Unit 4 - Ions.

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Presentation transcript:

Unit 4 - Ions

Ions IONS - atoms that have gained or lost electrons Charged particles because unequal number of p+ and e- Metals lose electrons to form CATIONS (positively charged ions) Non-metals gain electrons to form ANIONS (negatively charged ions) A Negative ION

Ions Metals LOSE electrons. Non-metals GAIN electrons.

Ion Notation HOW TO WRITE AN ION: ELEMENT SYMBOLCharge ** Charge is a SUPERSCRIPT Examples: Na+ charge = +1 O2- charge = -2 Al3+ charge = +3

Practice Find the number of protons, neutrons & electrons: p+ n0 e- 23Na+   16O2– 12C

Practice Find the number of protons, neutrons & electrons: p+ n0 e- 23Na+ 11 12 10   16O2– 8 8 10 12C 6 6 6

The Octet Rule The maximum number of valence electrons is 8 electrons: OCTET RULE. Atoms form bonds to have a full shell of valence electrons: the same number of electrons as the closest noble gas. In ionic bonds, atoms LOSE or GAIN electrons to meet the octet rule.

Electronegativity How “greedy” an atom is for electrons. Strong electronegativity = greedy, steals electrons Weak electronegativity = not greedy, gives away electrons Give away electrons Steal electrons

Formation of Cations Metals have LOW electronegativity and LOW ionization energy so they will LOSE electrons to form cations.

Ionization The process of when a metal loses electrons to become an ion. - +4 protons - 4 electrons -------------- 0 charge - +4 protons 3 electrons --------------- +1 charge + + + + +4 protons 2 electrons --------------- +2 charge - -

Formation of Anions Non-metals have HIGH electronegativity and HIGH ionization energy so they will GAIN electrons to form anions, negative ions.

Ionization The process of when a non-metal gains electrons to become an ion. - +8 protons - 8 electrons -------------- 0 charge - - - + +8 protons 9 electrons --------------- -1 charge + + - - + + + + + +8 protons 10 electrons --------------- -2 charge - - - -

Ions Atoms of metals (3 or less valence electrons) lose their valence electrons. Atoms of non-metals (5 or more valence electrons) gain electrons.

Charges of Ions Chlorine ion: Chlorine atom: 18 electrons 18- 17 protons 17 + Neutral 0 Chlorine ion: 18 electrons 18- 17 protons 17 + Net charge 1- Magnesium atom: 12 electrons 12- 12 protons 12 + Neutral 0 Magnesium ion: 10 electrons 10- 12 protons 12 + Net charge 2+

Predicting Ionic Charges Group 1A: Lose 1 electron to form 1+ ions H+ Li+ Na+ K+ Rb+

Predicting Ionic Charges Group 2A: Loses 2 electrons to form 2+ ions Be2+ Mg2+ Ca2+ Sr2+ Ba2+

Predicting Ionic Charges Loses 3 electrons to form 3+ ions Group 3A: B3+ Al3+ Ga3+

Predicting Ionic Charges Neither! Group 4A elements rarely form ions EXCEPTION: Sn and Pb!! Treat like transition metals Do they lose 4 electrons or gain 4 electrons? Group 4A:

Predicting Ionic Charges Nitride Gains 3 electrons to form 3- ions Group 5A: P3- Phosphide As3- Arsenide

Predicting Ionic Charges Oxide Gains 2 electrons to form 2- ions Group 6A: S2- Sulfide Se2- Selenide

Predicting Ionic Charges Gains 1 electron to form 1- ions Group 7A: F1- Fluoride Br1- Bromide Cl1- Chloride I1- Iodide

Predicting Ionic Charges Stable noble gases do not form ions! Group 8A:

Predicting Ionic Charges Some transition elements have only one possible charge: Silver = Ag+ Zinc = Zn2+ Cadmium = Cd2+

Predicting Ionic Charges Many transition metals and Pb and Sn (Group 4A) have more than one possible charge. Iron (III) = Fe3+ Iron (II) = Fe2+

Predicting Ionic Charges For transition metals and Pb and Sn: use a Roman numeral to show the charge Iron (II) = Fe2+ Iron (III) = Fe3+ Roman numerals: III 3 VII 7 IV 4 VIII 8 I 1 V 5 IX 9 II 2 VI 6 X 10

Ion Size Metals lose electrons Cations are always smaller than the original atoms. When a sodium atom loses an electron, it becomes a positively charged ion. When a chlorine atom gains an electron, it becomes a negatively charged ion. Interpreting Diagrams What happens to the protons and neutrons during these changes? Na+ has valence electrons in energy level 2 more pull on valence electrons – smaller ion.

