Chemistry Test 272

Hydrogen, the first in the list of elements is a special case and can be considered as making up the first period all by itself. The second and third period in Meyer's table included seven elements each, and duplicated Newlands's law of octaves.

Li Be B C N O F

Na Mg Al Si P S Cl 

However, the next wave had more than seven elements. The third wave had about 17 to 18 elements. This clearly showed where Newlands’ law had failed. One could not force the law of octaves to hold strictly throughout the table of elements, with seven elements in each row. After the first two periods, the length of the period had to be longer.so all the correct answer.

In Lothar Meyer’s atomic volume curve, elements at peaks (highest atomic volumes) are alkali metals (e.g., Li, Na), which are highly electropositive and have large atomic volumes.

The correct answer is Option B.

General electronic configuration is given:

(n − 2)f^1-14(n − 1)d⁰¹ns² , where(n=7)

5f^1-146d⁰¹ns²

The seventh period (n=7) is similar to the sixth period with the successive filling up of the 7s, 5f, 6d and 7p orbitals and includes most of the man-made radioactive elements. This period will end at the element with atomic number 118 which would belong to the noble gas family. Filling up of the 5f orbitals after actinium (Z=89) gives the 5f-inner transition series known as the Actinide Series.

Periods:

• Elements are arranged in increasing the atomic number of elements in a period.
• One extra electron gets added to the outermost shell as we move along the periods from left to right.
• The electron gets added to the same shell or orbit and thus the electrons present for bonding increase by one unit.
• Thus, the shell number remains the same but the number of electrons present for bonding increases along a period.

Groups:

• Elements having the same number of outer electrons are put in the same group of the periodic table.
• When we move down a group, one extra shell gets added to the elements.
• The outermost shell has electrons present for bonding.
• Though the number of shells increases as we go down in a group, the number of electrons in the outermost shell remains the same.
• For example, the Halogens F, Cl, Br, I, At all belong to group 17 and have 7 electrons in the outermost shell.
• Similarly, Group 16 elements have 6 electrons in the outermost shell, group 15 has 5 electrons in the outermost shell, and so on.

Hence, group 17 is called halogens.

• The element was to be called unununium (with the corresponding symbol of Uuu),a systematic element name as a placeholder, until the element was discovered (and the discovery then confirmed) and a permanent name was decided on.
• Although widely used in the chemical community on all levels, from chemistry classrooms to advanced textbooks, the recommendations were mostly ignored among scientists in the field, who called it element 111, with the symbol of E111, (111) or even simply 111.

The structure with more delocalization and more charge separation is the most stable.

Here, structure I has more delocalization and charge separation and hence is the most stable among the three.

Structures II and III have equal stability.

This explains that structure I is the most stable due to greater delocalization and charge separation, while structures II and III have similar stability.

Due to delocalisation of π-electrons, (C—Cl) bond is stable and it does not show S_N reactions; Cl directly attached (C=C) bond, i.e. vinyl group.

Strength of H-bonding depends on the electronegativity of the atom which follows the order: F > O > N .

Strength of H-bond is in the order:

H……. F > H…….. O > H…….. N

But each H₂O molecule is linked to 4 other H₂O molecules through H-bonds whereas each HF molecule is linked only to two other HF molecules.

Hence, correct decreasing order of the boiling points is H_zO > HF > NH₃.

In sp² hybridization, three hybrid orbitals are formed, arranged in a trigonal planar geometry with bond angles of 120°. This is seen in molecules like BF₃ or C₂H₄. Other hybridizations have different angles:

sp³: 109.5° (tetrahedral).

sp: 180° (linear).

90°: Not typical for standard hybridizations.

For sp²: ∠ = 120°.

This explanation clarifies the angles associated with different hybridizations and gives examples of molecules with sp² hybridization.

Vinyl acetylene is CH₂=CH-C≡CH (buta-1,3-enyne).

The carbon atoms are numbered as follows:

• C₁: CH₂, sp² hybridized (double bond).
• C₂: CH, sp² hybridized (double bond).
• C₃: C≡, sp hybridized (triple bond).
• C₄: C≡, sp hybridized (triple bond).

The bond between C₂ and C₃ is a single bond formed by the overlap of an sp² orbital from C₂ and an sp orbital from C₃.

C₂-C₃ bond: sp²-sp.

Answer: D.