Org. Elements
developed 1st periodic table
Who is Medeleev
how are elements organized today (modern table)
by atomic number
Depends on distribution of isotopes in nature and the mass of those isotopes
Atomic Mass
elements are classified as
metal, non-metal, metalloids
elements that fall between metal and non-metal
metalloids
how were elements first organized (row & columns)
in rows by increasing atomic mass - elements in each column have similar properities
each row is called a
period
how is atomic mass calculated
use weighted average of an elements isotopes
majority of elements are
metals
electron in highest energy level
valence electrons
why were there gaps in first table
spaces left for undiscovered elements
each column is called a
group
Most elements in nature exist as__________
mixture of isotopes
conduct heat & electricity well
metals
why do elements in a group have similar properties
they have the same number of valence electrons
usefulness of periodic table
to explain properties and predict undiscovered elements
elements in a group have
similar properties
what is atomic mass unit (ATU)
1/12th the mass of carbon-12
form a bridge between left and right sides of the table
transition metals
increases top to bottom
proved the usefulness of Medeleevs table
the close match between predicated elements and newly discovered ones
this repeating pattern of properties is called
periodic law
how Atomic Mass differs from mass number
mass number is protons and neutrons combined. Atomic mass is the
are poor conductors or heat & electricity
non-metals
how are differences in alkali metals shown
by how they react with water