What are atoms?

What are atoms?

1. Basic structural units of elements

   • Smallest unit of an element, each atom retains all the chemical properties of that element
   • There are 92 different types of elements in nature

2. Composed of still smaller particles

   • Neutrons, which have no charge; protons, which carry a positive charge; electrons, which carry a negative charge
   • Protons and neutrons cluster together in the center of the atom, while electrons are in continuous rapid motion around the nucleus

3. Elements are defined by their atomic numbers

   • The number of protons in the nucleus is what defines each element, called the atomic number

4. Isotopes are atoms of the same element with different numbers of neutrons

   • Isotopes can be distinguished from one another because each has a different mass number
   • Some isotopes are stable which means their nuclei do not change spontaneosly
   • Some isotopes are radioactive, meaning their nuclei spontaneously break apart or decay
   • Some radioactive isotopes release particles with enough energy that they can damage DNA, and can cause mutations

5. Nuclei and electrons play complementary roles in atoms

   • Nuclei, unless they are radioactive, provide stability. Electrons that occupy shells further away from the nucleus are at a higher energy state
   • An atom that is excited by energy can cause an electron to jump from a lower-energy electron shell to a higher-energy shell
   • Each electron shell can hold a specific number of electrons. Electrons always fill the shell nearest to the nucleus first to become stable