Chemistry Overview and Basics

Studying Chemistry

• Chemistry is the study of matter, how it changes and the energy associated with those changes.
• Studying Chemistry helps us understand the composition and properties of materials, chemical reactions, and the energy involved in these processes.

Matter and Elements

• Matter is anything that occupies space and has mass.
• All matter is composed of elements.
• Elements are substances that cannot be broken down into simpler substances by chemical means.
• Elements are made up of atoms.
• All atoms of a specific element are identical.

Atoms and The Periodic Table

• The Periodic Table is a directory of elements, with 118 elements currently known.
• Elements like gold, silver, copper, and carbon have been known for centuries, while others like livermorium and flerovium are newly discovered.
• Each element has a unique symbol, usually one-to-two letters, like H, Ag, and Co.
• The symbol often represents the English name of the element.
• The first letter of the symbol is always capitalized, while the second, if present, is lowercase.

Atoms and Element Properties

• An atom is the smallest unit of matter.
• Atoms are too small to be seen with microscopes.
• The number of protons in an atom determines its identity.
• For example, a hydrogen atom always has 1 proton, a carbon atom always has 6 protons, and a platinum atom always has 78 protons.

Atomic Number and Electrons

• Atoms with an equal number of protons and electrons are electrically neutral.
• Atoms with a positive or negative charge are called ions.
• The atomic number represents the number of protons and electrons in a neutral atom.
• For example, a neutral hydrogen atom has 1 electron, a neutral carbon atom has 6 electrons, and a neutral platinum atom has 78 electrons.

Mass Number and Isotopes

• The mass number (A) represents the total number of protons and neutrons in the nucleus of an atom.
• The number of neutrons can be calculated by subtracting the atomic number (Z) from the mass number (A): Number of neutrons = A - Z.
• Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
• Some elements exist as only one type of atom (no isotopes), such as aluminum-27 (Al-27).

Calculating Relative Atomic Mass

• Most elements have two or more isotopes.
• The relative atomic mass of an element, as shown in the Periodic Table, is the average mass of all its isotopes, accounting for their natural abundance.
• This results in relative atomic masses not always being whole numbers.
• The relative atomic mass is calculated as the average mass of the isotopes, considering their relative natural abundances.

Example Relative Atomic Mass Calculation: Carbon

• Carbon has two isotopes: 12C and 13C.
• The natural abundance of 12C is 98.89%, and its atomic mass is 12.00.
• The natural abundance of 13C is 1.11%, and its atomic mass is 13.0034.
• To calculate the average mass of 100 carbon atoms, you multiply the natural abundance of each isotope by its atomic mass and sum the results: ((98.89 x 12.00) + (1.11 x 13.0034)) / 100.
• This results in an average mass of 12.01 atomic mass units (a.m.u.) for a single carbon atom.

Example Relative Atomic Mass Calculation: Chlorine

• Chlorine has two isotopes: 35Cl and 37Cl.
• The natural abundance of 35Cl is 75.77%, and its atomic mass is 34.97.
• The natural abundance of 37Cl is 24.23%, and its atomic mass is 36.97.
• To calculate the average mass of 100 chlorine atoms, you multiply the natural abundance of each isotope by its atomic mass and sum the results: ((75.77 x 34.97) + (24.23 x 36.97)) / 100.
• This results in an average mass of 35.45 a.m.u. for a single chlorine atom.