Discovering a Pattern • In 1869, Russian chemist Dmitri Mendeleev arranged the elements in order of increasing atomic mass. •His Periodic table showed that •Elements with similar properties occurred in a repeating pattern •There were gaps in its pattern •He could predict the properties of the missing elements By 1886, all of the gaps had been filled and Mendeleev’s predictions were right. Changing the Arrangement • A few elements’ properties did not fit in the pattern of Mendeleev’s table. • 1914: British scientist Henry Moseley found the atomic number of atoms. • Elements arranged by atomic number fit the pattern in Mendeleev’s table. Elements are arranged: Vertically into Groups Horizontally Into Periods Why? Each group has distinct properties • The periodic Table is divided into several groups based on the properties of different atoms. If you looked at one atom of every element in a group you would see… Each atom has the same number of electrons in it’s outermost shell. • An example… The group 2 atoms all have 2 electrons in their outer shells Be (Beryllium) Atom Mg (Magnesium) Atom Valence electrons • Definition: the number of electrons in the outer shell of an element • Electrons held most loosely • an outer shell is considered complete when it contains 8 electrons • Each element has specific number from 1 to 8 • effects the way an atom bonds • Period ends when valence = 8 • determines many properties of the element • elements within a group usually have similar properties. • One way to represent atoms and molecules is to use electron-dot diagrams. An electron-dot diagram shows only the valence electrons in an atom. If you looked at an atom from each element in a period you would see… Each atom has the same number of electron holding shells. An example… The period 4 atoms each have 4 electron containing shells 4th Shell K (Potassium) Kr (Krypton) Atom Atom Fe (Iron) Atom The Periodic Table and Classes of Elements • Elements are classified as metals, nonmetals, and metalloids based on number of electrons in outer shell •The zigzag line on the periodic table can help you recognize which elements belong in which category. Metals • found to the left of the zigzag line • have few electrons in their outer energy level. • shiny, ductile, malleable, and are good conductors of electric current and thermal energy. Metalloids • border the zigzag line • have about half of a complete set of electrons in their outer energy level. • Metalloids have some properties of metals and some properties of nonmetals. • Metalloids are also called semiconductors. Nonmetals • to the right of the zigzag line • have an almost complete set of electrons in their outer energy level. •not shiny, ductile, or malleable, and poor conductors of electric current and thermal energy. Group 1: Alkali Metals Alkali metals properties: • metals • 1 electron in the outer level • very reactive • softness, color of silver, shininess, low density http://www.lyon. edu/webdata/U Alkali Metals sers/DMcDowel l/GenChem/alka lishow.html Soft, silvery colored metals Very reactive!!! Alkali Metals reacting with water: • Li (Lithium) • Na (Sodium) • K (Potassium) • Rb (Rubidium) • Cs (Cesium) What would you expect from Francium?!?! Group 2: Alkaline-Earth Metals Alkaline-earth metals properties: • metals • 2 electrons in the outer level • very reactive, but less reactive than alkali metals • color of silver, higher densities than alkali metals Alkaline Earth Metals Silvery -White Metals Fairly reactive Many are found in rocks in the earth’s crust Group 3–12: Transition Metals Properties of Transition Metals vary widely but include: • metals • 1 or 2 electrons in the outer level • less reactive than alkaline-earth metals • shininess, good conductors of electric current and thermal energy Transition Metals Most are good Malleable (easily Conductors of bent/hammered into electricity wires or sheets) How many things can you think of that have Transition Metals in them? Metalloids lie on either side of these “stairsteps” They share properties with both metals and non-metals Si (Silicon) and Ge (Germanium) are very important “semi-conductors” What are semiconductors used in? Nonmetals Brittle Do not conduct electricity Group 13: Boron Group Group 13 properties: •one metalloid and five metals • 3 electrons in the outer level • reactive • solids at room temperature Group 14: Carbon Group Group 14 properties: •one nonmetal, two metalloids, and two metals • 4 electrons in the outer level • reactivity varies among the elements • solids at room temperature Group 15: Nitrogen Group Group 15 properties: •two nonmetals, two metalloids, and two metals • 5 electrons in the outer level • reactivity varies among the elements • solids at room temperature (except for nitrogen, which is a gas) Group 16: Oxygen Group Group 16 properties: • group contains three nonmetals, one metalloids, and one metal • 6 electrons in the outer level • reactive • solids at room temperature (except for