Covalent bonds

• How do atoms form covalent bonds?

  By sharing electrons
• What happens when atoms transfer electrons?

  They form oppositely charged ions
• Why do atoms transfer electrons?

  To achieve a full outer shell
• What do two chlorine atoms need to achieve a full outer shell?

  Each needs one extra electron
• How do two chlorine atoms bond together?

  By sharing electrons
• What is a dot and cross diagram?

  A way to represent shared electrons
• How should you differentiate electrons in a dot and cross diagram?

  Use dots for one atom and crosses for another
• What is a displayed formula?

  A representation using chemical symbols and lines
• What is the advantage of using a displayed formula?

  It simplifies drawing large molecules
• What is the molecular formula for ammonia?

  NH₃
• How many hydrogen atoms are in ammonia?

  Three hydrogen atoms
• What is a disadvantage of displayed formulas?

  They don't show 3D shapes of molecules
• How does hydrogen fill its outer shell?

  By sharing one electron with nitrogen
• How many electrons can nitrogen hold in its outer shell?

  A maximum of eight electrons
• What happens when hydrogen shares electrons with nitrogen?

  All atoms achieve full outer shells
• What do you do to create a displayed formula from a dot and cross diagram?

  Remove shells and replace with lines
• What is a 3D model used for?

  To show the arrangement of atoms
• What are simple molecular substances?

  Small molecules with strong covalent bonds
• What are polymers made of?

  Repeating units called monomers
• What are giant covalent structures?

  Large structures with billions of atoms
• Why are giant covalent structures strong?

  All atoms are joined by covalent bonds