Topic 4: Chemical Bonds. IB Chemistry SL Ms. Kiely Coral Gables Senior High

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1 Topic 4: Chemical Bonds IB Chemistry SL Ms. Kiely Coral Gables Senior High

2 Bell-Ringer 1 Topic 3 Rebuild Quiz 15 min. Take out a PEN. Quiz next class on this slideshow; make sure to look through slides if we do not finish in class today. The 4.1 exercises in your book will be a great help!

3 Bell-Ringer Answer: B

4 Internal Assessment (IA) Experiments will be done in class one week in January. After topic 4, we have IB Prescribed labs #4(rate of reaction) and #5(thermochemistry). We will use these labs as a means of practice for the IA format. One draft will be due in February, and then the final will be due a few days after.

5 Why do atoms want to be chemically bonded? Atoms (except the noble gases) bond together in order to achieve the octet rule, which in turn means that they bond in order to be stable and expend the least amount of energy! Remember, filled orbitals lead to atoms spending less energy than when orbitals are partially filled. This is why most of our world is comprised of compounds and molecules instead of just pure elements.

6 Ionic compounds form during the process of ionization, where atoms become ions, transferring electrons between each other: a metal atom will lose its valence electrons, passing them onto a nonmetal atom which will gain them. For example, a sodium (Na) atom will transfer its one valence electron to a chlorine (Cl) atom, forming NaCl, table salt.

7 Determining the Formula of an Ionic Compound THE OVERALL CHARGE OF AN IONIC COMPOUND IS 0! ALL IONIC COMPOUNDS ARE NEUTRAL; the sum of positive charge cancels out the sum of negative charge. Therefore, writing the formula for an ionic compound involves balancing the total number of positive and negative charges so that the overall compound is neutral. Example: aluminum oxide, Al₂O₃

8 Naming Ionic Compounds -Metal atom(s) name does not change whatsoever when it becomes an ion. For example, the sodium (Na) atom becomes a cation when it loses its valence electron. It is then referred to as sodium ion. -Nonmetal atoms, however, take up the suffix -ide when they become ions. For example chlorine becomes chloride; oxygen becomes oxide To name an ionic compound, be sure to place the METAL ION FIRST. Positive ion (metal) is written first and the negative ion (nonmetal) is written second with the -ide ending. metal nonmetal-ide Example: sodium chloride (NaCl); magnesium fluoride (MgF₂)

9 Practice Determine whether the following combinations will result in an ionic compound or not. Write the formula for each of the following combinations, and then name the compound: a) potassium and bromine b) aluminum and hydrogen c) zinc (Zn) and oxygen [Exception: All group 12 elements have 2 valence electrons and form predictable ions]

10 Practice ANSWERS a) KBr = potassium bromide b) AlH₃ = aluminium hydride c) ZnO = zinc oxide

11 Alkali Metals Alkaline Earth Metals Transition metals Lanthanoides Actinoides Post-Transition Metals Metalloids Other nonmetals Noble gases Hydrogen

12 Compounds containing Transition & Post-Transition Metals! Recall that transition and post-transition metals can form more than one type of ion. Additionally, the ions they form are not necessarily predictable based on their group numbers. Common transition post-transition metal ions used in IB:

13 How to Name Transition & Post-Transition Metals! The Stock System is used to name ionic compounds that contain transition and post-transition metal ions. Since transition and post-transition metals can lose different amounts of electrons and consequently form different ions, the Stock System helps us ensure that we know which metal ion is part of the ionic compound. A Roman numeral in parentheses is written directly next to the name of the metal, indicating the amount of valence electrons lost by that metal. For example: the cation Fe²+ is named iron(ii) ion and the iron(iii) ion has the following formula Fe³+

14 Practice 1. Write the formula or name for each of the following: a) copper(i) selenide b) copper(ii) bromide c) Cr₂S₃ d) Ni₃N

15 Polyatomic Ions Some covalent molecules are charged. We refer to these as polyatomic ions since they are made up of more than one atom and together have experienced a loss or gain of electrons, consequently making the overall molecule charged instead of neutral. These polyatomic ions must be memorized. Any of these can act as the anion (or cation in the case of Ammonium) in an ionic compound.

