Atomic Structure and Subatomic Particles

Atomic Structure

• Atoms are the fundamental building blocks of matter.
• Atoms are composed of a positively charged nucleus surrounded by negatively charged electrons.
• The nucleus contains positively charged protons and neutral neutrons.
• The number of protons in the nucleus determines the element.
• Electrons orbit the nucleus in specific energy levels or shells.
• Electrons in the outermost shell are called valence electrons and are involved in chemical bonding.

Subatomic Particles

• Protons: Positively charged particles found in the atomic nucleus.
• Neutrons: Neutral particles found in the atomic nucleus.
• Electrons: Negatively charged particles that orbit the nucleus.
• The mass of a proton and neutron is approximately equal and much greater than the mass of an electron. Thus, the nucleus accounts for nearly all the atom's mass.

Atomic Number and Mass Number

• The atomic number (Z) is the number of protons in the nucleus of an atom.
• It uniquely identifies an element.
• The mass number (A) is the sum of protons and neutrons in an atom's nucleus.
• The number of neutrons in an atom is calculated as: Mass Number (A) - Atomic Number (Z)

Isotopes

• Atoms of the same element that have different numbers of neutrons are called isotopes.
• Isotopes have the same atomic number but different mass numbers.
• Isotopes have the same chemical properties.

Atomic Models

• Early models: Dalton's model proposed atoms as indivisible spheres. Thomson's model introduced the concept of electrons within the atom. Rutherford's model described a small, dense positive nucleus with electrons orbiting it.
• Modern models: The Bohr model depicted electrons orbiting the nucleus in specific energy levels. The modern quantum mechanical model describes electrons as occupying orbitals, regions of space where the probability of finding an electron is high.

Electron Configuration

• Electrons fill energy levels and sublevels in a specific order.
• The order of filling orbitals follows the Aufbau principle, Hund's rule, and the Pauli exclusion principle.
• Each orbital can hold a maximum of two electrons.
• Electron configuration describes how electrons are arranged in the different energy levels and sublevels within an atom.

Periodic Table

• Elements are organized in the periodic table based on their increasing atomic number.
• Elements with similar properties are grouped together in columns (groups or families).
• Elements are arranged in rows (periods) based on the electron configurations of their atoms.
• The arrangement of elements in the periodic table helps in predicting physical and chemical properties of different elements.