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 2

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 2

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 2

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 2

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 2

How Are Elements Classified?

〉What are the three main categories of

elements?

〉All elements are either metals, nonmetals, or

semiconductors.

The Periodic Table Section 2

How Are Elements Classified?,

continued

• Elements in each category have similar properties.

– metal: an element that is shiny and that conducts

heat and electricity well

– nonmetal: an element that conducts heat and

electricity poorly

– semiconductor (or metalloid): an element or

compound that conducts electric current better than

an insulator does but not as well as a conductor does

The Periodic Table Section 2

How Are Elements Classified?,

continued

The Periodic Table Section 3

Classifying Elements Further

〉What does each element family have in common?

〉In general, the elements in a family have the same number of valence electrons.

The Periodic Table Section 3

Metals

〉What are the families of metals?

〉Families of metals include the alkali metals, the

alkaline-earth metals, and the transition metals.

– alkali metal: one of the elements of Group 1 of the periodic table

– alkaline-earth metal: one of the elements of Group 2 of the periodic table

– transition metal: one of the metals that can use the inner shell before using the outer shell to bond

The Periodic Table Section 3

Metals, continued

• The alkali metals are very reactive.

– Alkali metals are in Group 1, on the left edge of the periodic table.

– They are reactive because they have one valence electron that is easily removed.

– They are soft and shiny,

and many have similar

melting points, boiling

points, and densities.

The Periodic Table Section 3

Metals, continued

• Alkaline-earth metals form compounds that are found in limestone and in the human body.

– Alkaline-earth metals are in Group 2.

– Alkaline-earth metals are less reactive than alkali metals, but still react to form positive ions.

– In general, alkaline-earth metals are harder, denser, stronger, and have higher melting points than alkali metals.

The Periodic Table Section 3

Metals, continued

• Transition metals are in the middle of the periodic table.

– With the exception of mercury, transition metals are

harder, more dense,

and have higher

melting points than

alkali metals and

alkaline-earth metals.

– They are also less

reactive, but they can

form positive ions.

The Periodic Table Section 3

Nonmetals

〉What are some of the families of nonmetals?

〉Families of nonmetals include the noble gases

and the halogens.

– noble gas: one of the elements of Group 18 of the

periodic table

– halogen: one of the elements of Group 17 of the

periodic table

The Periodic Table Section 3

Nonmetals, continued

• The noble gases are relatively inert.

– The noble gases are in Group 18.

– They exist as single atoms instead of as molecules.

– They are inert, or unreactive, because their s and p orbitals are filled. In general, they do not form ions or compounds.

The Periodic Table Section 3

Nonmetals, continued

• The halogens combine easily with metals to form salts.

– The halogens are in

Group 17.

– With the addition of a

single electron,

halogens become

stable.

– They combine easily

with metals (especially

alkali metals) to form

salts.

The Periodic Table Section 3

Nonmetals, continued

• Nonmetals and their compounds are plentiful on Earth.

– Six other nonmetals

are on the right side of

the periodic table.

• Carbon can form many

compounds.

– There are millions of

carbon-containing

compounds.

The Periodic Table Section 3

Semiconductors

〉What are semiconductors?

〉As their name suggests,

semiconductors are able to

conduct heat and electricity

under certain conditions.