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Grade 8 Periodic Table
 

Grade 8 Periodic Table

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  • Bohr Model
  • The electromagnetic force causes opposite electric charges to attract each other.
  • Because of the electromagnetic force, the negatively charged electrons in an atom are attracted to the positively charged protons in the atom’s nucleus.
  • Bohr Model
  • The electromagnetic force causes opposite electric charges to attract each other.
  • This force must overcome the electromagnetic force of repulsion the protons in a nucleus exert on one another. The strong force that occurs between protons alone, however, is not enough to hold them together. Other particles that add to the strong force, but not to the electromagnetic force, must be present to make a nucleus stable. The particles that provide this additional force are neutrons. Neutrons add to the strong force of attraction but have no electric charge and so do not increase the electromagnetic repulsion.
  • During the nineteenth century, chemists began to categorize the elements according to similarities in their physical and chemical properties. The end result of these studies was our modern periodic table.
  • During the nineteenth century, chemists began to categorize the elements according to similarities in their physical and chemical properties. The end result of these studies was our modern periodic table.
  • He suggested that elements be arranged in “octaves” because he noticed (after arranging the elements in order of increasing atomic mass) that certain properties repeated every 8th element.
  • Newlands' claim to see a repeating pattern was met with savage ridicule on its announcement. His classification of the elements, he was told, was as arbitrary as putting them in alphabetical order and his paper was rejected for publication by the Chemical Society.
  • So why is Mendeleev called the “father of the modern periodic table” and not Meyer, or both?
  • Stated that if the atomic weight of an element caused it to be placed in the wrong group, then the weight must be wrong. (He corrected the atomic masses of Be, In, and U)Was so confident in his table that he used it to predict the physical properties of three elements that were yet unknown.
  • Stated that if the atomic weight of an element caused it to be placed in the wrong group, then the weight must be wrong. (He corrected the atomic masses of Be, In, and U)Was so confident in his table that he used it to predict the physical properties of three elements that were yet unknown.
  • through his work with X-rays, he determined the actual nuclear charge (atomic number) of the elements*. He rearranged the elements in order of increasing atomic number.
  • His research was halted when the British government sent him to serve as a foot soldier in WWI. He was killed in the fighting in Gallipoli by a sniper’s bullet, at the age of 28. Because of this loss, the British government later restricted its scientists to noncombatant duties during WWII.
  • He is the only person to have an element named after him while still alive.106-Seaborgium

Grade 8 Periodic Table Grade 8 Periodic Table Presentation Transcript

  • If opposite charges attract, why are the negative electrons not attracted to the positive nucleus?
  • Electrons are always moving. Electrons have inertia in motion = momentum.
  • If electrons are always moving and they weigh very, very little, why don’t they get thrown away out of the atom?
  • Because of the electromagnetic force!
  • Forces inside the atom This force of attraction binds the electrons to the atom. The electromagnetic force becomes stronger as the distance between charges becomes smaller.
  • If opposite charges attract, how do the protons get attracted with the neutrons?
  • Because of the strong nuclear force!
  • Forces inside the atom Protons and neutrons in the nuclei of atoms are held together by the strong force.
  • If the atomic mass/weight is just the sum of the protons and neutrons, why are there decimal values for the atomic weight written on the periodic table?
  • Atomic Weight is an Average! It is the weighted average of the individual atomic weights, or mass numbers, of the isotopes.
  • Example • Chlorine = 35.48 (atomic weight) Isotopes of Chlorine Chlorine-35 = 76% abundance Chlorine-37 = 24% abundance Σ(mass number x %abundance)
  • Example • The mass of Isotope 1 is 6.015 amu and its abundance is 7.5% • The mass of Isotope 2 is 7.016 amu with a 92.5% abundance. • What is the average atomic mass? • What is the element?
  • The Periodic Table
  • Triads! Johann Dobereiner (1829)
  • Calcium, Strontium, Barium Chlorine, Bromine, Iodine The elements in a triad had similar chemical properties and orderly physical properties.
  • Octaves! John Newlands (1863)
  • After arranging the elements in order of increasing atomic mass, certain properties repeated every 8th element.
  • Increasing atomic mass! Lothar Meyer (1867)
  • Increasing atomic mass! Dmitri Mendeleev (1869) “Father of the Periodic Table”
  • Both scientists left vacant spaces where unknown elements should fit.
  • Periodic Table, I am your Father. Dmitri Mendeleev (1869)
  • The weight must be wrong. Reclassify! Dmitri Mendeleev (1869)
  • Increasing atomic NUMBER! Henry Moseley (1913)
  • Through his work with X-rays, he determined the actual nuclear charge (atomic number) of the elements. He rearranged the elements in order of increasing atomic number.
  • Actinide and Lanthanide Series! Glenn Seaborg (1944)
  • He reconfigured the periodic table by placing the actinide series below the lanthanide series
  • Periodic Table Geography
  • The Modern Periodic Table Columns of elements are called groups. George M. McKelvy, Ph.D. 33
  • The Modern Periodic Table Rows of elements are called periods. George M. McKelvy, Ph.D. 34
  • The Alkali Metals • 1 valence electron • Highly reactive with water • Form ionic compounds • Do not occur in nature as pure elements (always in compounds)
  • Alkali-Earth Metals • Have 2 valence electrons • Reactive, but less reactive than alkali metals • Are ductile, malleable and have a silvery luster
  • Transition metals… and inner transition metals • Are less reactive than groups 1 and 2. • Tend not to react in water. • Are malleable and ductile, but still harder than group 1 & 2. • Tend to be solids at room temperature. • Have variable chemical properties  Inner transition metals • Are good conductors of tend to be radioactive electricity and heat.
  • Nonmetals • Poor conductors of heat and electricity • Often are found as gases or liquids, sometimes solids.
  • Halogens • Are nonmetals • highly reactive with metalsmost reactive is flourine, lease reactive is astatine • Mostly exist as gases or liquids (except At -solid) • Have 7 valence electrons
  • Noble gases • At room temperature, exist as gases. • Are completely unreactive • Have full s and p orbitals • Are odorless, colorless, nonflammable
  • Metalloids • Tend to be solids • Have properties similar to both metals and nonmetals • Tend to be semiconductors (which means they are useful for technological uses)
  • Periodic Law When elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties.
  • Metals, metalloids (semi-metals) and nonmetals
  • Properties of Metals • Good conductors of heat and electricity: lots of mobile electrons to move energy and charge around • Have luster (shiny) • Are ductile (stretchable) and malleable (bendable) • Solids at room temp. except for Hg
  • Properties of Metalloids • Have properties of both metals and non-metals • Some of them are semiconductors (like silicon) which behave sometimes as conductors and sometimes as insulators • Solids at room temperature
  • Properties of Non-Metals • Poor conductors of heat and electricity • Can be solids, liquids or gases (contrary to popular belief not all non-metals are gases!) • Are not ductile, malleable
  • Periodic Trends - Reactivity –how likely or vigorously an atom is to react with other substances –Usually determined by how easily electrons can be removed and how badly they want to take other atom’s electrons since it is the transfer/interaction of electrons that is the basis of chemical reactions
  • Periodic Trends - Reactivity • Metals –Period: DECREASES from left to right –Group: INCREASES down a group WHY? The farther left and down the periodic table, the easier it is for elections to be given or taken away, resulting in a higher reactivity
  • Periodic Trends - Reactivity • Non-metals –Period: INCREASES from left to right –Group: DECREASES down a group WHY? The farther right and up the periodic table, the higher the electronegativity, resulting in a more vigorous exchange of electrons