Fundamental Building Blocks of Life 2.1

Fundamental Building Blocks of Life

• Life is composed of matter, which occupies space and has mass.
• Matter is made of elements, substances not chemically broken down.
• 118 elements are defined; 92 are naturally occurring, with fewer than 30 in living cells.
• Elements are designated by chemical symbols (e.g., H, N, O, C, Na).
• Atoms are the smallest units of elements retaining their properties.
• Hydrogen atoms, for example, are gases at room temperature and bond with oxygen to form water.

Atomic Structure

• Atoms contain protons, electrons, and neutrons.
• Protons are positively charged, found in the nucleus, with a mass of 1 and charge +1.
• Electrons are negatively charged, orbiting the nucleus, with negligible mass and charge -1.
• Neutrons are neutrally charged, found in the nucleus, with a mass of 1.
• A neutral atom has balanced protons and electrons, thus a zero net charge.
• Atomic mass equals the number of protons plus neutrons.
• Atomic number equals the number of protons in an element.
• The difference between atomic mass and atomic number equals the number of neutrons.

Isotopes

• Isotopes are different forms of the same element, with the same number of protons but a different number of neutrons.
• Carbon-12 (6 protons, 6 neutrons) and Carbon-14 (6 protons, 8 neutrons) are isotopes of carbon.
• Some isotopes are radioactive (radioisotopes), meaning they are unstable and decay to form more stable elements.
• Carbon-14 decays to Nitrogen-14 through beta decay.
• Half-life is the time for half of an isotope to decay.
• Carbon-14 dating (half-life ~5,730 years) is used to date fossils up to ~50,000 years old.
• Potassium-40 is used for older fossils.

Electron Arrangement

• Electrons occupy energy levels (shells) around the nucleus.
• The innermost shell holds a maximum of two electrons.
• Outermost shells can hold up to eight electrons (octet rule).
• Elements in the same row of the periodic table have the same number of electron shells.
• The number of electrons in the outermost shell affects how elements interact.

Chemical Bonds and Interactions

• Atoms bond to achieve stability (e.g., filling their outer electron shells).
• Ionic bonds form when one atom donates an electron to another, creating oppositely charged ions (cations and anions) that attract.
• Covalent bonds form when atoms share electrons. Can be polar or nonpolar.
• Polar covalent bonds occur when electrons are shared unequally, creating slightly charged regions (+/-) in a molecule.
  • Water molecules are an example of polar molecules bonded by covalent bonds.
• Nonpolar covalent bonds occur when electrons are shared equally.
• Hydrogen bonds are weak attractions between hydrogen atoms and negatively charged atoms in different molecules.
  • Water's liquid state at room temperature is due to hydrogen bonds between molecules.
• Van der Waals interactions are very weak attractions between molecules.
• These bonds are crucial for water's properties, DNA structure, and protein shape.

Ions

• Ions are atoms with an unequal number of protons and electrons, therefore having a net electrical charge.
• Positive ions are called cations (formed by losing electrons).
• Negative ions are called anions (formed by gaining electrons).
• Sodium (Na+) and Chloride (Cl-) are examples of ions.

Periodic Table

• The periodic table orders elements based on atomic number and properties.
• The table's arrangement shows how electrons are organized in atoms, and hence how they will react.
• Color-coding often indicates key element properties.

Medical Applications

• Medical imaging techniques (e.g., MRI, X-rays) utilize various isotopes or hydrogen nuclei to create images of body structures.
• Radiography technicians use specialized imaging equipment to produce and analyze such images.