Study the following table in which positions of six elements A, B, C, D, E and F are shown as they are in the modern periodic table:
Group
Period
1 1 2 3-12 13 14 15 16 17 18 2 A B C 3 D E F
On the basis of the above table, answer the following questions:
(i) Name the element which forms only covalent compounds.
(ii) Name the element which is a metal with valency three.
(iii) Name the element which is a non-metal with valency three.
(iv) Out of D and E, which is bigger in size and why?
(v) Write the common name for the family to which the elements C and F belong.
Study the following table in which positions of six elements A, B, C, D, E and F are shown as they are in the modern periodic table:
Group Period | |||||||||
| 1 | 1 | 2 | 3-12 | 13 | 14 | 15 | 16 | 17 | 18 |
| 2 | A | B | C | ||||||
| 3 | D | E | F |
On the basis of the above table, answer the following questions:
(i) Name the element which forms only covalent compounds.
(ii) Name the element which is a metal with valency three.
(iii) Name the element which is a non-metal with valency three.
(iv) Out of D and E, which is bigger in size and why?
(v) Write the common name for the family to which the elements C and F belong.
The periodic table is given as:
Group
Period
1 1 2 3-12 13 14 15 16 17 18 2 A (Li) B (N) C (Ne) 3 D (Al) E (Si) F (Ar)
Part (i): Element which forms only covalent bonds
- Covalent bonds are formed by the sharing of electrons between atoms. A covalent bond is formed between two non-metals.
- The element forming a covalent bond will be E; because it belongs to group 14 and it has four valence electrons.
- Its valency is four and therefore, it will share 4 electrons with other elements to obtain a stable electronic configuration, and thus, form covalent bonds. This is called a covalent bond.
Therefore, the element that forms only a covalent bond is element E.
Part (ii): Metal with valency 3
- Metals have a tendency to lose electrons to gain stability. Elements with less than 4 electrons in the valence shell have the tendency to lose the valence electrons to attain the stable octet configuration.
- The element D is in group 13 and therefore, it has three valence electrons.
- Therefore, it can lose its three valence electrons to obtain a stable configuration.
- Therefore, the valency of element D is 3 and it is a metal.
Thus, the metal having valency three is element D.
Part (iii): Non-metal with valency 3
- Non-metals have a tendency to gain electrons to gain stability. Elements with more than 4 electrons in the valence shell gain electrons in the outer shell to complete their octet. These elements are called non-metals.
- The element B is in group 15 and therefore, it has 5 electrons in the valence shell.
- Therefore, this element tend to accept three electrons to complete its octet therefore is a non-metal and has valency 3.
Thus, the elements which is a non-metal with valency three is B.
Part (iv): Comparing sizes of B and D
- Atomic size is the measure of the distance from the center of the nucleus of an atom to its outermost shell.
- There will be two forces acting on the atom with increasing atomic number. The repulsive force between the electrons increases with the addition of electrons thus increasing the size of an atom.
- The nuclear charge increases due to an increase in the number of protons in the nucleus, thus reducing the size of the atom.
- Across the period, the electrons are added to the same shell. Therefore, the force due to the nuclear charge outweighs the force due to repulsive forces between electrons. Therefore, atomic size decreases across a period.
- Therefore, the size of the atom decreases due to the increase in the effective nuclear charge.
- Element D is in group 13 and E is in the 14th group. Therefore, element D will be bigger in size because moving left to right in the period results in a decrease in atomic size.
Part (v): Family of elements C and F
- Elements C and F belongs to group 18 in the periodic table and have 8 electrons in their valence shells.
- Therefore, they have a stable electronic configuration. Due to this, they do not take part in any chemical reaction and remain in their homo atomic form and thus, they are called noble gases or inert gases.
Hence, C and F belong to the noble gases group.
The periodic table is given as:
Group Period | |||||||||
| 1 | 1 | 2 | 3-12 | 13 | 14 | 15 | 16 | 17 | 18 |
| 2 | A (Li) | B (N) | C (Ne) | ||||||
| 3 | D (Al) | E (Si) | F (Ar) |
Part (i): Element which forms only covalent bonds
- Covalent bonds are formed by the sharing of electrons between atoms. A covalent bond is formed between two non-metals.
- The element forming a covalent bond will be E; because it belongs to group 14 and it has four valence electrons.
- Its valency is four and therefore, it will share 4 electrons with other elements to obtain a stable electronic configuration, and thus, form covalent bonds. This is called a covalent bond.
Therefore, the element that forms only a covalent bond is element E.
Part (ii): Metal with valency 3
- Metals have a tendency to lose electrons to gain stability. Elements with less than 4 electrons in the valence shell have the tendency to lose the valence electrons to attain the stable octet configuration.
- The element D is in group 13 and therefore, it has three valence electrons.
- Therefore, it can lose its three valence electrons to obtain a stable configuration.
- Therefore, the valency of element D is 3 and it is a metal.
Thus, the metal having valency three is element D.
Part (iii): Non-metal with valency 3
- Non-metals have a tendency to gain electrons to gain stability. Elements with more than 4 electrons in the valence shell gain electrons in the outer shell to complete their octet. These elements are called non-metals.
- The element B is in group 15 and therefore, it has 5 electrons in the valence shell.
- Therefore, this element tend to accept three electrons to complete its octet therefore is a non-metal and has valency 3.
Thus, the elements which is a non-metal with valency three is B.
Part (iv): Comparing sizes of B and D
- Atomic size is the measure of the distance from the center of the nucleus of an atom to its outermost shell.
- There will be two forces acting on the atom with increasing atomic number. The repulsive force between the electrons increases with the addition of electrons thus increasing the size of an atom.
- The nuclear charge increases due to an increase in the number of protons in the nucleus, thus reducing the size of the atom.
- Across the period, the electrons are added to the same shell. Therefore, the force due to the nuclear charge outweighs the force due to repulsive forces between electrons. Therefore, atomic size decreases across a period.
- Therefore, the size of the atom decreases due to the increase in the effective nuclear charge.
- Element D is in group 13 and E is in the 14th group. Therefore, element D will be bigger in size because moving left to right in the period results in a decrease in atomic size.
Part (v): Family of elements C and F
- Elements C and F belongs to group 18 in the periodic table and have 8 electrons in their valence shells.
- Therefore, they have a stable electronic configuration. Due to this, they do not take part in any chemical reaction and remain in their homo atomic form and thus, they are called noble gases or inert gases.
Hence, C and F belong to the noble gases group.
