Periodic Table of Elements

Dr. M. Abd-Elhakeem

Faculty of Biotechnology

General Chemistry

Lecture 3

Mendeleev

• In 1869, Dmitri Ivanovitch Mendeléev created the first accepted version of the periodic table.

• He grouped elements according to their atomic number, and as he did, he found that the families had similar chemical properties. 

• Blank spaces were left open to add the new elements he predicted would occur. 

• A periodic table is a tabular display of the chemical elements, organized on the basis of their atomic numbers.

• The main body of the standard form of table is an 18 groups (columns) and 7 periods (rows).

Families

• 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.

Periods

• 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.

• Three major classes are immediately recognized.

– Metals

– non-metals

– Metalloids

Properties of Metals• Good conductors of heat and

electricity.• Shiny.• Ductile (can be stretched into

thin wires).• Malleable (can be pounded

into thin sheets).• A chemical property of metal

is its reaction with water which results in corrosion.

Properties of Non-Metals

• Poor conductors of heat and electricity.

• Not ductile or malleable.• Solid non-metals are

brittle and break easily.• Dull.• Many non-metals are

gases.

Sulfur

Properties of Metalloids

• Metalloids (metal-like) have properties of both metals and non-metals.

• They are solids that can be shiny or dull.

• They conduct heat and electricity better than non-metals but not as well as metals.

• They are ductile and malleable.

Silicon

Famous groups and periods

1. Alkali metals (Group IA)

2. Alkaline Earth Metals (Group IIA)

3. Halogens (Group VIIA)

4. Nobel gases (Group VIIIA)

5. Transition metals

6. Lanthanides

7. Actinides.

Alkali Metals

• The alkali family is found in the first column of the periodic table.

• Atoms of the alkali metals have a single electron in their outermost level (s subshell), in other words, 1 valence electron.

• They are shiny, have the consistency of clay, and are easily cut with a knife.

Alkali Metals

• They are the most reactive metals.• They react violently with water to

form alkali.• Alkali metals are never found as free

elements in nature. They are always bonded with another element.

Alkaline Earth Metals

• They are never found uncombined in nature.

• They have two valence electrons.

• Alkaline earth metals include magnesium and calcium, that present commonly in earth crust.

Transition Metals

• Transition Elements locate in the middle of the periodic table

• These are the metals you are probably most familiar: copper, tin, zinc, iron, nickel, gold, and silver.

Transition Metals

• The compounds of transition metals are usually brightly colored and are often used to color paints.

• Transition elements have more than one valence and so you must calculate the oxidation state in each compound

Transition Elements

Many transition metals combine chemically with oxygen to form compounds called oxides.

Halogen Family

• The elements in this family are fluorine, chlorine, bromine, iodine, and astatine.

• Halogens have 7 valence electrons, which explains why they are the most active non-metals. They are never found free in nature.

• Halogen atoms only need to gain 1 electron to fill their outermost energy level. i.e. oxidation state = -1

• They react with alkali metals to form salts.

• They are gases

Noble Gases

• Noble Gases or inert 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.

• 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.

• Note that There are four distinct rectangular areas or blocks.

• s block

• p block

• d block

• The f-block is usually not included in the main table, but rather is floated below.

s block elements

d block elements

p block elements

f block elements

Periodicity of chemical properties

1- Atomic radius:the atomic radii decrease in going from left to right across

a given period.

Atomic radii increase from top to bottom down a group

2- Ionization EnergyIonization energy is the amount of energy required to

remove an electron from a gaseous atom or ion.

Ionization energy generally increases from left to right across periods and decrease from top to bottom down groups.

Electronegativity

• It is the tendency of an atom or a functional group to attract electrons

• electronegativity increases on passing from left to right along a period, and decreases on descending a group

Polarity

• It is the charged pole in the compounds due to difference in electron negativity and the asymmetry of the compound's structure

Water is a polar molecule

Methane is nonpolar molecule

• Solubility is defined as the maximum mass of a substance that can be dissolved in a fixed mass of a solvent at a given temperature.

• A substance will have a different solubility in different solvents depending on polarity of both the substance and the solvent.

• Still remember about ”like dissolves like”?

Solubility

1. Temperature

2. Pressure

3. Polarity of solvent and solute

Factors affecting solubility

Name Solubility in waterException

Nitrates, acetates, perchlorates

SolubleAg+ for acetate

sulphatesSoluble Ba+2, Pb+2, Hg+2, Ca+2, Ag+1, and

Sr+2

Chlorides, bromides, iodides

SolublePb+2, Ag+2, Hg+2

Carbonates, , phosphates,

Sulfites, Sulphides

Insoluble Alkali metal and ammonium

Hydroxides, chromates

InsolubleBa+2, Sr+2, and Ca+2

• In fact you can predict most of physical properties of any unknown element only by its position in the periodic table.

• Ex. Predict the physical and chemical properties of 55Cs

Atomic Mass Unit (AMU)

• The unit of measurement for an atom is an AMU. It stands for atomic mass unit.

• One AMU is equal to the mass of one proton.

Atomic Mass Unit (AMU)

• There are

6 X 1023 or 600,000,000,000,000,000,000,000 amus in one gram.

• (Remember that electrons are 2000 times smaller than one amu).

Calculation of molecular weight