science

• Electrons


  • The only part of the atom involved in bonding
  • Reactivity of an atom is dependent on the electron configuration
• First electron shell


  Very close to the nucleus, can only hold 2 electrons
• Second electron shell


  Further from the nucleus, can hold 8 electrons
• Third electron shell


  Can also hold 8 electrons (technically can hold 18 but you don't need to know that yet)
• Electron configuration


  Shows how the electrons are arranged in an atom
• Only the outermost electrons are involved in bonding, known as valence electrons
• Identifying valence electrons


  1. Counting the electrons in the outer shell

  2. Taking only the last number of the electron configuration

  3. Identifying the column in the periodic table the atom is found in
• Many chemical substances produce coloured light when exposed to the heat of a flame
• Bohr's explanation of coloured light

  1. Electrons absorb energy and 'jump' to a higher energy shell (excited state)

  2. Excited electrons fall back to their normal shell (ground state)

  3. The fall releases energy in the form of light
• Alkali metals


  • Lithium
  • Sodium
  • Potassium
  • Rubidium
  • Caesium
• Alkali metals


  Highly reactive, have 1 valence electron, form ions with charge of +1
• Reactivity of alkali metals


  Increases as you move down the group
• Alkali metals react violently with water
• Alkali metals stored in school will be submerged in oil to avoid unwanted reactions
• Why hydrogen is not considered an alkali metal

  Hydrogen is a non-metal, forms covalent compounds with non-metals, does not react with water to form alkali metal hydroxides
• Alkali metals reacting with chlorine

  Form ionic compounds with formula XCl, where X is the alkali metal symbol
• Alkali metals reacting with oxygen


  Form ionic compounds with formula X2O, where X is the alkali metal symbol
• Alkali metals


  • Soft, can be cut with a knife, softness increases down the group
  • Low density, density increases down the group (except potassium)
  • Low melting and boiling points, melting point decreases down the group
• Uses of alkali metals


  • Lithium in batteries
  • Sodium in soaps and street lamps
  • Potassium in fertilizers and for human body function
  • Rubidium in optical glasses and laser cooling
  • Caesium in night-vision equipment and cancer treatment
• Alkaline earth metals


  Reactive (though less than alkali metals), have 2 valence electrons, form ions with charge of +2
• Reactivity of alkaline earth metals

  Increases as you move down the group
• Alkaline earth metals


  • Soft, shiny, silvery-white metals, with relatively low melting and boiling points and densities
• Alkaline earth metals reacting with chlorine

  Form ionic compounds with formula XCl2, where X is the alkaline earth metal symbol
• Alkaline earth metals reacting with oxygen


  Form ionic compounds with formula XO, where X is the alkaline earth metal symbol
• Melting points of group 2 elements


  Decrease as you move down the group (except magnesium)
• No simple explanation for the exceptions in melting and boiling point trends of group 2 elements
• Uses of alkaline earth metals

  • Calcium in bone health, muscle contraction, and neurotransmission, and in agriculture and flue gas treatment
  • Barium compounds in x-rays, beryllium alloys in mechanical parts
  • Magnesium in lightweight alloys
• "Beryllium is less reactive than sodium."
• Property of alkali and alkaline earth metals


  Reactivity, which increases down the groups
• Beryllium is less reactive than sodium
• Metallic bonding


  Bonding that occurs between metal atoms, where the valence electrons are free to move from atom to atom, forming a "sea" of electrons
• Metals


  • Malleable and ductile because free electrons have no defined arrangement around the metal atoms, allowing them to easily adapt to form new shapes
  • High melting point due to strong attraction between positive metal atoms and "sea" of negative electrons
• Se2- loses 2 electrons, Pb4+ loses 4 electrons, Br- gains 1 electron, Cr3+ loses 3 electrons
• The chemical formula formed when Mg2+ and Cl- ions combine is MgCl2, and when Al3+ and OH- ions combine is Al(OH)3
• Lithium ion and fluoride ion


  An ionic bond would form between them
• Number of covalent bonds formed by elements in different groups

  • Group 18 - 0 covalent bonds
  • Group 17 - 1 covalent bond
  • Group 16 - 2 covalent bonds
  • Group 15 - 3 covalent bonds
  • Group 14 - 4 covalent bonds
• Single bond


  Atoms share 1 pair of electrons
• Double bond


  Atoms share 2 pairs of electrons
• Triple bond


  Atoms share 3 pairs of electrons
• N2 contains a triple bond, O2 contains a double bond, H2 contains a single bond