(a) Why do we classify elements?
(b) What were the two criteria used by Mendeleev to classify the elements in his periodic table?
(c) Why did Mendeleev leave some gaps in his periodic table?
(d) In Mendeleev’s periodic table, why was there no mention of noble gases like helium, neon and argon?
(e) Would you place the two isotopes of chlorine, Cl-35 and Cl-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.
(a) Due to the discovery of different elements, it was difficult to organize the information and properties of the elements, hence, there was a need to find some pattern in the properties of different elements so that they can be grouped together. This is why we classify elements.
(b) The two criteria used by Mendeleev to classify the elements in his periodic table are given below:
- Increasing atomic masses.
- Grouping together of elements having similar properties.
(c) In order to make sure that the elements having similar properties fell in the same vertical column or group, Mendeleev left some gaps in his periodic table.
(d) The noble gases were not discovered at that time so there was no mention of noble gases like helium, neon, and argon in Mendeleev’s periodic table.
(e) The two isotopes of chlorine, Cl-35 and Cl-37 in different slots because their chemical properties are the same. The two isotopes of chlorine have same atomic number and chemical properties depend on the atomic number.
Related Articles
- Why do we classify elements?What were the two criteria used by Mendeleev in creating his Periodic Table?Why did Mendeleev leave some gaps in his Periodic Table?In Mendeleev's Periodic Table, why was there no mention of Noble gases such as Helium, Neon and Argon?Would you place the two isotopes of chlorine, Cl-35 and Cl-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.
- (a) State Mendeleev’s periodic law.(b) What chemical properties of elements were used by Mendeleev in creating his periodic table? (c) State any three limitations of Mendeleev’s classification of elements. (d) Besides gallium, which two other elements have since been discovered for which Mendeleev had left gaps in his periodic table ? (e) Which group of elements was missing from Mendeleev’s original periodic table?
- What were the criteria used by Mendeleev in creating his Periodic Table?
- What physical and chemical properties of elements were used by Mendeleev in creating his periodic table? List two observations which posed a challenge to Mendeleev's Periodic Law.
- Name two elements whose properties were predicted on the basis of their positions in Mendeleev’s periodic table.
- In Mendeleev's Periodic Table, gaps were left for the elements to be discovered later. Which of the following elements found a place in the Periodic Table later?ChlorineSiliconOxygenGermanium
- (a) State the periodic law on which Mendeleev’s periodic table was based. Why and how was this periodic law changed ?(b) Explain why, the noble gases are placed in a separate group.
- Around the year 1800, only 30 elements were known. Dobereiner in 1817 and Newlands in 1866 tried to arrange the then-known elements and framed laws which were rejected by the scientists. Even after the rejection of the proposed laws, many scientists continued to search for a pattern that correlated the properties of elements with their atomic masses.The main credit for classifying elements goes to Mendeleev for his most important contribution to the early development of a Periodic table of elements wherein he arranged the elements on the basis of their fundamental property, the atomic mass, and also on the similarity of chemical properties. The formulae of their hydrides and oxides were treated as basic criteria for the classification of the elements.However, Mendeleev’s classification also had some limitations as it could not assign the position to isotopes. He also left some gaps in the periodic table.(a) State Mendeleev’s Periodic Law.(b) Why did Mendeleev leave some gaps in the Periodic table?(c) If the letter ‘R’ was used to represent any of the elements in the group, then the hydride and oxide of carbon would respectively be represented as(i) RH4, RO (ii) RH4, RO2(iii) RH2, RO2 (iv) RH2, RO(d) Isotopes are-(i) Atoms of an element with similar chemical properties but different atomic masses. (ii) Atoms of different elements with similar chemical properties but different atomic masses. (iii) Atoms of an element with different chemical properties but same atomic masses. (iv) Atoms of different elements with different chemical properties but same atomic masses.
- Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table and the Modern Periodic Table.
- In Mendeleev’s periodic table, gaps were left for the elements to be discovered later. Which one of the following elements found a place in the periodic table later?GermaniumChlorineOxygenSilicon
- According to Mendeleev’s Periodic Law, the elements were arranged in the periodic table in the order of(a) increasing atomic number(b) decreasing atomic number(c) increasing atomic masses(d) decreasing atomic masses
- Which of the following statement is correct in regard to the classification of elements ?(a) Elements in the periodic table are arranged on the basis of increasing atomic masses (b) Elements in Mendeleev’s periodic table are arranged on the basis of increasing atomic numbers (c) In modern periodic table, the element nickel of lower atomic mass is kept before the element cobalt of higher atomic mass (d) In modern periodic table, the isotopes of chlorine having diffrenet atomic masses are kept in the same group.
- (a) Why does the size of the atoms progressively become smaller when we move from sodium (Na) to chlorine (Cl) in the third period of the periodic table?(b) Helium and neon are unreactive gases. What, if anything, do their atoms have in common?
- Isotopes belong to the same _________________ in the Periodic Table.
- Besides gallium, which other elements have since been discovered that were left by Mendeleev in his periodic table?
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