I. CHEMICAL PERIODICITY

"the variation in properties of elements

based on their positions in the periodic table”

Dmitri Mendeleev• a 19th cent. Russian chemist,

published (1862) an arrangement of elements based on chem. properties of the elements, so that elements with similar properties fell in the same column (62 known in his time)

• Brilliant b/c: he left spaces in columns for yet-undiscovered elements

Lothar Meyer

• a 19th century German chemist, published an arrangement of elements based on physical properties of elements

• the two tables were surprisingly similar, and emphasized regular periodic repetition of properties of elements with increasing a.w.

Periodic Law

• a revision of Mendeleev's/Meyer's groupings, states that "the properties of the elements are periodic functions of their atomic NUMBERS" (not their atomic weights!)

1. Groups/Families

• vertical columns -• elements in a group/family have

similar chem/phys prop's• e- dot notation is the same in a

group

1. Groups/Families

2. Periods/Rows

• horizontal rows -• elements in a period have

properties that change progressively across the periodic table

2. Periods/Rows

3. Group Numbers

1 2 3 4 5 6 7 8

-1-8 or 1-18 or A & B-makes sense to number them 1-8 (based on e- dots) when speaking in general-When getting specific, “column 17” would obviously mean the Halogens

4. Period Numbers

1

2

3

4

5

6

7

1-7 (correspond to "n", or principal quantum number), which gives an idea of distance from the nucleus

5. Major Categories

Transition Metals

Actinides

Transition Metals

Non-Metals

METALS Metalloids

Lanthanides

Actinides

Inert (Noble) Gases

6. Group Names

• a. Alkali Metals - Grp 1 - b/c they are metals that can react w/ water, forming alkaline sol'ns. Found combined in nature; not uncombined.

• b. Alkaline Earth Metals - Grp 2 - Found uncombined in nature

• c. Halogens - Grp 7 - "salt-formers"• d. Noble (Inert) Gases - Grp 8 - Tend

to be unreactive due to their completed octet of e-'s

6. Group NamesAlkali Metals

Alkaline Earth MetalsChalcogens

HalogensNoble Gases

(Inert

Gases)

Important Trends

• First Ionization Energy• Second Ionization Energy• Electron Affinity• Atomic Radii• Ionic Radii• Electronegativity

First Ionization Energy

• Def: “the min. am’t of energy required to remove the most loosely held e-”

• top to bottom: decreases, since as atomic size increases, e- from higher energy levels are "shielded*" from the nucleus and are therefore not as tightly bound. (the "*shielding effect")

• left to right: increases, as elem's closer to group 7 tend to want to gain e-'s. (Noble gases have the highest F.I.E.)

F.I.E.

• Which of these more easily loses e-’s?

• That’s the one with lower F.I.E.

First Ionization Energy

Second Ionization Energy

•Def: “the amount of energy required to remove the second e-

•Which is higher – FIE or SIE?•top to bottom and left to

right - same trend as F.I.E.

S.I.E.

Second Ionization Energy

Electron Affinity

• Def: the amount of energy absorbed when an e- is added to an isolated gaseous atom forming a -1 ion

• Elements w/very neg. E.A.'s gain e-'s easily to form anions.

• top to bottom - values become less negative

• left to right - values become more negative

Electron Affinity

Ionic Radii

• Defined as radius of the ion• top to bottom - increase, due to the

increase in "n"• left to right - decrease, due to the

addition of e- to same "n“ • Explanation: e- are added to same

“n”; there is a ‘tightening” of the overall atomic radius due to increased positive nuclear charge

For Metal Atoms forming Metal Ions…

• Ionic radii smaller since e- is lost from outermost level;

• ie: Na

For Nonmetal Atoms forming Nonmetal Ions

• As an e- is added to a valence shell, more room is needed (like charges repel) and the ion is larger

• ie: F

Electronegativity

• Def: a measure of the relative tendency of an atom to attract e-'s to itself when it is chemically combined with another atom

• Developed by Linus Pauling• EN has no units, since it's relative• top to bottom - decrease in EN• left to right - increase in EN

Using Electronegativity to Determine Bond Type

• there are two main types of chemical bonds,

• a) ionic - have a diff. in EN of > 1.67

• b) covalent - have a diff. in EN of < 1.67

• COVALENT < 1.67 < IONIC

Calculate the Bond Type

• i.e.: What kind of bond is likely to form in:

•H2O

•CO2

•NaBr

•MgO

For: H – O you would look up the EN’s for H and O and subtract

For: C – O you would look up the EN’s for C and O and subtract

For: Na – Br (same process)

For: Mg – O (same process)

More on this in the next unit!

Miscellaneous Terms

• anion - any negative ion• cation – any positive ion• isoelectronic – • (ie: N-3, O-2, F-1, Ne, Na+1, Mg+2, Al+3 )

What must this mean?

• For the next unit…• Polyatomic ion – a group of atoms that

behaves as a single ion (ie: NH4+, NO3

-, CO3

-2, SO4-2, etc etc)