16 Practice Write the formula for each of the following: a) sodium sulfate b) copper(ii) bromide c) chromium(iii) sulfate

17 ANSWERS a) Na₂SO₄ sodium sulfate b) CuBr₂ copper(ii) bromide c) Cr₂(SO₄)₃ chromium(iii) sulfate

18 Practice 1. Name the following compounds: a) Sn₃(PO₄)₂ b) Ti(SO₄)₂ c) Mn(HCO₃)₂ d) BaSO₄ e) Hg₂S 2. Write the formula for ammonium phosphate.

19 ANSWERS 1. Name the following compounds: a) Sn₃(PO₄)₂ Tin(II) phosphate b) Ti(SO₄)₂ Titanium(IV) sulfate c) Mn(HCO₃)₂ Manganese(II) hydrogencarbonate d) BaSO₄ Barium sulfate e) Hg₂S Mercury(I) sulfide 2. Ammonium phosphate (NH₄)₃PO₄

20 4.1 Physical Properties of Ionic Compounds 1. Ionic compounds have lattice structures The forces of electrostatic attraction between ions in a compound cause them to surround themselves with ions of opposite charge. As a result, the ionic compound takes on a predictable 3-d crystalline structure known as an ionic lattice. The layout of the lattice depends largely on the size of the ions in the compound, but it always involves this fixed arrangement of ions based on a repeating unit.

21 The term coordination number is used to express the number of ions that surround a given ion in the lattice. For example, in the sodium chloride lattice (pictured here), the coordination number is six because each Na+ ion is surrounded by six Cl ions and vice versa. Note that an ionic lattice consists of a very large number of ions and it can grow indefinitely! However, we always report the simplest ratio of ions in the formula of an ionic compound. Ionic compounds do not exist as units with a fixed number of ions, their formulas are simply an expression of the ratio of ions present. We call this simplest ratio formula a formula unit.

22 Physical Properties of Ionic Compounds 2. Ionic Compounds have high melting points and high boiling points due to the strength of ionic bonds. The force of the electrostatic attraction between ions in an ionic compound are very strong and therefore require large amounts of heat to break. The melting and boiling points are generally higher when the charge on the ions is greater, due to increased attraction between the ions. The high melting points of ionic compounds become an economic consideration for many industrial processes since such high temperatures are needed to melt ionic substances in order to extract them.

23 Physical Properties of Ionic Compounds 3. Due to their strong bonds, ionic compounds are solids at room temperature.

24 Physical Properties of Ionic Compounds 4. Ionic compounds have low volatility, and typically have low odor. Volatility is a term used to describe the tendency of a substance to vaporize. Since ionic compounds are held together with strong attractive forces, and thus require high temperatures to boil, they in effect have a low tendency to vaporize.

25 Physical Properties of Ionic Compounds 5. Ionic compounds are generally soluble in ionic or polar solvents, but not soluble in nonpolar solvents. Solubility refers to the ease with a solid (the solute) dissolves in a liquid (the solvent) to form a solution. As the Na+ and Cl ions separate from the ionic lattice, they become surrounded by water molecules and are said to be hydrated. When this happens, the solid is dissolved*. *If a liquid other than water is able to dissolve the solid, the ions are said to be solvated.

26 Physical Properties of Ionic Compounds 6. Ionic compounds do not conduct electricity in the solid state, but conduct when molten (l) or in aqueous solution (aq) (dissolved/solvated). The ability of a compound to conduct electricity depends on whether it contains ions that are able to move and carry a charge. Ionic compounds cannot conduct electricity in solid form where the ions are held within the lattice and limited in movement. However, if molten or dissolved, the ions are let loose, allowing for the flow of the ions. Electricity = flow of electrons Anions flowing = electricity

27 Physical Properties of Ionic Compounds 7. Ionic compounds are usually brittle, which means the crystal tends to shatter when force is applied. Ionic compounds are NOT malleable like metals. Applying too much pressure on an ionic solid will cause movement of the ions within the lattice towards ions of the same charge. The repulsive forces will cause the ions to split! Video: Ionic Properties