ELEMENTS
91
(^6) LANTHANIDES
These soft, reactive metals
were known as rare earths,
because they were wrongly
believed to occur only
scarcely in nature. Silvery-
white in appearance, they
tarnish easily on contact with
air. Holmium, the element
with the greatest magnetic
strength, is in this group.
(^7) NON-METALS
Around one-sixth of elements
are non-metals. They are poor
conductors of electricity and
melt at low temperatures.
Carbon, nitrogen, and oxygen
are all examples of non-
metals, as are the halogens,
a group of highly reactive
elements that combine with
other elements to form salts.
(^8) NOBLE GASES
There are seven noble gases
- also called rare or inert
gases because they do not
readily react with anything or
combine with other elements
to make compounds. They are
helium, neon, argon, krypton,
xenon, radon, and oganesson,
although the latter may be a
solid at room temperature.
(^9) POOR METALS
Metals that are fairly soft
and melt easily are known as
poor metals. They are readily
found as ores (minerals) in
Earth and can be very useful,
especially when made into
alloys (two metals mixed
together to make a harder
metal). Aluminium and lead
are both poor metals.
(^10) SEMI-METALS
These elements have some
properties of metals and
some of non-metals. Arsenic,
for example, is shiny like
a metal, but not a good
conductor. Some semi-metals
are semiconductors, behaving
as conductors or insulators
depending on what other
substances are added to them.
The halogen
bromine is a
red-brown
liquid at room
temperature,
but evaporates
quickly to form
a choking,
Radioactive sign poisonous gas
is used to show
elements that
emit radiation
Tin is often made
into alloys – mixing
it with copper makes
bronze, while
combining it with
lead forms pewter
After hydrogen,
helium is the
lightest element,
and is used to
fill balloons
and airships
because it is
lighter than air
Silicon is often
used to make
microchips for
electronic devices
Gadolinium,
like the other
lanthanides,
reacts easily
with air
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