The Study of Change
The scientific method--Define problem-->experiments-->make observations &
record data-->develop a hypothesis hypotheses (a tentative explanation for a set
of observations)-->extensive data is summarized as a law ( a concise statement of
a relationship between phenomena that is always the same under the same
--A hypotheses that survives many experimental tests of their validity may turn
into a theory (a unifying principle that explains a body of facts and/or those laws
that are based on them).
Chemistry in Action: Primordial Helium and the Big Bang Theory
-1940s, George Gamow developed the Big Bang Theory. Since then science has
been able to provide certain proof in favour of his theory. Measurements have
been made that indicate that the universe is expanding, scientists have detected
background radiation, and primordial helium has been found in the universe.
Hydrogen and helium should have formed first (they are the two most simple
elements) and diffused before many galaxies were formed. When ultraviolet light
is analyzed from quasars, it is found that helium absorbs the light; if hydrogen
ionizes is cannot absorb light, but helium can lose an electron and still have
another while still absorbing light.
Classifications of Matter-Substances, mixtures, elements, and
Also atoms and molecules in chapter 2. If this section is confusing, there is a diagram that
breaks it down in the textbook.
Substance: matter that has definite (constant) composition and distinct
properties (ex. Water, sucrose, gold, and oxygen). A substance can be an element
or a compound.
Element: a substance that cannot be separated into simpler substances by
chemical means. Compound: a substance composed of atoms of two or more elements chemically
united in fixed proportions. Compounds can only be separated by chemical
Mixture: a combination of two or more substances in which the substances retain
their distinct identities. The components of a mixture can be separated without
losing their composition or properties.
Homogeneous mixture: composition is the same throughout (ex.