Atomic Structure and Isotopes
Atomic Structure
- All matter is made up of tiny units called atoms.
- An atom consists of three main subatomic particles: protons, neutrons, and electrons.
- Protons are positively charged particles found in the atom's nucleus.
- Neutrons have no charge and are also located in the nucleus.
- Electrons are negatively charged particles that orbit the nucleus in electron shells.
- The nucleus is the central part of an atom and contains protons and neutrons.
- Atomic number is the number of protons in the nucleus of an atom. It determines the chemical element.
- Mass number is the sum of protons and neutrons in the nucleus. It indicates the mass of the atom.
Electron Arrangement
- Electrons are arranged in shells or energy levels around the nucleus.
- The first shell can hold up to 2 electrons, the second up to 8 electrons, and so on.
- The arrangement of electrons in shells is known as the atom's electron configuration.
- Electrons in the outermost shell are called valence electrons and are important for chemical bonding.
Isotopes
- Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons.
- Isotopes have the same atomic number but different mass numbers.
- Some isotopes are stable, while others are radioactive and can decay over time.
- The chemical properties of isotopes are mostly identical because they have the same electron configuration.
- The differences in isotopes can affect their physical properties, such as density and rate of diffusion.
Relative Atomic Mass
- The relative atomic mass (A_r) is the weighted average mass of the atoms of an element, taking into account all of its isotopes and their relative abundances.
- A_r is usually compared to one-twelfth of the mass of a carbon-12 atom.
- Relative atomic mass is useful for calculating the amount of substance in moles when dealing with different isotopes.