An Experiment too Dangerous to do in class… http://www.youtube.com/watch?v=ZjyRhH7PW24

Unit 4 – Chemical Bonding

Two Kinds of Bonding Ionic Bonding: Involves a transfer of electrons. One element loses electrons and the other gains electrons. Covalent Bonding: (we’ll talk about this later on)

Ionic Bonds Forces of attraction bind oppositely charged ions together Must be electrically neutral Positive charges equal negative charges

Example – Sodium Chloride

What is the key to Ionic Bonding? Octet Rule: Atoms will gain or lose enough electrons to make them isoelectronic with a noble gas. Except for He, there will be 8 electrons in their outermost s & p orbitals.

Ionic Bonds Always a metal (positive charge or “cation”) + non-metal (negative charge or “anion”) Look at valence electrons!

Electron Dot Structures A way to show the number of valence electrons in an atom Valence electrons must be labeled like this: X 4 6 3 1 2 7 5 8

The number of v.e. can be determined by the group 1 2 13 14 15 16 17 18 v.e. 1 2 3 4 5 6 7 8 Dot strux • : • • : • • : • • : : • • • : : Li • Be : • • • : • N B C O F Ne

Valence electrons determine chemical reactivity Elements in the same group behave the same! Group # 1 2 13 14 15 16 17 18 Electron activity Lose 1 Lose 2 Lose 3 Lose or gain 4 Gain 3 Gain 2 Gain 1 X Oxidation # +1 +2 +3 +4/-4 -3 -2 -1 X

Ionic Bonds Ionic bonds are not true “bonds”, which are shared electrons. Cations and anions align to form a crystal lattice

To write the formula write the metal first, then the non metal… Ionic Bonds Use electron dot structures to predict the compounds that would form between Mg and Cl: Mg -1 : . • Cl +2 To write the formula write the metal first, then the non metal… : : . -1 MgCl2 Cl •

Try Another! Use electron dot structures to predict the compounds that would form between Na and P: Na P Na . . . : . . . Na3P

Ionic Bonds Ionic bonds are not true bonds, but ratios of cations to anions. Formula unit shows lowest whole number ratio of ions in an ionic compound. Also called the Empirical Formula. Examples: NaCl – 1:1 MgCl2 – 1:2 AlBr3 – 1:3

Ionic Bonds When naming anions, change the suffix to “-ide” Examples: Cl- : Chloride Br- : Bromide O-2 : Oxide P-3 : Phosphide

How do you know when a bond is an Ionic Bond? We can look at the differences in (EN) electronegativity of each atom involved in the bond. If EN > 1.7, then it is ionic.

Properties of Ionic Compounds They have a very high melting points. They are solids and crystal shape at room temperature. They conduct electric current when melted or dissolved in water (electrolytes) Most of them are able dissolved in water

A) A two-dimensional cross section of a sodium chloride crystal is shown. (B) When struck by a hammer, the negatively-charged chloride ions are forced near each other. (C) The repulsive force causes the crystal to shatter.

(A) Distilled water does not conduct electricity (A) Distilled water does not conduct electricity. (B) A solid ionic compound is also not very conductive. (C) A solution of an ionic compound dissolved in water conducts electricity well.

In an ionic solution, the A+ ions migrate toward the negative electrode, while the B- ions migrate toward the positive electrode.

Naming Compounds A Love story…

Ionic Charges and the Octet Rule All atoms want to have noble gas electron configuration (8 valence, except H) To do this, they gain or lose electrons. If the number of valence e- is smaller than 4, e- are lost, and a cation is formed. If the number of valence e- is greater than 4, e- are gained, and an anion is formed.

Ionic charges of elements For metals in groups 1, 2, and 13, refer to the group number to find the charge Group 1 – What charge do they form? 1+ (Li+, Na+, K+) Group 2 – What charge do they form? 2+ (Mg 2+, Ca2+) Group 13 – What charge do they form? 3+ (Al 3+)

Ionic charges of elements When looking at non-metals (anions), subtract to find the charge → group number minus 18 Group 17 – What charge do they form? -1 (F1-, Cl1-, Br1-) Group 16 – What charge do they form? -2 (O2-, S2-, Se2-)

Forming Binary Ionic Compounds Ionic compounds are electrically neutral To accomplish this, we balance the charges with the number of ions. The number of ions is represented with a subscript, below and to the right H2O This means I have two hydrogen ions. I have one oxygen ion (the 1 is not written)

How do we do it? It’s the old “criss-cross” Like a crossing route in football NOT THIS!

Forming Binary Ionic Compounds Let’s try to balance potassium and chlorine Potassium Chlorine K1+ Cl1- KCl

Forming Binary Ionic Compounds Let’s try to balance calcium and bromine Calcium Bromine Ca2+ Br1- You need two bromine anions with a minus 1 charge to balance the one calcium with a +2 charge CaBr2

Forming Binary ionic compounds Let’s try aluminum and oxygen Aluminum Oxygen Al3+ O2- How many oxygen and aluminum atoms will you need to obtain a net ionic charge of zero? Al2O3

Forming Binary Ionic Compounds When balancing a compound, you must keep it to the simplest whole number ratio Calcium Oxygen Ca2+ O2- Ca2O2 Must simplify! For IONIC compounds, 2:2 ratio is the same as 1:1 CaO

Naming Binary Ionic Compounds Simply say the first element, which will be a metal Change the ending of the nonmetal to –ide KCl→ Potassium Chloride CaBr2 → Calcium Bromide Al2O3 → Aluminum Oxide CaO → Calcium Oxide

