

Remember that the atomic number found on the Remember that the atomic number found on the periodic table is equal to the number of electrons periodic table is equal to the number of electrons in an atom. in an atom.

Rows on the TableRows on the TableThe first row has hydrogen with one The first row has hydrogen with one

electron and helium with two electrons electron and helium with two electrons both in energy level one. both in energy level one.

Energy level one can hold only two Energy level one can hold only two electrons. Therefore, helium has a full or electrons. Therefore, helium has a full or complete outer energy level. complete outer energy level.

Rows on the TableRows on the TableThe second row begins with lithium, which The second row begins with lithium, which

has three electrons—two in energy level has three electrons—two in energy level one and one in energy level two. one and one in energy level two.

Lithium is followed by beryllium with two Lithium is followed by beryllium with two outer electrons, boron with three, and so outer electrons, boron with three, and so on until you reach neon with eight outer on until you reach neon with eight outer electrons.electrons.

Rows on the TableRows on the Table Do you notice how the row in the periodic Do you notice how the row in the periodic

table ends when an outer level is filled? table ends when an outer level is filled? In the third row of elements, the electrons In the third row of elements, the electrons

begin filling energy level three. begin filling energy level three. The row ends with argon, which has a full The row ends with argon, which has a full

outer energy level of eight electrons. outer energy level of eight electrons.

Regions on the Periodic TableRegions on the Periodic Table

The periodic table has several regions with The periodic table has several regions with specific names. specific names.

The horizontal rows of elements on the The horizontal rows of elements on the periodic table are called periodic table are called periodsperiods..

The elements increase by one proton and The elements increase by one proton and one electron as you go from left to right in one electron as you go from left to right in a period. a period.

Regions on the Periodic TableRegions on the Periodic Table

All of the elements in the blue squares are All of the elements in the blue squares are metals. metals.

Regions on the Periodic TableRegions on the Periodic Table Those elements on the right side of the periodic Those elements on the right side of the periodic

table, in yellow, are classified as nonmetals. table, in yellow, are classified as nonmetals.

Regions on the Periodic TableRegions on the Periodic TableThe elements in green are metalloids or The elements in green are metalloids or

semimetals. semimetals.