Chapter 4 vocab

2. Section 1 Atom: The smallest particle of an element. Electron: The negatively charged particles of an atom. Nucleus: The center of the atom. Protons: The positively charged particles in the nucleus. Neutrons: The neutrally charged particles in the nucleus that are the same size as the protons.

3. Energy Level: The specific amount of energy an electron has. Atomic Number: The number of protons in an atom’s nucleus. The number of protons equal the number of electrons. Mass Number: The number of protons and neutrons in the nucleus of the atom. Isotopes: Atoms of the same element with a different number of neutrons.

4. Section 2 Dmitri Mendeleev- Developed the periodic table based on atomic masses. Atomic Mass- the average mass of all the isotopes of an element. Periodic Table- an arrangement of elements showing the repeating pattern of their properties. The modern periodic table is arranged by atomic number. Mosley developed this.

5. Period: A horizontal row of the periodic table. Group: A vertical column of the periodic table. Chemical symbol: a representation of an element usually consisting of one or two letters.

6. Section 3 Metal: Elements that are good conductors of electric current and heat, shiny and bendable. Malleable: A material that can be hammered or rolled into flat sheets or other shapes. Ductile: Material that can be pulled out or drawn into a long wire. Thermal conductivity- The ability of an object to transfer heat. Electrical conductivity: The ability of an object to transfer electric current.

7. Reactivity: The ease and speed with which a substance reacts with other substances. Corrosion: The gradual wearing away of a metal due to a chemical reaction. Alkali Metals: The metals in Group 1 not including Hydrogen. They react by losing one electron. Highly reactive. Alkaline Earth Metals: Groups 2 elements of the periodic table. They react by losing two electrons. Transition metals: Elements in Groups 3 through 12. Particle Accelerators: Powerful machines that move atomic nuclei faster and faster until they have reached very high speeds.

8. Section 4 Nonmetals: Poor conductors of electric current and heat. Solid nonmetals are dull and brittle. Diatomic Molecule: A molecule that consists of two atoms. Halogens: Groups 17 elements that are called “salt-formers” Inert Gases: Groups 18 elements. Tend to be un-reactive. Semimetals: Have some properties of metals, but also have some properties of nonmetals. Solids at room temp. brittle and hard. Semiconductors: Substances that can conduct electric current under some conditions but not under others.

9. Section 5 Radioactive decay: A process in which the atomic nuclei of unstable isotopes release fast-moving particles and energy. Radioactivity: The ability to spontaneously emit radiation. Alpha particle: two protons and two neutrons with a positive charge. Beta particle: a fast-moving electron given off my a nucleus during radioactive decay. Gamma radiation: high-energy waves similar to X-rays. Tracers: radioactive isotopes that can be followed through the steps of a chemical reaction or an industrial process.