Understanding Atomic Structure: Number, Mass, Isotopes, and Ions
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Understanding Atomic Structure
Atomic Number
The atomic number (Z) is the number of protons in an atom. In a neutral atom, the number of electrons is equal to the number of protons.
Mass Number
The mass number (A) of an atom is the total number of protons (Z) and neutrons (n) in the nucleus. Therefore, A = Z + n.
Atomic Mass
The atomic mass is the mass of a single atom. Because the masses of atoms are very small, they are typically expressed using atomic mass units (amu) rather than SI units.
Isotopes
Isotopes are atoms of the same element that have the same atomic number but different mass numbers. Isotopes of an element have the same number of protons but different numbers of neutrons.
Atomic Orbitals (Electron Shells)
Atomic orbitals, or electron shells, occupy most of the volume of an atom. Electrons reside in these orbitals, which are located at different energy levels around the nucleus. The electron shells can hold a specific number of electrons:
- 1st shell (K): Up to 2 electrons
- 2nd shell (L): Up to 8 electrons
- 3rd shell (M): Up to 18 electrons
- 4th shell (N): Up to 32 electrons
Ions
Ions are atoms that have gained or lost electrons from their electron shells:
- Cations: A neutral atom that loses one or more electrons becomes positively charged and is called a cation.
- Anions: A neutral atom that gains one or more electrons becomes negatively charged and is called an anion.
Atomic Number
The atomic number (Z) is the number of protons in an atom. In a neutral atom, the number of electrons is equal to the number of protons.
Mass Number
The mass number (A) of an atom is the total number of protons (Z) and neutrons (n) in the nucleus. Therefore, A = Z + n.
Atomic Mass
The atomic mass is the mass of a single atom. Because the masses of atoms are very small, they are typically expressed using atomic mass units (amu) rather than SI units.
Isotopes
Isotopes are atoms of the same element that have the same atomic number but different mass numbers. Isotopes of an element have the same number of protons but different numbers of neutrons.
Atomic Orbitals (Electron Shells)
Atomic orbitals, or electron shells, occupy most of the volume of an atom. Electrons reside in these orbitals, which are located at different energy levels around the nucleus. The electron shells can hold a specific number of electrons:
- 1st shell (K): Up to 2 electrons
- 2nd shell (L): Up to 8 electrons
- 3rd shell (M): Up to 18 electrons
- 4th shell (N): Up to 32 electrons
Ions
Ions are atoms that have gained or lost electrons from their electron shells:
- Cations: A neutral atom that loses one or more electrons becomes positively charged and is called a cation.
- Anions: A neutral atom that gains one or more electrons becomes negatively charged and is called an anion.