Families Of Elements SS2 Chemistry Lesson 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 an increase in atomic number. Such a gradual change of property within a group is known as a 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. The properties are as follows:

1. They are good reducing agents since they can readily donate one electron to form a cation.
2. They are metals, thus they are good conductors of electricity and heat.
3. They react vigorously with cold water to liberate hydrogen gas and form alkali, hence, they are known as alkali metals.  Example:

2Na(s) + 2H2O(l)→ 2NaOH(aq) + H2(g)

4. 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:

1. They ionize by donating their two valence electrons; hence they are good reducing agents.
2. They are hard metals, ductile malleable and can conduct both electricity and heat.
3.  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.
4. Their oxides are insoluble in water except for calcium oxide which dissolves in water to form an alkali. Example:

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:

1. They are reducing in nature since they can donate their three electrons to form electrovalent compounds.
2. Only aluminium can react with steam at about750oC to liberate hydrogen gas.
3.  Oxide and hydroxide of aluminium are amphoteric, i.e., they have both acidic and basic properties. Example:

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

b) 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). 

1. They form covalent compounds.
2. They exhibit two oxidation states: +2 and +4. Due to the inert pair effect of electrons in the s-orbital of the valence shell, the +2 oxidation state becomes more prominent down the group.
3.  Electropositivity increases down the group. Carbon is a non-metal; silicon and germanium are metalloids while tin and lead are metals.
4. 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:

i. They exhibit oxidation states of -3 and -5.

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

They are electron acceptors, hence they are oxidizing in nature.

iii. 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:

1. They are non-metals and exist as solids at room temperature except for oxygen
2. They are electron acceptors and oxidizing in nature.
3. They do not react with water in any form. But oxygen and sulfur combine directly with hydrogen to yield water and hydrogen sulfide 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:

1. They ionize to form univalent anions.
2. They exist as diatomic molecules.

As electron acceptors, all halogens are good oxidizing agents.

3. They exhibit group trends. Fluorine and chlorine are gasses, 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 monatomic 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).