Key concepts in chemistry

• Who proposed the atomic model in 1803?

  John Dalton
• How has the Dalton model of an atom changed over time?

  • Discovery of subatomic particles
  • Introduction of protons, neutrons, and electrons
  • Understanding of atomic structure evolved
• What is the relative charge of a proton?

  +1
• What is the relative mass of a neutron?

  1
• What is the relative charge of an electron?

  • 1
• What is the relative mass of an electron?

  1/1836
• Why do atoms contain equal numbers of protons and electrons?

  • Atoms are neutral
  • Protons have a charge of +1
  • Electrons have a charge of -1
  • Equal numbers cancel out the charges
• How does the nucleus of an atom compare to the overall size of the atom?

  • The nucleus is very small
  • It is concentrated at the center of the atom
  • Overall size of the atom is much larger
• Where is most of the mass of an atom concentrated?

  In the nucleus
• What does the term mass number of an atom refer to?

  It is the number of protons plus neutrons
• What is unique about atoms of a given element?

  • They have the same number of protons
  • This number is unique to that element
  • Defines the identity of the element
• What are isotopes?


  • Different atoms of the same element
  • Same number of protons
  • Different numbers of neutrons in their nuclei
• How do you calculate the number of neutrons in an atom?

  Subtract the atomic number from the mass number
• Why do relative atomic masses of some elements not appear as whole numbers?

  • Isotopes have different numbers of neutrons
  • They have different atomic masses
  • Relative atomic mass is an average based on abundance
• What is the standard for comparing the masses of atoms?

  A carbon atom with a mass number of 12
• How is relative atomic mass denoted?

  It is written as A_r or R.A.M.
• How do you calculate the relative atomic mass of an element from its isotopes?

  Use the formula:

  $R.A.M. =$ \frac{(mass \ of \ isotope-A \times \% \ of \ isotope-A) + (mass \ of \ isotope-B \times \% \ of \ isotope-B)}{100}
• What is the R.A.M. of chlorine given 75% chlorine-35 and 25% chlorine-37?

  35.5

  
• What is the calculation for the R.A.M. of chlorine using the given isotopes?

  $R.A.M. =$ \frac{(35 \times 75) + (37 \times 25)}{100} =$35.5$
• How did Mendeleev arrange the elements in his periodic table?

  He arranged them by atomic mass and properties of the elements and their compounds.
• Why did Mendeleev leave gaps in his periodic table?

  He left gaps for elements that he thought had not yet been discovered.
• How did Mendeleev predict the existence of undiscovered elements?

  He realized that elements with similar properties belonged in the same groups.
• What did Mendeleev do with the discovered elements in his table?

  He placed them where they fit best according to their properties.
• What was the significance of the gaps Mendeleev left in his periodic table?

  They were later filled by elements with properties predicted by Mendeleev.
• Why was Mendeleev's arrangement of elements not always based on increasing atomic mass?

  Because of the relative abundance of isotopes of some pairs of elements.
• How did knowledge of isotopes affect Mendeleev's periodic table?

  It explained why the order based on atomic weights was not always correct.
• What does the atomic number of an element represent?

  The number of protons in the nucleus of the element.
• How are elements arranged in the periodic table?

  They are arranged in order of increasing atomic number in rows called periods.

  
• What are groups in the periodic table?

  Columns where elements with similar properties are placed.

  
• How can you identify metals and non-metals in the periodic table?

  By their position in the periodic table.

  
• What defines metals in the periodic table?

  Elements that react to form positive ions.

  
• Where are metals generally located in the periodic table?

  To the left and towards the bottom of the periodic table.

  
• What defines non-metals in the periodic table?

  Elements that do not form positive ions.

  
• Where are non-metals generally located in the periodic table?

  Towards the right and top of the periodic table.

  
• What does the electronic configuration of an element indicate?

  How many electrons are in each shell around an element's nucleus.
• What is the electronic configuration of sodium?

  2.8.1
• How is the electronic configuration related to an element's position in the periodic table?

  The group indicates the number of electrons in the outermost shell.

  
• How are ionic bonds formed between atoms?

  Ionic bonds are formed by the transfer of electrons between atoms to produce cations and anions.

  
• What happens to metal atoms during the formation of ionic bonds?

  Metal atoms lose electrons to become positively charged ions (cations).
• What does the period of an element tell you about its electrons?

  It tells you which shell the outermost electron is found in.