Atomic Structure

Subatomic Particles

The atom consists of a dense nucleus surrounded by electrons. The nucleus contains protons and neutrons, while electrons occupy the space around the nucleus.

• Proton (p+): Positively charged particle found in the nucleus. Relative charge: +1. Relative mass: 1.00727 amu.

• Neutron (n0): Neutral particle found in the nucleus. Relative charge: 0. Relative mass: 1.00866 amu.

• Electron (e-): Negatively charged particle found outside the nucleus. Relative charge: -1. Relative mass: 0.00055 amu.

Atomic mass unit (amu): Defined as 1/12 the mass of a carbon-12 atom.

• 1 amu = g

Atomic Number and Mass Number

Each element is defined by its atomic number (Z), which is the number of protons in its nucleus. The mass number (A) is the sum of protons and neutrons.

• Atomic Number (Z): Number of protons in the nucleus. Determines the element's identity.

• Mass Number (A): Total number of protons and neutrons in the nucleus.

• Element Symbol: One- or two-letter abbreviation for the element (e.g., C for carbon, Fe for iron).

Notation: Elements are often represented as:

• , where X is the element symbol, A is the mass number, and Z is the atomic number.

• Alternative notation: X-A (e.g., Ne-22).

Isotopes

Isotopes are atoms of the same element (same number of protons) but with different numbers of neutrons. Isotopes have identical chemical properties but may have different physical properties (such as mass or stability).

• Example: Carbon-12 () has 6 protons and 6 neutrons; Carbon-13 () has 6 protons and 7 neutrons.

Ions

An ion is an atom or molecule with a net electric charge due to the loss or gain of electrons.

• Cation: Positively charged ion (loss of electrons). Example: ,

• Anion: Negatively charged ion (gain of electrons). Example: ,

Net charge calculation:

• Net charge = Number of protons - Number of electrons

Atomic Mass and Isotopic Abundance

The atomic mass of an element is the weighted average of the masses of all its naturally occurring isotopes, based on their relative abundances.

• Formula:

• Example: For gallium (Ga):

amu

Periodic Table and Periodic Law

The Periodic Table organizes elements by increasing atomic number. The Periodic Law states that when elements are arranged in order of increasing atomic number, certain sets of properties recur periodically.

• Elements in the same group (column) have similar chemical properties.

• Periodic trends include atomic radius, ionization energy, and electronegativity.

Additional info:

• Some values and terms were clarified for accuracy (e.g., electron mass, isotope notation).

• Examples and formulas were expanded for clarity and completeness.