Download Charge of Ion = number of protons – number of electrons A neutral

• Proton = + charge
• Neutron = neutral charge
• Electron = - charge
Ions
• Ions are atoms that have
lost or gained one or
more electrons giving
them a positive or
negative charge!
If an ion gains an electron it
has a negative charge.
If an ion looses an election it has a
positive charge.
For example: Na (Sodium), has
originally 11 electrons but when an
electron is lost it becomes a postive
ion. Na +
What causes an atom to become an ion?
• When an atom loses or gains one or more
electrons it acquires a net electrical charge
called an ion.
• The net charge of an ion is found by subtracting
the number of electrons from the number of
protons
Charge of Ion = number of protons – number of
electrons
A neutral magnesium atom (atomic
number=12) has 12 protons/electrons.
If it loses 2 electrons it becomes an ion
with a charge of 2+.
Number of protons 12
Number of electrons - 10
Charge of Ion 2+
Ion
19. Cu²+
20. F-
Protons
Electrons
29
27
9
10
Isotopes
• Isotopes are atoms that have the same
number of protons but different numbers
of neutrons
• Most elements in the first two rows of the
periodic table have at least 2 isotopes with
one being more common than the other
• In nature, elements are almost always
found as a mixture of isotopes
Hmm
Isotopes of Hydrogen
•For example, the most common isotope of
hydrogen has no neutrons at all
•There's also a hydrogen isotope called deuterium,
with one neutron, and another, tritium, with two
neutrons.
Most common isotope
Neutron
Proton
Hydrogen
Deuterium
Tritium
• To identify an isotope more specifically, chemists
add a number after the elements name.
ex. Carbon-11 Carbon-12 Carbon-14
• This number is called the isotope’s mass number
and is the sum of the isotope’s number of protons
and neutrons.
• For example, an atom with 17 protons and 20
neutrons has a mass number of 37.
Q. What is the mass of
the Nitrogen isotope with
7 protons and 12
neutrons?
A. Nitrogen-19
Examples
Atom
iodine-128
potassium-40
Protons
53
Neutrons
75
Electrons
53
19
21
19
To name an isotope using
chemical symbols
 simply place the atom’s mass number to
the upper left of the element symbol. For
example 37Cl.
#neutrons = atomic mass – atomic
number
37 – 17 = 20 neutrons
How many protons, neutrons, and
electrons are present?
56
26Fe
2+
STEP 1: The atomic number in the lower left corner = 26
protons. The difference between the mass number and the
atomic number is 56 – 26 = 30. There are 30 neutrons.
STEP 2: The charge on the ion, 2+ shows us that there are 2
more protons than electrons, indicating that there are 24
electrons.
Isotope Symbols
Mass number (M)
141
Ba
56
Atomic number
(Z)
2+
Charge
Number of protons = Z
Number of neutrons = M – Z
charge = Z– Number of electrons