Basic Chemistry and Atomic Structure

Essential Elements of Life

• The four most abundant elements in living organisms are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N).

Atomic Structure

• Atoms consist of protons (+), neutrons (0), and electrons (-).

• Protons and neutrons reside in the atomic nucleus, while electrons occupy electron shells (electron cloud).

Atomic Number and Mass Number

• Atomic number: the number of protons in an atom, defining the element.

• Mass number: the sum of protons and neutrons in the nucleus.

• Isotopes: atoms of the same element with different numbers of neutrons, leading to different mass numbers.

Radioactive Isotopes

• Radioactive isotopes: unstable isotopes that decay, releasing particles and energy.

Electron Distribution

• Electrons are arranged in shells around the nucleus; the first shell holds up to 2 electrons, while the second and third shells can hold up to 8 electrons.

• Orbitals: 3D spaces within electron shells where electrons are most likely to be found. Each orbital holds a maximum of 2 electrons.

Atomic Reactivity

• Atoms with incomplete outer shells (valence shells) are reactive.

• Valence electrons: electrons in the outermost shell determine an atom's chemical behavior.

• Atoms fill valence shells by accepting, donating, or sharing electrons, forming chemical bonds and creating molecules or compounds.