PERIOIDic table

• What was the basis for early attempts to classify elements before the discovery of protons, neutrons, and electrons?

  They arranged elements in order of their atomic weights.
• What is the atomic weight of an element equivalent to in modern terms?

  It is equivalent to the relative atomic mass.
• Why were early periodic tables considered incomplete?

  Many elements were unknown and some were placed in incorrect groups.
• Who was Dmitri Mendeleev?

  A Russian chemist who organized the known elements.
• In what year did Mendeleev publish his first periodic table?

  1869
• How did Mendeleev arrange the elements in his periodic table?

  In order of increasing atomic weights and properties.
• What did Mendeleev's periodic table show about elements with similar chemical properties?

  They were lined up in groups.
• What issue did Mendeleev encounter with some pairs of elements in his table?

  Some pairs were in the wrong order based on atomic weights.
• What did Mendeleev do with the gaps in his periodic table?

  He left them for undiscovered elements and predicted their properties.
• What was the name of the element Mendeleev predicted that would fit below silicon?

  eka-silicon
• How did the discovery of germanium confirm Mendeleev's periodic table?

  Its properties matched Mendeleev's predictions for eka-silicon.
• What was the issue with iodine and tellurium in Mendeleev's table?

  Iodine had a lower atomic weight than tellurium but was placed after it.
• Why did Mendeleev swap the positions of iodine and tellurium?

  To align iodine with elements that had similar chemical properties.
• How are elements arranged in the modern periodic table?

  In rows called periods and columns called groups.
• What does the term "periodic" in periodic table refer to?

  Elements with similar properties occur at regular intervals.
• What explains the pair reversals in Mendeleev's table?

  The existence of isotopes.
• What is the atomic number of tellurium?

  52
• What is the atomic number of iodine?

  53
• What is an electronic structure?

  It is the arrangement of electrons in an atom.
• Where do electrons occupy in an atom?

  They occupy energy levels or electron shells outside the nucleus.
• What is the maximum number of electrons the first shell can hold?

  2
• What is the maximum number of electrons the second shell can hold?

  8
• What is the maximum number of electrons the third shell can hold?

  8
• How can the electronic structure of an atom be predicted?

  From its atomic number.
• What is the electronic structure of sodium?

  2,8,1
• How is the electronic structure of sodium represented in a diagram?

  Each shell is shown as a circle and each electron as a dot or cross.
• How is the electronic structure linked to the periodic table?

  It determines the period number and group number of the element.
• What is the group number for sodium?

  1
• What is the period number for sodium?

  3
• What is the atomic number of sodium?

  11
• How do most metal atoms behave in chemical reactions?

  They lose electrons to form positive ions.
• What happens when magnesium burns in air?

  Each magnesium atom loses two electrons to form a Mg$^{2+}$ ion.
• What do non-metals do in chemical reactions?

  They do not form positive ions.
• What is a characteristic of most metal oxides?

  They are basic.
• What is a characteristic of most non-metal oxides?

  They are acidic.
• How do metals and non-metals differ in melting and boiling points?

  Most metals have high melting and boiling points, while most non-metals have low melting and boiling points.
• What are the physical properties of metals and non-metals when solid?

  Properties of metals:

  • Good conductor of electricity
  • Good conductor of heat
  • Shiny
  • High density
  • Malleable
  • Ductile

  
  

  Properties of non-metals:

  • Poor conductor of electricity
  • Poor conductor of heat
  • Dull
  • Low density
  • Brittle
• Where are metal elements located in the periodic table?

  On the left of a stepped line starting at B-Al-Si.
• Where are non-metal elements located in the periodic table?

  On the right of the stepped line.
• How many electrons do group 1 elements have in their outer shell?

  One electron.