Covalent Bonds

• What is a covalent bond?

  When two atoms share a pair of electrons
• In which elements does covalent bonding occur?

  Most non-metal elements and their compounds
• Where are shared electrons found in covalent bonds?

  In the outer shells of the atoms
• How many electrons does each atom usually contribute to a shared pair?

  One electron from each atom
• What molecule is formed when a hydrogen atom bonds with a chlorine atom?

  Hydrogen chloride
• What defines a molecule in chemistry?

  • A group of two or more atoms
  • Joined together by covalent bonds
• What do molecules of the same element or compound contain?

  The same number of atoms of each element
• How are atoms in a molecule connected?

  By covalent bonds
• Do substances made up of ions form molecules?

  No, they do not form molecules
• What is the typical size range of small molecules?

  Around 0.1 nm or $1 \times 10^{-10} \text{ m}$
• Can individual atoms and molecules be seen with a light microscope?

  No, they are too small to see
• Which type of microscope can produce images of atoms?

  Some electron microscopes
• How large is a water molecule, H2O?

  About 0.3 nm or $3 \times 10^{-10} \text{ m}$
• What does the chemical formula of a substance with small molecules indicate?

  • Number of atoms of each element
  • In one molecule of the substance
• What is the formula for hydrogen gas?

  H2
• How many atoms are in a molecule of oxygen gas?

  Two oxygen atoms
• What is the formula for nitrogen gas?

  N2
• What is the formula for hydrogen chloride?

  HCl
• How many atoms are in a water molecule?

  Three atoms (2 H, 1 O)
• What is the formula for ammonia?

  NH3
• How many atoms are in an ammonia molecule?

  Four atoms (1 N, 3 H)
• What does a dot and cross diagram represent?

  Bonding in a small molecule
• How is the outer shell of each atom represented in a dot and cross diagram?

  As a circle
• What indicates a covalent bond in a dot and cross diagram?

  Circles overlapping
• How are electrons from one atom represented in a dot and cross diagram?

  As dots
• How are electrons from another atom represented in a dot and cross diagram?

  As crosses
• What forms a hydrogen molecule, H2?

  Two hydrogen atoms sharing outer electrons
• What does the dot and cross diagram for hydrogen illustrate?

  Bonding in hydrogen
• How does an ammonia molecule, NH3, form?

  One nitrogen shares electrons with three hydrogens
• What are the two types of dot and cross diagrams?

  With circles and without circles
• What does a structural formula show?

  The bonds between atoms in a molecule
• How is each atom represented in a structural formula?

  By its chemical symbol
• How is each covalent bond shown in a structural formula?

  As a straight line
• How many covalent bonds does an ammonia molecule have?

  Three covalent bonds
• What does a three-dimensional ball and stick model show?

  Arrangement of atoms and bonds in space
• What does the diagram of ammonia illustrate in three-dimensional models?

  A ball and stick model of ammonia
• How do atoms form covalent bonds?

  By sharing electrons for a full outer shell
• What does the number of covalent bonds an atom can form depend on?

  Electrons needed for a full outer shell
• For most elements, how many electrons are in a full outer shell?

  Eight electrons
• What is the number of covalent bonds formed by elements in groups 4 to 7?

  • Group 4: 4 bonds (Carbon, C)
  • Group 5: 3 bonds (Nitrogen, N)
  • Group 6: 2 bonds (Oxygen, O)
  • Group 7: 1 bond (Chlorine, Cl)