3.6: End of Chapter Key Terms

Atomic Theory and the Periodic Table Key Terms

1. Atom: The smallest unit of an element that retains the properties of that element, consisting of protons, neutrons, and electrons.
2. Nucleus: The dense central core of an atom, containing protons and neutrons.
3. Proton: A positively charged subatomic particle found in the nucleus of an atom.
4. Neutron: A neutral subatomic particle found in the nucleus of an atom.
5. Electron: A negatively charged subatomic particle that orbits the nucleus of an atom.
6. Atomic Number (Z): The number of protons in the nucleus of an atom, which determines the element's identity.
7. Mass Number (A): The total number of protons and neutrons in the nucleus of an atom.
8. Isotope: Atoms of the same element with the same number of protons but different numbers of neutrons.
9. Atomic Mass Unit (amu): A unit of mass used to express atomic and molecular weights, approximately equal to the mass of a proton or neutron.
10. Atomic Mass: The weighted average mass of the isotopes of an element, typically expressed in atomic mass units (amu).
11. Electron Cloud: The region around the nucleus where electrons are likely to be found.
12. Orbital: A region of space around the nucleus where an electron is likely to be found, described by quantum numbers.
13. Quantum Numbers: Numbers that describe the properties of atomic orbitals and the properties of electrons in orbitals.
14. Principal Quantum Number (n): Indicates the relative size and energy of atomic orbitals; larger nnn values correspond to higher energy levels.
15. Angular Momentum Quantum Number (l): Describes the shape of an atomic orbital; values range from 0 to n−1n-1n−1.
16. Magnetic Quantum Number (m_l): Describes the orientation of the orbital in space; values range from −l-l−l to +l+l+l.
17. Spin Quantum Number (m_s): Describes the spin of an electron; can be +12+\frac{1}{2}+21​ or −12-\frac{1}{2}−21​.
18. Electron Configuration: The arrangement of electrons in an atom's orbitals, described by the distribution of electrons among energy levels and orbitals.
19. Aufbau Principle: States that electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels.
20. Pauli Exclusion Principle: States that no two electrons in an atom can have the same set of four quantum numbers.
21. Hund's Rule: States that electrons will fill degenerate orbitals (orbitals of the same energy) singly before pairing up.
22. Periodic Table: A tabular arrangement of elements in order of increasing atomic number, with elements having similar properties placed in vertical columns (groups).
23. Period: A horizontal row in the periodic table, where elements have the same number of electron shells.
24. Group (Family): A vertical column in the periodic table, where elements have similar chemical properties and the same number of valence electrons.
25. Valence Electrons: Electrons in the outermost shell of an atom, which determine the chemical properties and reactivity of the element.
26. Alkali Metals: Elements in Group 1 of the periodic table (excluding hydrogen), characterized by having one valence electron.
27. Alkaline Earth Metals: Elements in Group 2 of the periodic table, characterized by having two valence electrons.
28. Transition Metals: Elements in Groups 3-12 of the periodic table, characterized by having d electrons.
29. Halogens: Elements in Group 17 of the periodic table, characterized by having seven valence electrons.
30. Noble Gases: Elements in Group 18 of the periodic table, characterized by having a full valence shell of electrons, making them very stable and unreactive.
31. Lanthanides: A series of elements from atomic numbers 57 to 71, characterized by filling of 4f orbitals.
32. Actinides: A series of elements from atomic numbers 89 to 103, characterized by filling of 5f orbitals.
33. Metals: Elements that are typically shiny, conductive, malleable, and ductile.
34. Nonmetals: Elements that are typically not shiny, poor conductors, and brittle in solid form.
35. Metalloids: Elements with properties intermediate between metals and nonmetals.
36. Atomic Radius: The distance from the nucleus to the outermost electron shell of an atom.
37. Ionization Energy: The energy required to remove an electron from a gaseous atom or ion.
38. Electron Affinity: The energy change that occurs when an electron is added to a neutral atom in the gas phase.
39. Electronegativity: A measure of the ability of an atom in a chemical compound to attract electrons.
40. Periodic Trends: Patterns observed in the periodic table for properties such as atomic radius, ionization energy, electron affinity, and electronegativity.