DO NOW Lithium Bromide Calcium Chloride Magnesium Oxide Sodium Sulfide Strontium Nitride LiBr CaCl2 MgO Na2S Sr3N2

Naming Ionic compounds For cations that have only one possible charge the name of the metal is used. Examples: Group I metals (charge 1+), Group II metals (charge 2+), Aluminium (charge 3+), Zinc (charge 2+), Silver (charge 1+)

What about those transition metals? Some transition metals have multiple oxidation numbers Fe can lose 2 or 3 electrons Fe2+ is called Iron (II) Fe3+ is called Iron (III) Iron (II) oxide would be: FeO Iron (III) oxide would be: Fe2O3

Stock System Use a Roman numeral to refer to the oxidation state of the cation, NOT how many cations are present! Other transition metals with more than one oxidation number: Pb, Hg, Mn, Co, Cr, Cu, Ni, Sn. MUST use a Roman numeral for any metal that has more than one oxidation #, any time you use it. NEVER use a Roman numeral when there is only one oxidation #. When in doubt, check your periodic table!

Naming Binary Ionic Compounds For many transition metals, you must use Roman numerals when naming to give oxidation state of the cation (NOT how many cations are present). Do a REVERSE CRISS-CROSS to find the oxidation number! SnCl2 : Sn Cl +2 -1 2

Naming Binary Ionic Compounds Tin (II) Chloride (tin two chloride) SnCl4 is Tin (IV) Chloride (tin four chloride) Cr2O3 is Chromium (III) Oxide (chromium three oxide)

Naming Binary Ionic Compounds Be careful with oxygen! Do a reverse criss-cross Cu O You might think this is Copper (I) Oxide… But is oxygen -1? What is the name of this compound?

Naming Binary Ionic Compounds CuO is Copper (II) oxide Cu2O is Copper (I) oxide Remember to check if the cations and anions have the oxidation numbers that they should…

Try these… KBr MgI2 CaS ZnO PbF4 PbS MnO2 Potassium Bromide Magnesium Iodide Calcium Sulfide Zinc Oxide Lead (IV) Fluoride Lead (II) Sulfide Manganese (IV) Oxide

The old-fashioned way Old naming system: Fe2+ is called ferrous (lower oxidation #) Fe3+ is called ferric (higher oxidation #) Name Co+2, Co+3, Pb+2, Pb+4 This system lead to confusion. How many oxidation states does Mn have?

DO NOW Calcium Chloride Hydrogen sulfide Iron (III) nitride Chromium (III) oxide Cs2Se Cu3P CaCl2 H2S FeN Cr2O3 Cesium Selenide Copper (I) phosphide

Polyatomic Ions Polyatomic ions are ions composed of two or more atoms Most end in “-ate” or “-ite” Examples: (NO3)- = Nitrate (SO4)2- = Sulfate (ClO2)- = Chlorite

Polyatomic Ions Look on your polyatomic ion sheet to find names and charges of polyatomic ions. Learn them quickly! Treat polyatomic ions like you would treat any other ion when writing the formula for the compound.

Polyatomic Ions Whenever you need more than a single polyatomic ion to balance the formula, use parentheses. If you don’t need more than a single polyatomic ion, don’t use parentheses! When naming, simply state the name of the polyatomic ion used.

Write the formula for potassium sulfate. Potassium Sulfate K1+ (SO4)2- Polyatomic Ions Write the formula for potassium sulfate. Potassium Sulfate K1+ (SO4)2- K2SO4

Write the formula for magnesium hydroxide. Magnesium Hydroxide Polyatomic Ions Write the formula for magnesium hydroxide. Magnesium Hydroxide Mg2+ (OH)1- Mg(OH)2

Try these: NaNO3 Sodium Nitrate K2CO3 Potassium Carbonate (NH4)2S Fe(OH)3 Pb3(PO4)2 Sodium Nitrate Potassium Carbonate Ammonium Sulfide Iron (III) Hydroxide Lead (II) Phosphate

Polyatomic Ions with Varying numbers of oxygen Some Ions have very similar names. Eg. Nitrate, nitrite, etc… Start with these “normal” number of oxygen NO3- = Nitrate ClO3- = Chlorate SO42- = Sulfate PO43- = Phosphate

Polyatomic Ions with Varying numbers of oxygen If the ion has one more number of oxygen than normal, the name becomes per-(stem)-ate Example: NO3- is nitrate NO4- is pernitrate Notice – Charge remains the same

Polyatomic Ions with Varying numbers of oxygen If the ion has one less oxygen than “normal”, the name becomes (stem)-ite Example: SO42- is sulfate SO32- is sulfite Notice: Charge remains the same

Polyatomic Ions with Varying numbers of oxygen If the ion has two less oxygen than “normal”, it becomes hypo-(stem)-ite Example: ClO3- is chlorate ClO- is hypochlorite Notice: Charge is the same

Polyatomic Ions with Varying numbers of oxygen NO4- = Pernitrate NO3- = Nitrate NO2- = Nitrite NO- = Hyponitrite This is all different from N3- = Nitride

Try these… NaNO3 Mg(ClO2)2 K2SO5 Fe3(PO4)2 Pb(ClO)2 Sodium Nitrate Magnesium Chlorite Potassium Persulfate Iron (II) Phosphate Lead (II) Hypochlorite