Section 6.3 “Ionic Bonding and Ionic Compounds” Pre-AP Chemistry

Sec 6.3 Vocabulary ionic compound formula unit lattice energy polyatomic ion

Chapter 6 Section 3 Ionic Bonding and Ionic Compounds Objectives Compare a chemical formula for a molecular compounds with one for an ionic compound. Discuss the arrangements of ions in crystals. Define lattice energy and explain its significance. List and compare the distinctive properties of ionic and molecular compounds. Write the Lewis structure for a polyatomic ion given the identity of the atoms combined and other appropriate information.

Ionic Compounds Most of the rocks and minerals that make up Earth’s crust consist of positive and negative ions held together by ionic bonding. example: table salt, NaCl, consists of sodium and chloride ions combined in a one-to-one ratio— Na+Cl–—so that each positive charge is balanced by a negative charge. An ionic compound is composed of positive and negative ions that are combined so that the numbers of positive and negative charges are equal.

Ionic Compounds Most ionic compounds exist as crystalline solids. A crystal of any ionic compound is a three-dimensional network of positive and negative ions mutually attracted to each other. In contrast to a molecular compound, an ionic compound is not composed of independent, neutral units that can be isolated.

Ionic Compounds, continued The chemical formula of an ionic compound represents not molecules, but the simplest ratio of the compound’s ions. A formula unit is the simplest collection of atoms from which an ionic compound’s formula can be established.

Ionic Vs. Covalent Bonding

D. Ionic vs Covalent (molecular) Bond Composition Chemical Formula Melting/boiling point State at room temperature transfer e- (lost and gained) share e- non-metal metal non-metal formula unit (ratio) molecular formula (actual) high low crystalline solid liquids and gases

Ionic Compound MAIN IDEA: Ionic bonds form from attractions between positive and negative ions - cation and anion

Describe how cations form. Section 6.3 - Ions OBJECTIVE: Describe how cations form.

Formation of Cations Metals lose electrons to attain a noble gas configuration. They make positive ions (cations) If we look at the electron configuration, it makes sense to lose electrons: Na 1s22s22p63s1 1 valence electron Na1+ 1s22s22p6 This is a noble gas configuration with 8 e- in the outer level.

Electron Dots For Cations Metals will have few valence electrons (usually 3 or less); calcium has only 2 valence electrons Ca

Electron Dots For Cations Metals will have few valence electrons Metals will lose the valence electrons Ca

Electron Dots For Cations Metals will have few valence electrons Metals will lose the valence electrons Forming positive ions Ca2+ This is named the “calcium ion”. NO DOTS are now shown for the cation.

Electron Dots For Cations Let’s do Scandium, #21 The electron configuration is: 1s22s22p63s23p63d14s2 Thus, it can lose 2e- (making it 2+), or lose 3e- (making 3+) Sc = Sc2+ Sc = Sc3+ Scandium (II) ion Scandium (III) ion

Electron Dots For Cations Let’s do Silver, element #47 Predicted configuration is: 1s22s22p63s23p64s23d104p65s24d9 Actual configuration is: 1s22s22p63s23p64s23d104p65s14d10 Ag = Ag1+ (can’t lose any more, charges of 3+ or greater are uncommon)

Electron Dots For Cations Silver did the best job it could, but it did not achieve a true Noble Gas configuration Instead, it is called a “pseudo-noble gas configuration”

OBJECTIVE: -Atoms of the metallic elements tend to loose their valence e-, leaving a complete octet in the next-lowest energy level

Explain how anions form. Section 6.3 - Ions OBJECTIVES: Explain how anions form.

Electron Configurations: Anions Nonmetals gain electrons to attain noble gas configuration. They make negative ions (anions) S = 1s22s22p63s23p4 = 6 valence electrons S2- = 1s22s22p63s23p6 = 8 = noble gas configuration. Halide ions are negative ions from chlorine or other halogens that gain electrons

Electron Dots For Anions Nonmetals will have many valence electrons (usually 5 or more) They will gain electrons to fill outer shell. 3- P (This is called the “phosphide ion”, and should show dots)

Stable Electron Configurations All atoms react to try and achieve a noble gas configuration. Noble gases have 2s and 6p electrons. 8 valence electrons = already stable! This is the octet rule (8 in the outer level is particularly stable). Ar

Ions Atoms of some non-metallic elements tend to gain e- or share e- with other nonmetallic elements to achieve a complete octet An atom’s loss of valence e- produces a cation, or positively charged ion The gain of negatively charged e- by a neutral atom produces an anion

Practice Give the name and symbol of the ion formed when a. A sulfur atom gains two electrons sulfide ion, S2- b. An aluminum atom loses three electrons aluminum ion, Al3+

Practice How many electrons are lost or gained in forming each ion? a. Ba2+ b. As3- c. Cu2+ 2 e- lost 3 e- gained 2 e- lost

Sec 6.3 Practice problems 1. Write the name and symbol of the ions formed by the elements: sulfur aluminum calcium nitrogen bromine f. potassium g. oxygen h. phosphorus i. fluorine j. hydrogen

“Perhaps one of you gentlemen would mind telling me just what it is outside the window that you find so attractive…?”

Section 6.3 Ionic Bonds and Ionic Compounds OBJECTIVES: Explain the electrical charge of an ionic compound.

Section 6.3 Ionic Bonds and Ionic Compounds OBJECTIVES: Describe three properties of ionic compounds.

Ionic Bonding Anions and cations are held together by opposite charges (+ and -) Ionic compounds are called salts. Simplest ratio of elements in an ionic compound is called the formula unit. The bond is formed through the transfer of electrons (lose and gain) Electrons are transferred to achieve noble gas configuration.

