Ions & ionic compounds

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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

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

Positive Ion Example Sodium loses one electron to become

stable Results in an ion that has a positive

charge

Positive Ion Example

The symbol “+” is written as a superscript to indicate that the sodium has a charge of 1+

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-

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”

When an atom gains one or more electron it become negative

Called an anion (“an-eye-on”)

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

Naming Multivalent CationsA 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 = 4 V = 5 VI = 6

Naming Multivalent CationsFor 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 ReactivityThe farther the valence electron is

from its positive nucleus, the more easily it is removed and the more reactive the atom is

Cation ReactivityReactivity generally increases for

cations as you move down the periodic table

Example: potassium is more reactive than sodium

Lithium SodiumPotassium Rubidium Cesium

tivity

Cation Reactivity

Reactivity generally increases for cations as you move down the periodic table.

But why?

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

Fluorine Bromine Iodine AstatineChlorine

tivity

Anion Reactivity

Reactivity generally decreases for anions as you move down the periodic table

But why?

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).

Na11p12n

+1 Al13p14n

+3Mg12p12n

+2 Ne10p10n

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 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.

Properties of Ionic CompoundAt 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

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

When an ionic compound dissolves in water, the crystal structure breaks down and the ions become free to move.

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 Compounds1. 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 CompoundsExample 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 Compounds1. 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 Compounds1. 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 CompoundsExample 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 CompoundsExample 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.

Ions & ionic compounds

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