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.
• What is a molecule?

  A molecule is a group of two or more atoms joined together by covalent bonds.
• 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 is the approximate size of a water molecule?

  A water molecule, H₂O, is about 0.3 nm ($3 \times 10^{-10} \text{ m}$) across.
• What does the chemical formula of a substance with small molecules indicate?

  • Shows the number of atoms of each element in one molecule
  • Example: H₂O indicates 2 hydrogen atoms and 1 oxygen atom
• What is the formula for hydrogen gas?

  The formula for hydrogen gas is H₂.
• How many atoms are in one molecule of oxygen gas?

  There are two oxygen atoms in one molecule of oxygen gas (O₂).
• What is the formula for nitrogen gas?

  The formula for nitrogen gas is N₂.
• What is the formula for hydrogen chloride?

  The formula for hydrogen chloride is HCl.
• How many atoms are in one molecule of ammonia?

  One molecule of ammonia (NH₃) contains one nitrogen atom and three hydrogen atoms.
• What is the composition of a methane molecule (CH₄)?

  A methane molecule is made up of one atom of carbon and four atoms of hydrogen.
• What is the composition of a chlorine molecule (Cl₂)?

  A chlorine molecule is made up of two chlorine atoms.
• What are the key features of covalent bonding?

  • Involves sharing of electrons
  • Forms between non-metal atoms
  • Results in the formation of molecules