Chapter 11 Lesson 2 The Structure of Atoms Ms. Diana and Ms. Amanda

Parts of an Atom The Nucleus Nucleus – The center part of an atom that contains most of the mass. The nucleus has most of the mass of an atom because it contains protons and neutrons. Proton – positively charged particle found in the nucleus of the atom. Neutron – a particle that has no charge.

Electrons Electron – negatively charged particle found outside of the nucleus. Electrons move very fast and they don’t have fixed locations. They are found moving around the nucleus.

Electron Clouds Electron Clouds – an area around the nucleus where you would find one or more electrons. You can find more than one electron cloud in an atom. Electrons have energy. The closer it is to the nucleus, the more energy it has. The farther it is from the nucleus, the less energy.

The Size of Atoms Atoms are extremely small particles that you cannot see.

Atomic Number Atomic Number – the total number of protons in the nucleus of an atom. The atomic number is found above the element’s symbol on the periodic table.

Neutrons and Isotopes Isotope – atoms of an element that have the same number of protons, but different numbers of neutrons. Example: Boron-10 and Boron-11 **Notice they are both Boron atoms, but the number of Neutrons is different.

Electrons and Ions Another way that atoms are different in their number of electrons. When Protons = Electrons, atom is neutral. When an atom loses an electron, it is positive. When an atom gains an electron, it is negative. Ion – an atom that has a charge because it has lost or gained an electron.