Unit 2: Chemical Bonds. Pre-IB Chemistry Ms. Kiely Coral Gables Senior High

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1 Unit 2: Chemical Bonds Pre-IB Chemistry Ms. Kiely Coral Gables Senior High

2 QUIZ! Take out a PEN Sit in Quiz seats :) Timed 20 minutes

3 Bell-Ringer Which types of elements combine chemically to make an ionic compound? A. Nonmetals only B. Metals and nonmetals C. Metals only

4 Answer Which types of elements combine chemically to make an ionic compound? A. Nonmetals only B. Metals and nonmetals C. Metals only Answer: B. Metals and nonmetals

5 Chemical Bonds Everything in our physical world is made up of atoms. How is it that only 118 (and really only about 100 of them) make up everything you and I have ever known? Atoms chemically combine in whole number ratios to form molecules and compounds. These chemical combinations have different properties from the singular elements that form them.

6 How do atoms try to achieve the octet rule and become stable? They bond with other atoms! By sharing valence electrons with each other, or by transferring valence electrons with each other, atoms can achieve the octet rule and become stable. This is why most of our world is comprised of compounds and molecules instead of just pure elements. The three types of bonds you will be introduced to in Ch.7 and 8 are ionic bonds, metallic bonds, and covalent bonds.

7 Ions As we learned in Unit 1, an ion is a charged atom. Ions form from atoms by losing or gaining valence electrons.

8 Ionic Compounds -Ionic compounds are held together with ionic bonds! Ionic bonds are therefore forces of attraction between cations (+) and anions (-). -This means ionic bonds form between nonmetals and metals. (Whereas, for instance, a covalent bond is a bond between nonmetals, and a metallic bond is a bond between metals.) -Ionic compounds are electrically neutral, despite being made up of ions.

9 Ionic compounds form during the process of ionization, where electrons are transferred between atoms: 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.

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11 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!

12 Determining the CHEMICAL FORMULA of an Ionic Compound The ionic bond is therefore 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.

13 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

14 Practice Write the ionic formula for each of the following chemical combinations: ANSWERS: a) potassium bromide b) Aluminum hydride c) Zinc oxide

15 Practice Write the ionic formula for each of the following combinations: a) potassium and oxygen b) aluminum and nitrogen

16 Practice ANSWERS: a) K₂O b) AlN

17 Ionic Compounds Q

18 PRACTICE: Solve for the chemical formulas of the following ionic combinations. Also, deduce the name of each one. 1) a compound that contains calcium (Ca) and chlorine (Cl) 2) a compound that contains aluminium (Al) and bromine (Br) 3) a compound that contains rubidium (Rb) and sulfur (S) 4) Explain what happens to the electron configurations of Mg and Br when they react to form the compound magnesium bromide.

19 ANSWERS 1) CaCl₂ calcium chloride 2) AlBr₃ aluminium bromide 3) Rb₂S rubidium sulfide 4) Mg: electron configuration [Ne]3s² Br: electron configuration [Ar]3d¹⁰4s²4p⁵ The magnesium atom loses its two electrons from the 3s orbital to form Mg²+. Two bromine atoms each gain one of the Mg valence electrons into their 4p subshell to form Br. The ions attract each other by electrostatic forces and form MgBr₂.