Classification of Elements
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Lesson – 14.
Classification of Element.
2) Give reason:
(a) Classification of elements is necessary.
Answer: Because to make the study of 118 elements easy and reliable.
(b) The size of atom increases on going from top to bottom in a group of the periodic table.
Answer: Because, as we move down a new shell gets added and electron in the outermost shell so the distance of from the nucleus increases.
(c) The size of atoms decreases on going from left to right of a period in the periodic table.
Answer: Because, due to increase of atomic number.
(d) Hydrogen is a non-metal but it is kept with metals in the modern periodic table.
Answer: Because, it gives one electron in reaction which shows the properties of metal.
(e) Potassium is more reactive than sodium.
Answer: Because, in potassium the atomic size is larger than sodium which result in the attraction of valence electron by lower force.
(f) Fluorine is more reactive than chlorine.
Answer: Because the size of fluorine’s electronic configuration is smaller than that of chlorine.
(g) The metallic characters of elements decreases and non-metallic characters increase on going from left to right of a period in the modern periodic table.
[No separate explanation is written under this item in the supplied source.]
(h) Inert gases are kept in group 0 of the modern periodic table.
Answer: The valency of inert gases is zero, so they are kept in group 0 in the modern periodic table.
(i) A portion of the periodic table is shown below. The atomic size decreases from Li to Ne.
| IA | IIA | IIIA | IVA | VA | VIA | VIIA | VIIIA |
|---|---|---|---|---|---|---|---|
| Li | Be | B | C | N | O | F | Ne |
Answer: The atomic size decreases from Li to Ne because when there is higher number of protons then in the higher the nuclear charge will be will cause atomic size smaller.
3) Difference between.
1) Periods and Groups
| Periods | Groups |
|---|---|
| They are the horizontal rows on the table. | They are the vertical columns on the table. |
| There are 7 periods. | There are 18 groups. |
2) Chlorine and Sodium
| Chlorine | Sodium |
|---|---|
| It have negatively charged ions. | It have positively charged ions. |
| It has 17 protons and 17 electrons. | It has 11 protons and 11 electrons. |
3) IA and VIIA
| IA | VIIA |
|---|---|
| They are called alkali metals. | They are called halogens. |
| They are highly reactive electropositive metals. | They are highly reactive electronegative non-metals. |
4) Electronegativity and Electropositivity
| Electronegativity | Electropositivity |
|---|---|
| The ability of chemical elements to gain electron. | The ability of chemical element to loose electron. |
| Eg: chlorine. | Eg: sodium. |
4) Answer Questions.
(a) State modern periodic law.
Answer: This law state that, the physical and chemical properties of element are periodic function on the increasing order of their atomic number.
(b) How many groups and periods are there in the modern periodic table?
Answer: There are 7 period and 18 groups in the modern periodic table.
(c) Write the position of sodium in the modern periodic table. Why is it known as alkali metal?
Answer: The sodium lies in group IA in the modern periodic table. It is known as alkali metal because it form alkaline in water.
(d) Write the position of following elements in the periodic table: alkali metal, alkaline earth metals, inert gases, transition metals, lanthanides and actinides.
Answer: They be long to following position:
- Alkali metal – IA.
- Alkaline earth metals – IIA.
- Inert gases – 0.
- Transition metals – IIA.
- Lanthanides → 57 – 71.
- Actinoides → 89 – 103.
(e) Write the electronic configuration of sulphur and write its position in the modern periodic table.
Answer: Sulphur.
no of electrons e–
1s2, 2s2, 2p6, 3s2, 3p4
period = 3rd.
Group = VIA
valency = 2.
(f) On which basis do the groups and periods are separated in the modern periodic table.
Answer: The groups and the periods are separated on the basis of number of valence electrons and the level of reactivity in the modern periodic table.
(g) In which group does fluorine, chlorine and Bromine lie in the periodic table? Which one is more reactive among them?
Answer: In group VIIA fluorine and chlorine and Bromine lie. chlorine is more reactive among them.
(h) If you were given a chance to make improvements in the modern periodic table, what changes would you make in it? Explain with reason.
Answer: If I got a chance to make improvements in the modern periodic table I will fix the position of hydrogen which will can either make halogens or alkali, that can solve the major problem of positioning of fixed hydrogen.
(f) continued/repeated in the supplied scan: The groups and the periods are separated on the basis of the number of valence electrons and the level of reactivity in the modern periodic table.
(g) In which group does fluorine, chlorine and Bromine lie in the periodic table? Which one is more reactive among them?
Answer: In group VIIA fluorine and chlorine and Bromine lie. chlorine is more reactive among them.
(h) If you were given a chance to make improvements in the modern periodic table, what changes would you make in it? Explain with reason.
Answer: If I got a chance to make improvements in the modern periodic table I will fix the position of hydrogen which will can either make halogens or alkali, that can solve the major problem of positioning of fixed hydrogen.
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