If an atom has extra electrons, it becomes negatively charged. This is called an anion. Anions are formed when an atom gains one or more electrons. This can happen when an atom reacts with another atom that has a lower electronegativity. Electronegativity is the ability of an atom to attract electrons. When an atom with a higher electronegativity reacts with an atom with a lower electronegativity, the atom with the higher electronegativity will attract electrons from the atom with the lower electronegativity. This will cause the atom with the lower electronegativity to become negatively charged.

Anions are important in many chemical reactions. They can react with other atoms or molecules to form new compounds. For example, when an anion reacts with a positively charged ion, the two ions will form a neutral compound. Anions can also react with other molecules to form salts. Salts are compounds that contain both positive and negative ions.

The presence of extra electrons in an atom can have a significant impact on the atom's properties. For example, anions are often more reactive than neutral atoms. This is because the extra electrons make the anion more likely to react with other atoms or molecules. Anions can also be more soluble in water than neutral atoms. This is because the water molecules can interact with the extra electrons on the anion.

The presence of extra electrons in an atom can also have a significant impact on the atom's size. For example, anions are often larger than neutral atoms. This is because the extra electrons repel each other, causing the atom to expand.

The presence of extra electrons in an atom can also have a significant impact on the atom's color. For example, anions are often colored. This is because the extra electrons can absorb light of certain wavelengths, causing the atom to appear colored.