Electron Configurations of Ions To write the electron configuration of an ion formed by a main group element: 1) Start with the configuration for the NEUTRAL atom. 2) Add or remove the appropriate number of electrons. Na: 1s 2 2s 2 2p 6 3s 1 Na + : 1s 2 2s 2 2p 6 Cl: 1s 2 2s 2 2p 6 3s 2 3p 5 Cl − : 1s 2 2s 2 2p 6 3s 2 3p 6 10 electrons total, isoelectronic with Ne 18 electrons total, isoelectronic with Ar 4.5

Write electron configurations for the following ions of main group elements: (a) N 3-, (b) Ba 2+, and (c) Be 2+. Worked Example 4.7 Worked Example 4.7 Strategy First write electron configurations for the atoms. Then add electrons (for anions) and remove electrons (for cations) to account for the charge.

Ions of d-Block Elements Ions of d-block elements are formed by removing electrons first from the shell with the highest value of n. For Fe to form Fe 2+, two electrons are lost from the 4s subshell not the 3d. Fe can also form Fe 3+, in which case the third electron is removed from the 3d subshell. Fe: [Ar]4s 2 3d 6 Fe 2+ : [Ar]3d 6 Fe: [Ar]4s 2 3d 6 Fe 3+ : [Ar]3d 5

Write electron configurations for the following ions of d-block elements: (a) Zn 2+, (b) Mn 2+, and (c) Cr 3+. Worked Example 4.8 Worked Example 4.8 Strategy First write electron configurations for the atoms. Then add electrons (for anions) and remove electrons (for cations) to account for the charge. The electrons removed from a d-block element must come first from the outermost s subshell, not the partially filled d subshell.

Ionic Radius The ionic radius is the radius of a cation or an anion. When an atom loses an electron to become a cation, its radius decreases due in part to a reduction in electron-electron repulsions in the valence shell. A significant decrease in radius occurs when all of an atom’s valence electrons are removed. 4.6

Comparing Ionic Radius with Atomic Radius When an atom gains one or more electrons and becomes an anion, its radius increases due to increased electron-electron repulsions.

Isoelectronic Series An isoelectronic series is a series of two or more species that have identical electron configurations, but different nuclear charges. O 2 − : 1s 2 2s 2 2p 6 F − : 1s 2 2s 2 2p 6 Ne: 1s 2 2s 2 2p 6 isoelectronic

Identify the isoelectronic series in the following group of species, and arrange them in order of increasing radius: K +, Ne, Ar, Kr, P 3-, S 2-, and Cl -. Worked Example 4.9 Worked Example 4.9 Strategy Isoelectronic series are species with identical electron configurations but different nuclear charges. Determine the number of electrons in each species. The radii of isoelectronic series members decreases with increasing nuclear charge. Text Practice:

Chemistry: Atoms First Second Edition Julia Burdge & Jason Overby Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 5 Ionic and Covalent Compounds M. Stacey Thomson Pasco-Hernando State College

A compound is a substance composed of two or more elements combined in a specific ratio and held together by chemical bonds. Familiar examples of compounds are water and salt (sodium chloride).Compounds 5.1

When atoms form compounds, it is their valence electrons that undergo changes. A Lewis dot symbol consists of the element’s symbol surround by dots representing its valence electrons. Each dot represents a valence electron. Boron1s 2 2s 2 2p 1 3 valence electrons B Lewis dot symbol for boron B B B other reasonable Lewis dot symbols for boron Lewis Dot Symbols 5.2

Atoms combine to achieve a more stable electron configuration. Maximum stability results when a chemical species is isoelectronic with a noble gas. Na 1s 2 2s 2 2p 6 3s 1 Na + 1s 2 2s 2 2p 6 10 electrons total, isoelectronic with Ne Cl 1s 2 2s 2 2p 6 3s 2 3p 5 Cl ‒ 1s 2 2s 2 2p 6 3s 2 3p 6 18 electrons total, isoelectronic with Ar Lewis Dot Symbols

Lewis dot symbols of the main group elements.

