To determine the shape of a molecule like HC≡N (hydrogen cyanide), we need to consider the hybridization of the central atom and the number of electron domains around it. This approach is based on the VSEPR (Valence Shell Electron Pair Repulsion) theory.
Identify the central atom: In HC≡N, carbon (C) is the central atom, bonded to hydrogen (H) and nitrogen (N).
Draw the Lewis structure:
The Lewis structure for HC≡N is:
\( \text{H} - \text{C} \equiv \text{N} : \)
Here, H is bonded to C by a single bond, and C is bonded to N by a triple bond. Nitrogen also has one lone pair of electrons.
Determine the number of electron domains around the central atom (Carbon):
For the central carbon atom:
Total electron domains around carbon = \(1 + 1 = 2\).
Determine the hybridization of the central atom:
With 2 electron domains, the carbon atom undergoes sp hybridization.
Predict the molecular geometry based on VSEPR theory:
According to VSEPR theory, if a central atom has two electron domains and no lone pairs, the electron domains will arrange themselves as far apart as possible, resulting in a linear geometry. The bond angle will be \(180^\circ\).
Conclusion: The HC≡N molecule has a linear shape.
Correct Option: D) Linear
The central carbon atom in HC≡N is sp hybridized and has two electron domains (one single bond to H and one triple bond to N). According to VSEPR theory, two electron domains will arrange themselves in a linear fashion to minimize repulsion, resulting in a bond angle of \(180^\circ\) and a linear molecular geometry.
A) Tetrahedral — This shape is associated with sp3 hybridization and four electron domains, typically with bond angles of approximately \(109.5^\circ\) (e.g., methane, CH4). HC≡N does not have four electron domains around its central carbon.
B) Parabolic — Parabolic is a mathematical curve, not a standard molecular geometry term used in VSEPR theory for simple molecules.
C) Curved — While some molecules can be bent or curved (e.g., water, H2O, which has a bent shape due to lone pairs), HC≡N has no lone pairs on its central carbon and its two bonding domains lead to a straight arrangement, not a curve.
The question asks to identify what a single dash represents in chemical notation. This is a fundamental concept in chemistry, specifically in understanding chemical bonds.
Correct Option: A) A single dash represents a single bond, where two atoms share one pair of electrons.
The question asks for the chemical formula of ethyne. Ethyne is an alkyne, which is a hydrocarbon containing at least one carbon-carbon triple bond. The general formula for alkynes is \(C_nH_{2n-2}\).
C) C₂H₂ is the correct chemical formula for ethyne, derived from the alkyne general formula \(C_nH_{2n-2}\) with \(n=2\).
Statement: The structural formulas can be further abbreviated by omitting some or all of the dashes representing covalent bonds and by indicating the number of identical groups attached to an atom by a subscript.
Question: The resulting expression of the compound is called a _____ formula.
Small structural
Condensed structural
Expanded structural
Both a and b
The question describes a method of representing chemical compounds where covalent bonds are omitted or abbreviated, and identical groups are indicated by subscripts. We need to identify the specific type of formula that results from this representation.
B) Condensed structural — A condensed structural formula is a way to write organic molecules without showing all the individual bonds. Instead, groups of atoms are written together, and the number of identical groups attached to an atom is indicated by a subscript. For example, propane, which has the expanded structural formula \(\text{CH}_3-\text{CH}_2-\text{CH}_3\), can be written as \(\text{CH}_3\text{CH}_2\text{CH}_3\) in its condensed form. This method precisely matches the description provided in the question.
Match the following compounds with their chemical formula.
| List I | List II |
| a) Ethane | i.) CH₃OH |
| b) Ethene | ii.) HC≡CH |
| c) Ethyne | iii.) H₂C=CH₂ |
| d) Methanol | iv.) CH₃CH₃ |
a-iii,b-ii,c-iv,d-i
a-iv,b-i,c-iii,d-ii
a-ii,b-iii,c-iv,d-i
a-iv,b-iii,c-ii,d-i
To match the compounds with their chemical formulas, we need to recall the basic nomenclature and structures of simple organic compounds, specifically alkanes, alkenes, alkynes, and alcohols. The prefixes 'eth-' and 'meth-' indicate the number of carbon atoms, while suffixes like '-ane', '-ene', '-yne', and '-ol' indicate the type of functional group or saturation.
Combining these matches:
This corresponds to option D.
D) a-iv,b-iii,c-ii,d-i is the correct match based on the chemical formulas and nomenclature of the given compounds.
Statement: In the bond-line structural representation of organic compounds, carbon and hydrogen atoms are not shown.
Question: The lines representing carbon-carbon bonds are drawn in a _____ fashion.
The question asks about the standard representation of carbon-carbon bonds in bond-line structures of organic compounds. This is a fundamental concept in organic chemistry nomenclature and representation.
A) The lines representing carbon-carbon bonds are drawn in a zig-zag fashion. This convention is used to depict the tetrahedral geometry of carbon and to clearly show the connectivity of the carbon skeleton.