Chemistry Fundamentals: Atoms, Volume, and Naming

Fundamental Concepts in Chemistry

Molar Volume Definition and Calculation

The molar volume is the volume occupied by a gas measured at 273 K (0 ºC) and 1 atm (Standard Temperature and Pressure, STP).

It has been estimated that the molar volume of any gas at 273 K and 1 atm is 224 L.

In 224 L of any gas, measured at 273 K and 1 atm, there are 6.022 × 10²³ atoms or molecules (Avogadro's number).

Atomic Structure: Nucleus and Electron Shell

The atom has a central core, the nucleus, in which almost all its mass is concentrated. This mass is provided by the neutrons and protons.

Outside the nucleus is the electron shell (or cortex), containing negatively charged electrons. These negative charges are offset by the positive charge of protons in the nucleus, ensuring the atom is electrically neutral.

Atomic Number (Z)

The number of protons in an atom is called the atomic number and is represented by the symbol $Z$.

Atomic Number = Number of Protons

The atomic number is represented by a subscript in front of the element's symbol:

• ₆C: Carbon has 6 protons.
• ₁₇Cl: Chlorine has 17 protons.

Mass Number (A)

The number of protons and neutrons in an atom is called the mass number and is symbolized by the letter $A$.

Mass Number = Number of Protons + Number of Neutrons

The mass number is represented by a superscript in front of the symbol for the element in question and is always an integer:

• ¹²C: The sum of neutrons and protons is 12. Knowing that Carbon has 6 protons, the number of neutrons is also 6.
• ³⁵Cl: The mass number is 35.

Isotopes

Isotopes are atoms of the same element that have the same atomic number but different mass numbers.

Relative Atomic Mass

The atomic mass of an element corresponds to the mass of one of its atoms and is practically equivalent to the sum of the masses of its protons and neutrons.

Therefore, the relative atomic mass ($A_r$) is the mass of an atom compared with that of the carbon-12 atom.

Remember that the carbon-12 isotope atom has been chosen as the reference to determine the relative atomic mass.

Practice Problems: Subatomic Particle Calculation

Remember that a neutral atom is electrically neutral, so the number of electrons must equal the number of protons.

Sulfur Example: Protons, Electrons, and Neutrons

If Sulfur has an Atomic Number ($Z$) of 16 and a Mass Number ($A$) of 32:

• Protons = 16
• Electrons = 16
• Neutrons = 16

Generic Element Example: Protons, Electrons, and Neutrons

If a generic element (labeled 'Carbon' in the source text) has an Atomic Number ($Z$) of 20 and a Mass Number ($A$) of 40:

• Protons = 20
• Electrons = 20
• Neutrons = 20

Chemical Nomenclature: Peroxides

Peroxides are compounds containing the O₂^2- ion.

Chemical Nomenclature: Metal Hydrides

Metal hydrides are compounds where hydrogen is bonded to a metal.