Buds Public School

By – Joanna Coutinho

Chemistry Project

Modern PeriodicTable and its

trends

Development of the Periodic TableIn 1864, John Newlands noted that when the elements were arranged in order of atomic number that every eighth element had similar properties.He referred to this as the law of octaves.

In 1869, Dmitri Mendeleev and Lothar Meyer independently proposed the idea of periodicity.

Mendeleev grouped elements (66) according to properties.

Mendeleev predicted properties for elements not yet discovered, such as Ga.

Development of the Periodic TableHowever, Mendeleev could not explain

inconsistencies such as argon coming before potassium in the periodic table, despite having a

higher atomic mass.In 1913, Henry Moseley discovered the correlation

between the number of protons (atomic number) and frequency of X-rays generated.

Ordering the periodic table by atomic number instead of atomic mass enabled scientists to make

sense of discrepancies.Entries today include atomic number and symbol;

and are arranged according to electron configuration.

Dmitri Mendeleev (1869)In 1869 Mendeleev and Lothar Meyer (Germany) published nearly identical classification schemes for elements known to date. The periodic table is base on the similarity of properties and re-activities exhibited by certain elements.

Classification of ElementsThe main group elements (also called the representative elements) are the elements in Groups 1A through 7A.

The Modern Periodic TableThe transition metals are found in Group 1B and 3B through 8B. Group 2B have filled d subshells and are not transition metals.

The Modern Periodic TableThe lanthanides and actinides make up the f-block transition elements.

Across the Periodic TablePeriods: Are arranged horizontally across the periodic table (rows 1-7)

These elements have the same number of valence shells.1

IA18

VIIIA

12

IIA13

IIIA14

IVA15VA

16VIA

17VIIA

2

33

IIIB4

IVB5

VB6

VIB7

VIIB8 9

VIIIB10 11

IB12IIB

4

5

6

7

2nd Period

6th Period

Down the Periodic TableFamily: Are arranged vertically down the periodic table (columns or group, 1- 18 or 1-8 A,B)

These elements have the same number electrons in the outer most shells, the valence shell.

1IA

18VIIIA

12

IIA13

IIIA14

IVA15VA

16VIA

17VIIA

2

33

IIIB4

IVB5

VB6

VIB7

VIIB8 9

VIIIB10 11

IB12IIB

4

5

6

7

Alkali Family:

1 e- in the valence shell

Halogen Family:

7 e- in the valence shell

• Columns of elements are called groups or families.

• Elements in each family have similar but not identical properties.

• For example, lithium (Li), sodium (Na), potassium (K), and other members of family IA are all soft, white, shiny metals.

• All elements in a family have the same number of valence electrons.

• Each horizontal row of elements is called a period.

• The elements in a period are not alike in properties.

• In fact, the properties change greatly across even given row.

• The first element in a period is always an extremely active solid. The last element in a period, is always an inactive gas.

Families Periods

Infamous Families of the Periodic TableNotable families of the Periodic Table and some important members

1IA

18VIIIA

12

IIA13

IIIA14

IVA15VA

16VIA

17VIIA

2

33

IIIB4

IVB5

VB6

VIB7

VIIB8 9

VIIIB10 11

IB12IIB

4

5

6

7

Alkali

Alkaline

(earth)

Transition Metals

Noble GasHalogen

Chalcogens

Classification of Elements

The noble gases are found in Group 8A and have completely filled p subshells.

Noble GasesNoble Gases are colorless gases that are extremely un-

reactive. One important property of the noble gases is their inactivity.

They are inactive because their outermost energy level is full. Because they do not readily combine with other

elements to form compounds, the noble gases are called inert.

The family of noble gases includes helium, neon, argon, krypton, xenon, and radon. All the noble gases are found in small amounts in the earth's atmosphere.

Reading the Periodic Table: Classification

Trend in Atomic RadiusAtomic Radius:

The size of at atomic specie as determine by the boundaries of the valence e-. Largest atomic species are those found in the SW corner since these atoms have the largest n, but the smallest Zeff.

Trend in Ionization PotentialIonization potential:

The energy required to remove the valence electron from an atomic specie. Largest toward NE corner of PT since these atoms hold on to their valence e- the tightest.

Trend in Electron AffinityElectron Affinity:

The energy release when an electron is added to an atom. Most favorable toward NE corner of PT since these atoms have a great affinity for e-.

What does it mean to be reactive?We will be describing elements according to their reactivity. Elements that are reactive bond easily with other elements to make compounds.Some elements are only found in nature bonded with other elements. What makes an element reactive?

1. An incomplete valence electron level.2. All atoms (except hydrogen) want to have 8 electrons in their very

outermost energy level (This is called the rule of octet.)3. Atoms bond until this level is complete. Atoms with few valence

electrons lose them during bonding. Atoms with 6, 7, or 8 valence electrons gain electrons during bonding.

Cation Formation

11p+

Na atom

1 valence electron

Valence e-lost in ion formation

Effective nuclear charge on remaining electrons increases.

Remaining e- are pulled in closer to the nucleus. Ionic size decreases.

Result: a smaller sodium cation, Na+

Anion Formation

17p+

Chlorine atom with 7 valence e-

One e- is added to the outer shell.

Effective nuclear charge is reduced and the e- cloud expands.

A chloride ion is produced. It is larger than the original atom.

The End