Chapter 5 Review The Periodic Table

Chapter 5 Review Mendeleev arranged the known chemical elements in a table according to increasing mass. When Mendeleev organized elements in his periodic table in order of increasing mass, elements with similar properties were in the same column, or group. Mendeleev gave the name eka-aluminum to an unknown element he predicted would have properties similar to those of aluminum. This element was later discovered and named gallium. The usefulness of Mendeleev’s periodic table was confirmed by the discovery of elements with predicted properties.

Chapter 5 Review In a periodic table, a set of properties repeats from row to row. This is called the periodic law. In the periodic table, the rows are called periods and the columns are called groups. The modern periodic table is organized by increasing atomic number. The atomic mass unit is based on 1/12th the mass of a carbon-12 atom. The atomic mass of an element is the weighted average of the masses of an element’s isotopes.

Chapter 5 Review There are three classes of elements: metals, nonmetals, and metalloids Metals conduct heat and electricity, are malleable, and are ductile. All metals except mercury are solids at room temperature. Nonmetals do no conduct heat or electricity, and they are brittle. Many nonmetals are gases at room temperature. Metalloids can have properties of both metals and nonmetals.

Chapter 5 Review The metals are on the left side of the stair-step line on the periodic table. The nonmetals are on the right side of the stair-step line on the periodic table. The metalloids are either right above or right below the stair-step line. As you move across a period from left to right, the elements become less metallic and more nonmetallic.

Chapter 5 Review Valence electrons: electrons in the highest occupied energy level of an atom The chemical properties of elements are determined by their valence electrons. Elements in a group have similar properties because they have the same number of valence electrons The number of valence electrons in a Group A elements matches its group number

Chapter 5 Review Group 1A Group 7A Group 2A Alkali metals Halogens 1 valence electron 7 valence electrons Reactivity increases going down Reactivity decreases going down Group 2A Group 8A is called the noble gases. Alkaline earth metals 2 valence electrons Noble gases 8 valence electrons (He has 2) Emit color when electric current is applied

Chapter 5 Review Some highly reactive elements are stored in argon gas to protect them. Carbon is in most of the compounds in your body except water.