Covalent bonds

• What is a covalent bond?

  A covalent bond is a shared pair of electrons.
• What do covalent bonds form?

  Covalent bonds form molecules.
• What are the properties of substances with small molecules?

  They have low melting and boiling points, and do not conduct electricity.
• What is the smallest part of an element that can exist?

  • An atom
• What is an electron?

  An electron is a subatomic particle with a negative charge and negligible mass relative to protons and neutrons.
• In which types of elements does covalent bonding occur?

  Covalent bonding occurs in most non-metal elements and in compounds formed between non-metals.
• How do atoms achieve a full outer shell of electrons in covalent bonding?

  Atoms share electrons to achieve a full outer shell of electrons.
• How many electrons does each atom usually contribute to the shared pair in a covalent bond?

  Usually, each atom contributes one electron to the shared pair of electrons.
• What is a molecule?

  • A molecule is a group of two or more atoms joined together by covalent bonds.
  • Molecules of the same element or compound always contain the same number of atoms of each element.
• What is the size range of small molecules?

  Small molecules are typically around 0.1 nm or $1 \times 10^{-10} \text{ m}$ across.
• Why can't individual atoms and molecules be seen with a light microscope?

  They are too small to see even with the most powerful light microscope.
• What type of microscope can produce images of atoms and simple molecules?

  Some electron microscopes can produce images of atoms and simple molecules.
• What is the chemical formula of a water molecule?

  The chemical formula of a water molecule is $H_2O$.
• What do the chemical formulas of substances with small molecules indicate?

  • The chemical formula shows the number of atoms of each element in one molecule of the substance.
  • Example formulas:
  • Hydrogen: $H_2$
  • Oxygen: $O_2$
  • Nitrogen: $N_2$
  • Hydrogen chloride: $HCl$
  • Water: $H_2O$
  • Ammonia: $NH_3$
• How many atoms are in one molecule of methane, $CH_4$?


  A methane molecule is made up of one atom of carbon and four atoms of hydrogen.
• How many atoms are in one molecule of chlorine, $Cl_2$?


  A chlorine molecule is made up of two chlorine atoms.
• What are the key characteristics of covalent bonds and small molecules?

  • Covalent bonds involve sharing electrons.
  • Small molecules consist of a few atoms.
  • They have low melting and boiling points.
  • They do not conduct electricity.