atoms

Fundamental Structure of the Atom

An atom is the basic unit of matter that defines the structure of an element. It consists of a dense central core known as the nucleus surrounded by a cloud of negatively charged electrons.

• Subatomic Particles:

  • Protons: Positively charged particles found within the nucleus. The relative charge is $+1$ and the relative mass is $1$.

  • Neutrons: Uncharged (neutral) particles found within the nucleus. The relative charge is $0$ and the relative mass is $1$.

  • Electrons: Negatively charged particles orbiting the nucleus in energy levels or shells. The relative charge is $-1$ and the relative mass is $\frac{1}{1836}$.

Atomic Notation and Key Terms

• Atomic Number ($Z$): The number of protons in the nucleus of an atom. This defines the chemical identity of an element.

• Mass Number ($A$): The total number of protons and neutrons in the nucleus of an atom.

  • Calculation for number of neutrons: $\text{Number of neutrons} = A - Z$

• Isotopes: Atoms of the same element with the same number of protons (same $Z$) but different numbers of neutrons (different $A$).

  • Example: Carbon-12 ($^{12}\text{C}$) has $6$ protons and $6$ neutrons, while Carbon-14 ($^{14}\text{C}$) has $6$ protons and $8$ neutrons.

Electron Configuration

Electrons occupy specific regions around the nucleus called energy levels or electron shells.

• Shell Capacity:

  • The maximum number of electrons that can occupy a given energy level $n$ is given by the formula $2n^2$.

  • First shell ($n = 1$): Maximum of $2$ electrons.

  • Second shell ($n = 2$): Maximum of $8$ electrons.

  • Third shell ($n = 3$): Maximum of $18$ electrons.

Relative Atomic Mass

• Relative Atomic Mass ($A_r$): The weighted average mass of an atom of an element relative to $\frac{1}{12}\text{th}$ of the mass of an atom of Carbon-12.

• Calculation:

  • $A_r = \frac{\text{Isotope Abundance}_1 \times \text{Isotope Mass}_1 + \text{Isotope Abundance}_2 \times \text{Isotope Mass}_2}{\text{Total Abundance}}$