oxygen, which is a gas) Halogens Most are Poisonous Fairly reactive Chapter 12 Section 2 Grouping the Elements Group 17: Halogens Halogens are the elements in Group 17. Group 17 properties: • group contains nonmetals • 7 electrons in the outer level • very reactive • poor conductors of electric current, never in uncombined form in nature Chlorine Gas was used as a chemical weapon during World War I. It was used by the Nazis in World War II. Chapter 12 Section 2 Grouping the Elements Group 18: Noble Gases Noble gases are the elements in Group 18. Group 18 properties: • group contains nonmetals • 8 electrons in the outer level (except helium, which has 2) • unreactive • colorless, odorless gases at room temperature Noble Gases Unreactive Gases at room temperature Jellyfish lamps made with noble gases artist- Eric Ehlenberger Colors Noble Gases produce in lamp tubes: • Ne (Neon): orange-red • Hg (Mercury): light blue • Ar (Argon): pale lavender • He (Helium): pale peach • Kr (Krypton): pale silver • Xe (Xenon): pale, deep blue Group 3–12: Transition Metals, continued • Lanthanides and Actinides Some transition metals from Periods 6 and 7 appear in two rows at the bottom of the periodic table. Elements in the first row are called lanthanides and elements in the second row are called actinides. Lanthanide Series Actinide Series Hydrogen The properties of hydrogen do not match the properties of any single group, so hydrogen is set apart. • a nonmetal • 1 electron in the outer level • reactive • colorless, odorless gas at room temperature, low density Chapter 11 Section 2 The Atom Isotopes • Isotopes are atoms that have the same number of protons but have different numbers of neutrons. Chapter 11 Section 2 The Atom Isotopes, continued • Properties of Isotopes An unstable atom is an atom with a nucleus that will change over time. This type of isotope is radioactive. • Telling Isotopes Apart You can identify each isotope of an element by its mass number. The mass number is the sum of the protons and neutrons in an atom. Chapter 11 Section 2 The Atom Isotopes, continued • Naming Isotopes: write the name of the element followed by a hyphen and the mass number of the isotope. Example: Uranium-238 •The atomic mass of an element is the weighted average of the masses of all the naturally occurring isotopes of that element. Chapter 11 Section 2 The Atom Chapter 12 The Periodic Tables Concept Map Use the terms below to complete the concept map on the next slide. elements nonmetals periods periodic table metals groups (families) electrons Chapter 12 The Periodic Table Chapter 12 The Periodic Table Chapter 12 Standardized Test Preparation 1. Which of the following statements is correct for the elements shown? A Lithium has the greatest atomic number. B Sodium has the least atomic mass. C Atomic number decreases as you move down the column. D Atomic mass increases as you move down the column. Chapter 12 Standardized Test Preparation 1. Which of the following statements is correct for the elements shown? A Lithium has the greatest atomic number. B Sodium has the least atomic mass. C Atomic number decreases as you move down the column. D Atomic mass increases as you move down the column. Chapter 12 Standardized Test Preparation 2. Which of the following statements best describes the outer electrons in atoms of the elements shown? F The atoms of each element have 1 outer-level electron. G Lithium atoms have 3 outer-level electrons, sodium atoms have 11, and potassium atoms have 19. H Lithium atoms have 7 outer-level electrons, sodium atoms have 23, and potassium atoms have 39. I The atoms of each element have 11 outer-level electrons. Chapter 12 Standardized Test Preparation 2. Which of the following statements best describes the outer electrons in atoms of the elements shown? F The atoms of each element have 1 outer-level electron. G Lithium atoms have 3 outer-level electrons, sodium atoms have 11, and potassium atoms have 19. H Lithium atoms have 7 outer-level electrons, sodium atoms have 23, and potassium atoms have 39. I The atoms of each element have 11 outer-level electrons. Chapter 12 Standardized Test Preparation 3. The elements featured in the image belong to which of the following groups? A noble gases B alkaline-earth metals C halogens D alkali metals Chapter 12 Standardized Test Preparation 3. The elements featured in the image belong to which of the following groups? A noble gases B alkaline-earth metals C halogens D alkali metals Chapter 12 Standardized Test Preparation 2. A chemical company is preparing a shipment of 10 g each of four elements. Each element must be shipped in its own container that is completely filled with the element. Which container will be the largest? F the container of aluminum Density Mass Element (g/cm3) (g) G the container of arsenic Aluminum 2.702 10 H the container of germanium Arsenic 5.727 10 I the container of silicon Germanium 5.350 10 Silicon 2.420 10 Chapter 12 Standardized Test Preparation 2.