Ions Non-metals gain electrons Anions are always larger than the original atoms. When a sodium atom loses an electron, it becomes a positively charged ion. When a chlorine atom gains an electron, it becomes a negatively charged ion. Interpreting Diagrams What happens to the protons and neutrons during these changes? More electrons, more repulsion, so electrons “spread out”: larger atom.

ISOELECTRIC SERIES N3- O2- F- He Na+ Mg2+ Al3+ Each has 10 electrons. “Isoelectronic” means ions/atoms with the same number of electrons. N3- O2- F- He Na+ Mg2+ Al3+ Each has 10 electrons. This diagram lists the atomic radii of seven nonmetals. An atomic radius is half the distance between the nuclei of two atoms of the same element when the atoms are joined.

ISOELECTRIC SERIES N3- O2- F- He Na+ Mg2+ Al3+ Each has 10 electrons. What is the trend of atomic size for these isoelectric atoms/ions? largest smallest N3- O2- F- He Na+ Mg2+ Al3+ Each has 10 electrons. This diagram lists the atomic radii of seven nonmetals. An atomic radius is half the distance between the nuclei of two atoms of the same element when the atoms are joined. Decreasing radius with increasing # of protons. (Due to stronger pull from MORE protons.)

Naming Ions NAMING CATIONS (+ metal ions): 04/10/99 NAMING CATIONS (+ metal ions): Write the name of the metal. Ca2+ = calcium ion Li+ = lithium ion NAMING ANIONS (- non-metal ions): Root name of element plus “ide”. Cl- = chloride ion O2- = oxide ion

Naming Ions 04/10/99 Transition Metals (and Pb & Sn) use Roman Numeral for charge Cobalt (II) Cobalt (V) Nickel (III) Co2+ Co5+ Ni3+

Write symbols for these ions: Titanium (III) ion Silver ion Copper (II) ion Chromium (IV) ion Nickel (I) ion Chromium (VI) ion Ti3+ Ag+ Cu2+ Cr4+ Ni+ Cr6+

Chemical Bonds Three basic types of bonds Ionic Covalent Metallic Between a metal and nonmetal Attraction between positive and negative ions Transfer of electrons from one atom to another Covalent Sharing of electrons Two nonmetal atoms Metallic Two or more metal atoms © 2009, Prentice-Hall, Inc.

Ionic Bonding Electrons are transferred from the metal ion (CATION) to a a nonmetal ion (ANION).

Ionic Bonding: The Formation of Sodium Chloride Sodium has 1 valence electron Chlorine has 7 valence electrons An electron transferred gives each an octet Na: 1s22s22p63s1 Cl: 1s22s22p63s23p5

Ionic Bonding: The Formation of Sodium Chloride This transfer forms ions, each with an octet: Na+ 1s22s22p6 Cl- 1s22s22p63s23p6

Ionic Bonding: The Formation of Sodium Chloride The resulting ions come together due to electrostatic attraction (opposites attract): Na+ Cl- The net charge on the compound must equal zero

Ionic bonding (Li + Cl) Lithium loses 1 electron; 04/10/99 Lithium loses 1 electron; chlorine gains 1 electron Li Cl [ Cl ]– [Li]+

Ionic bonding: Mg + O Magnesium loses 2 electrons; 04/10/99 Magnesium loses 2 electrons; oxygen gains 2 electrons O Mg [ O ]2– [Mg]2+

Writing Ionic Compound Formulas Formulas tell how many of each ion is present in a formula. Use subscripts to indicate the number of ions. The overall charge of a compound must be ZERO. Fe3+ Cl- Cl- Cl- Iron (III) chloride The formula is FeCl3

Formation of Ionic Compounds - Each calcium loses 2 electrons; each chlorine atoms gain 1 electron each - Overall charge has to be ZERO, so you need TWO chlorides (Cl-) for every one calcium ion Ca2+

