Overview
This lecture reviews the arrangement and characteristics of elements on the periodic table, focusing on their relevance to the human body and key atomic concepts.
Atomic Structure and Elements
- The atomic number equals the number of protons in an atom and defines the element.
- Changing the number of protons changes the element's identity.
- Elements are substances that cannot be broken down by chemical means.
- The periodic table organizes elements by chemical properties and assigns them unique symbols, often from Latin names.
Key Elements in the Human Body
- Hydrogen, carbon, oxygen, and nitrogen are the four major elements in the body.
- Carbon, hydrogen, and oxygen are found in all macromolecules; nitrogen is found in proteins and nucleic acids.
- Other important elements include sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), copper (Cu), zinc (Zn), selenium (Se), sulfur (S), and phosphorus (P).
- Calcium and phosphate are important for bone mineralization; phosphorus is also key in ATP.
Periodic Table Organization
- Groups (columns) indicate the number of electrons in the outer shell: group 1 has 1, group 2 has 2, etc., up to group 8.
- Group 1 elements tend to give up one electron to achieve a full shell, forming positive ions.
- Group 2 elements give up two electrons; group 3 gives up three; group 4 usually shares electrons.
- Groups 5 to 7 tend to accept or share electrons to complete their shells, forming negative ions or covalent bonds.
- Group 8 (noble gases) have full outer shells and are chemically unreactive.
Electronegativity
- Electronegativity is the tendency of an atom to attract electrons.
- The upper right corner of the periodic table (excluding noble gases) contains the most electronegative elements.
- Lower left corner elements have low electronegativity and easily give up electrons.
- Fluorine is the most electronegative; hydrogen is very weak at holding electrons.
Atomic Mass and Isotopes
- Mass number is the sum of protons and neutrons in the nucleus.
- Electrons have negligible mass.
- Isotopes are atoms of the same element with different numbers of neutrons.
- Unstable isotopes (radioisotopes) emit radiation as they decay to become stable.
- Radiation from radioisotopes can be damaging but is also used in medical imaging (e.g., PET scans).
Key Terms & Definitions
- Atomic Number — Number of protons in an atom's nucleus; defines the element.
- Element — Substance that cannot be broken down by chemical means.
- Isotope — Atom of the same element with a different number of neutrons.
- Electronegativity — Atom's tendency to attract and hold electrons.
- Noble gases — Group 8 elements with full outer electron shells; chemically inert.
Action Items / Next Steps
- Be able to identify the valence shell, atomic number, and basic structure for hydrogen, carbon, oxygen, and nitrogen.
- Lab: Draw and label the four major elements’ atomic structures.
- Prepare for next lecture on chemical bonds determined by valence shell electrons.