Ionic Bonding Na Cl The metal (sodium) tends to lose its one electron from the outer level. The nonmetal (chlorine) needs to gain one more to fill its outer level, and will accept the one electron that sodium is going to lose.

Ionic Bonding Na+ Cl - Note: Remember that NO DOTS are now shown for the cation!

Ionic Bonding Lets do an example by combining calcium and phosphorus: Ca P All the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable).

Ionic Bonding Ca P

Ionic Bonding Ca2+ P

Ionic Bonding Ca2+ P Ca

Ionic Bonding Ca2+ P 3- Ca

Ionic Bonding Ca2+ P 3- Ca P

Ionic Bonding Ca2+ P 3- Ca2+ P

Ionic Bonding Ca Ca2+ P 3- Ca2+ P

Ionic Bonding Ca Ca2+ P 3- Ca2+ P

Ionic Bonding Ca2+ Ca2+ P 3- Ca2+ P 3-

= Ca3P2 Ionic Bonding Formula Unit This is a chemical formula, which shows the kinds and numbers of atoms in the smallest representative particle of the substance. For an ionic compound, the smallest representative particle is called a: Formula Unit

Ionic Compound MAIN IDEA: Differences in attraction strength give ionic and molecular compounds different properties

Formation of Ionic Compounds, continued In an ionic crystal, ions minimize their potential energy by combining in an orderly arrangement known as a crystal lattice. Attractive forces exist between oppositely charged ions within the lattice. Repulsive forces exist between like-charged ions within the lattice. (electrons repel each other) The combined attractive and repulsive forces within a crystal lattice determine: the distances between ions the pattern of the ions’ arrangement in the crystal

Characteristics of Ion Bonding in a Crystal Lattice Chapter 6 Section 3 Ionic Bonding and Ionic Compounds Characteristics of Ion Bonding in a Crystal Lattice Click below to watch the Visual Concept. Visual Concept

NaCl and CsCl Crystal Lattices Chapter 6 Section 3 Ionic Bonding and Ionic Compounds NaCl and CsCl Crystal Lattices

NaCl CsCl TiO2

Lattice Energy Chapter 6 Section 3 Ionic Bonding and Ionic Compounds Click below to watch the Visual Concept. Visual Concept

Properties of Ionic Compounds Ionic Compounds are electrically neutral – charges of the cations and anions balance Crystalline solids - a regular repeating arrangement of ions in the solid: Fig. 3.3-5 Ions are strongly bonded together. Structure is rigid. 3) High melting points Coordination number- number of ions of opposite charge surrounding it

Do they Conduct? Conducting electricity means allowing charges to move. In a solid, the ions are locked in place. Ionic solids are insulators. When melted, the ions can move around. 4) Melted ionic compounds conduct. NaCl: must get to about 800 ºC. Dissolved in water, they also conduct (free to move in aqueous solutions)

- Page 198 The ions are free to move when they are molten (or in aqueous solution), and thus they are able to conduct the electric current.

E. Properties of Ionic Compounds Although they are composed of ions, ionic compounds are electrically neutral. Most ionic compounds are crystalline solids at room temperature (crystals, salts). Ionic compounds generally have high melting points Ionic compounds can conduct an electric current when melted or dissolved in water

A Comparison of Ionic and Molecular Compounds Section 3 Ionic Bonding and Ionic Compounds Chapter 6 A Comparison of Ionic and Molecular Compounds The force that holds ions together in an ionic compound is a very strong electrostatic attraction. In contrast, the forces of attraction between molecules of a covalent compound are much weaker. This difference in the strength of attraction between the basic units of molecular and ionic compounds gives rise to different properties between the two types of compounds.

A Comparison of Ionic and Molecular Compounds Chapter 6 Section 3 Ionic Bonding and Ionic Compounds A Comparison of Ionic and Molecular Compounds Molecular compounds have relatively weak forces between individual molecules. They melt at low temperatures. The strong attraction between ions in an ionic compound gives ionic compounds some characteristic properties, listed below. very high melting points hard but brittle not electrical conductors in the solid state, because the ions cannot move

Ionic solids are brittle Force + -

Ionic solids are brittle Strong Repulsion breaks a crystal apart, due to similar ions being next to each other. + - Force + - + - + -

Polyatomic Ions Certain atoms bond covalently with each other to form a group of atoms that has both molecular and ionic characteristics. A charged group of covalently bonded atoms is known as a polyatomic ion. Like other ions, polyatomic ions have a charge that results from either a shortage or excess of electrons.

Polyatomic Ions An example of a polyatomic ion is the ammonium ion: . It is sometimes written as to show that the group of atoms as a whole has a charge of 1+. The charge of the ammonium ion is determined as follows: The seven protons in the nitrogen atom plus the four protons in the four hydrogen atoms give the ammonium ion a total positive charge of 11+.

Polyatomic Ions, continued The charge of the ammonium ion is determined as follows, continued: When nitrogen and hydrogen atoms combine to form an ammonium ion, one of their electrons is lost, giving the polyatomic ion a total negative charge of 10–. The total charge is therefore (11+) + (10–) = 1+.

Polyatomic Ion MAIN IDEA: Multiple atoms can bond covalently to form a single ion.

Sec 6.3 Vocabulary ionic compound formula unit lattice energy polyatomic ion

Chapter 6 Section 3 Ionic Bonding and Ionic Compounds Objectives Compare a chemical formula for a molecular compounds with one for an ionic compound. Discuss the arrangements of ions in crystals. Define lattice energy and explain its significance. List and compare the distinctive properties of ionic and molecular compounds. Write the Lewis structure for a polyatomic ion given the identity of the atoms combined and other appropriate information.

6.3 Practice problems p. 201 #24 #

Sec 6.3 Practice problems p. 201 #24

End of Section 6.3