Number and arrangement of the electron pairs around:
a. C in CCl4
b. S in H2S
c. Al in AlH3
d. Ga in GaCl3
To determine the number and arrangement of electron pairs around an atom, we need to consider its Lewis structure. The Lewis structure shows the valence electrons of the atom and any bonds it forms with other atoms.
a. Carbon (C) in CCl4:
Carbon has 4 valence electrons. Chlorine (Cl) also has 7 valence electrons. In CCl4, there is one Carbon atom bonded to four Chlorine atoms. To determine the electron pairs around carbon, we can start by drawing the Lewis structure:
Cl:Cl
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C-Cl
In this Lewis structure, each line represents a bond. Carbon forms four bonds, one with each chlorine atom. In CCl4, carbon is in the center, with four single bonds to chlorine atoms surrounding it. Each bond consists of two electrons, so there are eight electrons involved in the bonds. Additionally, there are four unshared (non-bonding) pairs of electrons on each chlorine atom, which are not involved in bonding. Therefore, the total number of electron pairs around carbon in CCl4 is 8 (from the bonds) + 4 (from the unshared pairs) = 12.
b. Sulfur (S) in H2S:
Sulfur has 6 valence electrons. Hydrogen (H) has 1 valence electron. In H2S, there is one sulfur atom bonded to two hydrogen atoms. We can draw the Lewis structure as follows:
H-S-H
In this Lewis structure, the sulfur atom forms two single bonds with hydrogen atoms. Each bond consists of two electrons, so there are four electrons involved in the bonding. Additionally, there are two unshared pairs of electrons on the sulfur atom, which are not involved in bonding. Therefore, the total number of electron pairs around sulfur in H2S is 4 (from the bonds) + 2 (from the unshared pairs) = 6.
c. Aluminum (Al) in AlH3:
Aluminum has 3 valence electrons. Hydrogen has 1 valence electron. In AlH3, there is one aluminum atom bonded to three hydrogen atoms. The Lewis structure can be represented as follows:
H-Al-H-H
In this Lewis structure, the aluminum atom forms three single bonds with hydrogen atoms. Each bond consists of two electrons, so there are six electrons involved in the bonding. Therefore, the total number of electron pairs around aluminum in AlH3 is 6.
d. Gallium (Ga) in GaCl3:
Gallium has 3 valence electrons. Chlorine has 7 valence electrons. In GaCl3, there is one gallium atom bonded to three chlorine atoms. The Lewis structure can be represented as follows:
Cl-Ga-Cl
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Cl
In this Lewis structure, the gallium atom forms three single bonds with chlorine atoms. Each bond consists of two electrons, so there are six electrons involved in the bonding. Therefore, the total number of electron pairs around gallium in GaCl3 is 6.
Remember, the number and arrangement of electron pairs around an atom can assist in determining the molecular geometry and the properties of a molecule.