When elements combine to make molecules they sometimes
loose the state of matter they were in when they were an element. For
instance, hydrogen and oxygen are gases, but when you combine them the
normal condition would be liquid (water). Silicon is a solid, and oxygen is
a gas; when you combine them they sometimes become quartz, which is a solid.
Carbon is a solid and oxygen is a gas; when they combine they become a gas.
States of matter can change even within normal
conditions on Earth. If water (hydrogen + oxygen) is frozen, it is ice; when
heated, it is a gas. Water is actually one of the few molecules that can
change from the three states of matter easily on Earth. Most other elements
and compounds cannot do that.
- Pass out the Periodic Table placemats and the student worksheets. Ask
them to count all the gaseous elements. Record this number on the
worksheet. Next ask them to count all the liquids. Again, record this
number on the worksheet. Finally, have them count all the solids.
On the Periodic Table Placemat, the elements that are solids,
liquids, and gases are differentiated by color. This refers to the state
of matter that they are in on the Earth’s surface, under normal
conditions. Note that plasma is not a form of matter that elements take.
There are 11 gases, 4 liquids, and 94 solids on this periodic table.
- Tell students that not all elements can be found in a pure state,
meaning that the element naturally occurs in combination with other
elements rather than by itself. There are 18 elements that are
synthetically made. These are created by scientists. We really do not
know what their natural form would be since they are unstable in the
natural environment of Earth's surface. These synthetic elements have
the atomic numbers 61, 93-109. Have the students write the symbol of
these elements on their worksheets. Say the name of each of the elements
and have the students repeat the name.
- Explain to the students that when an element combines with other
elements it forms a compound, which can be a different state of matter
then its component elements. For example, hydrogen and oxygen are gases,
but when combined they become water, a liquid.