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