Ions and Ionic Compound

Ions and Ionic Compound

When atoms lose or gain electrons, they become ions, charged particles.

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Cation Formation

e-

Note: Nucleus is unchanged!!!!!!! 2

Anion Formation

e-

Note: Nucleus is unchanged!!!!!!!3

Ions

When atoms lose or gain electrons, they become ions.Cations are positive and are formed by elements on the left side of the periodic chart: metals (H can form 1+ ion)Anions are negative and are formed by elements on the right side of the periodic chart: nonmetals (H can form 1- ion)

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Learn common ions listed in syllabus p 12!!

Ions of Transition Metals

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More about ions later now:

closer look at atoms and electron arrangements in atoms

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Isoelectronic Series

• When atoms ionize, they form ions with the same number of electrons as the nearest (in atomic number) noble gas.Na = 1s22s22p63s1 = [Ne]3s1

Na+ = 1s22s22p6 = [Ne]

Cl = 1s22s22p63s23p5 = [Ne]3s23p5

Cl- = 1s22s22p63s23p6 = [Ar]

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• N (7 e-): 1s22s22p3

• O (8 e-): 1s22s22p4

• F (9 e-): 1s22s22p5

N3- (10 e-): 1s22s22p6 = [Ne]

O2- (10 e-): 1s22s22p6 = [Ne]

F- (10 e-): 1s22s22p6 = [Ne]

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• Na (11 e-): 1s22s22p63s1

• Mg (12 e-): 1s22s22p63s2

• Al (13 e-): 1s22s22p63s23p1

Na+ (10 e-): 1s22s22p6 = [Ne]

Mg2+ (10 e-): 1s22s22p6 = [Ne]

Al3+ (10 e-): 1s22s22p6 = [Ne]

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H

Li Be

Na Mg

Rb

Cs

Fr Ra

Ba

Sr ITeSbSnInCdAgPdRhRuTcMoNbZrY

La

Ac Rf

Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At

Db Sg Bh Hs Mt

LuYbTmErHoDyTbGdEuSmPmNdPrCe

Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

F

ClSPSiAl

B C N O

1A

2A

3B 4B 5B 6B 7B 8B 8B 8B 1B 2B

3A 4A 5A 6A 7A

CaK Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Xe

Rn

Ar

Ne

He

8AIons of the highlighted elements are

isoelectronic with Ne.

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• Isoelectronic: having the same number of electrons

• N3-, O2-, F-, Ne, Na+, Mg2+, and Al3+ form an isoelectronic series.– A group of atoms or ions that all contain the

same number of electrons

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• Examples of isoelectronic series:– N3-, O2-, F-, Ne, Na+, Mg2+, Al3+

– Se2-, Br-, Kr, Rb+, Sr2+, Y3+

– Also: Cr, Fe2+, and Co3+

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Sizes of Ions - Trends

• In an isoelectronic series, ions have the same number of electrons.

• Ionic size decreases with an increasing nuclear charge.

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Mass

Number Charge (=0 for atoms)

AtomicNumber

Chemical Symbols of Ions

XCharge = # p - # e-

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Chemical Symbol of Neutral O

• Using nuclear symbols to determine the number of p, n, e, and total charge

O16

8

Mass Number =

Atomic Number =

16

8

# protons = atomic number = 8

# neutrons = Mass # - Atomic # = 16 - 8 = 8

# electrons = # protons = 8

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Chemical Symbol of O-ion

Mass Number =

Atomic Number =



# electrons = # protons - charge = 8 - (-2) = 10

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8O16

8

2-

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Chemical Symbol of Ions

Ba137

56

2+ Mass Number =

Atomic Number =

137

56



# electrons = # protons - charge = 56 - (+2) = 54

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Chemical Symbols - IonsPractice writing nuclear symbols from information

given:

1) 53 p, 74 n, 54 e-

53 proton (= atomic number) I (Iodine)74 neutrons + 53 proton mass number = 12754 electrons (one more than protons) 1-

127I1- 53

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More practice:Given information: 23 e-, 30 n, net charge = +3 # protons?23 electrons, but charge of 3+ie 3 more protons than electrons p= 26 Atomic number = 26 element = Fe

Fe56

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3+

What atom/ion does the following show? Write the chemical symbol.

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Practice writing chemical symbols from given information:

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Periodic Properties:Cation and anion sizesTrends to know:

Cations (+) are smaller than their parent atoms.

