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Ions & Ionic Compound
+ =
Na Cl NaCl
Compounds
A compound is a pure substance made up of two or more elements in which the elements are chemically combined
Compounds
Two types of compounds: Ionic and Molecular
Ionic compounds: composed of positive and negative ions
Ion
An ion is an atom or group of atoms that has either a positive charge or a negative charge
Ion
Ions form when atoms gain or lose electrons to become stable
A atom is stable when the valence shell is full
=
Na
Positive Ion Example
Sodium loses one electron to become stable
Results in an ion that has a positive charge
x
Positive Ion Example
The symbol “+” is written as a superscript to indicate that the sodium has a charge of 1+
Na+
=
Cl
Negative Ion Example
Chlorine gains one electron to become stable
Results in an ion with a negative charge
Negative Ion Example
The symbol “-” is written as a superscript to indicate that the chlorine ion has a charge of 1-
Cl-
Ion
Both ions have a full valence shell containing the maximum number of electrons possible
This new arrangement of valence electrons has less energy than the previous arrangement and is stable
CationWhen an
atom gives up one or more electrons it becomes positive
Called a cation “cat-eye-on”
Anion
When an atom gains one or more electron it become negative
Called an anion (“an-eye-on”)
Ion
Ca+ions are posi+ive
Anions are negative
Writing Ion Symbols
Write the symbol of the element and show the ion charge as a superscript
Example: the symbol of a calcium ion is Ca2+
When an ion has a charge of 1+ or 1- the symbol has no number in the superscript, such as Na+ or F-
Naming Univalent Cations
When an element can form only one type of ion, the ion has the same name as the element
Eg: Ca2+ = calcium ion
CaCa20p20p
20n20n
+2+2
Naming Multivalent Cations A multivalent
element is an element that can form an ion in more than one way
Example: An atom of copper can form two different ions: Cu+ or Cu2+
Naming Multivalent Cations
The name of an ion of a multivalent element always contains a Roman numeral that indicates the ion charge
I = 1 II = 2 III = 3 IV = 4V = 5VI = 6
Naming Multivalent Cations
For example, Cu+ is named copper(I) (read as “copper one”)
Cu2+ is named copper(II) (read as “copper two”)
Only multivalent metals have Roman numerals in their names
Naming Anions
A nonmetal that has gained electrons to become an ion has the the same name as the element but with the ending changed to -ide
Eg: Cl- = chloride ion
Naming Anions
nitrogen nitrnitrideideoxygen oxoxideidefluorine fluorfluorideide
phosphorous phosphphosphideidesulfur sulfsulfideide
chlorine chlorchlorideidebromine brombromideide
iodine iodiodideide
Ion Reactivity
Metal atoms tend to lose electrons Non-metal atoms tend to gain electrons
Ion Reactivity
The farther the valence electron is from its positive nucleus, the more easily it is removed and the more reactive the atom is
Cation Reactivity
Reactivity generally increases for cations as you move down the periodic table
Example: potassium is more reactive than sodium
LithiumLithium SodiumSodiumPotassiumPotassium RubidiumRubidium CesiumCesium
reac
tivity
incr
ease
s
Li
K
Na
Cation Reactivity
Cation Reactivity
Reactivity generally increases for cations as you move down the periodic table.
But why?
Li
K
Na
Electrons that are further away from the nucleus are more easily lost.
Thus atoms with more orbitals will be more reactive.
Anion Reactivity
Reactivity generally decreases for anions as you move down the periodic table
Example: fluorine is more reactive than chlorine
FluorineFluorine BromineBromine IodineIodine AstatineAstatineChlorineChlorine
reac
tivity
incr
ease
s
ClF
Anion Reactivity
Anion Reactivity
Reactivity generally decreases for anions as you move down the periodic table
But why?
Cl
F
Elements whose valence shell is closer to the nucleus will gain electrons more readily because they are closer to the nucleus.
Negative electrons have a stronger attraction for the positive nucleus when the valence shell is closer to the nucleus.
