Lecture on Atoms and Isotopes
Elements and Compounds
- Element: Consists of only one type of atom, cannot be broken down further.
- Example: Oxygen is composed solely of oxygen atoms.
- Compound: Consists of more than one type of atom and can be broken down into its elements.
- Example: Water (Hâ‚‚O) can be broken down into hydrogen (H) and oxygen (O) through electrolysis.
Structure of an Atom
- Nucleus:
- Very small, dense, positive due to protons and neutrons.
- Protons: Positive charge.
- Neutrons: No charge (neutral).
- Electrons:
- Negative charge.
- Located in the electron cloud, which is larger in volume than the nucleus.
- In a neutral atom, the number of protons equals the number of electrons.
Atomic Mass and Charge
- Atomic Mass: Primarily from protons and neutrons; electrons have negligible mass.
- Atomic Charge: Determined by the number of protons (positive) and electrons (negative).
- Neutral atoms have equal numbers of protons and electrons.
Periodic Table
- Contains 118 elements with specific numbers:
- Atomic Number: Number of protons, changes the element if altered.
- Atomic Mass: Average mass considering naturally occurring isotopes (rounded to two decimal places).
Isotopes
- Atoms of the same element with the same number of protons but different numbers of neutrons.
- Example: Carbon has isotopes like carbon-12, carbon-13, and carbon-14.
- Carbon-14 is used in dating (e.g., fossils), with 8 neutrons and 6 protons.
- Mass Number: Sum of protons and neutrons.
Isotope Notations
- Hyphen Notation: Element name/symbol followed by mass number (e.g., Carbon-12).
- Nuclear Notation: Mass number as a superscript, atomic number as a subscript, followed by element symbol.
- Example: Carbon-12 is written with 12 above and 6 below the symbol C.
Practical Application: Calculating Neutrons
- Formula: Mass number = protons + neutrons.
- Example: Barium-131
- Atomic number (protons) = 56.
- Neutrons = Mass number - protons = 131 - 56 = 75.
Finding Elements and Isotope Names
- Use the atomic number on the periodic table to identify elements.
- Example: Element with atomic number 80 is Mercury.
- Isotope name: Symbol followed by a dash and the mass number (e.g., Hg-197).
These notes summarize the lecture on atoms, isotopes, and associated calculations and notations.