Ch. No. 1. SCHOOL OF ELEMENTS
Q1. A. Fill in the blanks.
1. The formula of chloride of metal M is MCl2. The metal M belongs to group 2.
2. 18th group in the periodic table contains elements that are all gases at room temperature.
3. The arrangement of elements in a group of three is known as traids.
4. The law used by Newlands to arrange elements is known as Newlands’ Octaves.
5. The element eka – aluminum in Mendeleev’s periodic table is known as Gallium in modern periodic table.
6. Elements showing properties of both metals and non – metals are known as metalloids.
Q1. B. Match the columns.
| Column I | Column II |
| 1. Sodium 2. Cerium 3. Sulphur 4. Manganese | a. Lanthanide b. Metalloid c. Transition metal d. Noble metal e. Metal f. Non – metal. |
Ans.
| Column I | Column II |
| 1. Sodium 2. Cerium 3. Sulphur 4. Manganese | e. Metal a. Lanthanide f. Non – metal c. Transition metal b. Metalloid |
Q2. Give scientific reasons.
1. Atomic size increases down the group.
Ans.
i. The atomic numbers of the elements increase as we go down the group. Thus, the elements placed lower have more electrons.
ii. To accommodate these electrons new shells are added to the atom.
iii. These new shells take the outermost electrons farther from the nucleus causing atomic size (radius) to increase as we go down the group.
2. Metallic character decreases from left to right in a period.
Ans.
i. Atoms of metals tend to lose electrons, whereas those of non – metals tend to gain them.
ii. In a period, as we go from left to right, atomic number increases, increasing the number of electrons and protons.
iii. These additional electrons are placed in the same outer shell and are strongly attracted towards the positively – charged nucleus.
iv. This strong attraction does not allow loss of electrons, causing metallic character to decrease from left to right in a period.
3. Elements in the same group show the same valency.
Ans.
i. Valency is the number of electrons given, taken or shared by an atom to complete its outermost shell.
ii. All the elements in the same group have the same number of electrons in their outermost shells.
iii. Thus, all these elements take, give or share the same number of electrons.
iv. Hence, elements in the same group show the same valencys.
Q3. Answer the following
1. How could the modern periodic table remove various anomalies of Mendeleev’s periodic table?
Ans.
i. A periodic table is a tabular arrangement of elements such that the elements can be classified on the basis of their common properties.
ii. Properties of elements are related to their electronic configuration which in turn depends on their atomic numbers.
iii. In the modern periodic table, the elements are arranged in the ascending order of their atomic numbers such that the elements having similar properties fall in the same group.
iv. This arrangement removed various anomalies of Mendeleev’s periodic table which depended on atomic masses of the elements.
2. In modern periodic table, which are the metals, non metals and metalloids among the first 20 elements?
Ans. In the modern periodic table, among the first 20 elements, following are the metals, non – metals and metalloids.
| Metals | Non metals | Metalloids |
| Lithium (Li) Beryllium (Be) Sodium (Na) Magnesium (Mg) Aluminium (Al) Potassium (K) Calcium (Ca) | Hydrogen (H) Helium (He) Carbon (C) Nitrogen (N) Oxygen (O) Fluorine (F) Neon (Ne) Phosphorus (P) Sulphur (S) Chlorine (Cl) Argon (Ar) | Boron (B) Silicon (Si) |
3. What are the demerits of Mendeleev’s periodic table?
Ans.
i. Mendeleev could not assign a correct position to hydrogen in the periodic table as hydrogen resembles alkali metals as well as halogens.
ii. Isotopes had to be given the same position in the periodic table though isotopes of the same elements have different atomic masses.
iii. It was observed that at certain places, an element of higher atomic mass Cobalt (Co=58.93) has been placed before an element of lower atomic mass Nickel (Ni = 58.71).
iv. Some elements placed in the same sub - group varies in their properties. Manganese is placed with halogens which totally differ in the properties.
4. Define atomic size. How does it vary in a period and in a group?
Ans.
i. Atomic size is determined by the atomic radius.
ii. For an isolated atom, its atomic radius is the distance between the centre of the atom (i.e. centre of its nucleus) and its outermost shell.
iii. Generally, in the period, the atomic radius decreases from left to right.
iv. In a group, the atomic radius increases from top to bottom.
Q. 4. Name
1. Three elements having a single electrons in their outermost shell.
Ans. Hydrogen, Lithium, Sodium, Potassium.
2. Three elements with filled outermost shell.
Ans. Helium, Neon, Argon, Krypton, Xenon.
3. Three elements having 7 electrons in their outermost shell.
Ans. Fluorine, Chlorine, Bromine, Iodine.