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The Periodic Table. Physical Science Chapter 5. Why do we need a periodic table?. To organize the elements To show trends. What does periodic mean?. Repeating in a pattern. The days of the week repeat themselves every seven days, so they are periodic.
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The Periodic Table Physical Science Chapter 5
Why do we need a periodic table? • To organize the elements • To show trends Physical Science chapter 5
What does periodic mean? • Repeating in a pattern. • The days of the week repeat themselves every seven days, so they are periodic. • The notes on a musical scale repeat themselves every octave, so they are periodic. Physical Science chapter 5
Dimitri Mendeleev • Came up with a periodic table of the elements in 1871 • Elements arranged in order of increasing mass. • Properties are repeated in an orderly, periodic, fashion. Physical Science chapter 5
Blanks in the table • Mendeleev saw that sometimes there seemed to be an element missing from the table – without it, the pattern didn’t work. • So, he left blank spaces in the table for elements that he predicted would be discovered. Physical Science chapter 5
Germanium • Mendeleev predicted the existence and properties of “ekasilicon”, now known as germanium. • See the table on page 146 • Mendeleev predicted 5 other elements. • Extra credit opportunity: Find out what they were and how accurate his predictions were. Earn up to ten extra credit points. Physical Science chapter 5
Periodic Law • When the elements are arranged in order of increasing atomic number, their properties repeat at regular intervals. Physical Science chapter 5
Groups • The vertical columns in the periodic table are called groups. • The groups are numbered from 1 to 18. • Elements in the same group have similar properties. Physical Science chapter 5
Periods of elements • The horizontal rows of elements in the periodic table are called periods. • They are numbered from 1 to 7. • Elements become less metallic as you move across the periods from left to right Physical Science chapter 5
Discuss • Describe how Mendeleev organized his periodic table. • Explain why Mendeleev left spaces in his periodic table. • State the property used to organize elements in the modern periodic table. Physical Science chapter 5
Properties • Determined by the number of valence electrons. • Even though all elements have different total numbers of electrons, elements in the same group have the same number in their outer energy level. • That’s why they have similar properties. Physical Science chapter 10
Forming ions • Atoms gain or lose electrons to form ions. • Since the number of protons no longer equals the number of electrons, the atom is no longer neutral. • Electrons gained – negative ions (called anions) • Electrons lost – positive ions (called cations) Physical Science chapter 5
Group 1 elements • Have 1 valence electron • Can become more stable by losing that electron • Form (positive) cations with a charge of 1+ • Written as Li+, Na+, K+, etc. Physical Science chapter 5
Group 17 elements • Have 7 valence electrons • Can become more stable by gaining 1 electron to fill their outer energy level • Form (negative) anions with a charge of 1- • Written as F-, Cl-, Br-, etc. Physical Science chapter 5
Metals • Hard and shiny • Conduct heat and electricity well • Usually are solid at room temperature. Physical Science chapter 10
Nonmetals • Gases or brittle solids at room temperature • Dull surfaces • Good insulators of heat and electricity Physical Science chapter 10
Semiconductors • Also called metalloids • Have properties of both metals and nonmetals. • Found along the heavy stairstep in the periodic table. Physical Science chapter 10
Discuss • Explain why elements in a group have similar chemical properties. • Compare the number of valence electrons in an atom of oxygen with the number of valence electrons in an atom of selenium. Are oxygen and selenium in the same period or group? Physical Science chapter 5
Alkali metals • Most reactive metals • Not found alone in nature – always in compounds • Group 1 on the periodic table • Have similar properties
Alkaline Earth metals • Group 2 • Very reactive • not found alone in nature • 2 electrons in outer level. • Lose them to become cations with a charge of 2+ • Be2+, Mg2+, etc.
Transition elements • Groups 3 through 12 of the periodic table. • Most familiar metals, because they occur in nature as elements. • Have 1 or 2 outer level electrons. • Often form brightly colored compounds.
Synthetic elements • Not found in nature • Produced in laboratories • Used in smoke detectors and pacemakers, among other things. • All are radioactive
Synthetic elements • Can be very harmful • Plutonium is the most poisonous substance known • Its production has been banned • Used as nuclear energy sources • Power • weapons • Also used to study the structure of matter
Hydrogen • 90% of all the atoms in the universe • Most hydrogen on earth is in water • Hydrogen gas is a diatomic molecule • Two atoms of hydrogen are covalently bonded together. • Very reactive
The halogens • Group 17 • Used in bright lamps and headlights • Form ionic compounds called salts by gaining one electron • NaCl, table salt is one salt • Other ionic compounds of halogens are also salts • The word halogen means salt-former
Noble gases • Don’t naturally form compounds • Don’t mix with the commoners • We can make them form compounds under high heat and pressure. • Stable, because their outer level holds 8 electrons
Carbon • Can form many compounds • Found naturally as graphite, diamond, or fullerenes Physical Science chapter 5
Semiconductors • Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium • Have some properties of metals and some properties of nonmetals Physical Science chapter 5
Discuss • Classify the following elements as alkali, alkaline-earth, or transition metals • Iron • Potassium • Strontium • Platinum • Describe why chemists might sometimes store reactive chemicals in argon. To which family does argon belong?
