Ionic and Metallic Bonding

Concepts to Master• Understand the difference between an

element and a compound.• Understand ionic bonding and the

properties of ionic compounds• Realize the differences between the ionic

bonding and metallic bonding.• Write chemical formulas for ionic

compounds using oxidation number.• Learn the polyatomic ions.• Use polyatomic ions when writing

chemical formulas.• Learn two methods for balancing

chemical formulas: stacking and criss-cross.

• Understand how and why Lewis dot diagrams work for ionic compounds.

• Compare and contrast the Lewis dot diagrams for atoms and ions.

• Learn the definition of exothermic and endothermic.

• Apply the above definitions to chemical bonding

• Learn how ions and conductivity are related.

• How does ionization energy relate to bond formation?

• How are ions in a compound held together?

• How many atoms are in a binary compound?

• How many atoms are in a ternary compound?

• If a compound is ternary, what type of ion does it usually contain?

• Be able to calculate formula mass.• Be able to calculate percent hydration

when given experimental data or the chemical formula.

• Be able to calculate percent composition when given experimental data or the chemical formula.

• What is a sea of mobile electrons and in what types of substances is it found?

Vocab

• Alloys• Anhydrate• Anion• Atom• Binary• Cation• Chemical bond• Chemical properties• Compound• Conductivity• Electrostatic attraction• Element• Endothermic• Exothermic• Formula mass

• Hydrate• Ionic • Ionic Charge• Ionization energy• Ions• Lewis dot structure• Metallic• Mobile electrons• Oxidation number• Physical properties• Polyatomic ion• Ternary

• Labs– Exo / Endo Rxns– Percent Hydration– Determining oxidation number

Review Elements versus Compounds

• Atoms are the smallest particle of an element that can exist.

• Elements are substances that cannot be separated into simpler substances.

• A compound is a substance formed when two or more elements are chemically joined. Like atoms, they are NEUTRAL.

Compounds • The smallest unit of a substance that can exist

alone and still retain the properties of that substance.

• These properties are different than the properties of the atoms alone.

• Atoms are Chemically Bonded and can only be separated by a chemical process.

+ =

Properties ofMg?

Properties ofCl?

Properties ofMgCl?

What is a Chemical Bond?

• A chemical bond is an attraction between atoms brought about by a sharing of electrons between two atoms or a complete transfer of electrons.

• Bonding occurs so atoms can satisfy the octet rule.

• There are three types of chemical bonds:– Ionic– Covalent– Metallic 

Forming Bonds is Exothermic

When the atoms form a bond they become lower in energy and the system is more stable. The energy saved by moving to a more stable situation is released as heat. The more energy released the greater the compound’s stability.

Breaking Bonds is Endothermic

Since atoms form bonds to become more stable, energy is required to break them apart. When more energy is required to break the bond, the more stable the bond is.

Chemical Equations

• Bond Formation = exothermic

• Breaking of Bond = endothermic

2 KClO3 -->  2 KCl + 3 O2

Exo or Endo ?

Exo or Endo ?

Once bonds are formed…

• compounds are made.

• and they are written as chemical formulas – represent the

composition of a compound

• group of elemental symbols

• possibly subscript numbers

Formula Composition

NaCl

Total # of atoms = ____

Total of 2 elements in each compound.

1 sodium and 1 chlorine

NH4OH

Total # of atoms = ____

Total of 3 elements in each compound.

1 oxygen, 5 hydrogen, and 1 nitrogen

KSCN

Total # of atoms = ____

Total of 4 elements in each compound.

1 potassium, 1 sulfur, 1 carbon, 1 nitrogen

• When metallic atoms react…– They lose electrons to form

cations. – They acquire an electron

configuration that satisfies the octet rule.

– Their radii decrease.– They want to give electrons

away so electronegativity is low.

• When non-metal atoms react…– They gain electrons to form

anions.– They acquire an electron

configuration that satisfies the octet rule.

