Chemical Bonding and Lewis Dot Symbols

Chemical Bonding

• Chemical bonding is the joining of atoms to form molecules or compounds
• Two main types of bonds are ionic and covalent bonds
• Ionic bonds form between a metal and nonmetal or polyatomic ions
• Ionic bonding involves a transfer of electrons, creating positive and negative ions that are held together by electrostatic attraction
• Covalent bonds form between two nonmetals
• Covalent bonding involves sharing of electrons between atoms
• Electronegativity (EN) is a measure of an atom's ability to attract shared electrons
• Different EN values between atoms lead to different types of bonds

Lewis Dot Symbols

• Gilbert Lewis developed Lewis dot symbols to track valence electrons
• Valence electrons are the outermost electrons in an atom and are the main actors in bonding
• Lewis dot symbols show the elemental symbol and valence electrons as dots around the symbol
• Atoms combine to achieve a more stable electron configuration, often isoelectronic with a noble gas
• Stability is achieved by fulfilling the octet rule, where atoms tend to have eight valence electrons

Ionic Compounds

• Ionic compounds form lattices, a repeating three-dimensional pattern of ions
• The strength of this lattice is described by lattice energy, which is the energy required to completely separate one mole of solid ionic compound into gaseous ions
• The lattice energy depends on the charges of the ions and the distance between them
• Ionic compounds are typically solids at room temperature with high melting points and boiling points
• Ionic compounds conduct electricity when dissolved or molten

Lattice Energy

• Lattice energy is the energy needed to break apart an ionic compound into its component ions
• Lattice energy is directly proportional to the product of the ionic charges (q₁q₂) and inversely proportional to the distance (r) between the ions
• Larger charges will result in a higher lattice energy
• Larger distances will result in a lower lattice energy

Covalent Bond Lengths

• Covalent bond lengths impact the properties of molecules
• Single bonds are longer than double bonds, and double bonds are longer than triple bonds
• This difference in length is due to the varying number of shared pairs of electrons in each bond
• Multiple bonds are more stable

Electronegativity

• Electronegativity is the measure of an atom's ability to attract shared electrons in a covalent bond
• Electronegativity is periodic
• Differences in electronegativity between atoms determine the polarity of the bond and molecule

Drawing Lewis Dot Structures

• Place the least electronegative atom at the centre
• Add up the total valence electrons
• Place single bonds around the central atom first, then add non-bonding pairs to complete the octet of each atom
• Multiple bonds are formed to complete the octet only if needed

Molecular Geometries (VSEPR)

• Valence Shell Electron Pair Repulsion (VSEPR) theory describes molecular shapes by considering electron repulsions between electron domains
• Electron domains include bonding electron pairs and lone electron pairs (non-bonding)
• Electron domains are arranged as far apart as possible to minimize repulsion
• Experimentally determined bond lengths and angles determine molecular geometries which impact properties (melting point, boiling point, density, types of reactions)

Polar and Nonpolar Molecules

• Polarity, either of a bond or a molecule, is determined by the difference in electronegativity of the bonded atoms or the vector sum of all bond dipoles
• Nonpolar molecules exhibit no dipole moment, meaning the centers of positive and negative charge coincide
• Polar molecules have a permanent dipole moment resulting from an asymmetric arrangement of polar bonds
• Bond polarity is determined by the difference in electronegativity of the two atoms in a bond; the larger the difference, the more polar the bond; atoms with large electronegativity values attract shared electrons more strongly

Explore the fundamentals of chemical bonding, including ionic and covalent bonds. Understand how Gilbert Lewis's dot symbols help visualize valence electrons and their role in forming stable molecules. This quiz will reinforce key concepts in the formation of bonds between different elements.