Lewis Dot Symbols Na O For main group metals such as Na, the number of dots is the number of electrons that are lost. For nonmetals in the second period, the number of unpaired dots is the number of bonds the atom can form. B 1s22s22p11s22s22p1 C 1s22s22p21s22s22p2 N 1s22s22p31s22s22p3 5 valence electrons; first pair formed in the Lewis dot symbol

Lewis Dot Symbols Ions may also be represented by Lewis dot symbols. Text Practice: Na Na 1s 2 2s 2 2p 6 3s 1 Na + 1s 2 2s 2 2p 6 Na + O O 1s 2 2s 2 2p 4 O 2 ‒ 1s 2 2s 2 2p 6 O 2‒2‒ Valence electron lost in the formation of the Na + ion.

Activity: For each symbol, draw a Lewis symbol and predict whether it is the most commonly found form of the element in nature. H O 3- Ca 3+ Fe 3+ K - Ar

Ionic bonding refers to the electrostatic attraction that holds oppositely charged ions together in an ionic compound. The resulting electrically neutral compound, sodium chloride, is represented with the chemical formula NaCl. The chemical formula, or simply formula, of an ionic compound denotes the constituent elements and the ratio in which they combine. Ionic Compounds and Bonding 5.3 Na + + − Cl The attraction between the cation and anion draws them together to form NaCl

Ionic Compounds and Bonding A three-dimensional array of oppositely-charged ions is called a lattice. Lattice energy is the amount of energy required to convert a mole of ionic solid to its constituent ions in the gas phase. Activity: Do Na and Cl atoms have to meet in nature to exchange electrons to form NaCl? Explain why Na explodes when placed in water − + − + − + − + − + − + − + NaCl(s)  Na + (g) + Cl − (g)  H lattice = +788 kJ/mol

Ionic Compounds and Bonding The magnitude of lattice energy is a measure of an ionic compound’s stability. Lattice energy depends on the magnitudes of the charge and on the distance between them.  d Q1Q1 Q2Q2 Q = amount of charge d = distance of separation

Ionic Compounds and Bonding The magnitude of lattice energy is a measure of an ionic compound’s stability. Lattice energy depends on the magnitudes of the charge and on the distance between them.

Ionic Compounds and Bonding

Naming Ions and Ionic Compounds

Al 3+ O 2– Al 2 O 3 For ionic compounds to be electronically neutral, the sum of the charges on the cation and anion in each formula must be zero. Aluminum oxide: Sum of charges:2(+3) + 3(–2) = 0 Formulas of Ionic Compounds

Worked Example 5.4 Strategy Identify the ions in each compound, and determine their ratios of combination using the charges on the cation and anion in each. Text Practice: Deduce the formulas of the following ionic compounds: (a) mercury(II) chloride, (b) lead(II) bromide, and (c) potassium nitride.

Study Guide for Sections , DAY 10, Terms to know: Sections , : ionic radii, isoelectronic, compound, Lewis dot symbol, ionic bonding, ionic compound, chemical formula, lattice energy DAY 10, Specific outcomes and skills that may be tested on exam 2: Sections , Be able to give a complete or abbreviated electron configuration for an ion in either its ground state or a possible excited state Be able to give a complete or abbreviated orbital diagram for an ion either its ground state or a possible excited state Be able to rank the radii of isoelectronic particles and explain your answer Be able to rank relative radii, electron affinity, and ionization energy ionic radii for a series of particles including atoms and ions, and explain WHY they are ranked based on attractions and repulsions within the atom Be able to give the Lewis dot symbol for any main group element or ion Be able to predict the chemical formula for an ionic compound resulting from any two given ions

Extra Practice Problems for Sections , Complete these problems outside of class until you are confident you have learned the SKILLS in this section outlined on the study guide and we will review some of them next class period (just formulas) 5.123

Prep for Day 11 Must Watch videos: (Tyler DeWitt: ionic vs. molecular) (Crash Course Chemistry: bonds) (electronegativity) (Lewis structures, crash course chemistry) (Lewis structures) Other helpful videos: (covalent versus ionic) (MIT lecture 10: covalent bonds) (Lewis Structures) (UC-Berkeley lesson 10) k32U&list=PLqOZ6FD_RQ7kTjN4O2MNzf5YfeiIx7SGIhttps:// k32U&list=PLqOZ6FD_RQ7kTjN4O2MNzf5YfeiIx7SGI (UC-Irvine start at 15 min mark) (MIT lecture 11) Read sections 5.5, 6.1, 6.2 (pages ), 6.3