– Their radii increase.– They want electrons so

electronegativity is high.

Which color is the cation?Which color is the cation?

Which color is the anion?

When Metals lose electrons, they get smaller!

When Nonmetals gain electrons, they get bigger!

Cation is +

Anion is -

Ionic Compounds

• Complete TRANSFER of electrons from METAL to NONMETAL.

– Metal loses electron to become cation.

– NonMetal gains electron to become anion.

– An electrostatic attraction occurs between the + cation and – anion. (Opposites attract.)

• Properties (Physical or Chemical?)

– Crystals / salts have a lattice formation with repeating pattern

– Very hard solids

– Not malleable (brittle), shatters

– Easily dissolve in water

– Conduct electricity when dissolved in water and when molten

– Do not conduct electricity as solids

– High melting point: What does this tell you about chemical bond energy?

Ionic Compounds

ZnS

CsCl

Are they solid, liquid, or gas? How do you know?

Na and Cl

Na

(Metal)

Cl

(non-Metal)

Electron configuration is?

# of valence electrons?

How many will be lost or gained to achieve an octet?

Lewis Dot Diagram

Lewis Dot Formula: Compound Formula:

Ca and ClCa

(Metal)

Cl

(non-Metal)

Electron configuration is?

# of valence electrons?

How many will be lost or gained to achieve an octet?

Lewis Dot Diagram

Lewis Dot Formula: Compound Formula:

Al and OAl

(Metal)

O

(non-Metal)

Electron configuration is?

# of valence electrons?

How many will be lost or gained to achieve an octet?

Lewis Dot Diagram

Lewis Dot Formula: Compound Formula:

Lewis Dot Diagram for Ionic Compounds– Brackets required

– Each bracket must show charge

– Metallic brackets will have no electron dots

– Non-metallic brackets will show 8 electrons dots

– Stack the positive and negative brackets

– Examples:

RbBr

Na2S CaF2

AlCl3

K3P

NaI

K3P

Using oxidation numbers to determine compound formulas

• Oxidation numbers are used to determine the ratio in which elements combine to form compounds.

– Cations• +

• Metals

– Anions• -

• Non-metals

• Chemical formulas are composed of a positive half and a negative half.

• Sodium Chloride is a compound you know to have a formula of NaCl.

• The element with the positive oxidation number is always written first: Na

• The element with the negative oxidation number is always written second: Cl

• The total of the oxidation numbers in a compound must equal zero.

• Na oxidation number is +1 and Cl is -1.

• With one Na and one Cl, the total is 0.

StepsWhat is the formula of Calcium Nitride?

1. Identify the symbols of each part of the name.

a) Calcium symbol is Ca.

b) Nitride symbol is N.

2. Identify the charge for each.

a) Calcium is +2.

b) Nitride is -3.

3. Balance the charges.-Criss-cross method

4. Write the symbol beginning with the symbol that is first in the name and include the subscript after each symbol Ca3N2.

5. Check to be sure that the subscript numbers are “reduced”.

Binary compounds

• Contain only 2 elements

• Write formulas for the following:

– Potassium and sulfur

– Rubidium and sulfur

– Magnesium and chlorine

– Sodium and nitrogen

Binary Cmpds with Roman Numerals

• Many of the transition metals have more than 1 oxidation number.

• The name of the compound contains a roman numeral to indicate which oxidation number was used to determine the compound formula.

• Examples:

• Copper (II) sulfide

• Mercury (II) iodide

• Iron (III) oxide

• Tin (IV) fluoride

Polyatomic Ions

• Polyatomic ions are charged group of atoms.

• Contain BOTH ionic and covalent bonds

• Act as a single unit.

• Use parentheses when more than one is present in the compound formula.

• Use Table E on the reference booklet.

Ternary Compounds• Contain 3 or more different elements• Often a polyatomic ion is present.

