PSC Chap. 4

The Periodic Table

In modern periodic table, elements in the same column have

similar properties.

John Newlands - Law of Octaves

– arranged first 16 elements in order of atomic mass

– found that similar properties were found every 8th element

Dmitri Mendeleev - invented the modern periodic system - basis of

the modern periodic table

– arranged all known elements in order of atomic mass

– placed elements w/ similar properties in vertical columns

A couple of problems w/ Mendeleev's table

• Some elements did not fit into the right columns when put in order of atomic mass. If switched, they fit.– -ex. Te and I, Co and Ni

A couple of problems w/ Mendeleev's table

• In order to put some elements in the right column, gaps had to be left in his table.

• He predicted elements would be discovered to fill the gaps

• Also correctly predicted properties of these undiscovered elements

Henry Mosely, using X-rays, discovered the atomic number of

elements.

When elements in Mendeleev's table were placed in order of

atomic number, they fell into the right columns.

Periodic Law

• - the physical and chemical properties of elements are a periodic function of their atomic numbers

Period or Series

• elements that form a horizontal row in the periodic table

• all elements in the same series have the same outer energy level

Group or Family

• elements that form a vertical column in the periodic table

• elements in the same group have similar electron configurations

• also have similar properties.

Periodic Table can be divided into 2 regions

• Metals - left side of table– good conductors of

electricity and heat

– shiny

– malleable

– groups 1-12 and some of groups 13-16

• Nonmetals - right side of table– poor conductors of

electricity and heat

– dull

– brittle

– some of groups 14 -16 and all of groups 17 & 18

Metalloids

• Semiconductors (semi-metals)

• Have properties of both metals and nonmetals

• lie on dividing line

• used to make transistors and computer chips

Main-Group Elements

• Also called representative elements

• s and p block elements

• have consistent electron configurations

Group 1

• Alkali Metals

• all end in s1

• lose the outer e- to form +1 ions

• Very reactive metals

• React w/ water and oxygen

• soft

Group 2

• Alkaline Earth Metals

• Active metals

• end in s2

• lose 2 outer e-’s to form +2 ions

• not as soft as group 1 metals

Transition Metals

• d block elements– highest energy e-’s are in the d sublevel

• not as reactive as groups 1 and 2

• have varied properties

Lanthanides and Actinides

• f block elements– highest energy e-’s are in the f sublevel

• sometimes called rare earth elements or inner-transition elements

• Lanthanide series fills 4f sublevel– shiny, reactive, irregular configurations

Lanthanides and Actinides

• Actinide series fills 5f sublevel– radioactive

Group 16

• Chalcogens

• Contains active nonmetals (top) to metalloids to less active metals

• end in s2p4

• nonmetals gain 2 e-’s to form -2 ions

Group 17

• Halogens

• Most reactive nonmetals

• react with metals to form salts

• end in s2p5

• gain 1 e- to form -1 ions

Group 18

• Noble Gases

• Mostly unreactive

• end in s2p6

Hydrogen

• In a class by itself

• Behaves unlike other elements because it has only 1 p+ and 1 e-

• Most common element in the universe

• Properties of elements are determined by their electron configurations.

• Elements with similar properties have similar electron configurations.

Periodic Trends

• Atomic radii

• Reactivity

Atomic radius

• Atomic radius increases as you move down a group– Add an energy level as you move down

• Atomic radius decreases as you move across a period– Increased nuclear charge pulls e- cloud in

tighter

Reactivity of Metals

• Metals tend to lose e-’s

• As you move down a group, reactivity of metals increases– Atoms are bigger and e-’s are held less tightly

• As you move to the left, reactivity of metals increases– atoms are bigger to the left

Reactivity of Metals

• The most active metal is in the lower left corner of the periodic table.

• Fr

Reactivity of Nonmetals• Nonmetals tend to gain e-’s

• As you move up a group, reactivity of nonmetals increases– Atoms are smaller and hold e-’s more tightly

• As you move to the right, reactivity of nonmetals increases (noble gases not considered)– Atoms are smaller

Reactivity of Nonmetals

• The most active nonmetal is in the upper right corner of the periodic table.

• F