Chem Mod 1 Ch 4

• Core Charge


  The measure of the attractive force felt by the valence shell electrons towards the nucleus
• Shielding


  The inner shell electrons blocking the valence electrons from the attraction of the nucleus
• Electronegativity


  The ability of an atom to attract electrons towards itself
• Atomic Radius


  A measurement of an atoms size – the distance from the nucleus to the valence shell electrons
• Cation


  A positively charged ion
• Anion


  A negatively charged ion
• Ionisation


  The process of removing an electron from an atom and forming an ion
• First Ionisation Energy


  The energy required to remove one electron from an atom of an element in the gas phase
• Metallic Character


  The tendency of a metal to lose electrons and form positive ions or cations
• Reactivity


  The tendency of an electron to lose or gain electrons
• Periodicity (periodic pattern)


  • The arrangement of electrons in atoms is responsible for the periodicity of element properties
• Mendeleev's Periodic Law: the properties of elements vary periodically with their atomic weights
• Triad


  A set of three chemically similar elements. The atomic mass of the middle element equals the mean of the other two element's atomic mass.
• Law of Octaves


  Every 8th element has similar properties, if arranged by increasing atomic weight
• Modern Periodic Table


  • Elements are arranged in rows, in order of increasing atomic number. The number of valence electrons are used to organise elements into columns.
• Features of the Modern Periodic Table


  • Arranged in order of increasing atomic number
  • Horizontal rows (periods) are labelled 1-7
  • Vertical columns (groups) are labelled 1-18
  • Main group elements are elements in groups 1,2 and 13-18
  • Elements in groups 3-12 are known as transition metals
• Groups


  The group number can be used to determine the number of valence electrons in an atom of an element. In groups 1-2, the number of valence electrons is equal to the group number. Elements in groups 3-12 are transition metals. In groups 13-18, the number of valence electrons is equal to the group number minus 10.
• Periods


  The number of a period gives information about the electronic configuration of an element. The period an element is in is equal to the number of occupied shells in the element's atoms.
• Blocks


  The periodic table has four main blocks – s, p, d, f. For every element in a block, the element's highest energy subshell is the same as the name of the block.
• As the core charge increases


  The valence electrons are more strongly attracted to the nucleus, increasing the electronegativity
• As the core charge increases

  The atomic radius decreases as the shells are pulled closer to the nucleus
• As the number of shells increases down a group


  The core charge remains constant but the valence electrons are held less strongly, decreasing the electronegativity. The greater number of shells also means a larger atomic radius.
• As the core charge increases across a period

  The valence electrons are more strongly attracted to the nucleus, increasing the first ionisation energy required to remove an electron
• As the number of shells increases down a group


  The first ionisation energy decreases as the valence electrons are less attracted to the nucleus
• As the core charge increases across a period

  The first ionisation energy increases as the valence electrons are more strongly attracted to the nucleus
• As the number of shells increases down a group for metals

  Reactivity increases as the weaker core charge makes it easier to lose electrons
• As the core charge increases across a period for metals

  Reactivity decreases as the stronger core charge makes it harder to lose electrons
• As the number of shells increases down a group for non-metals


  Reactivity decreases as the greater number of shells makes it harder to attract electrons
• As the core charge increases across a period for non-metals

  Reactivity increases as the stronger core charge makes it easier to attract electrons
• Who created the following periodic law?

  the properties of elements vary periodically with their atomic weights