Overview
This lecture explains the structure of the atom, the identity and notation of elements, and how to determine the numbers of subatomic particles.
Atomic Structure
- The nucleus, located at the atom's center, contains protons (positive charge) and neutrons (no charge).
- The nucleus is dense due to the mass of protons and neutrons.
- Electrons (negative charge) orbit the nucleus and are in constant motion.
Subatomic Particles and Element Identity
- Elements are defined by their number of protons.
- The number of protons is called the atomic number, abbreviated as Z.
- Changing the number of protons changes the element to a different one.
Elemental Symbol Notation
- Element symbols are written as:
[ ^A_Z X ]
where X = element symbol, A = atomic mass number, Z = atomic number.
- Mass number (A) = protons + neutrons.
- Atomic number (Z) = number of protons.
- The number of neutrons = mass number (A) minus atomic number (Z).
Examples
- Oxygen (O): Atomic number Z = 8;
if mass number A = 17, neutrons = 17 - 8 = 9.
- For a neutral oxygen atom, electrons = protons = 8.
- Californium (Cf): Z = 98, A = 251;
neutrons = 251 - 98 = 153;
neutral atom electrons = 98.
Charge and Electrons
- The charge is shown in the notation as a superscript; if blank, the atom is neutral.
- Neutral atoms have equal numbers of protons and electrons.
Key Terms & Definitions
- Proton — positively charged subatomic particle found in the nucleus.
- Neutron — neutral subatomic particle found in the nucleus.
- Electron — negatively charged subatomic particle orbiting the nucleus.
- Atomic number (Z) — number of protons in an atom, defines the element.
- Mass number (A) — total number of protons and neutrons in the nucleus.
Action Items / Next Steps
- Prepare for a discussion on atoms with unequal protons and electrons (ions) in the next class.