Electrons are removed from the outer shell.

Anions (-) are larger than their parent atoms.

Electron-electron repulsion causes the electrons to spread out more in space.

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Sizes of Ions – Periodic Trends

• Ions increase in size as you go down a column/group in periodic table.

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Ionization Energy= amount of energy required to remove an

electron of a gaseous atom or ion to form a cation or more positively charged cation.– The first ionization energy is the energy

required to remove first electron.– The second ionization energy is the energy

required to remove second electron, etc.

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Ionization Energy• The higher the ionization energy, the harder it is to

remove an electron.• It requires more energy to remove each successive

electron.• When all valence electrons have been removed, the

ionization energy takes a quantum leap.Na (g) Na+ (g) + e-

1st electron2nd electron

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Trends in First Ionization Energies

• As one goes down a column, less energy is required to remove the first electron.– valence electrons are

farther from the nucleus.

Within each row, the ionization energy increases from left to right

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Ionization EnergyWhich element has the higher ionization energy, Br or Ca? Which one will lose an electron easier?

Br has the higher ionization energyfurther to the right

Ca will lose an electron easier because its ionization energy is lower.

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Electron Affinity• The energy change that occurs when an electron is added to

a gaseous atom is called the electron affinity.

Cl (g) + e- Cl- (g)

• The electron affinity becomes increasingly negative as the attraction between an atom and an electron increases– more negative electron affinity = more likely to gain an

electron and form an anion

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Electron Affinity• Trends:

– Halogens have the most negative electron affinities.

– Electron affinities become increasing negative moving from the left toward the halogens.

– Electron affinities do not change significantly within a group.

– Noble gases will not accept another electron.• To do so would require adding an electron to a new

electron shell (significantly higher in energy)

So:

Why do ions form to begin with?

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Ionic CompoundsBonds occur between atoms as a result

of interactions among the electrons.

When the interaction is to strip electrons, the resulting bond is said to be ionic and the entity formed is an ionic compound.

“Atoms” – now ions – are held together by electrostatic interactions, ionic bonds. NaCl

formula unit AND empirical formula

This is a crystal of NaCl.

Na+

Cl-

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Ionic BondsIonic compounds (such as NaCl) are generally formed between metals and nonmetals.

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Ionic Compounds• Ionic compounds are made of cations and anions,

held together by electrostatic attraction:– opposite electrical charges attract each other– like electrical charges repel each other.

• Ionic compounds do not exist as discrete molecules, but as structured aggregates (crystals).

– In NaCl, an ionic compound, Na exists as Na+ and Cl exists as Cl-.

• Important: The overall charge of the ionic compound is ZERO! Equal negative and positive charges.

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Properties of Molecular

Compounds

• held together by covalent bonds

• form discrete molecules• soft• low melting point• generally

nonconductive• includes all organic

compounds

• held together by ionic bonds

• do NOT form discrete molecules

• hard, rigid, brittle• high melting points• conductive when

melted or when dissolved in water

Properties of Ionic Compounds

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More about molecular compounds in Unit 3

Identify

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Which of the following compounds would you expect to be ionic:

N2O, Na2O, CaCl2, SF4?

Which of the following compounds are molecular: CBr4, FeS, P4O6, PbF2?

Ion ChargesMetal ions typically have a positive

charge.– Group 1A metals always have a +1 charge:

• Li+, Na+, K+, etc. – Group 2A metals always have a +2 charge:

• Mg2+, Ca2+, Ba2+, etc.– Some metal ions can form differently charged

ions (Fe2+ and Fe3+)

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Ion ChargesNonmetal ions typically have a

negative charge.– Group 7A nonmetals typically have a -1

charge:• F-, Cl-, Br -, etc.

– Group 6A nonmetals typically have a -2 charge:• O2-, S2-, Se2-, etc.

!!! Knowing what the Groups mean and knowing where the metal/nonmetal boundary is on the periodic table is a BIG help when dealing with ions and ionic compounds !!!

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Practice

• Give the chemical symbol, including mass number, for the ion with 22 protons, 26 neutrons, and 19 electrons:Metal or nonmetal?Anion or cation?

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A group of atoms that is covalently bonded yet still has an overall charge is a polyatomic ion.NO3

- SO4

2- PO4

3- ClO2

-

Polyatomic Ions

O

O

O

O P

3-

phosphate ion

!!! You are responsible for knowing the names, symbols, and correct charges for the ions listed in Unit 2 of the syllabus !!!

