Bellringer No bags in class. If you need to go to your locker do so now, before the bell rings. What elements are in the same period as Carbon? As Argon? What elements are in the same family as Carbon? As Argon?

The Periodic Table Chapter 6

Organizing the Elements Chapter 6 Section 1

Searching for an Organizing Principle Prior to 1700 only 13 elements had been discovered and isolated. The use of scientific methods in science led to the discovery and isolation of many more elements by 1780. Chemists used the properties of the elements to sort them into groups.

Mendeleev’s Periodic Table Dmitri Mendeleev Russian chemist and teacher 1869 developed chart (periodic table) for his students to show relationships among elements Periodic table is arranged into groups based on a set of repeating properties. Arranged the elements in order of increasing atomic mass Predicted discovery of more elements

Revision of Mendeleev’s Table Henry Moseley Discovered number of proton in nucleus (atomic number) Proposed arranging elements in order of increasing atomic number Solved problems encountered by Mendeleev Work resulted in a clear periodic pattern of properties In the modern periodic table, elements are arranged in order of increasing atomic number.

Periodic Law The chemical and physical properties of the elements are periodic functions of their atomic numbers.

Classifying the Elements

Classifying the Elements Metals Left side of periodic table Shiny Good conductors Ductile and malleable

Metals Group 1 = Alkali Metals (IA) Group 2 = Alkaline Earth Metals (IIA Both of these groups very chemically active; alkali metals more active Transition Metals = Groups 3-12 (B) Large group of metals with characteristic metallic properties Inner Transition Metals = Lanthanides and Actinides (at bottom of periodic table) Little known but widely used metals Actinides are all radioactive

Nonmetals Upper right hand side of periodic table Wider variation in properties Generally poor conductors Brittle as solids; many occur as gases at room temperature

Nonmetals Group 16 = Chalcogens (chalk formers) (IVA) Group 17 = Halogens (salt formers) (IIVA) Group 18 = Noble Gases (chemically inert)

Metalloids 8 elements bordering “stair-step” line that have properties of both metals and nonmetals B, Si, Ge, As, Sb, Te, Po, At Silicon and germanium used extensively in computer chips and solar cells

Classifying the Elements Chapter 6 Section 2

Squares in the Periodic Table The periodic table displays the symbols and names of the elements, along with information about the structure of their atoms. Every periodic table must, at the least, display the symbol, atomic number, and atomic mass of each element. Many periodic tables are color coded to illustrate groups of elements.

Electron Configuration in Groups Elements can be sorted into noble gases, representative elements, transition, or inner transition elements based on their electron configuration. Electrons and electron configuration determine many of the properties of elements.

Electron Configuration in Groups Noble Gases Completely full outer s and p orbitals Octet (8) electrons in outer shell Most stable electron configuration Representative Elements (“A” groups) Elements in the s and p blocks (excluding noble gases) Wide variety of properties representative of all types of elements s and p orbitals being filled For elements in the s and p blocks, the number of valence electrons equals the last digit of the group number (in new system) or the group “A” number (older system). Transition Metals (“B” groups) Characterized by filling of d orbitals Connection between 2 sets of representative elements Inner Transition Metals Characterized by filling of f orbitals

Chapter 6 Section 3 Periodic Trends

Atomic Radius Generally measured as ½ the distance between the nuclei of identically bonded atoms For main group elements the trends are: Increases down a group – addition of energy levels; outer electrons SHIELDED from pull of nucleus by inner electrons Decreases across a period – electrons added in same energy level; increased positive charge of nucleus pulls electrons closer

Atomic Radius Atoms get larger as you move down a group Atoms get smaller as you go across a period

SAMPLE PROBLEM 1 Ranking Elements by Atomic Size PROBLEM: Using only the periodic table (not Figure 8.15)m rank each set of main group elements in order of decreasing atomic size: (a) Ca, Mg, Sr (b) K, Ga, Ca (c) Br, Rb, Kr (d) Sr, Ca, Rb PLAN: Elements in the same group increase in size and you go down; elements decrease in size as you go across a period. SOLUTION: (a) Sr > Ca > Mg These elements are in Group 2A(2). (b) K > Ca > Ga These elements are in Period 4. (c) Rb > Br > Kr Rb has a higher energy level and is far to the left. Br is to the left of Kr. (d) Rb > Sr > Ca Ca is one energy level smaller than Rb and Sr. Rb is to the left of Sr.

Ionic Radius Positive ions (cations) are always smaller than the atoms from which they formed. Cations form when atoms lose electrons. Negative ions (anions) are always larger than the atoms from which they formed. Anions form when atoms gain electrons. Trends Increases down a group – atoms are larger therefore ions are larger Across a period – decreases due to smaller size of atoms from which they form (for both positive and negative ions)

SAMPLE PROBLEM 2 Ranking Ions by Size PROBLEM: Rank each set of ions in order of decreasing size, and explain your ranking: (a) Ca2+, Sr2+, Mg2+ (b) K+, S2-, Cl - (c) Au+, Au3+ PLAN: Compare positions in the periodic table, formation of positive and negative ions and changes in size due to gain or loss of electrons. SOLUTION: (a) Sr2+ > Ca2+ > Mg2+ These are members of the same Group (2A/2) and therefore decrease in size going up the group. The ions are isoelectronic; S2- has the smallest Zeff and therefore is the largest while K+ is a cation with a large Zeff and is the smallest. (b) S2- > Cl - > K+ (c) Au+ > Au3+ The higher the + charge, the smaller the ion.

Ionization Energy Amount of energy required to remove an outer electron Removing one or more electrons creates a positively charged CATION Trends Decreases down a group – outer electrons are shielded from nucleus; requires less energy to remove Increases across a period – increased nuclear charge holds outer electrons more tightly

SAMPLE PROBLEM 3 Ranking Elements by First Ionization Energy PROBLEM: Using the periodic table only, rank the elements in each of the following sets in order of decreasing IE1: (a) Kr, He, Ar (b) Sb, Te, Sn (c) K, Ca, Rb (d) I, Xe, Cs PLAN: IE decreases as you proceed down in a group; IE increases as you go across a period. SOLUTION: (a) He > Ar > Kr Group 8A(18) - IE decreases down a group. (b) Te > Sb > Sn Period 5 elements - IE increases across a period. (c) Ca > K > Rb Ca is to the right of K; Rb is below K. (d) Xe > I > Cs I is to the left of Xe; Cs is furtther to the left and down one period.

Octet Rule Atoms tend to gain, lose, or share electrons in order to acquire a full set of eight valence electrons which is the most stable electron configuration.

Electronegativity Tendency of an atom to attract electrons to itself when bonding with other atoms Atoms with higher EN have greater attraction of electron Allows prediction of bond type – ionic or covalent Trends Increases across a period – increased nuclear charge, atomic radius, and shielding create greater attraction for electrons Decreases down a group – bonding electrons in outer shell; farther from nucleus and shielding creates less pull for electrons

Periodic Table of Electronegativities

Summary of Periodic Trends