THE PERIODIC TABLE Dmitri Mendeleev (1834-1907)

THE PERIODIC TABLE Dmitri Mendeleev (1834-1907) put elements in columns in order of increasing atomic mass arranged columns so elements with similar prop’s were side by side

THE PERIODIC TABLE left blank spaces where there were no known elements with the appropriate properties or mass. predicted the properties of the missing elements

THE PERIODIC TABLE Henry Mosely (1887-1915)

THE PERIODIC TABLE Henry Mosely (1887-1915) Determined atomic numbers of the elements. Arranged elements in table by atomic number instead of mass.

HORIZONTAL ROWS: PERIODS seven periods 2 to 32 elements in a period properties of the elements change as you move across a period this pattern repeats from period to period: The Periodic Law

VERTICAL COLUMNS: GROUPS/FAMILIES Elements in a group have similar physical and chemical properties. Groups identified by A or B and a # Group A are the representative elements Group A can be divided into three broad classes

1. METALS high electrical conductivity high luster when clean ductile malleable

1. METALS divided into: alkali metals – group 1A alkaline earth metals – group 2A transition metals – group B inner transition metals

2. NONMETALS poor electrical conductivity non-lustrous group 7A – halogens group 8A – noble gases

3. METALLOIDS properties are intermediate between metals and nonmetals