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Naming Binary Ionic Compounds1. Name the cation (metal).2. Name the anion (nonmetal).

– replace the end of the nonmetal with –ide– oxygen becomes oxide– fluorine becomes fluoride– sulfur becomes sulfide– more: N3- nitride

P3- phosphideC4- carbideCl- chloride

NaClBaI2

Ba3P2

K2S

sodium chloridebarium iodidebarium phosphidepotassium sulfide

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Naming Metal Ions When More Than One Ion is Possible

Two methods• Stock system (Roman numeral is the charge of the cation)

– Fe2+ is iron(II)– Fe3+ is iron(III)– Sn2+ is tin(II)– Sn4+ is tin(IV)

• Classic (-ic, -ous) system– -ic is for the ion with the higher charge– -ous is for the ion with the lower charge – Fe2+ is ferrous– Fe3+ is ferric– Sn2+ is stannous– Sn4+ is stannic

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Naming Binary Ionic Compounds

• MgCl2

• CuS• Cu2S• Fe2O3

• Na2O

magnesium chloridecopper(II) sulfide or cupric sulfidecopper(I) sulfide or cuprous sulfideiron(III) oxide or ferric oxidesodium oxide

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Writing Formulas for Binary Ionic Compounds

• The overall ionic compound MUST BE electrically neutral (have a net charge of 0).

• If you do not know the charges of the ions in the compound, you will not be able to write the correct formula for the compound!

Write the formula for potassium fluoride.1. Write the two elements K F2. Write their charges K+ F-

3. If the charges are equal and opposite, then just put the two elements together: KF

Note: there are NO charges in the formula!

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Write the formula for silver oxide.1. Write the two elements Ag O2. Write their charges Ag+ O2-

3. When the charges are different, perform a swap:Ag+ O2-

Ag2O

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Why do we not write Ca2O2 for calcium oxide?


calcium iodidetitanium(II) nitridelead(IV) chlorideiron(III) oxide

CaI2

Ti3N2

PbCl4

Fe2O3

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Naming Polyatomic Ions and Polyatomic Oxyanions

• Polyatomic ions – memorize list in your syllabus. The names and formulas for other polyatomic ions will be provided to you.

• Polyatomic oxyanions• sulfate: SO4

2- (more O’s, -ate)• sulfite: SO3

2- (less O’s, -ite)

• perchlorate: ClO4- (one more O, per-)

• chlorate: ClO3-

• chlorite: ClO2-

• hypochlorite: ClO- (one less O, hypo-)

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Writing Formulas for Ionic Compounds with Polyatomic Ions

Write the formula for magnesium sulfate.

1. Write the two ions with their charges. Mg2+ SO4

2-

2. If the charges are equal and opposite, put the two ions together, DO NOT include the charges in the formula.

MgSO4

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Write the formula for ammonium sulfate.

1. Write the two ions with their charges. NH4

+ SO42-

2. If the charges are not equal and opposite, do the “swap.”

NH4+ SO4

2-

(NH4)2SO4

Note the parentheses!48


sodium hydroxidemagnesium hydroxidealuminum hydroxide

aluminum phosphatesodium phosphateammonium phosphatecalcium phosphate

NaOHMg(OH)2

Al(OH)3

AlPO4Na3PO4

(NH4)3PO4

Ca3(PO4)2

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Practice• Name the following compounds: • (a) K2SO4

• (b) Ba(OH)2

• (c) FeCl3

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Naming Hydrates• Hydrates are ionic compounds with a specific

number of water molecules attached to lattice structure. CuSO4 • 5H2O

• Name the ionic compound as usual, then add the word “hydrate” and use the Greek prefix to indicate the number of waters of hydration.

CuSO4•5H2O copper(II) sulfate pentahydrate

BaCl2•2H2O barium chloride dihydrate

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Names of Common Chemicals Containing Ions

common name or use

chemical name formula

water water H2Oammonia, window cleaner

ammonia NH3(aq)

baking soda sodium bicarbonate NaHCO3

natural gas methane CH4

vinegar acetic acid (5% solution)

CH3COOH

table salt sodium chloride NaClbleach sodium hypochlorite NaClOmuriatic acid hydrochloric acid HCl(aq)

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Ions and Ionic Compound