Atoms, Molecules and Ions Builder

Every atom has a dense nucleus containing protons and neutrons, surrounded by electrons arranged in shells. The number of protons (Z) defines the element and its chemical properties.

• Protons carry a +1 charge and determine the element.
• Neutrons are neutral; changing them creates isotopes with the same chemical behavior but different mass.
• Electrons carry a -1 charge and govern chemical bonding.

The atomic mass number A equals protons plus neutrons. Carbon-12 has 6 protons and 6 neutrons (A = 12); Carbon-14 has 6 protons and 8 neutrons (A = 14).

An ion is an atom that has gained or lost electrons. The driving force is the octet rule: atoms are most stable when their outermost electron shell is full (8 electrons for most elements, 2 for hydrogen).

• Cations form when an atom loses electrons, leaving more protons than electrons. Example: Na loses 1 electron to become Na+ with the neon configuration.
• Anions form when an atom gains electrons. Example: Cl gains 1 electron to become Cl- with the argon configuration.

The charge equals protons minus electrons. A sodium atom (Z = 11, e = 11) is neutral; Na+ (Z = 11, e = 10) has a charge of +1.

Chemical bonds hold atoms together in molecules and compounds. The two main types differ in how electrons are shared or transferred.

• Covalent bonds form when two atoms share one or more electron pairs. Both nuclei attract the shared electrons. Examples include H2, O2, H2O, CO2, NH3, and CH4.
• Ionic bonds form when one atom completely transfers electrons to another, creating oppositely charged ions. The ions are held together by electrostatic attraction. Example: NaCl (Na+ and Cl-).

Polar covalent bonds (like H-Cl) lie between the two extremes: electrons are shared but unequally, creating partial charges.