– Na2CO3

– KClO3

– LiOH

– CuSO4

• Writing Formulas for Ternary Compounds

•Ammonium hydroxide Calcium phosphate Potassium oxalate

Conductivity and IONS

• Conductivity is the ability of a material to conduct

electric current.

• Ions are charged atoms so they conduct electricity

when dissolved in water.

• Conductivity is proportional to the number of ions

in solution.

• Increasing the number of ions in a solution

increases the solution’s conductivity.

Conductivity and IONS

Ionic Compound

# of Cations

# of

Anions

Total # of

IONS

KCl

Al2(SO4)3

MgBr2

AgOH

Which one will have the GREATEST Conductivity?

Naming Ions

• Metals: name of metal + “ion”.• Transition Metals: name of

metal + (charge of metal) + “ion”.

• Non-metals: root of non-metal + “-ide“.

• Polyatomic ions: name on Reference Table E

• Examples:1. Cu+2. Mg2+3. F-4. OH-5. Fe3+

• Answers:1. Copper (I) ion 2. Magnesium ion 3. Fluoride ion 4. hydroxide ion 5. iron (III) ion

Hints that you have a polyatomic ion:1. 3 or more capital letters in the compound

(ternary)2. Parenthesis are present3. Compound’s name ends in “ate” or “ite”.

Exceptions are hydroxide, peroxide, and cyanide

Naming Compounds1. Name the positive part (this always comes first).

1. If the positive part is a monatomic cation (a single symbol positive ion) - name the element.

2. If the positive part is a polyatomic ion (Table E) - name it.

2. Name the negative part (this is the last part of the compound).

1. If the negative part is a monatomic anion (a single symbol negative ion) - take the root of the element and add "ide."

2. If the negative part is a polyatomic ion (Table E) - name it.

3. Check to see if a Roman Numeral is needed:

1. A Roman numeral is not needed if the positive part has only one positive oxidation state on the periodic table. (With only one positive oxidation state, there is only one possible combination of how the elements will bond together.)

2. A Roman numeral is needed if the positive part has two or more positive oxidation states on the periodic table. (With more than one positive oxidation state, there are as many combinations of how the elements will bond together as there are positive oxidation states.)

4. A Roman Numeral is the value of the Positive Oxidation State on one cation.

1. It is not a subscript.

2. It is not the total positive charge.

Practice Naming

• Ga2(SO3)3

• Ba(OH)2

• Li3N

• Al2(CO3)3

• FeF3

• NH4Cl

In the old days…• Metals

– "ous" is added to the root of the element for the smaller oxidation state.

– "ic" is added to the root of the element for the larger oxidation state.

• Examples: – Copper

• Cuprous = Cu+1

• Cupric = Cu+2

– Iron• Fenous = Fe+2

• Ferric = Fe+3

Cupric Bromide = CuBr2

Formula Mass• The formula mass is the total mass of all the atoms

within the formula.

• When a formula contains polyatomic ions, the number of atoms inside the brackets are multiplied by any subscript immediately behind the brackets.

Determine the Formula Mass for each of the following.

KBr LiOH NaNO3

Ba(OH)2 (NH4)2O CaCO3

Hydrate vs Anhydrate

• Hydrates contain water.– Water is “associated” with the chemical. – The water is not chemically bound because it can be

removed by simply heating.

• Anhydrates contain NO water. They are dehydrated.

MgBr2 ·6 H2O(s) + HEAT → MgBr2 (s) + 6 H2O(g)       Hydrate  Anhydrate

“Hydrated” Formula Mass• Sometimes when ionic crystals form, water becomes a part of the

crystal structure. – water of hydration– the crystals are called "hydrates" or "hydrated salts“– Formulas for hydrates always include a dot separator, followed by

the number of water molecules attached,• CuSO4●5H2O• FeCl2●4H2O

% Hydration - ExperimentalWhen a 1.000 g sample of CuSO4 ·5 H2O(s) was heated so that the waters of hydration

were driven off, the mass of the anhydrous salt remaining was found to be 0.6390 g. What is the experimental value of the percent water of hydration?

