THE STRUCTURE OF THE ELEMENTS
Recall:
STANDARD ATOMIC NOTATION
The Atomic Number is the number of protons in the nucleus and is designated by
the letter Z.
The Mass Number is the total number of protons plus neutrons in an atom and is
designated by the letter A. Also the Mass Number is approximately equal to the
mass of the atom.
In general, atoms are symbolized using the standard atomic notation as
follows:
mass number
A
X
chemical symbol
Z
atomic number
Example:
35
From this symbol we observe and calculate the following:
Cl
17
(a) Chlorine has 35 neutrons plus protons.
(b) Chlorine has 17 protons.
(c) Therefore chlorine has 35 – 17 = 18 neutrons.
(d) Chlorine has 17 electrons. (All atoms are neutral.)
NOTE:
The chlorine atom can also be represented as chlorine-35 or Cl-35.
Try this one!
24
Mg
12
Recall also:
BOHR DIAGRAMS
Hydrogen
(atomic number 1)
Nitrogen
(atomic number 7)
Phosphorus
(atomic number 15)
Recall this too!
BOHR-RUTHERFORD DIAGRAMS
FORMING CHARGED ATOMS OR “IONS”
ATOMS LOSE OR GAIN ELECTRONS TO HAVE A “STABLE
ARRANGEMENT” OF ELECTRONS.
THE NOBLE GASES ALL HAVE STABLE ARRANGEMENTS OF
ELECTRONS.
ALL OTHER ATOMS TRY TO ACHIEVE ARRANGEMENTS OF
ELECTRONS LIKE NOBLE GASES BY LOSING OR GAINING ONE
OR MORE ELECTRONS!
Examples:
HOW ELEMENTS FORM COMPOUNDS
Many elements form compounds by transferring electrons from one atom to
another.
For example:
Calcium joins with fluorine to make calcium fluoride as follows:
One calcium atoms gives away two electrons, one each to two fluorine
atoms.
Fluorine
Calcium
atoms
atom
The atoms become charged ions and attract each other forming a
compound.
Fluoride ions [F]1Calcium ion [Ca]2+