Final answer:
To find the total valence electrons in 1.42 gm of methane, calculate the moles of methane from its mass and multiply by the number of valence electrons per molecule. There are approximately 708 valence electrons in 1.42 gm of methane.
Step-by-step explanation:
To calculate the total number of valence electrons in 1.42 gm of methane (CH₄), we must first convert the mass of methane to moles and then multiply by the number of valence electrons per molecule.
Methane has a molar mass of 16.04 g/mol (carbon's molar mass is 12.01 g/mol, and hydrogen's is 1.01 g/mol for each of the four hydrogen atoms, adding to 4.04 g/mol). The number of moles in 1.42 g of methane is calculated by:
n = mass / molar mass = 1.42 g / 16.04 g/mol = 0.0885 mol
The number of valence electrons in one molecule of methane is 8 (carbon has 4 valence electrons and each hydrogen atom has 1 valence electron).
The total number of valence electrons is:
Total valence electrons = moles × valence electrons per molecule = 0.0885 mol × 8 e⁰/mol = 0.708 e⁰ = 708 e⁰
Therefore, 1.42 gm of methane contains approximately 708 valence electrons.