A metal atom that has lost electrons (cation) and a nonmetal atom that has gained electrons (anion) will have the same number of electrons as its nearest noble gas.
Cations
An metal atom that has lost electrons (cation) will have the same number of electrons as its nearest noble gas.
For example, neon is the closest noble gas in the periodic table to sodium, magnesium and aluminum
Cations
Cations
The cations Na+, Mg2+, and Al3+ all have the same number of electrons as atoms of neon.
This relationship is known as being isoelectronic (having the same number of electrons).
NaNa11p11p
12n12n
+1+1AlAl
13p13p
14n14n
+3+3MgMg
12p12p
12n12n
+2+2 NeNe10p10p
10n10n
Anions Apply concept to anions For example, neon is the closest noble gas in the
periodic table to nitrogen, oxygen and fluorine
Isoelectronic Prove that these atoms are isoelectronic by drawing
the Bohr diagrams.
Ne N3- O2- F-
Ionic Compounds
In general, an ionic compound consists of a metal and nonmetal
It is more accurate to say that ionic compounds form when atoms of different elements transfer electrons resulting in ions of opposite charges.
Thus there is always an electron donor and acceptor.
+ =
Na Cl NaCl
Ionic Compound
For example, this process occurs when atoms of sodium metal (Na) combine with atoms of chlorine (Cl) to form sodium chloride (NaCl), or table salt
Ionic Compound
During the formation of NaCl, one electron is transferred from a sodium atom to a chlorine atom
Ionic Compound
In general, a cation will react with an anion to acquire a full valence shellIn general, a cation will react with an anion to acquire a full valence shell
Ionic Compound
The attraction between the cation and the anion is known as an ionic bond. This bond is what holds the ionic compound together.
The attraction between the cation and the anion is known as an ionic bond. This bond is what holds the ionic compound together.
Properties of Ionic Compound
At room temperature, most are hard, brittle solids that can be crushed
Ionic compounds form crystals that have an alternating arrangement of positively charged ions and negatively charged ions, so that when they break their edges are well-defined
Properties of Ionic Compound
Properties of Ionic Compound
In an ionic crystal, every ion is attracted to every other ion in the crystal. As a result, ionic crystals have very high melting pointsex.) NaCl melts at 800oC
In an ionic crystal, every ion is attracted to every other ion in the crystal. As a result, ionic crystals have very high melting pointsex.) NaCl melts at 800oC
Properties of Ionic Compound
When an ionic compound dissolves in water, the crystal structure breaks down and the ions become free to move.
Properties of Ionic Compound
Solutions of ionic compounds can conduct electricity
Naming Univalent Ionic Compounds
Univalent Ionic Compounds are compounds where the metal ion only has one possible charge.
Naming Univalent Ionic Compounds
1. Name the metal ion first• The name of the metal ion is the same as the element name• Example: in KBr, the name of the K+ ion is potassium
2. Name the non-metal ion second• When a non-metal becomes a negative ion, the ending of its
name changes to “ide”• Example: a bromine atom become bromide ion (Br -)
3. The formulas of ionic compounds often contain numbers called subscripts which can be ignored when determining the name.• Example: Na3P is sodium phosphide
Naming Univalent Ionic Compounds
Example Problem 1:
Write the name of the ionic compound ZnF2
1. Name the metal ion: • Zn forms only one type of ion (Zn2+), so the name is
zinc2. Name the non-metal ion:
• The atom is fluorine so the ion is fluoride3. Combine the names:
• ZnF2 = zinc fluoride
Naming Multivalent Ionic Compounds
Multivalent Ionic Compounds are compounds where the metal ion only has two or more possible charges.
