The atomic number of boron is 5. The correct electronic configuration of boron i

Question

The atomic number of boron is 5. The correct electronic configuration of boron is A) 2s^2 2p^3 B) 1s^2 2p^3 C) 1s^2 2s^2sp^1 D) 1s^22s^3 E) 1s^22s^23s^1 A carbon-hydrogen bond in ethane (CH_3CH_3) is best described a _____A) essentially nonpolar B) resonance stabilized C) a multiple bond D) highly polar E) ionic The compound methylamine, CH_3NH_2, contains a C- N bond. In this bond, which of the following best describes the charge on the carbon atom? A) +1 B) slightly positive C) uncharged D) slightly negative E) -1 According to the Lewis definition, which of the following may act as acids? A) HCl B) NH_3 C) AlCl_3 D) A & B E) A, B, & C Which the following terms comes closest to describing an electrophile? A) nucleophile B) nonpolar C) anion D) Lewis acid E) Lewis base 6) The hydroxide ion (HO^-) cannot function well as which of the following? A) a Bronsted-Lowry base B) a proton acceptor c) a Lewis base D) an electron-pair acceptor E) a nucleophile Which atomic orbital combination would result in a molecular sigma bond? How many carbon-carbon sigma bonds are present in the molecule shown? A) 1 B) 2 C) 3 D) 4 E) 5

Explanation / Answer

Solution:

Ans to Q No 1:   The correct answer is (C) 1s22s22p1

Explanation: In writing the electron configuration for Boron the first two electrons will go in the 1s orbital. Since 1s can only hold two electrons the next 2 electrons for B goes in the 2s orbital. The remaining electron will go in the 2p orbital. While writing electronic configuration of an element Aufbau principle is followed. Aufbau comes from the German word "Aufbauen" which means "to build". In essence when writing electron configurations we are building up electron orbitals as we proceed from atom to atom. As we write the electron configuration for an atom, we will fill the orbitals in order of increasing atomic number. The arrangement of orbitals in order of increasing energy is as follows

1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p

<6s<4f<5d<6p<7s<5f<6d<7p

Note: The number of electrons that each orbital can occupy is limited by the Pauli exclusion principle to two.

Ans to Q No 2: The correct answer is (A) Essentially nonpolar

Explanation: In ethane, the carbon is bonded to hydrogen atoms through single covalent bonds. The difference in electronegativity between carbon ( C) and hydrogen (H) is not much (0.35) and hence the bond is essentially non polar. (Using Pauling's electronegativity scale—C (2.55) and H (2.2) difference = 0.35)

Ans to Q No 3: The correct answer is (B) Slightly positive

Explanation: The C-N bond is polar since nitrogen has a greater electronegativity, then the N will be slightly negative and the carbon will be slightly positive ( In Pauling’s electronegativity scale electronegativity of C = 2.55 and N = 3.04)

Ans to Q No 4: The correct answer is ( E) A, B & C

A Lewis acid is an electron pair acceptor. Aluminum in AlCl3 has an empty p orbital that can accommodate the pair of electrons provided by a Lewis base. HCl acts as a Lewis acid because Chlorine is more electronegative than hydrogen, and that means that the hydrogen chloride will be a polar molecule. The electrons in the hydrogen-chlorine bond will be attracted towards the chlorine end, leaving the hydrogen slightly positive and the chlorine slightly negative.

Although ammonia is well-known as a base, it can also act as an extremely weak acid. It is a protic substance and is capable of formation of amides (which contain the NH2 ion), for example lithium and ammonia react to give a solution of lithium amide:

2 Li3N + 2 NH3 3Li+ + 3 NH2-   Ammonia also acts as an acid. Here, it donates a proton to form amide.

Ans to Q No 5: The correct answer is (D) Lewis acid

Explanation: An electrophile is a species that accepts a pair of electrons to form a new covalent bond. Again, according to the definition of a Lewis acid, a Lewis acid is an electron pair acceptor.

Ans to Q No 6: The correct answer is (D) An electron pair acceptor

Explanation: The oxygen in OH- has a full octet and therefore it can't accept any additional electrons

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