Understanding Matter - Ions (Happy Atoms)

• Ions are atoms that achieved a filled outer energy level.

• Because the electron has very little mass (almost none) the mass does not change. However, the charge of the atom does change.

Ions (Happy Atoms)

• The reason atoms form ions is that certain electron configurations have a lower energy (are more desirable).

• These configurations are also called noble gas or inert gas configurations.

• If an element can give up or gain electrons it will try to form an ion that has the same configuration as a noble gas it will be happy

• For Example:

Composition of Chemical Compounds - Ionic Compounds

Ionic compounds • Ionic compounds form because some elements

would really like to pick up an extra electron or two or three. They can only do this if they can find another element that is willing to give them up.

• Take lithium and fluorine below. Lithium could attain the electron configuration of helium if it could give away its valence electron. Fluorine could become like neon if to could only gain an electron.

Ionic Rules

• Ionic compounds are made of just one metal and one non-metal ion.

• Ionic compounds are always named with the positive ion (cation) first followed by the anion (a negative ion).

• When the formula for the compound is written, it must be written in such a way that it has a neutral charge.

Example (do not need to write)

• potassium iodide

• magnesium chloride

Putting Ions Together - Writing Formulas Using Ions

• Any atom that gives away electrons to become a positively charged ion is called a metal.

• These atoms become positively charged because they are losing negative charges.

METALLoses electronsPositive charge

Putting Ions Together - Writing Formulas Using Ions

• When atoms take on electrons they become negatively charged ions.

• Any atom that takes on electrons to become a negatively charged ion is called a nonmetal.

Non-METALGains

electronsNegative charge

Exercise:

Complete page 35 & 36

Page 37

• If we wish to represent several single atoms of an element we use a coefficient in front of the symbol.

• Atoms combine together to form molecules. A molecule is represented by symbols placed side by side to become a formula. Different kinds of atoms combined together produce a molecule of a compound.

In the formula H2O the number 2 is called a subscript. The subscripts in a formula tell the number of each kind of atom in the molecule.

Exercise:

• Determine the number of atoms in the following formulas by adding the subscripts together. Don’t forget about the brackets!!

• Eg. P2O5 ________

• Eg. Al(OH)3 ________

Ionic Compounds

Students will:• Explain, using the periodic table, how

elements combine to form compounds, and follow IUPAC guidelines for naming ionic compounds and simple molecular compounds

• predict formulas and write names for ionic compounds using a periodic table, a table of ions and IUPAC rules

Members of the IUPAC commission appointedto study chemical notation systems. 1951

To prevent confusion, the International Union of Pure and Applied Chemists (IUPAC)

Ionic Naming Rules – page 39

• 1) Name the metallic ion first, followed by the non-metallic ion.

(the non-metallic ion ends in “ide”)

• 2) Ionic compounds always start with a metal or an ammonium ion.

• Lets do the first ones together...

Continued

Ionic compounds• Formed when metals ions bind to non-metal

ions; called an ionic bond.• Called salts (just like table salt). When the

positive and negative charges attract each other a crystal lattice structure is formed.

• Each crystal could contain thousands, millions or trillions of ions; the number varies from crystal to crystal.

– Formulas for ionic compounds tell you the ratio of metal ions to non-metal ions.

– It is impractical to use a chemical formula showing the exact number of ions since the exact number varies from crystal to crystal. Instead we create a RATIO using subscript numbers

Ionic compounds

To tell what the ratio is we rely on the knowledge

that ionic compounds are formed from ions.

– Since chloride ions have a charge of one negative, and calcium ions have a charge of positive two, it takes two chloride ions to cancel the charge of one calcium ion.

To tell what the ratio is we rely on the knowledge

that ionic compounds are formed from ions.

