WEEK 2 NOTE.

 FAMILIES OF ELEMENTS

Elements in the same group may be said to belong to a family since they show similar properties because their atoms have the same number of valence electrons. At the same time, certain properties of the element in the same group show a gradual change with increase in atomic number. Such gradual change of property within a group is known as GROUP TREND.

GROUP I

The group I elements include: Lithium (Li), Sodium(Na), Potassium(K), Rubidium(Rb), Caesium (Cs), and Francium (Fr). They are univalent elements. They properties are as follows:

They are good reducing agent since they can readily donate one electron to form cation.

They are metals, thus they are good conductors of electricity and heat.

They react vigorously with cold water to liberate hydrogen gas and form alkali, hence, they are known as ALKALI METALS. Example2Na(s) + 2H2O(l)→ 2NaOH(aq) + H2(g)

The oxides of group I elements dissolve in water to give a very strong alkalis. Example

K2O(s) + H2O(l)→ 2KOH(aq)

GROUP II

Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra) belong to group II. They are divalent elements and are also known as alkaline earth metals. Their properties include:

They ionize by donating their two valence electrons; hence they are good reducing agent.

They are hard metals, ductile malleable and can conduct both electricity and heat.

Beryllium does not react with cold water or steam, magnesium reacts with steam only while calcium reacts slowly with cold water to liberate hydrogen gas.

Their oxides are insoluble in water except fort calcium oxide which dissolves in water to form an alkali. 

CaO(s) + 2H2O(l)→Ca(OH)2(aq)

GROUP III

The group III elements are: Boron (B), Aluminum (Al), Gallium (Ga), Indium (In) and Thallium (Tl). They are trivalent elements. Their properties are:

They are reducing in nature since they can donate their three electrons to form electrovalent compounds.

Only aluminum can react with steam at about750oC to liberate hydrogen gas.

Oxide and hydroxide of aluminum is amphoteric in nature, i.e, they have both acidic and basic properties. Example

Al2O3(s) + 3H2SO4(aq)→ Al2(SO4)2(aq) + 3H2O(l)

2Al(OH)3(s) + NaOH(aq)→NaAl(OH)4(aq)

GROUP IV

Group IV elements include: Carbon (C), Silicon (Si), Germanium (Ge), tin (Sn) and lead (Pb). They form covalent compounds.

They exhibit two oxidation states: +2 and +4. Due to inert pair effect of electrons in the s-orbital of the valence shell, the +2 oxidation state becomes more prominent down the group.

Electropositivity increases down the group. Carbon is a non-metal; silicon and germanium are metalloids while tin and lead are metals.

Carbon does not react with water in any form; but silicon and tin react with steam at red heat to form +4 state oxides and hydrogen. 

Si(s) + 2H2O(l)→ SiO2(s) +  2H2(g)

GROUP V

Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb) and Bismuth (Bi) belong to group V. They have the following properties

They exhibit oxidation states of -3 and -5.

They also show group trend. Nitrogen and phosphorus are non-metals; arsenic and antimony are metalloids while bismuth is a metal.

They electron acceptors, hence they are oxidizing in nature.

They form oxides that dissolve in water to form acids except nitrogen (I) oxide.

GROUP VI

Elements in group VI include: Oxygen (O), Sulphur (S), Selenium (Se), Tellurium (Te), and Polonium (Po).their properties are as follows:

They are non-metals and exist as solid at room temperature except for oxygen

They are electron acceptors and oxidizing in nature.

They do not react with water in any form. But oxygen and sulphur combine directly with hydrogen to yield water and hydrogen sulphide respectively.

GROUP VII

Elements in this group include: Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) and Astatine (At). They are known as halogens (salt-makers). Their properties include:

They ionize to form univalent anions.

They exist as diatomic molecules.

As electron acceptor, all halogens are good oxidizing agent.

They exhibit group trend. Fluorine and chlorine are gases, bromine is a liquid and iodine and astatine are solids at room temperature.

GROUP VIII (0)

The elements in group 0 are known as rare or noble gases because they are non-reactive and exist freely as monoatomic molecules in the atmosphere. The elements that belong to this group are: Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe) and Radon (Rn).

TRANSITION ELEMENTS

These are elements found in-between group II and III of the periodic table. The first transition series consists of elements: Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Manganese (Mn), Iron (Fe), Cobalt (Co), Nickel (Ni), Copper (Cu) and Zinc (Zn). Transition elements have the following properties:

1. High tensile strength 

2. High melting and boiling points 

3. Variable oxidation states

4. Formation of colored ions

5. Formation of complex ions 

6. Paramagnetic in mixture 

7. Catalytic ability 

LANTHANIDES (RARE EARTH ELEMENTS): These are found in period six. This series begins with Lanthanum (La), and ends with Lutetium (Lu). They are altogether 15 and resemble one another greatly.

ACTINIDES AND THE ARTIFICIAL ELEMENTS: The actinides are similar to the Lanthanides. They are found in the seventh period, which starts with Actinium (Ac) and ends with Lawrencium, (Lr). The famous Uranium is in this group.

The elements with atomic number from 93 to 103 are known as the artificial elements. This is because they do not occur naturally but were formed during nuclear reaction.