Naming Multivalent Ionic Compounds
1. Identify all the possible charges of the ions.• Example: FeO• Fe can be Fe2+ or Fe3+
• O is O2-
2. Determine which charge on the multivalent ion is needed to make the compound neutral• Example: Need to use Fe2+ to balance O2-
RULE:
• Although ionic compounds are made of charged particles, the compound itself has no net charge
• All ion charges of an ionic compound must add up to zero
• The positive and negative charges in an ionic compound must be equal
Naming Multivalent Ionic Compounds
1. Identify all the possible charges of the ions.• Example: FeO• Fe can be Fe2+ or Fe3+
• O is O2-
2. Determine which charge on the multivalent ion is needed to make the compound neutral• Example: Need to use Fe2+ to balance O2-
3. Name the metal ion indicating the charge in brackets using Roman numerals• 1 = I, 2 = II, 3 = III, 4 = IV, 5 = V
4. Name the non-metal ion changing the ending to ‘ide’• Example: FeO = Iron (II) oxide
Naming Multivalent Ionic Compounds
Example Problem 2:
Write the name of the ionic compound MnCl4
1. Identify the ions that form the compound: Mn2+ or Mn4+ and Cl-
2. Determine the charge of the multivalent ion that would make the compound neutral.
1. Cl4 means there are 4 x Cl- = a total charge of 4-2. Would need to use Mn4+
3. Name the metal ion indicating the charge using Roman numerals in brackets and adding the nonmetal –ide.1. Manganese (IV) iodide
Polyatomic Ions
Poly = 2 or more Atomic = atoms
A polyatomic ion is a group of atoms, usually of different elements, that act as a single ion
Example: one atom of sulphur and four atoms of oxygen form the polyatomic ion called sulphate, or SO42-
Polyatomic Ions
Similar polyatomic ions are named using the suffixes “-ate” or “-ite”
Example: NO3- is nitrate; NO2- is nitrite
Most common polyatomic ions have a negative charge
However, the ammonium ion NH4+ has a positive charge
Name Formula
ammonium NH4+
carbonate CO32-
bicarbonate HCO3-
hydroxide OH-
nitrate NO3-
nitrite NO2-
permanganate MnO4-
phosphate PO43-
phosphite PO33-
sulphate SO42-
sulphite SO32-
Polyatomic Ions
Naming Polyatomic Ionic Compounds
Example Problem 3:
Write the name of the ionic compound LiHCO3
1. Name the metal/positive ion:• Example: Li+ = lithium
2. Identify the polyatomic ion (use table):• Example: HCO3
- = hydrogen carbonate
3. Combine the names. Do not change the polyatomic ending.• LiHCO3 = lithium hydrogen carbonate
Writing Chemical Formula for Uni & Multivalent Ionic Compounds1. Identify the charge of the ions in the compound
• Example: Calcium chloride• Ca2+ and Cl-
2. Determine the number of positive and negative ions needed to make the compound neutral• Need 2 Cl- to balance 1 Ca2+
3. Write the metal atom first. Use subscript to indicate the number of ions if it is more than 1. Make sure to use on the lowest common multiple.• Calcium chloride = CaCl2• Wrong: Ca2Cl4
Writing Chemical Formula for Uni & Multivalent Ionic CompoundsExample Problem 4:
Write the chemical formula for Bismuth (V) Phosphide.• Bi5+ and P3-
• How many of each do we need to make the compound neutral?
• Write the chemical formula using subscripts as needed.
Writing Chemical Formula for Polyatomic Ionic Compounds1. Identify the charge of the ions in the compound
• Example: Calcium chlorate• Ca2+ and ClO4
-
2. Determine the number of positive and negative ions needed to make the compound neutral• Need 2 ClO4
- to balance 1 Ca2+
3. Write the metal atom first. If subscripts are needed for the polyatomic ion, place a bracket around it first. Make sure to use on the lowest common multiple.• Calcium chlorate = Ca(ClO4)2
Writing Chemical Formula for Polyatomic Ionic CompoundsExample Problem 5:Write the chemical formula for arsenic (III) acetate.• As3+ and C2H3O2
-
• How many of each do we need to make the compound neutral?
• Write the chemical formula using subscripts and brackets as needed.
