The Periodic Table

Period

• The 7 horizontal

rows

Example:

• Period 1 has 2

elements: Hydrogen

(H) and Helium (He)

• Period 2 has 8

elements

Group

• Vertical column of the

Periodic Table

• A group is also called

a family of elements

because all elements

in the same group

share some physical

and chemical

properties

Metals • Include all members of

Groups 1 through 12 as

well as some elements

of Groups 13 through 16

• All metals are good

conductors of electricity

• Conductivity increases

as temperature

decreases

• All are solid at room

temperature except

Mercury

Transition Metals

• Elements in Groups 3 through 12 including

the two long rows below the main table

• Have varied properties

• Not as reactive as Group

1 and 2 elements

Nonmetals • Elements in Groups 17

and 18 as well as some

members of Groups 14

through 16

• Poor conductors of

electricity

• Conductivity increases

as temperature

increases

• Can be gases, solids or

liquids at room

temperature

Semiconductors

(metalloids)

• Not in one group but spread across groups

13-16 starting with Boron, Silicon,

Germanium, Arsenic, Antimony and

Tellurium

• Conduct electricity better than nonmetals

but not as well as metals

• Useful in electronic devices

• Solid at room temperature

Lanthanides and Actinides

• Lanthanides –

rare earth metals

(lanthanum)

• Actinides –

radioactive elements

(uranium)

Group Names

• Group 1: Alkali Metals (Note – Hydrogen

is not a metal but it is in group 1)

• Group 2: Alkali Earth Metals (Be, …)

• Groups 3 – 12: Transition Metals

• Metalloids/Semiconductors: Not in one

group but spread across groups 13-16

starting with Boron, Silicon, Germanium,

Arsenic, Antimony and Tellurium

Group Names (cont.)

• Group 17: Halogens (F, Cl, Br, I, …)

• Group 18: Noble Gases (He, Ne, Ar, …)

• Lathanides: elements after Lanthanum to

Lutetium

• Actinides: Actinium to Lawrencium

6

C Carbon

12.011

Atomic #: # of Protons

Element Symbol

Element Name

Atomic Mass: # of

Protons + # of Neutrons

Julius Meyer

• 1830-1895

• Used atomic weights

to arrange 28

elements into 6

families that had

similar chemical and

physical properties

• Incomplete periodic

table

Dmitri Mendeleev

• 1834-1907

• Left gaps (worked on Meyers)

• Predicted that new elements would be discovered

• Arranged elements known at

the time by similarities in their

physical and chemical

properties

• Ordered by increasing atomic mass

Henry Moseley

• 1888-1915

• Arranged elements by increasing atomic number

• Discrepancies disappeared

• Similar physical and chemical properties occur at regular intervals (periodic law)

Moseley (cont.)

• Moseley’s discovery was consistent with

Mendeleev’s ordering of the periodic table

by properties rather than strictly atomic

number

• He showed that there were gaps in the

sequence at numbers 43, 61 and 75 (now

known to be radioactive, non-naturally-

occurring, technetium and promethium,

and the last discovered naturally-occurring

element rhenium, respectively)

Periodic Law

• Periodic Law states: ‘the physical and

chemical properties of the elements are

periodic functions of their atomic

numbers’

• The periodic table is an arrangement of

the elements in order of their atomic

numbers so the elements with similar

properties fall in the same group or column

Past to Present

• The periodic table has changed since

Mendeleev’s time

• Chemists have discovered new elements

• In recent years chemists have synthesized

new elements in the laboratory

• Significant addition to the periodic table

was discovery of the noble gases