what are atoms?

what are atoms?

1. Atoms are the basic structural units of elements

   • Elements are substances that cannot be broken down into simpler substances
     • Elements form all matter alone and when combined with other elements

2. An atom is the smallest unit of an element, and retains all the chemical properties of that element

   • All atoms belong to one of the 92 naturally occurring elements

3. Atoms are composed of still-smaller particles

   • Atoms are composed of subatomic particles
     • In the central atomic nucleus, there are positively charged protons and uncharged neutrons
       • In orbit around the nucleus are negatively charged particles called electrons
         • Atoms are electrically neutral because their number of positive protons and negative electrons is equal

4. The mass number of an atom is the total mass of the protons and neutrons contained in the nucleus

   • The atomic nucleus is formed by the cluster of protons and neutrons in the center of the atom

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

   • Variant atomic forms of an element are called isotopes
     • Some isotopes are radioactive
       • At room temperature, elements may occur as solids, liquids, or gases

6. Electrons can capture and release energy