Elements arranged by atomic number

Periodic repetition of properties

Dmitri Mendeleev

Lothar Meyer

Horizontal rows

Vertical columns

sblock

pblock

dblock

fblock

Left side of the table

Good conductors of heat and electricity

Malleable and ductile

Right side of the table

Poor conductors of heat and electricity

Brittle and not malleable

Borderline between metals and nonmetals

Exhibit properties of both

Number of protons in the nucleus

Determines the element's identity

Average mass of an element's isotopes

Arrangement of electrons in shells

Tendency to form chemical bonds

Influenced by electron configuration

Size of an atom

Decreases across a period

Increases down a group

Energy required to remove an electron

Increases across a period

Decreases down a group

Ability to attract electrons in a bond

Increases across a period

Decreases down a group

Tendency to lose electrons

Decreases across a period

Increases down a group

Understanding reactivity

Predicting compound formation

Development of new materials

Improving existing materials

Understanding chemical cycles

Impact on ecosystems

Designing new drugs

Understanding molecular interactions