Elements and atoms form the foundation of matter. These building blocks combine to create everything around us, from the air we breathe to the cells in our bodies. Understanding their structure and behavior is crucial for grasping the complexities of chemistry and biology.

Atomic structure, isotopes, and electron configurations play vital roles in determining an element's properties and reactivity. These concepts help explain how atoms interact, form bonds, and create the diverse compounds that make up our world. Mastering these basics is essential for comprehending more advanced topics in science.

Elements and Atoms

Relationships in atomic structure

• Matter consists of anything that has mass and occupies space
  • Composed of various elements, the fundamental substances that cannot be broken down into simpler substances by ordinary chemical means
    • Each element is made up of a single type of atom (hydrogen, oxygen, carbon, nitrogen)
• Atoms are the smallest unit of an element that retains its properties
  • Composed of subatomic particles: protons, neutrons, and electrons
• Compounds are substances made up of two or more elements chemically combined in a specific ratio
  • Possess properties that differ from those of the component elements
  • Water (H2O), carbon dioxide (CO2), glucose (C6H12O6)

Atomic number vs mass number

• Atomic number (Z) represents the number of protons in an atom's nucleus
  • Unique to each element and determines its identity
  • Carbon has an atomic number of 6
• Mass number (A) is the sum of the number of protons and neutrons in an atom's nucleus
  • Varies among isotopes of the same element
  • Carbon-12 has a mass number of 12 (6 protons + 6 neutrons)
• Significance in identifying elements
  • Atomic number uniquely identifies an element
  • Mass number helps distinguish between isotopes of an element
• Atomic mass is the weighted average mass of all isotopes of an element

Isotopes and elemental properties

• Isotopes are atoms of the same element with different numbers of neutrons
  • Have the same atomic number but different mass numbers
  • Carbon-12, carbon-13, carbon-14
• Impact on an element's properties
  • Chemical properties are largely unaffected by isotopes
  • Physical properties, such as atomic mass, can vary slightly between isotopes
  • Radioactive isotopes undergo radioactive decay, emitting particles and energy
    • Used in applications like radiometric dating, medical imaging, and cancer treatment

Electron shells and atomic behavior

• Electrons occupy specific energy levels (shells) around the nucleus
  • Shells are labeled K, L, M, N, and so on, with K being the closest to the nucleus
  • Each shell has a maximum number of electrons it can hold:
    1. K shell: 2 electrons
    2. L shell: 8 electrons
    3. M shell: 18 electrons
    4. N shell: 32 electrons
• Valence electrons, those in the outermost shell of an atom, determine an atom's chemical properties and reactivity
• Stability and reactivity
  • Atoms with a full valence shell (2 or 8 electrons) are generally stable and less reactive
    • Noble gases (He, Ne, Ar, Kr, Xe, Rn)
  • Atoms with partially filled valence shells are more reactive
    • Tend to gain, lose, or share electrons to achieve a stable configuration
    • Alkali metals (1 valence electron) and halogens (7 valence electrons)
• Bonding occurs when atoms form chemical bonds to achieve a stable electron configuration
  • Ionic bonds involve the transfer of electrons between atoms
    • Formed between metals (lose electrons) and nonmetals (gain electrons)
    • Sodium chloride (NaCl), potassium oxide (K2O)
  • Covalent bonds involve the sharing of electrons between atoms
    • Formed between nonmetals
    • Water (H2O), methane (CH4), oxygen (O2)

Atomic Structure and Periodic Trends

• The periodic table organizes elements based on their atomic structure and properties
• Electrons occupy specific orbitals within electron shells, which determine an atom's electron configuration
• Electronegativity is the tendency of an atom to attract electrons in a chemical bond
• Atomic radius is the distance from the center of an atom's nucleus to its outermost electron shell