Chemistry 103 Lecture 8

Outline Electron Dot Symbols Lewis Dot Diagrams Predicting Formulas I. Electronic Structure (CH5) Brief Review Orbital Diagrams Valence Electrons Atomic & Ionic Radii II. Chemical Bonds - Ionic Compounds (CH6) Electron Dot Symbols Lewis Dot Diagrams Predicting Formulas

Electron Configuration Write the full electron configuration and the nobel gas shorthand electron configuration for tin (Sn, element 50)

Basic Questions about the Model Which of the following orbitals will not be found in our quantum mechanical model? A. 1s B. 3p C. 2f D. 4p Justify your answer based on quantum number rules. When n=2, can only have l=0 (s) and l=1(p) orbitals.

Basic Questions about the Model What shell will be the first in which a “4” orbital will be found? n = 4 , l = 0, 1 ,2, 3 n = 4 (first time l can equal “3” (f)) How many individual orbitals are in the n=2 shell? 1 (s), l = 0, ml = 0 (1 value, 1 orbital) 3 (p), l = 1, ml = -1, 0, 1 (3 orbitals) TOTAL = 4 orbitals in the n=2 shell

Orbital (Box) Diagrams Visual Representations of Electron Configurations Each line (or circle) represents an orbital Arrows represent electrons The rules of electron configurations are followed 1s 2s 2p 3s 3p 4s

Orbital Occupancy The Maximum Number of Electrons any single orbital can hold is two. They are distinguished from each other an arrow convention - one must be up, one must be down if electrons are in the same orbital. He ____ 1s

Writing Orbital Diagrams Electron configurations tells us which energy levels the electrons for each element are located. THREE rules: 1. Electrons fill orbitals starting with lowest energy first 2. There can be no more than 2 electrons in any orbital, and those electrons must have different “spins”

Writing Orbital Diagrams Electron configurations tells us which energy levels the electrons for each element are located. THREE rules: 1. Electrons fill orbitals starting with lowest energy first 2. There can be no more than 2 electrons in any orbital, and those electrons must have different “spins” 3. For orbitals in the same subshell, electrons fill each orbital singly before any orbital gets a second electron

Writing Orbital Diagrams Nitrogen ___ ___ ___ ___ ___ 2s 2p 1s

Writing Orbital Diagrams Unpaired electrons Nitrogen ___ ___ ___ ___ ___ 2s 2p 1s Paired electrons

Learning Check Write the orbital diagrams for: A. oxygen B. phosphorus C. calcium

Question! Which electrons are most likely to be involved in chemical reactions? A) those nearest to the nucleus B) those farthest from the nucleus C) all are equally likely to be involved

Atomic Families What differentiates one family from another? Li Na K Let’s look at the electron configurations of the alkali metals to find out. Li Na K Rb Cs Fr

The Properties of Atoms Are Dependent on Their Valence Electrons Elements that similar properties have the same number of valence electrons! Valence Electrons: For elements in the “s” and “p” block - valence electrons are the electrons in the outer-most electron shell (the shell with the highest n value) Example: Mg: 1s22s22p63s2 Example: Cl: 1s22s22p63s23p5

How Many Valence Electrons? How many valence electrons do the following elements have? Na: 1 Al: 3 S: 6 Cl: 7

Atomic Radius Atomic radius is the distance from the nucleus to the valence electrons. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Atomic Radius Within a Group Atomic radius increases going down each group of representative elements. Li Atom Na Atom K Atom INCREASE Radius = distance between nucleus and valence electrons

Atomic Radius Across a Period Atomic radius decreases from left to right across a period because more protons increase nuclear attraction for valence electrons. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check Select the element in each pair with the larger atomic radius. A. Li or K B. K or Br C. P or Cl

EXAM I - Summer 09 Material

General Course structure Atoms ---> Compounds ---> Chemical Reactions

Atomic Radius Atomic radius is the distance from the nucleus to the valence electrons. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Ionic Radii An atom (or group of atoms) that is electrically charged as a result of the loss or gain of electrons.

Sizes of Metal Atoms and Ions A positive ion Lost its valence electrons Is smaller (about half the size) than its corresponding metal atom Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Size of Sodium Ion The sodium ion Na+ is smaller than Na atom because the valence electrons have been lost from the 3rd energy level. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Sizes of Nonmetal Atoms and Ions A negative ion Increased its number of valence electrons. Is larger (about twice the size) than its corresponding metal atom. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Size of Fluoride Ion The fluoride ion F- is larger than F atom because the added valence electron increase repulsions between the outer electrons. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Chapter 6 - Names & Formulas of Compounds Compounds - Compounds result from the formation of chemical bonds between two or more different elements.

Bonds Chemical bond: attractive force holding two or more atoms together.

Bonds Ionic Bonds - electron transfer process. Typically between a metal and a nonmetals Covalent Bonds - electrons shared. Typically involving nonmetals.

Periodic Table of Elements

Electron Dot Symbols Focus on valence electrons - highest “n” quantum number for representative elements Electron Dot Symbols consists of symbol for the element with one dot for each valence e-. Na .

Rules for Electron Dot Symbols 1. Representative elements in the same group of the periodic table have the same number of valence electrons 2. The number of valence electrons is represented by “dots” around the symbol of the representative element. 3. The maximum number of valence electrons for any representative element is 8 - Octet Rule.

The Representative Elements Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Octet Rule - What is special about “8”? An octet Is 8 valence electrons Is associated with the stability of the noble gases He is stable with two valence electrons (duet). valence electrons He 1s2 2 Ne 1s2 2s2 2p6 8 Ar 1s2 2s2 2p6 3s2 3p6 8 Kr 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 8

Ionic and Covalent Bonds Atoms acquire octets To become more stable By losing, gaining, or sharing valence electrons By forming ionic bonds or covalent bonds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Focus on Ionic Compounds Formed between a positively charged metal ion and a negatively charged nonmetal ion

Metals Form Positive Ions Octets by losing all of their valence electrons. Positive ions have the electron configuration of the nearest noble gas. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Metal Ions – Why Are They Positive? Let’s look at Mg. Its electron configuration is 1s22s22p63s2. If it loses two electrons to become Mg2+, it will have the electron configuration 1s22s22p6 8 Valence Electrons! If it gains 6 electrons to become Mg6-, it will have the electron configuration 1s22s22p63s23p6 The question is which is easier? To lose TWO electrons or to gain SIX? Losing two: Therefore, Mg tends to form Mg2+ ions

Nonmetals Form Negative Ions Octets by gaining valence electrons to acquire eight. Negative ions have the electron configuration of the nearest noble gas Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Nonmetal Ions – Why Are They Negative? Let’s look at Cl. Its electron configuration is 1s22s22p63s23p5. If it loses seven electrons to become Cl7+, it will have the electron configuration 1s22s22p6 8 Valence Electrons! If it gains 1 electron to become Cl-, it will have the electron configuration 1s22s22p63s23p6 The question is which is easier? To lose SEVEN electrons or to gain ONE? Gaining ONE: Therefore, Cl tends to form Cl- ions