Glossary
Anion
An anion is a negatively charged ion, formed when an atom gains one or more electrons. Nonmetals typically form anions.
Example:
A chlorine atom gains an electron to become a Cl- anion.
Bond Dipoles
A bond dipole is a measure of the polarity of a chemical bond, represented as a vector pointing from the partially positive end to the partially negative end of the bond. It arises from the unequal sharing of electrons in a polar covalent bond.
Example:
The O-H bonds in water each have a significant bond dipole because of the electronegativity difference between oxygen and hydrogen.
Cation
A cation is a positively charged ion, formed when an atom loses one or more electrons. Metals typically form cations.
Example:
When a calcium atom loses two electrons, it becomes a Ca2+ cation.
Coulomb's Law
This law describes the electrostatic force of attraction or repulsion between two charged particles. The force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
Example:
According to Coulomb's Law, the strong attraction between a Na+ ion and a Cl- ion in table salt is due to their opposite charges and relatively small distance.
Covalent Bonding
Covalent bonding is a type of chemical bond formed by the sharing of valence electrons between two nonmetal atoms. This sharing allows both atoms to achieve a more stable electron configuration.
Example:
In a methane molecule (CH4), carbon and hydrogen atoms are connected by covalent bonding, sharing electrons to complete their outer shells.
Crystal Lattice
A crystal lattice is a highly ordered, repeating three-dimensional arrangement of atoms, ions, or molecules in a crystalline solid. This structure is characteristic of ionic compounds.
Example:
Sodium chloride forms a cubic crystal lattice where Na+ and Cl- ions alternate in a precise, repeating pattern.
Electronegativity
Electronegativity is a measure of an atom's ability to attract electrons towards itself within a chemical bond. It generally increases across a period and decreases down a group on the periodic table.
Example:
Oxygen has a high electronegativity, pulling electrons strongly towards itself when bonded to hydrogen in a water molecule.
Ionic Bonding
Ionic bonding is a type of chemical bond formed by the complete transfer of one or more valence electrons from a metal atom to a nonmetal atom. This transfer results in the formation of oppositely charged ions that are held together by strong electrostatic forces.
Example:
When potassium (K) reacts with fluorine (F), potassium transfers an electron to fluorine, forming K+ and F- ions, which are then held together by ionic bonding in KF.
Molecular Compounds
Molecular compounds are substances formed by covalent bonds between nonmetal atoms, existing as discrete molecules. They typically have lower melting and boiling points compared to ionic compounds.
Example:
Sugar (sucrose, C12H22O11) is a molecular compound that dissolves easily in water and has a relatively low melting point.
Network Solids
Network solids (or covalent network solids) are substances in which atoms are held together by an extensive network of covalent bonds throughout the entire structure. They are characterized by very high melting points and hardness.
Example:
Diamond is a classic example of a network solid, where each carbon atom is covalently bonded to four other carbon atoms in a continuous, strong lattice.
Nonpolar Covalent Bond
A nonpolar covalent bond occurs when electrons are shared equally between two atoms. This typically happens when the bonded atoms have very similar or identical electronegativities.
Example:
The bond in a diatomic oxygen molecule (O2) is a nonpolar covalent bond because both oxygen atoms have the same electronegativity, leading to equal sharing of electrons.
Partial Charges (δ+ and δ-)
Partial charges, denoted by delta (δ+ or δ-), represent the unequal distribution of electron density within a polar covalent bond. δ+ indicates a slight positive charge, and δ- indicates a slight negative charge.
Example:
In a water molecule, the oxygen atom carries a δ- and the hydrogen atoms carry δ+ partial charges due to oxygen's higher electronegativity.
Polar Covalent Bond
A polar covalent bond occurs when electrons are shared unequally between two atoms due to a significant difference in their electronegativities. This unequal sharing creates partial positive and partial negative charges on the bonded atoms.
Example:
The bond between oxygen and hydrogen in water is a polar covalent bond because oxygen is more electronegative and pulls the shared electrons closer to itself.
Valence Electrons
These are the outermost electrons of an atom, residing in the s and p orbitals of the highest energy shell. They are the primary electrons involved in chemical bonding.
Example:
A nitrogen atom has 5 valence electrons, which explains why it often forms three bonds to achieve a stable octet.