Unit 3 – Chemical Periodicity

Elements & Atoms

Element-a pure substance that has one kind of atom

⚛ The periodic table lists all the different elements that are either found in nature or prepared in the laboratory synthetically

⚛ Atom-the smallest particle of matter

⚛ Example of an element is hydrogen. It contains only hydrogen atoms.

⚛ PERIODIC TABLE: an arrangement of elements organized with respect to similar traits shared by different elements

Definition

Development of the PT

"...if all the elements be arranged in order of their atomic weights a periodic repetition of properties is obtained.”

Dmitri Mendeleev (1869)- First published periodic table

Development of the Periodic Table

⚛Arranged in rows (periods) of increasing mass

Development of the Periodic Table

MASS

⚛Arranged in columns (groups or families) by similarities in physical and chemical properties

Development of the Periodic Table

⚛Most important feature: Holes were left in the table to allow for the discovery of new elements

Development of the Periodic Table

⚛Mendeleev predicted the discovery of germanium (which he called eka-silicon) as an element with an atomic weight between that of zinc and arsenic, but with chemical properties similar to those of silicon.

Development of the Periodic Table

Henry Moseley (1913) - Modified into the modern PT

⚛Arranged in rows (periods) of increasing Atomic Number

⚛Arranged in columns (groups or families) by similarities of physical and chemical properties

Development of the Periodic Table

⚛The Periodic Law: Chemical and physical properties of elements are periodic functions of their atomic numbers; properties of the elements occur at repeated intervals called periods.

Development of the Periodic Table

Organization of the PT

⚛The PT lists each element in order of their atomic number

⚛Elements are classified into three major categories based upon their properties: metals, nonmetals, and metalloids

Organizing the Periodic Table

Metals

METALS: located on the left side of the PT (exception of H, which is a nonmetal)

⚛Most elements are metals (~80%)

⚛Good conductors of heat and electricity

⚛Lustrous (shiny)

⚛Solids at room temperature (except Hg)

⚛Ductile and malleable

Metals

Nonmetals

NONMETALS: located on the right side of the PT

Greater variation in physical properties among nonmetals than metals.

Some are solids, bromine is a liquid, but most are gases at room temperature

Do not conduct electricity

Good insulators

Dull and Brittle

Nonmetals

Metalloids

METALLOIDS: indicated by the BOLD “staircase”

B, Si, Ge, As, Sb, Te, At

⚛Properties of both metals and nonmetals

⚛Semiconductors

Metalloids

GROUPS – vertical columns containing elements with similar properties.

⚛There are 18 groups

⚛Groups are also called families due to their similar properties

Organizing the PT

⚛The groups are numbered 1-18 with Group 1 being on the far left and Group 18 being on the far right of the periodic table.

Organizing the PT

1 18

• Groups may also be numbered using Roman Numerals ⚛ “A elements” referring to the Main

Group or Representative Elements⚛ “B elements” referring to the Transition Metals

Organizing the PT

PERIODS – horizontal rows on the periodic table; each period represents an exact grouping of elements

⚛There are 7 periods

⚛They are simply numbered 1-7

Organizing the PT