chemistry 101-chapter 4

Overview of Atoms

• Structure of Atoms

  • Atoms are made of protons, neutrons, and electrons.

  • Protons: Positively charged particles found in the nucleus.

  • Neutrons: Neutral particles found in the nucleus.

  • Electrons: Negatively charged particles that orbit the nucleus.

  • Overall, atoms can be neutral when the number of protons equals the number of electrons.

The Periodic Table

• The periodic table includes all known chemical elements and their properties.

  • Electronegativity: Key concept for understanding an atom's ability to attract electrons. This will be important for future chapters.

  • Important trends in the periodic table influence chemical behavior and reactions, particularly focusing on groups and periods.

Historical Perspectives

• Democritus: Proposed the idea of indivisible atoms and coined the term "atomos."

• John Dalton: Formulated modern atomic theory explaining the existence of atoms based on experimentation.

• J.J. Thomson: Discovered the electron and developed the plum pudding model, which was later refuted.

• Ernest Rutherford: Conducted gold foil experiment revealing the existence of a dense nucleus within the atom.

Subatomic Particles

• Protons and Neutrons:

  • Protons and neutrons have similar masses, while electrons are much lighter (approximately 1/1836 of a proton/neutron).

  • The mass number of an atom is the total number of protons and neutrons.

• Ions:

  • Ions form when an atom gains or loses electrons.

  • Cations: Positively charged ions (loss of electrons).

  • Anions: Negatively charged ions (gain of electrons).

Atomic Number and Mass Number

• Atomic Number (Z): Identifies the element, equal to the number of protons.

• Mass Number (A): Total number of protons and neutrons.

  • Difference between mass number and atomic number gives the number of neutrons.

Isotopes

• Isotopes: Atoms of the same element with different numbers of neutrons.

  • Example: Neon has isotopes such as Neon-20 and Neon-21, which vary by the number of neutrons.

  • Average atomic mass on the periodic table accounts for the abundance of isotopes.

Groups and Periods on the Periodic Table

• Groups: Vertical columns that group elements with similar properties (e.g., alkali metals, alkaline earth metals, halogens, noble gases).

  • Alkali Metals (Group 1): Highly reactive, tend to lose one electron.

  • Alkaline Earth Metals (Group 2): Reactive, tend to lose two electrons.

  • Halogens (Group 17): Reactive nonmetals that usually gain one electron, forming anions.

  • Noble Gases (Group 18): Inert gases with full valence shells, very stable.

Chemical Reactions and Electron Transfer

• Atoms undergo reactions to achieve stable electron configurations, often resembling noble gases.

• Octet Rule: Atoms gain, lose, or share electrons to fill their outermost shell, typically aiming for eight electrons for stability.

• Valence Electrons: Electrons in the outermost shell that participate in chemical bonding.

Review Notes for Exams

• Focus on understanding periodic trends, electron behaviour in groups 1, 2, and 17, and the significance of stability in noble gases.

• Review the definitions and differences between cations and anions, as well as the basics of isotypes and their importance in atomic mass calculations.