Chem Revision
Element:
A pure substance made of only one type of atom.
Each element is defined by the number of protons in its nucleus.
Elements can have different chemical and physical properties depending on the material formed by their atoms.
Examples of elements and their chemical symbols include carbon (C), hydrogen (H), sodium (Na), and mercury (Hg).
Atomic Number (Z):
Represents the number of protons in the nucleus of an atom.
Each element has a unique atomic number.
For example, oxygen has an atomic number of 8, meaning it has 8 protons in its nucleus.
The atomic number is usually written as a subscript before the chemical symbol in atomic notation.
Mass Number (A):
Represents the total number of protons and neutrons present in the nucleus of an atom.
It's calculated as: Mass number = number of protons + number of neutrons.
The mass number is usually written as a superscript before the chemical symbol in atomic notation.
Isotopes:
Atoms of the same element with the same number of protons but a different number of neutrons. Isotopes have the same atomic number but different mass numbers.
They have identical chemical properties but may have different physical properties such as mass and density.
Some isotopes are radioactive, meaning their nucleus is unstable and will decay into a more stable form.
Ions:
Atoms that have gained or lost one or more electrons, resulting in a net electrical charge.
○ Cations: Positively charged ions formed when an atom loses electrons. For example, a sodium ion (Na+) forms when a sodium atom loses one electron.
○ Anions: Negatively charged ions formed when an atom gains electrons. For example, an oxygen ion (O2−) forms when a fluorine atom gains two electrons.