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