Atom Structure and Isotopes

Atom Structure

• Protons, Neutrons, and Electrons
  • Protons are positively charged particles located in the nucleus.
  • Neutrons are neutral particles located in the nucleus.
  • Electrons are negatively charged particles that orbit the nucleus.
• Atomic Mass Unit (amu)
  • Protons and neutrons each have a mass of approximately 1 amu.
  • Electrons have a very small mass, almost negligible.

Isotopes

• Definition: Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.
• Properties:
  • Isotopes of the same element share similar chemical properties but can have slightly different physical properties.
  • This difference in physical properties can be attributed to the variation in mass caused by different numbers of neutrons.

Periodic Table Organization

• Invention: Dmitri Mendeleev invented the periodic table in the 1800s.
• Main Categories:
  • Metals: Elements on the left side of the periodic table that are generally shiny, malleable, ductile, good conductors of heat and electricity.
  • Non-metals: Elements on the right side of the periodic table that are generally not shiny, not malleable, not ductile, poor conductors of heat and electricity.
  • Metalloids (semimetals): Elements found along the border between metals and non-metals, possessing properties of both.

Periodic Table Structure

• Periods (Horizontal Rows): Elements in the same period have the same number of electron shells or energy levels.
• Groups/Families (Vertical Columns): Elements in the same group have similar chemical properties due to sharing the same number of electrons in their outermost shell, also known as valence electrons.

Key Groups

Group 1: Alkali Metals

• Examples: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), Francium (Fr)
• Valence Electrons: 1
• Physical Properties:
  • Solid at room temperature
  • Shiny, silvery color
  • Soft metals
• Chemical Properties:
  • Highly reactive
  • React with water to produce hydrogen gas
  • Exist in nature only as compounds
  • Lose 1 electron to form +1 ions

Group 2: Alkaline Earth Metals

• Examples: Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), Radium (Ra)
• Valence Electrons: 2
• Physical Properties:
  • Solid, denser than Group 1 metals
  • Metallic
• Chemical Properties:
  • Reactive, although less than Group 1 metals
  • Exist in nature only as compounds
  • Lose 2 electrons to form +2 ions

Group 17: Halogens

• Examples: Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At), Tennessine (Ts)
• Valence Electrons: 7
• Physical Properties:
  • Non-metals
  • Varied states:
    • Fluorine (F) is a yellow gas
    • Chlorine (Cl) is a yellow-green gas
    • Bromine (Br) is a red-brown liquid
    • Iodine (I) is a violet/black solid
• Chemical Properties:
  • Highly reactive and corrosive
  • Exist in nature only as compounds