Chemistry Chapter: Periodic Table and Isotopes

Periodic Table Setup and Organization

• The periodic table arranges elements based on increasing atomic number, reflecting the number of protons in the atom's nucleus.
• Elements with similar chemical properties are grouped vertically into columns (groups or families).
• Elements are also organized horizontally into rows (periods).
• Elements within the same group share similar valence electron configurations, leading to common chemical reactions and properties.
• Metals are typically located on the left side and middle of the table, while nonmetals are predominantly on the right side.
• Transition metals are found in the central block.
• Metalloids exhibit properties intermediate between metals and nonmetals, located along a stair-step line.
• The table provides a visual representation of electron relationships among elements, aiding in predicting chemical behavior.

Isotopes

• Isotopes are atoms of the same element with the same number of protons but a different number of neutrons.
• The number of protons defines the element's identity.
• The difference in neutrons causes variations in atomic mass.
• Isotopic notation shows the element symbol, mass number (protons + neutrons), and sometimes atomic number (protons).
• Isotopes can be stable or unstable (radioactive).
• Radioactive isotopes decay over time, emitting radiation.
• The relative abundance of isotopes is crucial in calculating the average atomic mass of an element.

Atomic Theory

• Dalton's atomic theory proposed that all matter is composed of indivisible atoms of varying mass and properties.
• Atoms of the same element are identical and have the same mass.
• Atoms of different elements combine in simple whole number ratios to form chemical compounds.
• Atoms are neither created nor destroyed during chemical reactions.
• Modern atomic theory builds upon Dalton's concept, acknowledging the subatomic constituents: protons, neutrons, and electrons.
• Atoms are mostly empty space with a dense nucleus containing protons and neutrons.
• Electrons orbit the nucleus in specific energy levels.
• Quantum mechanics describes the behavior of electrons and other subatomic particles.

Atomic Mass and Mass Number

• Atomic mass is the average mass of all isotopes of an element, weighted by their relative abundance.
• It is measured in atomic mass units (amu) or daltons (Da).
• Mass number is the sum of the protons and neutrons in an atom's nucleus.
• It is a whole number and describes the mass of a specific isotope.
• The atomic mass of an element is not a whole number due to the weighted average of various isotopes' abundances.
• Atomic mass is often rounded to more convenient values.