– Since the aluminum ion has a charge of positive three, and the oxide ion has a charge of positive two the ratio of aluminum ions to oxide ions 2:3

• All ionic compounds have a net charge of zero.• Two ways to think about it:

1) Accountant:e.g. Barium Fluoride

Ba2+ 2+

F- 1-

Net Charge 1+

x2 2-

0

F-

The formula is: BaF2(s)

Ionic Compound Formulas

e.g. magnesium nitride

Mg2+ 2+

N3- 3-

Net Charge 1+

x2 6-

0

The formula is: Mg3N2(s)

x3 6+

e.g. calcium sulfide

Ca2+ 2+

S2- 2-

Net Charge 0

The formula is: CaS(s)

2) The “Switch-A-Roo”e.g. barium fluoride

Ba1

Ba2

+

F-

F2The formula becomes:

BaF2(s)

Mg3

Mg2

+

N3

-

N2

The formula becomes:Mg3N2(s)

e.g. magnesium nitride

Ca2

Ca2+ S2-

S2

The formula becomes:CaS(s)

e.g. calcium sulphide

Always Reduce to the simplest

ratio!

• Quick Practice:

Try the practice problems on p.42

• Let’s try the first few...

Page 42 – Big Kid Formulas• When given the name, write the symbol and charge for each ion.• Remember all compounds are electrically neutral.• Use subscripts to equalize the total number of positive and

negative charges.

• aluminum oxide

• silver fluoride

• potassium sulfide

Page 42 Continued

Stock System• Some ions can exist with different ion

charges in different situations. For example, iron can exist as Fe 3+ and Fe 2+

Stock System• To distinguish one from the other, Roman

numerals are used in the name of compounds that are made with ions that can have different charges.

• Fe 3+ is called the iron (III) ion and• Fe 2+ is called the iron (II) ion.• Write the chemical formula for

– iron (II) oxide. ________,

– for iron (III) oxide. ________

Other Examples

Page 43 continued

Ternary Ionic Compounds

• compounds made from polyatomic ions.

• polyatomic ions are identified on your periodic table in a separate table near the top

• if you don't recognize the name of a substance it is a polyatomic ion.

Ternary Ionic Compounds• For example: If asked to write the

formula for sodium sulfate.

Ternary Ionic Compounds

• Whenever you need multiple polyatomic ions, you must put brackets around the polyatomic ion and add the subscript outside the brackets.

Ternary Ionic Compounds

• Take a look on the back of the periodic table for the following polyatomic ions:

Review of Naming

Page 45 – Polyatomic Naming

• Page 45

Page 45 continued

Page 46 – Polyatomic and Stock

Page 46- Continued

Hydrated Compounds – page 47

• Hydrated compounds are compounds that contain water as part of their structure. Some compounds are water seeking and are most stable when they are attached to many water molecules.

Naming• The common substance,

Epsom salts, is named magnesium sulfate heptahydrate and its formula is MgSO47H2O.

• If you remove the water by heating or by some other means, the compound can be used to soak up water as it gets back the water you have taken away. Anti-perspriants are made in this way.

Write this down• Generally the chemical formula ends

with __H2O where the blank is the correct value for the number of water molecules that are bonded to the ionic compound.

• For the above example MgSO47H2O would be written;– using the prefix system as

magnesium sulfate heptahydrate

Example

• Cu(NO3)2 4 H2O

• Complete page 48

Hydrates page 48

Page 48 continued

Solubility of Ionic Compounds – pg 49• Ionic compounds

have either high solubility or low solubility when placed into water. A solubility chart is provided on the periodic table.

• Ionic compounds are deemed to be high solubility and is therefore said to be aqueous (aq).

• Low solubility (L) substances dissolve only very slightly in water and the compound is a solid (s).

• Eg AgNO3

Predict whether the following Ionic Compounds are

high solubility or low solubility.

Forming a Precipitate

• The following ionic species (ions) were placed in an aqueous environment (in water). Describe what will happen when each pair of ions reacts to form an ionic compound. Write the chemical formula for the ionic compound, including the state in the aqueous environment, then indicate whether they are high or low solubility and whether a precipitate forms.

• If a low solubility substance forms when the ions combine, the evidence will be the formation of a precipitate. You can tell when a precipitate forms because it becomes a solid (usually white and cloudy). In this case the chemical formula will be written with a (s).

• High solubility substances that form will remain in solution (no cloudiness), are written as (aq).

Writing States

Naming Review

• Naming Reviews 1-4 pages 59-62