In
the
1800
?
s
Dmitri
Mendeleev
developed
a
clever
way
to
organize
the
elements
into
what
is
now
known
as
the
____________________
____________________
of
____________________
.
In
this
system
,
the
elements
are
organized
into
rows
called
____________________
and
into
columns
called
____________________
.
Each
group
has
elements
with
the
same
number
of
____________________
____________________
,
which
affect
how
the
elements
in
each
group
react
.
Each
period
has
elements
with
the
same
number
of
____________________
____________________
.
Due
to
the
fact
that
the
elements
are
organized
by
their
characteristics
into
periods
and
groups
,
elements
in
similar
areas
of
the
periodic
table
are
also
organized
by
their
physical
____________________
.
The
category
that
most
of
the
elements
are
in
is
the
____________________
,
which
is
characterized
by
shiny
,
malleable
,
and
conductive
elements
.
Another
category
found
in
the
upper
right
of
the
period
table
is
the
____________________
,
which
is
characterized
by
brittle
,
dull
,
and
nonconductive
elements
.
A
special
section
of
the
non
-
metals
found
in
group
18
are
called
the
____________________
____________________
because
of
their
stability
.
Finally
,
along
the
?
steps
?
of
the
periodic
table
is
a
category
of
elements
that
have
both
metal
and
non
-
metal
properties
,
called
the
____________________
.
