Chapter 4: Atoms Combining

Formation of Ions

• Cations: Positive ions formed from metals.

• Anions: Negative ions formed from non-metals.

  

Ionic Bonds

• Strong electrostatic attraction between oppositely charged ions.

• Typically formed between Group I and Group VII elements via electron transfer.

• Giant lattice structure: Regular arrangement of alternating positive and negative ions.

Properties of Ionic Compounds

• High melting and boiling points due to strong electrostatic forces.

• Good electrical conductivity when aqueous or molten, poor when solid due to fixed ion positions in solid state.

  

Covalent Bonds

• Formed when a pair of electrons is shared between two atoms to achieve noble gas electronic configurations.

• Occur in simple molecules like $H<em>2$, $Cl</em>2$, $H<em>2O$, $CH</em>4$, $NH_3$, and $HCl$.

  

Properties of Simple Molecular Compounds

• Low melting and boiling points due to weak intermolecular forces.

• Poor electrical conductivity as they do not contain ions.

Covalent Bonds in Complex Molecules

• Formed in molecules like $CH<em>3OH$, $C</em>2H<em>4$, $O</em>2$, $CO<em>2$, and $N</em>2$.

Giant Covalent Structures

• Graphite:

  • Used as a lubricant and electrode.

  • Layers of carbon atoms arranged in hexagonal rings, enabling the free movement of electrons, which contributes to its electrical conductivity and lubricating properties.

• Diamond:

  • Used in cutting tools.

  • Each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement

• Silicon (IV) oxide ($SiO_2$):

  • Similar properties to diamond due to tetrahedral structure, forming a giant network of silicon and oxygen atoms.

Metallic Bonding

• Electrostatic attraction between positive ions in a giant metallic lattice and a 'sea' of delocalized electrons.

• High electrical and thermal conductivity.

• Valence electrons delocalize, creating a 'sea of electrons' and positively charged metal ions. This results in properties such as malleability and ductility, allowing metals to be shaped without breaking.

Properties of Metals

• Good electrical conductivity due to delocalized electrons.

• Malleability and ductility.

Chemical Bonds

• Intramolecular forces (strong): Ionic, covalent, and metallic bonds.

• Intermolecular forces (weak): van der Waals forces.

Bonding

• Covalent: Sharing of electrons between non-metals.

• Metallic: Delocalization of valence electrons forming a 'sea of electrons' around metal ions.

• Ionic: Transfer of electrons between metal and non-metal atoms.

Ionic Bonding

• Metal atoms lose electrons to form cations.

• Non-metal atoms gain electrons to form anions.

• Cations and anions attract each other through strong electrostatic forces.

Covalent Bonding

• Sharing of one or more electrons from both atoms to form single, double, or triple bonds.

Properties Comparison

• Ionic compounds: Mostly solid, high melting/boiling points, conduct electricity when molten or aqueous.

• Covalent compounds: Can be solid, liquid, or gas; low melting/boiling points, generally do not conduct electricity.

Structure of Chemical Substances

• Simple molecular: Fixed number of atoms, held by weak van der Waals forces.

• Giant molecular: Limitless number of atoms, all atoms strongly bonded by covalent bonds.

Allotropes

• Two or more distinct forms of the same element in the same physical state (e.g., diamond and graphite).

Alloys

• Parent metal with residue/impurity/foreign atoms, which prevents metal atoms from sliding over each other.