Writing Ionic Compound Formulas Example: Beryllium fluoride 1. Write the symbols for the cation and anion, including CHARGES! Be2+ F- 2 1 2. Check to see if charges are balanced. Now balanced. Not balanced! 3. Balance charges , if necessary, using subscripts. Use the criss-cross method to balance subscripts. = BeF2

Writing Ionic Compound Formulas Example: Aluminum sulfide 1. Write the symbols for the cation and anion, including CHARGES! Al3+ S2- 2 3 2. Check to see if charges are balanced. Now balanced. Not balanced! = Al2S3 3. Balance charges , if necessary, using subscripts. Use the criss-cross method to balance subscripts.

Writing Ionic Compound Formulas Example: Magnesium Oxide 1. Write the symbols for the cation and anion, including CHARGES! Mg2+ O2- 2. Check to see if charges are balanced. Balanced! = MgO 3. If they’re already balanced, you don’t need to do the criss-cross method. Just write the element symbols. (Use the lowest whole number ratio of subscripts: 1: 1)

Writing Ionic Compound Formulas

Polyatomic ions are… Groups of atoms that stay together, have an overall charge, and one name. Usually end in –ate or -ite Acetate: CH3COO- Carbonate: CO32- Sulfate: SO42- Sulfite: SO32- Nitrate: NO3- Nitrite: NO2- Phosphate: PO43- Phosphite: PO33-

More Common Polyatomic Ions The two polyatomic ions ending in –ide: Hydroxide: OH- Cyanide: CN- Ammonium: NH4+ (One of the few positive polyatomic ions)

Writing Ionic Compound Formulas Example: Magnesium carbonate 1. Write the symbols for the cation and anion, including CHARGES! Mg2+ CO32- 2. Check to see if charges are balanced. They are balanced! = MgCO3

Writing Ionic Compound Formulas Example: Barium nitrate 1. Write the symbols for the cation and anion, including CHARGES! ( ) Ba2+ NO3- 2 1 2. Check to see if charges are balanced. Now balanced. Not balanced! 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance subscripts. = Ba(NO3)2

Writing Ionic Compound Formulas Example: Ammonium sulfate ( ) 1. Write the symbols for the cation and anion, including CHARGES! NH4+ SO42- 2 1 Now balanced. 2. Check to see if charges are balanced. Not balanced! = (NH4)2SO4 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance subscripts.

Writing Ionic Compound Formulas Example: Zinc hydroxide 1. Write the symbols for the cation and anion, including CHARGES! ( ) Zn2+ OH- 1 2 Now balanced. 2. Check to see if charges are balanced. Not balanced! = Zn(OH)2 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance subscripts.

Writing Ionic Compound Formulas Example: Aluminum phosphate 1. Write the symbols for the cation and anion, including CHARGES! Al3+ PO43- 2. Check to see if charges are balanced. They ARE balanced! = AlPO4

Naming Ionic Compounds Name the cation first, then anion CaCl2 = calcium chloride For transition metals use a Roman numeral in the name: PbCl2 = lead (II) chloride Polyatomic anion: (NH4)2SO4 = ammonium sulfate

Practice by writing the name for polyatomic ions Circle the anion and cation in each compound MgSO4 NH4Cl AlPO4 Magnesium sulfate Ammonium chloride Aluminum phosphate

Hints: If you need more than one polyatomic ion to balance the charges put ( ) around the ion. If anions end in -ide they are monoatomic [Except OH-, hydroxide & CN-, cyanide] If anion ends in -ate or –ite, then it is polyatomic

Properties of Ionic Compounds Solid ionic compounds are arranged in a 3-D crystalline pattern = CRYSTAL LATTICE They have very high melting points Sodium cations and chloride anions form a repeating three-dimensional array in sodium chloride (NaCl). Inferring How does the arrangement of ions in a sodium chloride crystal help explain why the compound is so stable?

Properties of Ionic Compounds Ionic compounds can conduct an electric current when melted or dissolved in water. When sodium chloride melts, the sodium and chloride ions are free to move throughout the molten salt. If a voltage is applied, positive sodium ions move to the negative electrode (the cathode), and negative chloride ions move to the positive electrode (the anode). Predicting What would happen if the voltage was applied across a solution of NaCl dissolved in water?