Chemical compounds of a cell

Atoms

• Matter is made of elements, substances that cannot be broken down further by chemical means.
• The smallest unit of an element that retains its chemical properties is an atom.
• Atoms are composed of a central nucleus surrounded by a cloud of negatively charged electrons.
• The nucleus contains protons (positively charged) and neutrons (no charge).
• The number of protons determines the atomic number, which defines the element.
• The number of electrons equals the number of protons, ensuring electrical neutrality.
• The electrons determine the chemical behavior of an atom.

Isotopes

• Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
• Different isotopes have the same chemical properties but different physical properties.
• Carbon 12 (6 protons, 6 neutrons) is the most common isotope of carbon.
• Carbon 14 (6 protons, 8 neutrons) is a radioactive isotope used in carbon dating.

Atomic Weight

• Atomic weight is the mass of an atom relative to a hydrogen atom.
• It is determined by the number of protons and neutrons since electrons have negligible mass.
• The atomic weight of carbon 12 is 12, while carbon 14 has an atomic weight of 14.
• Atomic mass is often expressed in daltons, where one dalton is approximately the mass of a hydrogen atom.

Size of Atoms

• Atoms are incredibly small, with a carbon atom measuring roughly 0.2 nm in diameter.
• A single gram of hydrogen contains 6 × 10^23 atoms, also known as Avogadro's number.

Moles and Molar Solutions

• A mole of a substance contains 6 × 10^23 molecules.
• The mass of one mole of a substance in grams is equal to its molecular weight.

Essential Elements of Life

• There are 92 naturally occurring elements.
• Living organisms primarily consist of four elements: carbon (C), hydrogen (H), nitrogen (N), and oxygen (O).
• These four elements account for 96.5% of an organism's body mass.