NSES Content Standard B
Physical Science: Properties and changes of properties in matter
Grades 5-8, page 154
Chemical elements do not break down by normal laboratory reactions such
as heating, exposure to electric current, or reaction with acids. There
are more than 100 known elements that combine in a multitude of ways to
produce compounds, which account for the living and nonliving substances
that we encounter.
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Benchmark 4D The Physical Setting: Structure
of Matter
Grades 6-8, page 78
Scientific ideas about elements were borrowed from some Greek philosophers
of 2,000 years earlier, who believed that everything was made from four
basic substances: air, earth, fire, and water. It was the combinations
of these "elements" in different proportions that gave other substances
their observable properties. The Greeks were wrong about those four, but
now over 100 different elements have been identified, some rare and some
plentiful, out of which everything is made. Because most elements tend
to combine with others, few elements are found in their pure form.