Topic 4: Chemical Bonds IB Chemistry SL Ms. Kiely Coral Gables Senior High
Bell-Ringer 1
Bell-Ringer Answer: B
ANNOUNCEMENT Quiz next WEEK, Thursday 1/31/19, on ionic formulas and naming ionic compounds ANSWERS for the exercises from the book, are already uploaded on the website as Topic_4_Book_Answers
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.
Ionic Compounds Ionic compounds are held together with ionic bonds! Ionic compounds tend to be made up of metals and nonmetals. DEFINITION OF IONIC BOND: Force of attraction between cations (+) and anions (-). Ionic compounds are electrically neutral, despite being made up of ions.
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.
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)
Be sure to write the name of the METAL ION FIRST. Then, write the name of the nonmetal with the suffix -ide. Examples: a) KBr b) AlH₃ c) ZnO How to Name an Ionic Compound metal nonmetal-ide
Practice Write the ionic formula for each of the following chemical combinations: ANSWERS: a) potassium bromide b) Aluminum hydride c) Zinc oxide
Determining the CHEMICAL FORMULA of an Ionic Compound The ionic bond is a result of an electrostatic attraction between oppositely charged ions. WHEN THE IONS BOND TOGETHER, THEY FULFILL EACH OTHER S INSTABILITY! EACH ATOM THEREFORE BECOMES AN ION TO BECOME STABLE. THIS MEANS THE OVERALL CHARGE OF AN IONIC COMPOUND IS 0! ALL IONIC COMPOUNDS ARE NEUTRAL. 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.
Ionic Formulas must be in SIMPLEST RATIO Form the ionic compound between magnesium and oxygen: Mg²+ O² Mg₂O₂ MgO Ionic Compounds must be in simplest form!
Practice Write the ionic formula for each of the following combinations: a) potassium and oxygen b) aluminum and nitrogen
Practice ANSWERS: a) K₂O potassium oxide b) AlN aluminum nitride
Alkali Metals Alkaline Earth Metals Transition metals Lanthanoides Actinoides Post-Transition Metals Metalloids Other nonmetals Noble gases Hydrogen
Transition Metals & Post-Transition metals as Ions We have been discussing how elements lose or gain valence electrons in order to become stable, consequently becoming ions. They lose or gain valence electrons depending on which scenario is spends the least amount of energy. Since metals tend to have few valence electrons, it makes energetic sense for them to lose them. However, nonmetals tend to have many valence electrons, making it easier for them to gain a few more and complete an octet instead of trying to lose each one.
Transition Metals & Post-Transition metals as Ions Using the periodic table, it is easy to predict the ions that elements will make because you can refer to their group number for the amount of valence electrons. For transition metals, though, it is difficult to predict the ion that will form from its position in the periodic table because they can actually lose different amounts of electrons from their d-orbitals, and so are able to form more than one type of ion. Iron, Fe, for example, can form two ions by either losing 2 valence electrons or 3, depending on the reacting conditions. The two ions have distinct properties, such as forming compounds with different colors.
How to Name Transition & Post-Transition Metals! Two methods are used to name transition and post-transition metals. This is called the Stock System, which places a Roman numeral in parentheses directly after the name of the metal in order to indicate the amount of valence electrons lost. For example: the cation Fe²+ is named iron(ii) ion and the iron(iii) ion has the following formula Fe³+
Practice Write the symbols and names for the following ions: 1. potassium 2. tin (2 electrons lost) 3. cobalt (3 electrons lost) 4. iron (4 electrons lost)
Answers 1. potassium 2. tin (2 electrons lost) 3. cobalt (3 electrons lost) 4. iron (4 electrons lost) ANSWERS: 1. K+, potassium ion 2. Sn²+, tin(ii) ion 3. Co³+, cobalt(iii) ion 4. Fe⁴+, iron(iv) ion
Practice 1. Write the formula for each of the following: a) copper(i) selenide b) copper(ii) bromide c) chromium(iii) sulfide d) nickel(i) nitride
Answers 1. Write the formula for each of the following: a) Cu₂Se b) CuBr₂ c) Cr₂S₃ d) Ni₃N
Practice 1. Write the NAME for each of the following: a) CuN b) Cu₂S c) CuF₃ d) Cu₃N₂
Answer 1. Write the NAME for each of the following: a) CuN - copper(iii) nitride b) Cu₂S - copper(i) sulfide c) CuF₃ - copper(iii) fluoride d) Cu₃N₂ - copper(ii) nitride
Practice Write the NAME for each of the following: a) FeN b) Ni₂S c) CrF₃ d) Fe₃N₂
Answer Write the NAME for each of the following: a) FeN - iron(iii) nitride b) Ni₂S - nickel(i) sulfide c) CrF₃ - chromium(iii) fluoride d) Fe₃N₂ - iron(ii) nitride
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. Nitrite NO₂ Sulfite SO₃² Phosphite PO₃³ 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.
Practice 1. Name the following compounds: a) Sn₃(PO₄)₂ b) Ti(SO₄)₂ c) Mn(HCO₃)₂ d) BaSO₄ 2. Write the formula for ammonium phosphate.
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 2. Ammonium phosphate (NH₄)₃PO₄
Practice Name the following ionic compounds: 1) Ni(NO₃)₃ 2) NiNO₃ 3) Ni(NO₃)₂ 4) Sn₂(SO₄) 5) Sn(SO₃)₂
1) Ni(NO₃)₃ Nickel(III) nitrate 2) NiNO₃ Nickel(I) nitrate 3) Ni(NO₃)₂ Nickel(II) nitrate 4) Sn₂(SO₄) Tin(I) sulfate 5) Sn(SO₃)₂ Tin(IV) sulfite Answer