3.00_Chemistry of Biology
Biology I
(Ions)
Slides 84-100
1
What’s an Ion?
https://www.youtube.com/watch?v=WWc3k2723IM
2
Ions
• An atom usually has a neutral charge. That
means it has the same number of protons as
electrons
• Remember, a proton has a positive charge and an
electron has a negative charge
• ION – an atom that has lost or gained one or
more electrons and has become charged either
positively or negatively
3
How do atoms form Ions
An ion is an atom or group of atoms that has
an electrical charge, either positive or negative.
Atoms have an equal number of protons and electrons and so do
not have an overall charge.
Atoms with incomplete outer electron shells
are unstable. By either gaining or losing
electrons, atoms can obtain full outer electron
shells and become stable, just like the noble
gases.
When this happens, atoms have an unequal number of protons and
electrons and so have an overall charge.
4
This is how atoms become ions.
Positive Ions
• When an atom LOSES electrons, it becomes
more POSITIVE
– Why?
• If you are getting rid of negative particles
(electrons) but your number of positive
particles (protons) are staying the same.
– In other words, you are subtracting negative
numbers
5
Positive Ions
• What would the charge be if:
• The neutral form of Gold (Au) lost 4 of its 79
electrons. It now has 79 protons and 75
electrons
• The neutral form of Mg lost 2 of its 12
electrons. It now has 12 protons and 10
electrons.
6
Negative Ions
• When an atom GAINS electrons it becomes
more NEGATIVE
– Why?
• Electrons have a negative charge, so the more
you have, the more negative you become
7
Ions
• Ions are represented by placing a “superscript”
charge number next to the atomic symbol.
• Ex.
–
–
–
–
O-2 = oxygen with a negative 2 charge
K+ = potassium with a positive 1 charge
N-3 = nitrogen with a negative 3 charge
And so on
8
Isotopes or Ions
9
Isotopes or Ions
• How many P’s, N’s, and E’s does each of the
following have?
• Label each as an isotope, ion, or the version
10
found on the P.T.
What is a compound ion?
Ions can be made up of a single atom or a group of atoms. An ion
made up of a group of atoms is called a compound ion.
What atoms are present in the following compound ions?
Ion
Formula Charge
hydroxide
OH-
sulfate
SO42-
nitrate
Atoms present
O
H
-2
S
O
O
O
NO3-
-1
N
O
O
O
carbonate
CO32-
-2
C
O
O
O
ammonium
NH4+
+1
N
H
H
H
O
H
11
Naming Ions and Compound Ions
There are two common types of ions: –ide ions and –ate ions.
What is the difference?
Generally, –ide ions are negatively-charged ions of an
element, e.g. sulfide (S2-), fluoride (F-), oxide (O2-).
The exception to this rule is the hydroxide ion, which contains both
hydrogen and oxygen (OH-).
–ate ions are negatively-charged compound ions
that include oxygen, e.g. sulfate (SO42-), nitrate (NO3-),
carbonate (CO32-).
12
Ions and Compound Ions
• IONS are atoms or groups of atoms with a
positive or negative charge.
• Taking away an electron from an atom gives a
CATION with a positive charge
• Adding an electron to an atom gives an ANION
with a negative charge.
• To tell the difference between an atom and an ion,
look to see if there is a charge in the superscript!
Examples: Na+ Ca+2 I- O-2
Na
Ca
I
O
Forming Cations and Anions
A CATION forms
when an atom loses
one or more
electrons.
An ANION forms
when an atom gains
one or more
electrons
Mg --> Mg2+ + 2 e-
F + e- --> F-
Predicting Ion Charges
• metals (Mg) lose electrons ---> cations
• nonmetals (F) gain electrons ---> anions
Learning Check
State the number of protons, neutrons, and electrons in each of these
ions.
39
K+
19
16O -2
8
41Ca +2
20
#p+ ______
______
_______
#no ______
______
_______
#e-
______
_______
______
Learning Check
Write the nuclear symbol form for the following
atoms or ions:
A. 8 p+, 8 n, 8 e-
___________
B. 17p+, 20n, 17e-
___________
C. 47p+, 60 n, 46 e-
___________
Charges on Common Ions
-3
+1
-2
-1
+2
By losing or gaining e-, atom has same number of
e-’s as nearest Group 8A atom.