Transcript The periodic table

The Periodic Table of
Elements
What is an element?
 An
element is a pure chemical made of
only one type of atom
 Each
box on
the periodic
table represents
one element
Reading the Periodic Table
(Z)
(A)
Atomic number (Z)
 Each
element has its own unique atomic
number
 It
is based on the number of protons
present in the atom
 Always
 Ex:
a whole number
7, 22, 91, etc
 In
a true atom, the number of protons is
equal to the number of electrons.
Element Symbol
 Each
element is given a 1 or 2 letter
abbreviation. The first letter has to be
capitalized. If there is a second
letter, it is always lowercase.
Atomic Mass (A)
 This
tells you how heavy an individual
atom is.
 Since
atoms are so small, we must use a
special unit.
 It
is called the atomic mass unit (amu).
Calculating the Atomic Mass
 Each
proton weighs ~1amu
 Each
neutron weighs ~1amu
 Electrons
the mass
are so small they do not affect
 Atomic
mass = # of protons + # of neutrons
Why isn’t the atomic mass a whole
number?
 The
atomic mass shown on the periodic
table is actually an average of the various
isotopes that exist. When making
calculations, we round to the nearest
whole number.
Calculating Average Atomic Mass
(mass of isotope1 x % in nature)+ (mass of isotope2 x % in nature)
100
* You may have more than two isotopes
 Example:
Mass of carbon
(12 x 98.9%) + (13 x 1.1%) + (14 x 0.0001%)
100%
=12.01amu