- Mendeleev corrected atomic masses to correctly place elements.
- He predicted new elements like Sc, Ga, and Ge with correct properties.
- He later added a zero group for noble gases.
- Co and Ni have similar masses, which can cause confusion about their order.
- Isotopes couldn’t be placed due to different masses.
- Atomic mass gaps are uneven, so new elements couldn’t be predicted.
- Hydrogen's position is unclear—it’s like both alkali metals and halogens.
Definitions [5]
Define periods of modern periodic table.
The horizontal rows are called periods. The table consists of 7 periods, numbered from 1 to 7 from top to bottom.
Define:
Periodic table
The periodic table is a tabular arrangement of elements in horizontal rows, called periods, and vertical columns, called groups, to classify elements and facilitate their systematic study.
Define groups of modern periodic table.
In the modern periodic table, groups (also known as families) are the 18 vertical columns that organize chemical elements by shared properties. Unlike periods, which are horizontal rows representing electron shells, groups are vertical columns of elements with similar chemical properties.
Definition: Elements
Elements are pure substances made up of one type of atom.
Definition: Modern Periodic Table
A tabular arrangement of elements in groups (vertical columns) and periods (horizontal rows), highlighting the regular trends in properties of elements, is called a Periodic Table.
OR
The classification of elements resulting from an arrangement of the elements in an increasing order of their atomic numbers is the modern periodic table.
Key Points
Key Points: Modern Periodic Table
- Dobereiner grouped elements in threes (triads) with similar properties and a pattern in atomic masses.
- Newlands found that every 8th element shared similar properties (the Law of Octaves).
- Mendeleev arranged elements by atomic mass and predicted new elements, but couldn’t explain isotopes and rare earths.
- Moseley fixed the flaws by arranging elements by atomic number, forming the modern periodic table.
- Bohr proposed the long-form periodic table based on electron arrangement.
Key Points: Insights into Mendeleev’s Periodic Table
Key Points: Insights into Mendeleev’s Periodic Table
- Mendeleev corrected atomic masses to correctly place elements.
- He predicted new elements like Sc, Ga, and Ge with correct properties.
- He later added a zero group for noble gases.
- Co and Ni have similar masses, which can cause confusion about their order.
- Isotopes couldn’t be placed due to different masses.
- Atomic mass gaps are uneven, so new elements couldn’t be predicted.
- Hydrogen's position is unclear—it’s like both alkali metals and halogens.
Key Points: Periods and Electronic Configuration
- Elements in the same period have the same number of electron shells, while valence electrons increase by one from left to right.
- Periods are determined by the number of shells; e.g., second-period elements have electrons in K and L shells.
- Valency and reactivity depend on the number of valence electrons and the shell number, both identifiable from the element’s position in the periodic table.
Important Questions [16]
- Fill in the Blank: the Modern Periodic Table Consists of ……………. Periods.
- Write the Merits of the Modern Periodic Table Over Mendeleev’S Periodic Table
- Define periods of modern periodic table.
- Define groups of modern periodic table.
- Select the appropriate options and complete the following paragraph: (metals, non-metals, metalloids, four, seven, s-block, p-block, d-block, f-block). On the basis of electronic configuration,
- The Element Eka-silicon in Mendeleev’S Periodic Table is Known as in the Modern Periodic Table.
- Classify the following elements into metals, non-metals and metalliods As, C, Hg, Mg, S, Si
- Answer the Following Question: State the Four Blocks of the Modern Periodic Table Based on the Electronic Configuration of Elements.
- Differentiate Between Normal Elements and Transition Elements.
- Taking into Consideration the Period of the Elements Given Below, Answer the Following Questions : (Pm)
- Fill in the Blank and Rewrite the Completed Statement: ________ Group in the Periodic Table Contains Elements that Are All Gases at Room Temperature.
- Give Scientific Reason: Atomic Size Increase Down the Group.
- Fill in the Blank: the Formulae of Chloride of Metal M is Mcl2. the Metal M Belongs to ……………. Group.
- Elements in the Same Group Show the Same Valency. Give Scientific Reason.
- The atomic masses of three elements A, B and C having similar chemical properties are 7, 23 and 39, respectively
- Write the Electronic Configuration of K and Ne.
