Periodic Table of Elements 4.1

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Periodic Table of Elements4.1

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Dmitri Menveleev

• In the last century, a scientist named Dmitri
  Mendeleev looked for ways to organize the current
  knowledge about newly discovered elements and
  their atoms.
• He invented a periodic table an organized
  arrangement of elements that explained and
  predicted physical and chemical properties.
• Mendeleevs table was key to understanding
  elements and discovering new elements and
  compounds.

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• Initially, Mendeleev organized elements based on
  their atomic mass (average weight of the atoms in
  the element).
• He found that this did not always work.
• So he decided to group elements based on their
  atomic number (the number of protons in the
  nucleus) instead.
• Using the periodic table, Mendeleev was able to
  actually predict the existance of certain
  elements even before they were discovered!
• Ex. Gallium was predicted in 1871 and not
  actually discovered until 1875.

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• Mendeleevs decision to use the atomic number
  rather than atomic mass proved to be a good one.
  When subatomic particles (protons, neutrons, and
  electrons) were later discovered, it became clear
  that the atomic number (number of protons in the
  nucleus) held the key to the identity of an
  element.

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Groups of Elements

• The periodic table groups elements with similar
  properties. You can quickly identify an element
  as a metal if it is on the left or in the centre
  of the table.
• Non-metals are generally found on the right side.

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Chemical Groups

• The set of elements in the same column in the
  table is called a chemical group (having similar
  chemical and physical properties).
• These properties, however, vary from element to
  element in a column.

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Periods

• The horizontal rows of elements are called
  periods. The first period contains two elements
  hydrogen and helium.
• As you go from left to right within a row, the
  atomic number increases and the elements
  gradually change from metallic (lithium) to
  non-metallic (flourine), and then finally to
  noble gases (neon) at the far right.

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Today, the modern periodic law states

• If the elements are arranged according to their
  atomic number, a pattern can be seen in which
  similar properties occur regularly.
• Hand out tables and colour groups to match the
  table at the back of the book.

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Assignment

• Refer to your periodic table as the class reads
  pages 110-113 in the text.
• Use a colour code and colour your in the
  following sections on your periodic table
• Noble gases
• Alkali Metals
• Halogens
• Group of One
• Metalloids
• Metals

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Group of One

• Hydrogen is a unique element (yellow).
• Its most common isotope has only a single proton
  and no neutron in its nucleus.
• Hydrogen doesnt have much in common with the
  alkali metals. Its a colourless, odourless,
  tasteless, highly flammable gas.
• Almost all of Earths hydrogen exists in
  combination with other elements. Its reactivity
  is too great for it to exist in the atmosphere as
  a free element.

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Alkali Metals

• Occupy the far left column of the periodic table
  (green).
• Extremely reactive.
• Found in nature only as compounds, and are found
  everywhere on Earth.
• Most common are sodium compounds, which occur in
  plants, animals, soil and sea water.
• Lithium, sodium, potassuim, etcshiny, silvery.

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Metalloids

• Elements that possess both metallic and
  non-metallic properties. Found on both sides of
  the zigzag line that divides the metals from the
  non-metals.
• Ex. silicon, boron, germanium, arsenic, selenium,
  antimony, tellurium, polonium, and astatine.

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Halogens

• Occupy the 17th column of the periodic table
  (fluorine, chlorine, bromine)
• Most reactive non-metals.
• Because of their reactivity, they almost always
  appear naturally as compounds, not as elements.
• Most common halogen compounds are chlorine
  compounds found in living things, ocean water and
  rocks.

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Noble Gases

• Occupy the far right column of the periodic table
  (blue).
• All gases at room temperature, the noble gases
  are often called inert gases because they are so
  unreactive, almost never forming chemical
  compounds with other elements.
• Argon makes up 1 of every breath you inhale.
• Very useful elements. Ex. neon, helium