Chapter 12 The Periodic Table

Section 1: Objectives Describe how Mendeleev arranged elements in the first periodic table. Explain how elements are arranged in the modern periodic table. Compare metals, non-metals, and metalloids based on their properties and on their location in the periodic table. Describe the difference between a period and a group.

How to Read the Periodic Table Before we can sketch elements, we have to know how to read the periodic table. Elements are divided into squares. Each square tells you 5 things: Element symbol Atomic number Element name Atomic mass (mass number) Physical state of element (M, NM, Mt)

Discovering a Pattern Before the 1860s, scientists had never arranged the elements. In 1869, Russian chemist Dmitri Mendeleev arranged the elements in order of increasing atomic mass. These repeating patterns are periodic, meaning that they happen at regular intervals.

Discovering a Pattern His pattern had gaps in it though. He predicted that elements that had not been discovered would fill these gaps. By 1886, all the gaps had been filled and his predictions were right.

Discovering a Pattern A few elements did not fit the pattern. In 1914, British scientists Henry Moseley found the number of protons in an atom. When the elements were arranged by atomic number, they fit the pattern.

Discovering a Pattern

Discovering a Pattern Elements are classified as metals, nonmetals, or metalloids. Valence electrons (number of electrons in outer shell) helps determine an element’s properties. The zigzag line on the periodic table helps you determine this.

Discovering a Pattern Metals are found to the left of the zigzag line. Atoms of most metals have few electrons in their outer shell. Most metals are: Shiny Malleable Good conductors of heat/electricity

Discovering a Pattern Nonmetals are found to the right of the zigzag line. Almost all nonmetals have a complete set of electrons in their outer shell. Nonmetals are: (the opposite of metals) Not shiny Not ductile Not malleable Poor conductors of heat/electricity

Discovering a Pattern Metalloids are elements that border the zigzag line. Atoms of metalloids have about half the number of electrons in their outer shell. Metalloids have some properties of metals and some of nonmetals. Metalloids are also called semiconductors. (Si)

Discovering a Pattern Each square on the periodic table includes an element’s name, chemical symbol, atomic number, and atomic mass. For most elements, the chemical symbol have one or 2 letters. Why would some elements have 3 letters?

Discovering a Pattern Each horizontal row of elements is called a period. The chemical and physical properties of elements in a row follow a repeating pattern. Each vertical column of elements is called a group. Elements in the same group often have similar chemical and physical properties.

Discovering a Pattern Elements in a group have the same number of valence electrons. Atoms can give, take, or share electrons with other atoms. An atom’s goal is to complete the outer energy level.

Section 1: Review Questions 1)What is Mendeleev famous for? 2) What did he predict about the periodic table? 3) What did Moseley discover? 4) What are valence electrons? 5) List 2 properties of metals and nonmetals. 6) What are metalloids also called? 7)What does each square on the periodic table include?

Electron Cloud Rules For today, there are 2 rules to know before adding electrons to a sketch: Electron number will equal proton number. The first level can hold only 2 electrons.

Identifying and Sketching Atoms Directions: Draw each element square along with all information for that element. Under the square write the number of protons, neutrons, and electrons. Next sketch your element including all protons, neutrons, and electrons.

Identifying and Sketching Atoms 1) Hydrogen (1 V.E.) 2) Beryllium (2 V.E.) 3) Boron (3 V.E.) 4) Nitrogen (5 V.E.) 5) Oxygen (6 V.E.) 6) Fluorine ( 7 V.E.) 7) Helium (2 V.E.)

Section 2: Objectives Explain why elements in a group often have similar properties. Describe the properties of the elements in the groups of the periodic table.

Group 1: Alkali Metals Contain 1 valence electron. Share physical and chemical properties. Most reactive metals. Can easily give away one outer level electron. Alkali metals are so reactive, in nature they are only found combined with other elements. Examples: (Li) (K)

Group 2: Alkaline-Earth Metals Contain 2 valence electrons. Less reactive than alkali metals. It uses more energy for elements to give 2 outer shell electrons than to give one. Examples: (Be) (Mg)

Groups 3-12: Transition Metals Either 1 or 2 valence electrons. Do not give away electrons as easily as elements in Groups 1 and 2. Less reactive than Groups 1 and 2. Share all properties of metals, but other properties vary widely. Some transition metals appear at the bottom of the periodic table: Lanthanides Actinides

Lanthanides Shiny Reactive Metals Some of these elements are used to make steel.

Actinides Radioactive (unstable) The atoms of a radioactive element can change into atoms of another element. Elements after Plutonium (94) on the periodic table are only man-made in laboratories.

Group 13: Boron Group Contain 3 valence electrons. Solid at room temperature. Reactive Contains all metals and 1 metalloid (Boron) Examples: (Al) (Ga)

Group 14: Carbon Group Contains 4 valence electrons. Solid at room temperature. The reactivity varies among the elements. Contains one nonmetal, 2 metalloids, and 2 metals Examples: (C) (Si)

Group 15: Nitrogen Group Contains 5 valence electrons. Solid at room temperature (except for nitrogen). The reactivity varies among elements. Examples: (N) (P)

Group 16: Oxygen Group Contains 6 valence electrons. All but oxygen are solid at room temperature. Reactive. Examples: (O) (S)

Group 17: Halogens Contains 7 valence electrons. Poor conductors of electric current. Causes violent reactions with alkali metals. Very reactive. Examples: (Br) (F)

Group 18: Noble Gases Contain 8 valence electrons. (except helium) Colorless, odorless gases at room temperature. Unreactive because their outer shell is full. (do not need to gain or lose electrons) Examples: (Ne) (Ar) (Rn)

Hydrogen Contains 1 valence electron. Reactive. Colorless, odorless gas at room temperature. Low density. Explosive reactions with oxygen. The properties of hydrogen do not match the properties of any single group, so it is set apart from other elements on the periodic table.

Chapter 12 Review Questions What are group 13 elements called? How many valence electrons does the carbon group contain? List 3 properties of lanthanides. _____ found the # of protons in an atom. ____ _____ are outer shell electrons Name the 2 most reactive groups.

Chapter 12 Review Questions List the Group #, V.E. #, Group Name, and Element Symbol: Nitrogen Phosphorous Radon Francium Rhodium Cobalt Lead Bismuth Indium Bromine