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THE CHEMISTRY
OF LIFE
CHAPTER 2
ATOMS
AN ATOM IS THE BASIC
UNIT OF MATTER
ATOMS
ATOMS ARE MADE UP OF
PROTONS, NEUTRONS, AND
ELECTRONS
ATOMS
PROTONS ARE POSITIVELY CHARGED
PARTICLESNEUTRONS HAVE NO CHARGEELECTRONS ARE NEGATIVELY
CHARGED PARTICLES
ATOMS
THE CENTER OF THE ATOM
IS THE NUCLEUS, AND IS
MADE UP OF PROTONS AND
NEUTRONS
ATOMS
ELECTRONS, THE
NEGATIVELY CHARGED
PARTICLES, ARE IN
CONSTANT MOTION IN THE
SPACE AROUND THE
NUCLEUS
ATOMS
ATOMS
ATOMS HAVE AN EQUAL
NUMBER OF PROTONS AND
ELECTRONS, AND HAVE
EQUAL BUT OPPOSITE
CHARGES. ATOMS ARE
THEREFORE NEUTRAL.
ELEMENTS
AN ELEMENT IS A PURE SUBSTANCE
THAT CONSISTS OF ONE TYPE OF
ATOMTHERE ARE OVER 100 KNOWN
ELEMENTS, WHILE ONLY ABOUT 24
ARE COMMONLY FOUND IN LIVING
ORGANISMS
ELEMENTS
THE NUMBER OF PROTONS IN AN
ATOM OF AN ELEMENT IS THE
ATOMIC NUMBERFOR EXAMPLE,THE ATOMIC # FOR
CARBON IS 6. CARBON THEREFORE
HAS 6 PROTONS, AND 6 ELECTRONS
ISOTOPES
ISOTOPES ARE ATOMS OF
THE SAME ELEMENT THAT
DIFFER IN THE NUMBER OF
NEUTRONS THEY CONTAIN
ISOTOPES
THE MASS NUMBER IS THE
SUM OF THE PROTONS AND
NEUTRONS IN AN ATOMS
NUCLEUS
ISOTOPES
ISOTOPES ARE IDENTIFIED
BY THEIR MASS NUMBER
ISOTOPES
BECAUSE ISOTOPES HAVE
THE SAME NUMBER OF
ELECTRONS, ALL ISOTOPES
OF AN ELEMENT HAVE THE
SAME CHEMICAL
PROPERTIES