Ions and Ionic Compound
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Transcript of Ions and Ionic Compound
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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
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Anion Formation
e-
Note: Nucleus is unchanged!!!!!!!3
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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!!
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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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Isoelectronic Series
• 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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Isoelectronic Series
• 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 Series
• 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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Isoelectronic Series
• 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 =
# protons = atomic number = 8
# neutrons = Mass # - Atomic # = 16 - 8 = 8
# 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
# protons = atomic number = 56
# neutrons = Mass # - Atomic # = 137 - 56 = 81
# 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
26
3+
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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)
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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
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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?
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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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Writing Formulas for Binary Ionic Compounds
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?
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Writing Formulas for Binary Ionic Compounds
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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Writing Formulas for Ionic Compounds with Polyatomic Ions
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
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Writing Formulas for Ionic Compounds with Polyatomic Ions
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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