The Periodic Table

ChemistryChapter 5

Sept 1860, group of chemists met in Germany to review scientific matters & coming to consensus about:measurement of atomic massesdetermining composition of

compounds using atomic masses

Cannizzaro presented method for measuring mass & scientists agreed upon the std values for atomic masses

in 1869, Dmitri Mendeleev used Cannizzaro’s method for measuring relative masses of atoms in textbook he wrote

published the arrangement of elements in – periodic table

only 60 elements known at this time

organized elements acc to properties & new atomic masses on cards

“game of patience”Mendeleev grouped elements according to incr atomic mass & noticed certain properties appeared at regular intervals- periodic

in 1871, Mendeleev predicted properties of elements that weren’t even discovered at that time!

not all elements fit in according to increasing atomic mass:I & Te Ar & K Co & Ni

Mendeleev couldn’t explain whyother scientist accepted the

periodic table & considered him the Father of the Periodic Law

in 1913, Henry Moseley discovered patterns w/ x-ray tubes that led to atomic number (ch 3 notes)

he noticed that when he reordered elements on table acc to incr atomic number they fit into their patterns in better way

led to the Modern periodic table

periodic law- phy & chem properties of the elements are periodic functions of the atomic #

Getting Acquainted

With the Periodic Table

valence e- same for all elements in group

group 1: Alkali metals e- conf: ns1

group 2: Alkaline Earth metalse- conf: ns2

groups 3-12: Transition metalse- conf: (n-1)d1ns2

Group Properties

groups 4-11 deviations occursum of outer s & d e- equal to group

#

group 13: ns2np1

group 14: ns2np2

group 15: ns2np3

group 16: ns2np4

group 17: Halogens ns2np5

group 18: Noble gases ns2np6

noble gases have 8 valence e-

have stable octet very stable & unreactive

f-block elementslanthanides- rare earth metals 1st row

actinides- all radioactive; most synthetic

phy & chem properties vary in periodic fashion

properties arise from e- configuration

5 properties:

Periodic Properties

½ distance betw nuclei of identical atoms joined in a molecule

e- occupy large region around nucleus & size atom varies

periodic trends- gradual decrease in radii across periodsdue to increasing pos chrg of nucleus

(pulled tighter by nucleus)

1. Atomic Radii

group trends: as go down group, atomic radii increases due to addition of e- to larger orbitals in higher energy levels

minimum amount of energy required to remove the most loosely bound e- from an isolated gaseous atom to form an ion w/ a +1 charge

if enough energy is supplied, e- can be removed from atoms

ex: 1st IE for Ca is 590 kJ/mol

Ca + 590kJ/mol Ca+ + e-

2. Ionization Energy

ionization- process that results in the formation of ion

2nd IE is 1145kJ

IE2 > IE1ALWAYS more difficult to remove additional e- from positive ion

IE measures how tightly e- are bound to atoms

low IE indicates ease of e- removal & cation formation

group trends: as atomic radii increases in a group, 1st IE decreases b/c the valence e- are further

from nucleus “shielding effect”

period trends: IE incr from L to R due to increasing nuclear charge which holds e- tighter

nonmetals tend to have higher IE than metals

amount of energy involved in the process in which an e- is added to an isolated gaseous atom to produce an ion w/ a -1 charge

many atoms readily add e- & release energyex: Cl + e- Cl- + energy

(exothermic)

Why?

3. E- affinity

some have to be forced to gain e- by the addition of energyBe + e- + energy Be-

period trends: group 17 elements gain e- most easily ( large neg values) reason for the reactivity of these halogens

exceptions are seen betw groups 14 & 15 b/c ½ filled sublevels are a little more stable than ones not ½ full

group trends: generally more difficult to add e- to larger atoms than to smaller atoms

elements w/ very negative EA gain e- readily to form anions (ions w/ neg chrg)

more difficult to add e- to an anion so 2nd EA are all positive

cation- positive ionanion- negative ion

½ the diameter of an ion in a chemical compound

formation of a cation leads to a decrease in radius due to the e- cloud being drawn inward as valence e- are removed

formation of anion leads to an increase in radius as additional e- repel one another

4. Ionic radii

periodic trends- metals form cationsnonmetals form anions

group trends- IR increases down group Why?

as you add higher energy levels, radius of ion incr

chemical compounds form b/c e- are lost, gained, or shared to bring an atom to a stable octet

measure of the power of an atom in a chemical compound to attract e-

valence e- hold atoms in compound together & properties of compound are influenced by conc of neg chrg closer to one atom than another

ex: NaCl

5. Electronegativity EN

numerical values assigned to indicate the tendency of atom to attract e-

Fluorine – most EN element & assigned value of 4

periodic trends- gradual incr in EN from L to R across period

nonmetals tend to be more EN than metals

groups 1 & 2 least EN elements

halogens are most EN elements

group trends- EN either decreases down group or remains similar