Organizing the Elements

How do you organize a collection of different things?

Elements are organized into groups based upon their chemical properties

Elements that have similar chemical behavior are grouped together

Mendeleev is the father of the modern periodic table (1869)

Organized elements by◦ increasing atomic

mass◦ Repeating pattern of

properties Was able to predict

unknown elements using his table

Reorganized periodic table based upon increasing atomic number

Resolved inconsistencies of Mendeleev’s table

When elements are arranged by increasing atomic number….

Their physical and chemical properties repeat in a periodic fashion (repeating pattern)

Properties of elements within a group are very similar. Why?

Properties of elements vary in a regular way across a period

Most elements are metals (~ 80%) Properties of metals

◦ Solid at RT (except for Hg)◦ Good conductors of heat◦ Electrical conductivity◦ Luster◦ Ductile◦ Malleable

Most nonmetals are gases at RT Some solids, one liquid (Br) Properties of Nonmetals

◦ Poor conductors of heat◦ Poor electrical conductivity (except C)◦ Brittle

Metalloids sometimes called “semi-metals” What does this tell you about metalloids? Seven Metalloids Properties of Metalloids

◦ Intermediate between metals and nonmetals◦ Often depends upon conditions◦ Example: Si is a poor electrical conductor, but is

a good conductor when mixed with small amounts of boron.

Groups◦ vertical columns◦ 1-18◦ IA – VIII A are

“representative elements” Periods

◦ horizontal rows◦ 1-7

Squares◦ element symbol and other

information◦ ~115

Inner Transition Metals

Group 1: ___________________? Group 2: ___________________? Groups 3-12: ___________________? Group 17: ___________________? Group 18: ___________________?

Elements are within a group have the same ending electron configurations

This is why elements within a group have similar chemical properties

Atomic Radius: half the distance between nuclei of two like atoms joined together

Increases from top to bottom down a group Decreases from left to right across a period

Arrow points toward increase

Down a group, added energy levels increase radius

Because atomic number increases across a period, there is greater nuclear (+) charge

No energy levels are added across a period This tends to draw electrons closer to

nucleus, decreasing atomic radius

Ions are atoms which have gained or lost electrons

Cations are positively charged because they have lost electrons (negative charges)

Anions are negatively charged because they have gained electrons (negative charges).

Na0 → Na+ + e-

Cl0 + e- → Cl-

Positive and negative ions form when electrons are transferred between atoms.

6.3

Positive and negative ions form when electrons are transferred between atoms.

6.3

Cations and Anions Relative Sizes

Cations are smaller than their parent atoms

Anions are larger than their parent atoms

Ionic radius follows the same pattern as atomic radius but remember…

Cations are smaller than their parent atoms

Anions are larger than their parent atoms

This is because of a change in the relative strength of the nucleus, i.e…. ◦ The ratio of protons to electrons changes

In the case of cations, an energy level is lost

Energy required to remove an e- from an atom

Decreases from top to bottom down a group Increases from left for right across a period

A0 + Ei → A+ + e-

Na0 + Ei → Na+ + e-

Energy required to remove 1st, 2nd, & 3rd e-

Al0 → Al+ + e- Ei1= 578 kJ/mol

Al+ → Al2+ + e- Ei2 = 1816 kJ/mol

Al2+ → Al 3+ e- Ei3 = 2744 kJ/mol

Why would it require more energy to remove the 2nd electron?

The 3rd electron?

Why are these important?◦ These explain trends in atomic size, ionic size, and

ionization energy Nuclear charge

◦ tends to draw e-s toward nucleus (reducing atomic radius)

◦ The bigger the atomic number, the more positive it is◦ Increases across a period

Electron Shielding:◦ Inner (core) electrons “screen” outer electrons from

attractive force of the nucleus◦ Allows outer e-s to move further from nucleus

(increasing atomic radius)◦ Decreases down a group◦ Does not change across a period

Tendency of an atom to attract electrons to itself when bonded to another atom

A very important property!

Increases left to right across a periodDecreases down a group