Periodic Relationships Among the Elements Chapter 7 Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display.

When the Elements Were Discovered 8.1

Atomic radius – one-half the distance between the two nuclei in two adjacent metal atoms or in a diatomic molecule 8.3

8.3

General Trend in First Ionization Energies Increasing First Ionization Energy Increasing First Ionization Energy 8.4

Electron affinity is the negative energy change that occurs when an electron is accepted by an atom in the gaseous state to form an anion. X (g) + e- X-(g) F (g) + e- F-(g) DH = -328 kJ/mol EA = +328 kJ/mol O (g) + e- O-(g) DH = -141 kJ/mol EA = +141 kJ/mol 8.5

Electron affinity – the energy change in kJ accompanying the addition of 1 mol of e- to 1 mol of gaseous atoms or ions.

SAMPLE PROBLEM 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.

SAMPLE PROBLEM 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.

Group 1A Elements (ns1, n  2) 8.6

Increasing reactivity Group 1A Elements Increasing reactivity Low Ionization energies. Tendency to lose the single valance electron They are very reactive, never found in nature in pure state 8.6

Group 2A Elements (ns2, n  2) 8.6

Increasing reactivity Group 2A Elements Increasing reactivity Alkaline earth metals Metallic character increases from top to bottom 8.6

Group 3A Elements (ns2np1, n  2) 8.6

Group 3A Elements Boron is a metalloid; the rest are metals 8.6

Group 4A Elements (ns2np2, n  2) 8.6

Group 4A Elements Carbon a non metal Silicon and Germanium are metalloids Then all metals 8.6

Group 5A Elements 8.6

Group 5A Elements Nitrogen and Phosphorous are non metals Arsenic and antimony are metalloids Bismuth is a metal 8.6

Group 6A Elements 8.6

Group 6A Elements The 1st three are non metals The last two are metalloids 8.6

Group 7A Elements 8.6

Increasing reactivity Group 7A Elements Increasing reactivity All are halogens and are non metals Great reactivity Never found in their element form in nature High ionization energies Large positive electron affinity 8.6

No tendency to accept extra electrons. Group 8A Elements Completely filled ns and np subshells. Highest ionization energy of all elements. No tendency to accept extra electrons. 8.6

Trends in metallic behavior.