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A chemical bond is the attractive force that holds two atoms together in a chemical compound. These bonds involve the sharing or transferring of electrons between atoms, allowing them to combine into more stable forms.

Atoms form bonds with each other to achieve a stable electron configuration in their outermost shell, known as the valence shell. This stability is commonly achieved by having a full valence shell, usually with eight electrons (octet rule). Atoms can either share electrons with other atoms, which is known as covalent bonding, or they can transfer electrons to other atoms, which is known as ionic bonding. In both cases, the result is an overall reduction in the system's energy, making the atom more stable.

Some elements exist as molecules in nature instead of as free atoms due to their more stable electron configuration when bonded. For example, elemental oxygen (O) exists in nature as a diatomic molecule (O2) because each oxygen atom shares a pair of electrons with another oxygen atom to fill their valence shells, satisfying the octet rule. This sharing of electrons creates a stable covalent bond and a more stable molecular arrangement than free oxygen atoms. Similarly, elemental hydrogen (H) exists as diatomic molecules (H2) in nature because each hydrogen atom shares its single electron with another hydrogen atom, creating a stable covalent bond and satisfying the duet rule, which means that the atom will have a full valence shell with 2 electrons. In summary, the existence of these molecules in nature is due to the increased stability provided by their bonded states compared to the free atoms.