GENERAL, ORGANIC, AND BIOCHEMISTRY – ATOM
WHAT IS MATTER MADE OF?
The Greek philosopher Democritus (circa 460–370 BCE) was the first person to
propose an atomic theory of matter. He stated that all matter is made of very tiny
particles, which he called atoms.
HOW DO WE CLASSIFY MATTER?
We classify matter as elements, compounds, or mixtures.
Matter can be divided into two classes: pure substances and mixtures
a. Elements
An element is a substance (for example, carbon, hydrogen, and iron) that
consists of identical atoms. At this time, 116 elements are known. Of
these, 88 occur in nature; chemists and physicists have made the others
in the laboratory. A list of the known elements appears on the inside front
cover of this book, along with their symbols. Their symbols consist of one
or two letters. Many symbols correspond directly to the name in English
(for example, C for carbon, H for hydrogen, and Li for lithium), but a few
are derived from the Latin or German names. Others are named for
people who played significant roles in the development of science—in
particular, atomic science. Still other elements are named for geographic
locations.
b. Compounds
A compound is a pure substance made up of two or more elements in a
fixed ratio by mass. For example, water is a compound made up of
hydrogen and oxygen and table salt is a compound made up of sodium
and chlorine. There are an estimated 20 million known compounds, only a
few of which we will introduce in this book.
, ELEMENTS NECESSARY FOR HUMAN
Life To the best of our knowledge, 20 of the 116 known elements are necessary
for human life. The six most important of these—carbon, hydrogen, nitrogen, oxygen,
phosphorus, and sulfur—are the subjects of organic chemistry and biochemistry.
Carbon, hydrogen, nitrogen, and oxygen are the big four in the human body. Seven
other elements are also quite important, and our bodies use at least nine additional
ones (trace elements) in very small quantities. The table lists these 20 major elements
and their functions in the human body.
A compound is characterized by its formula. The formula gives us the ratios of the
compound’s constituent elements and identifies each element by its atomic symbol. For
example, in table salt, the ratio of sodium atoms to chlorine atoms is 1:1. Given that Na
is the symbol for sodium and Cl is the symbol for chlorine, the formula of table salt is
NaCl. In water, the combining ratio is two hydrogen atoms to one oxygen atom. The
symbol for hydrogen is H, that for oxygen is O, and the formula of water is H 2O. The
subscripts following the atomic symbols indicate the ratio of the combining elements.
The number 1 in these ratios is omitted from the subscript. It is understood that NaCl
means a ratio of 1:1 and that H2O represents a ratio of 2:1.
WHAT IS MATTER MADE OF?
The Greek philosopher Democritus (circa 460–370 BCE) was the first person to
propose an atomic theory of matter. He stated that all matter is made of very tiny
particles, which he called atoms.
HOW DO WE CLASSIFY MATTER?
We classify matter as elements, compounds, or mixtures.
Matter can be divided into two classes: pure substances and mixtures
a. Elements
An element is a substance (for example, carbon, hydrogen, and iron) that
consists of identical atoms. At this time, 116 elements are known. Of
these, 88 occur in nature; chemists and physicists have made the others
in the laboratory. A list of the known elements appears on the inside front
cover of this book, along with their symbols. Their symbols consist of one
or two letters. Many symbols correspond directly to the name in English
(for example, C for carbon, H for hydrogen, and Li for lithium), but a few
are derived from the Latin or German names. Others are named for
people who played significant roles in the development of science—in
particular, atomic science. Still other elements are named for geographic
locations.
b. Compounds
A compound is a pure substance made up of two or more elements in a
fixed ratio by mass. For example, water is a compound made up of
hydrogen and oxygen and table salt is a compound made up of sodium
and chlorine. There are an estimated 20 million known compounds, only a
few of which we will introduce in this book.
, ELEMENTS NECESSARY FOR HUMAN
Life To the best of our knowledge, 20 of the 116 known elements are necessary
for human life. The six most important of these—carbon, hydrogen, nitrogen, oxygen,
phosphorus, and sulfur—are the subjects of organic chemistry and biochemistry.
Carbon, hydrogen, nitrogen, and oxygen are the big four in the human body. Seven
other elements are also quite important, and our bodies use at least nine additional
ones (trace elements) in very small quantities. The table lists these 20 major elements
and their functions in the human body.
A compound is characterized by its formula. The formula gives us the ratios of the
compound’s constituent elements and identifies each element by its atomic symbol. For
example, in table salt, the ratio of sodium atoms to chlorine atoms is 1:1. Given that Na
is the symbol for sodium and Cl is the symbol for chlorine, the formula of table salt is
NaCl. In water, the combining ratio is two hydrogen atoms to one oxygen atom. The
symbol for hydrogen is H, that for oxygen is O, and the formula of water is H 2O. The
subscripts following the atomic symbols indicate the ratio of the combining elements.
The number 1 in these ratios is omitted from the subscript. It is understood that NaCl
means a ratio of 1:1 and that H2O represents a ratio of 2:1.
