Unit 6: Introduction to the Atom

An atom is the basic unit of matter, representing the smallest particle of an element that retains the chemical properties of that element. Here are key features of an atom:

• Protons:

  • Positively charged particles.
  • Found in the nucleus of the atom.
  • The number of protons defines the element.

• Neutrons:

  • Neutral particles with no charge.
  • Also located in the nucleus.
  • Contribute to the atomic mass.

• Electrons:

  • Negatively charged particles.
  • Orbit the nucleus in electron shells.
  • Determine the atom's chemical behavior.

Central, dense region of the atom.

• Contains protons and neutrons.
• Accounts for most of the atom's mass.

• Region surrounding the nucleus where electrons move.
• Electrons do not follow fixed paths but exist in probability distributions.

• Number of protons in an atom.
• Determines the element's identity.
• Elements are arranged on the periodic table based on atomic number.

• Sum of protons and neutrons in the nucleus.
• Written as a superscript to the left of the elemental symbol.

• Atoms of the same element with different numbers of neutrons.
• Have the same atomic number but different mass numbers.

• Energy levels where electrons are organized.
• Electrons fill inner shells before occupying outer ones.
• The first shell can hold up to 2 electrons, the second up to 8, and so on.

• Represent elements in the periodic table.
• Usually one or two letters (e.g., H for hydrogen, O for oxygen).

• Atoms are extremely small, typically measured in angstroms (10^(-10) meters).
• The size varies depending on the element.

• The arrangement of electrons determines the chemical properties of an atom.
• Chemical reactions involve the rearrangement of electrons.

Understanding the structure and properties of atoms is fundamental to the study of chemistry. It provides insights into the behavior of elements, the formation of compounds, and the basis for the diversity of matter in the universe.