  CuSO4 ·5 H2O(s) + HEAT → CuSO4 (s) + 5 H2O (g)

1.000 g 0.6390 g

  1. Find the difference between the mass of hydrate before heating and the mass of the

anhydrate after heating. The difference is the mass of water lost.

1.000 g - 0.6390 g = 0.3610 g

  2. Dividing the mass of the water lost by the mass of hydrate used is equal to the fraction of

water in the compound. Multiplying this fraction by 100 gives the percent water in the hydrate.

(0.3610 g /1.000 g)(100) = 36.10%

% Hydration – Chemical FormulaThe theoretical (actual) percent hydration (percent water) can be calculated from the

formula of the hydrate by dividing the mass of water in one unit of the hydrate by the total mass of the hydrate and multiplying this fraction by 100.

  What is the percent water in copper(II) sulfate pentahydrate, CuSO4 ·5 H2O?  1. Calculate the formula mass.

2. Divide the mass of water in one unit of the hydrate by the total mass of the hydrate and multiply this fraction by 100.

Percent hydration = (90.10 g /249.72 g)(100) = 36.08%

Determine the % hydration of…

• Na2SO4•10H2O

• CaCl2•6H2O

% Composition• The % composition of each element is the mass of that

element (ionic or covalent) divided by the total mass of the compound multiplied by 100.

• What is the % composition of sulfur in sodium sulfide?– Determine formula mass.

– Divide formula mass by the mass of sulfur and multiply by 100.• (32.07 / 78.05) x 100 = 41.09 % sulfur

Determine % Composition of the underlined element

• Sn3P4

• AcF3

Determine % Composition of each

element

• CaCO3

• KBr

Metallic Bonding• The electrons can move freely within these

molecular orbitals, and so each electron becomes detached from its “parent atom”.

• The metal is held together by the strong forces of attraction between the positive nuclei and the delocalized electrons.

• This is sometimes described as "an array of positive ions in a sea of mobile electrons".

• Is a metal made up of atoms or ions? It is made of atoms.

• Each positive center in the diagram represents all the rest of the atom apart from the outer electron, but that electron hasn't been lost - it may no longer have an attachment to a particular atom, but it's still there in the structure. Sodium metal is therefore written as Na (not Na+).

Metallic Bonds

• Positive ions immersed in a sea of electrons– Low ionization energies cause electrons to be loosely

held– So valence electrons move among the atoms and

around the many kernels– “Mobile sea of electrons”

• Properties– Good conductors of electricity and heat as a solid or

liquid– Moderately to very hard (Au vs Zr)– Lustrous since electrons absorb and emit light as they

move around– Malleable (not brittle)– High melting point

Metallic Bonds

Alloys

• Material that contains more than one element and has the characteristic properties of metals

• Brass– 67% Cu– 33% Zn

• Stainless Steel– 80.6% Fe– 0.4% C– 18% Cr– 1% Ni

• Gold (14K)– 58% Au– 42% Cu

• Sterling Silver– 92.5% Ag– 7.5% Cu

• Bronze– 88% Cu– 12% Sn

Check

• Draw the Lewis Dot diagrams for aluminum bromide

• Al+3 Br-1

• Criss cross AlBr3

• [Al] +3 [Br] -1

[Br] -1 DOTS?[Br] -1

check

• Name BaH2

• barium hydride

• Name Mn2(CrO4)3

• Manganese (III) chromate

check

• Determine the % composition for all of the elements in barium hydroxide using its chemical formula.

• Ba(OH)2

• FW = 137.33+2(1)+2(16) = 171.33

• Ba : (137.33/171.33)x100 = 80.2%

• O : (32/171.33)x100 = 18.7%

• H : (2/171.33) x100 = 1.1%