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Valence electrons are the outermost electrons of an atom that are involved in chemical bonding. They play a crucial role in determining how atoms interact with each other. In the case of water (\( \mathrm{H}_{2}\mathrm{O} \)), the total number of valence electrons can be calculated by summing the valence electrons of each individual atom in the molecule.

- Each hydrogen atom has 1 valence electron.- The oxygen atom has 6 valence electrons.
For two hydrogen atoms and one oxygen atom, the total number of valence electrons is \( (2 \times 1) + (1 \times 6) = 8 \) valence electrons. These electrons are used in chemical bonding and in forming lone pairs around atoms. Understanding valence electrons is fundamental to writing the Lewis structure for a molecule.

The central atom in a molecule is typically the atom with the highest ability to attract electrons, known as electronegativity, or having the most bonds with other atoms. In water (\( \mathrm{H}_{2}\mathrm{O} \)), oxygen becomes the central atom due to its higher electronegativity compared to hydrogen.

A skeleton structure is first drawn with oxygen at the center and hydrogen atoms bonded to either side, forming a rough "H-O-H" shape.
Positioning in a molecule is vital because it guides the bonding and arrangement of electrons, thus predicting molecular shape and reactivity.

Lone pairs consist of valence electrons that are not involved in bonding and remain with a single atom. They are very important in shaping the molecule and determining its polarity and properties.

For water (\( \mathrm{H}_{2}\mathrm{O} \)), we start with 8 valence electrons. Two are used for the \( O-H \) bonds, leaving 6 electrons.
These remaining electrons are arranged as three lone pairs on the oxygen atom. - These lone pairs make the oxygen electron-rich.- Each pair contributes to the bent shape of the molecule.With the presence of these lone pairs, the shape of water is angular rather than linear, influencing many properties like its high boiling point and solvent abilities.

The Lewis structure of a molecule visualizes its valence electrons, bonds, and lone pairs. It's a simple way to represent how electrons are distributed around atoms.

For \( \mathrm{H}_{2}\mathrm{O} \), the Lewis structure displays oxygen as the central atom:
- Two single bonds link oxygen to each hydrogen atom, using 2 electrons per bond.- Three pairs of lone electrons (\( 6 \) electrons) are depicted around the oxygen.This structure visually shows how all 8 valence electrons are accounted for:
- Bonding electrons in \( O-H \) bonds- Lone pairs on the oxygen atom
Understanding the Lewis structure helps predict molecular geometry, bond angles, and even reactivity, making it a foundational tool in chemistry for students and professionals alike.