Physical Science Reviewer: Formation of Elements

Formation of Elements

• An atom is the smallest unit that constitutes all matter.
• An element is a pure substance representing a variety of a specific atom.
• Isotopes are atoms of the same element with different atomic masses due to variations in the number of neutrons.
• Protons carry a positive charge, electrons have a negative charge, and neutrons are uncharged particles.

The Big Bang Theory

• The universe's formation began about 13 billion years ago from a primordial atom's explosion.
• Evidence supporting the Big Bang includes cosmic expansion (discovered by Edwin Hubble), cosmic microwave background radiation (identified by George Gamow), and primordial nucleosynthesis.

Nucleosynthesis Types

• Big Bang Nucleosynthesis formed light elements like hydrogen, helium, and trace amounts of lithium shortly after the Big Bang.
• Stellar Nucleosynthesis occurs in stars, creating elements heavier than helium through nuclear fusion processes. Two primary processes include:
  • Proton-Proton Chain or Hydrogen Burning produces helium from hydrogen fusion.
  • CNO Cycle uses carbon as a catalyst to convert hydrogen to helium in massive stars.
• Supernova Nucleosynthesis produces elements heavier than iron through neutron capture during a star's explosion.

Life Cycle of a Star

• Stars generate energy via nuclear fusion, maintaining heat and light.
• As they age and exhaust hydrogen, they transition to burning helium, producing heavier elements through processes like the Tri-Alpha Process.
• This process ultimately leads to the creation of heavier nuclei up to iron using the Alpha Ladder Process.

Neutron Capture Mechanisms

• Neutron capture creates heavier isotopes, leading to stable or radioactive forms.
• S-process (slow) captures neutrons slowly enough to allow for beta decay, while R-process (rapid) captures neutrons quickly before decay happens.

Astrochemistry

• Astrochemists study elements in space, focusing on molecular interactions and cosmic formation processes.

Laboratory Formation of Elements

• Historical concepts introduced by philosophers like Thales and Democritus shaped the understanding of matter.
• Alchemy led to the discovery of phosphorus by Hennig Brand in the 17th century.
• The development of the periodic table evolved from efforts by scientists like John Newland and Dmitri Mendeleev.
• X-ray spectroscopy is essential for understanding chemical properties and organizing elements by atomic number.

Atomic Characteristics

• Atomic number indicates the number of protons in an atom.
• Atomic mass is derived from the sum of protons and neutrons.
• Nuclear reactions involve changes in atomic nuclei, often leading to transmutations.

Discovery of Synthetic Elements

• The first synthetic element, Technetium, was created through nuclear reactions.
• Significant synthetic elements, including Promethium and Astatine, have been produced using particle accelerators.

Artificial Elements

• Transuranic elements (Z > 92) are made through nuclear reactions and accelerators, including heavy elements like Neptunium and Plutonium.

Polarity of Molecules

• Metals exhibit conductivity, luster, ductility, and malleability, while non-metals are poor conductors and often brittle.
• Metalloids possess properties of both metals and non-metals, showing variability in conductivity and malleability.

Valence Electrons and Lewis Dot Structures

• Valence electrons are involved in chemical bonding and represented in Lewis Dot Structures.
• The Octet Rule states that atoms form compounds to achieve eight valence electrons.

Understanding Polarity

• Polarity involves unequal electron distribution within molecules, influenced by electronegativity differences:
  • Nonpolar covalent: AEN ≤ 0.4
  • Polar covalent: 0.4 < AEN < 1.9
  • Ionic: AEN ≥ 1.9

Molecular Geometry and Polarity

• Molecular geometry impacts overall molecular polarity, assessed via the VSEPR theory, which evaluates repulsion between electron groups.
• The shape of the molecule determines its polarity and is affected by lone pairs and bonding groups surrounding the central atom.

Additional Concepts

• Matter is defined as anything that has mass and occupies space.
• Chemosynthesis refers to the creation of atomic nuclei from pre-existing nucleons.
• Isotopes have the same atomic number but different mass numbers, identifiable via isotopic notation.