1. Different Elements— Different Numbers of Protons An element is a pure substance made from atoms that all have the same number of protons. Atoms of a particular element always have the same number of protons. 4.3 Elements, Isotopes, and Ions— How Atoms Differ

2. Different Elements— Different Numbers of Protons The number of protons in an atom of an element is the element’s atomic number. The periodic table shows elements that increase in atomic number horizontally. Elements in the same column have similar properties. 4.3 Elements, Isotopes, and Ions— How Atoms Differ

3. Protons, Neutrons, and Mass Number An atom’s mass number is the sum of the number of protons and the number of neutrons. To calculate the number of neutrons, subtract the atomic number from the mass number. 4.3 Elements, Isotopes, and Ions— How Atoms Differ

4. Periods A horizontal row of elements in the periodic table is called a period. The atomic numbers increase by one from left to right across a period. 7.1 Organization of the Periodic Table

5. Groups A vertical column of elements in the periodic table is called a group. Groups are numbered 1–18 across the top of the periodic table. Elements in the same group have similar properties. 7.1 Organization of the Periodic Table

6. The Lanthanide and Actinide Series The two rows of elements at the bottom of the table are the Lanthanide Series and the Actinide Series. 7.1 Organization of the Periodic Table

7. Metals Elements that are on the left side and in the middle of the periodic table are metals. 7.1 Organization of the Periodic Table

8. Metals Metallic refers to the properties of common metals. Luster, or shine, is one property of metals. Metals are also ductile and malleable. Conductivity is the ability of a material to transfer electricity or thermal energy— metals are good conductors. 7.1 Organization of the Periodic Table

9. Nonmetals Elements on the right side of the periodic table are nonmetals. 7.1 Organization of the Periodic Table

10. Nonmetals Nonmetals exhibit properties that are the opposite of metals. They are poor conductors of heat and electricity, are brittle, and do not have luster. Nonmetals make up most of the matter in the living world. The most reactive nonmetals are the halogens in Group 17. 7.1 Organization of the Periodic Table

11. Semimetals A few elements are semimetals, or metalloids. 7.1 Organization of the Periodic Table

12. Semimetals Semimetals have the properties of both metals and nonmetals. Semimetals conduct electricity but not as well as metals. 7.1 Organization of the Periodic Table

13. Noble Gases Group 18 elements are the noble gases. Noble gases are extremely stable by themselves and occur in nature as single atoms. 7.1 Organization of the Periodic Table