Uploaded August 2025 | Updated September 2026, 2 weeks ago
What the Box on the Periodic Table Tells You
Dr. DeBacco
Atomic Number
The atomic number is the number of protons in the nucleus of an atom of a given element.
Element Identity: The atomic number uniquely identifies an element.
Hydrogen: Atomic number 1 (1 proton)
Carbon: Atomic number 6 (6 protons)
Oxygen: Atomic number 8 (8 protons)
Role in the Periodic Table: Elements are arranged in the periodic table in order of increasing atomic number
Element Symbols
Element symbols are shorthand notations (mostly 1 or 2 letter abbreviations) used to represent chemical elements in the periodic table.
The first letter is always capitalized, and the second letter (if present) is lowercase.
Hydrogen: H
Carbon: C
Oxygen: O
Gold: Au
Sodium: Na
Symbols are typically derived from the element’s name in English, Latin, or another language. For instance:
English: Hydrogen (H), Nitrogen (N).
Latin: Gold (Au, from aurum), Iron (Fe, from ferrum).
Other languages: Tungsten (W, from German wolfram).
Atomic Mass
The atomic mass is a measure of the total mass of an atom, primarily determined by the particles in its nucleus (protons and neutrons) and to a much lesser extent electrons of the atom expressed in atomic mass units (amu).
The number of protons (atomic number) and neutrons (which varies in isotopes) determines most of the atomic mass.
1 amu is defined as approximately 1/12 the mass of a carbon-12 atom.
Atomic Mass Typically Ignore Electrons
Electrons contribute negligibly to the atomic mass (since each is about 1/1,836 that of a proton)
Their contribution is often ignored in calculations.
Average Atomic Mass
The atomic mass listed in the periodic table is a weighted average of the masses of an element’s naturally occurring isotopes, based on their relative abundances.
For example, chlorine’s atomic mass is ~35.45 amu, reflecting a mix of chlorine-35 (~75.8%) and chlorine-37 (~24.2%).
Link to Lecture Slides: drive.google.com/file/d/1qzdh4rFhW3l5bkhRE531FnDeHQRO2J91/view?usp=drive_link
*Due to the description character limit the full work cited for "What the Box on the Periodic Table Tells You" can be viewed at... docs.google.com/document/d/1ESoQy8IzOkvb5wFOhWVfqkiDLLj8ifPM/edit?usp=drive_link&ouid=104237452697237972847&rtpof=true&sd=true
What the Box on the Periodic Table Tells You
Dr. DeBacco
Atomic Number
The atomic number is the number of protons in the nucleus of an atom of a given element.
Element Identity: The atomic number uniquely identifies an element.
Hydrogen: Atomic number 1 (1 proton)
Carbon: Atomic number 6 (6 protons)
Oxygen: Atomic number 8 (8 protons)
Role in the Periodic Table: Elements are arranged in the periodic table in order of increasing atomic number
Element Symbols
Element symbols are shorthand notations (mostly 1 or 2 letter abbreviations) used to represent chemical elements in the periodic table.
The first letter is always capitalized, and the second letter (if present) is lowercase.
Hydrogen: H
Carbon: C
Oxygen: O
Gold: Au
Sodium: Na
Symbols are typically derived from the element’s name in English, Latin, or another language. For instance:
English: Hydrogen (H), Nitrogen (N).
Latin: Gold (Au, from aurum), Iron (Fe, from ferrum).
Other languages: Tungsten (W, from German wolfram).
Atomic Mass
The atomic mass is a measure of the total mass of an atom, primarily determined by the particles in its nucleus (protons and neutrons) and to a much lesser extent electrons of the atom expressed in atomic mass units (amu).
The number of protons (atomic number) and neutrons (which varies in isotopes) determines most of the atomic mass.
1 amu is defined as approximately 1/12 the mass of a carbon-12 atom.
Atomic Mass Typically Ignore Electrons
Electrons contribute negligibly to the atomic mass (since each is about 1/1,836 that of a proton)
Their contribution is often ignored in calculations.
Average Atomic Mass
The atomic mass listed in the periodic table is a weighted average of the masses of an element’s naturally occurring isotopes, based on their relative abundances.
For example, chlorine’s atomic mass is ~35.45 amu, reflecting a mix of chlorine-35 (~75.8%) and chlorine-37 (~24.2%).
Link to Lecture Slides: drive.google.com/file/d/1qzdh4rFhW3l5bkhRE531FnDeHQRO2J91/view?usp=drive_link
*Due to the description character limit the full work cited for "What the Box on the Periodic Table Tells You" can be viewed at... docs.google.com/document/d/1ESoQy8IzOkvb5wFOhWVfqkiDLLj8ifPM/edit?usp=drive_link&ouid=104237452697237972847&rtpof=true&sd=true
