Chemistry Lecture Notes: Chemical Formulas, Species, and Isotopes

This set of flashcards covers fundamental chemistry concepts including chemical formulas, the differences between elements, compounds and mixtures, types of chemical species, atomic structure notation, and the role of isotopes.

Oil of Vitriol

The common name for Sulphuric acid, which has the chemical formula $H_2SO_4$.

Chemical Formula

A description of the composition of a compound in terms of symbols of the elements and the ratio between them in one formula unit or molecule.

Molecular Formula

A type of chemical formula that describes the composition of $1$ molecule or formula unit of a compound in terms of the actual ratio of atoms.

Empirical Formula

Also known as the simplest or experimental formula, it describes the composition of a compound in terms of the simplest ratio between its elements.

Element

A pure substance made up of the same atoms that cannot be decomposed into simpler substances and is represented by a symbol.

Compound

A pure substance made up of the same molecules or formula units formed by the chemical combination of different elements.

Mixture

An impure substance made of different substances physically combined that has no fixed formula and can be separated by physical means.

Chemical Species

A term for an atom or group of atoms that undergoes a chemical reaction, classified into free radicals, molecules, and ions.

Free Radical

An atom or group of atoms with an incomplete octet or duplet that is neutral and contains unpaired valence electron(s), denoted by a dot over the symbol.

Molecule

A neutral species made of atoms with a complete octet or duplet and all paired valence electron(s), making it stable under normal conditions.

Ion

An atom or group of atoms having a positive or negative charge; it is the building unit of an ionic compound.

Homolytic bond cleavage

The process by which a molecule breaks into free radicals.

Heterolytic bond cleavage

The process by which a molecule breaks into ions, such as $HCl \rightarrow H^+ + Cl^-$.

Cation

A positively charged ion formed when a metal atom loses electron(s) (oxidation) to complete its octet or duplet.

Anion

A negatively charged ion formed when a non-metal atom gains electron(s) (reduction) to complete its octet or duplet.

Simple Ion

An ion composed of a single atom having a positive or negative charge, such as $Na^+$ or $Cl^-$.

Molecular Ion

A group of atoms having a positive or negative charge, formed when a molecule loses or gains electrons.

Atomic Number ($Z$)

The total number of protons in the nucleus of an atom of an element, also known as the Proton Number.

Mass Number ($A$)

The total number of protons and neutrons in the nucleus of an atom of an element, also known as the Nucleon Number.

Atomic Mass

The mass of $1$ atom of an element measured in a.m.u., obtained by comparison with the twelfth part by mass of the lightest isotope of carbon.

Gram Atomic Mass (Gram Atom)

The atomic mass of an element expressed in grams, representing the mass of $6.02 \times 10^{23}$ atoms.

Isotopes

Atoms of an element that have the same number of protons (same atomic number) but different number of neutrons (different mass numbers).

Cobalt-60

A radioactive isotope used in radiotherapy for body cancer and for the sterilization of medical instruments and dressings.

Americium

A radioactive isotope used in safety measures and industrial applications, including smoke detectors and back scatter gauges.

Phosphorus-32

A radioactive isotope used in radiotherapy specifically for the treatment of skin cancer.

Iodine isotopes

Radioactive isotopes used in radiotherapy for the detection of thyroid glands in the neck.