Atomic Structure and Periodic Table

Atomic Structure

• An atom consists of:
  • Protons (positively charged) in the nucleus
  • Neutrons (no charge) in the nucleus
  • Electrons (negatively charged) in energy levels around the nucleus
• Atomic number: number of protons in an atom (defines the element)
• Mass number: number of protons and neutrons in an atom (defines the isotope)
• Atomic mass: average mass of an element's naturally occurring isotopes

Periodic Table

• Organizes elements by their atomic number and chemical properties
• Elements are arranged in:
  • Periods (rows): elements with similar energy levels
  • Groups (columns): elements with similar chemical properties
• Periodic trends:
  • Atomic radius: decreases from left to right and increases down a group
  • Electronegativity: increases from left to right and decreases down a group

Electron Configuration

• The arrangement of electrons in an atom's energy levels
• Energy levels (shells): 1, 2, 3, ... (each with a specific capacity)
• Subshells: s, p, d, f (each with a specific capacity)
• Aufbau principle: electrons occupy the lowest available energy level
• Hund's rule: electrons occupy degenerate orbitals with parallel spin
• Electron configuration notation: 1s2 2s2 2p6, ...

Chemical Reactions

• A process involving the transformation of one or more substances
• Types of chemical reactions:
  • Synthesis: two or more substances combine to form a new substance
  • Decomposition: a single substance breaks down into two or more substances
  • Single displacement: one element replaces another in a compound
  • Combustion: a substance reacts with oxygen to produce heat and light
• Chemical equations: a representation of a chemical reaction using chemical formulas and arrows

Chemical Bonding

• The attractive forces between atoms that hold them together
• Types of chemical bonds:
  • Ionic bond: transfer of electrons between atoms (e.g., NaCl)
  • Covalent bond: sharing of electrons between atoms (e.g., H2)
  • Polar covalent bond: unequal sharing of electrons between atoms (e.g., HCl)
• Bonding theories:
  • Valence shell electron pair repulsion (VSEPR) theory: predicts molecular shape
  • Molecular orbital (MO) theory: predicts molecular structure and bonding

Atomic Structure

• An atom consists of protons, neutrons, and electrons, with protons and neutrons in the nucleus and electrons in energy levels around the nucleus.
• The atomic number, which defines the element, is the number of protons in an atom.
• The mass number, which defines the isotope, is the sum of protons and neutrons in an atom.
• Atomic mass is the average mass of an element's naturally occurring isotopes.

Periodic Table

• The periodic table organizes elements by their atomic number and chemical properties.
• Elements are arranged in periods (rows) and groups (columns), with similar energy levels in periods and similar chemical properties in groups.
• Atomic radius decreases from left to right and increases down a group, while electronegativity increases from left to right and decreases down a group.

Electron Configuration

• Electron configuration is the arrangement of electrons in an atom's energy levels, with each energy level (shell) having a specific capacity.
• Subshells, including s, p, d, and f, also have specific capacities.
• The Aufbau principle states that electrons occupy the lowest available energy level, while Hund's rule states that electrons occupy degenerate orbitals with parallel spin.
• Electron configuration notation is written in the format 1s2 2s2 2p6, etc.

Chemical Reactions

• Chemical reactions involve the transformation of one or more substances, with types including synthesis, decomposition, single displacement, and combustion reactions.
• Chemical equations represent chemical reactions using chemical formulas and arrows.

Chemical Bonding

• Chemical bonds are the attractive forces between atoms that hold them together, with types including ionic, covalent, and polar covalent bonds.
• Ionic bonds involve the transfer of electrons between atoms, while covalent bonds involve the sharing of electrons.
• Polar covalent bonds involve the unequal sharing of electrons between atoms.
• Bonding theories, including VSEPR and MO theories, predict molecular shape and structure.