ionic, covalent, periodic trends in bonding and structure

ionic bonding

strong electrostatic attraction between a positive and a negative (cation and anion)

• it holds cations and anions in ionic compound

giant ionic lattice

structure containing billions of billiond of ions

properties of ionic compounds

• most ionic compound have high melting and boiling points (solid at RT)

high temps needed to provide large quantity of energy to overcome the electrostatic attraction between the ions

• many ionic compounds dissolve in polar solvents such as water

polar water molecules breaks down the lattice. in a compound made of ions with large charges, the ionic attraction may be too strong for water to be able to break down the lattice structure (maybe insoluble)

• solid state → not conduct electricity

• melted or dissolved in water → does conduct electricity

simple covalent bond and its properties

is the strong electrostatic attraction between a shared pair of electrons and the nucleid of the bonded atoms (non-metals)

simple covalent bond properties

• Low Melting and Boiling Points:

  Covalent bonds form discrete molecules. The forces between these molecules (intermolecular forces) are weak, requiring little energy to break. 

• Poor Electrical Conductivity:

  In most simple covalent substances, there are no free-moving, charged particles (like electrons or ions) to carry an electric current. 

• insoluble (Often):

  Simple molecules often do not dissolve well in water, as they are typically non-polar and cannot interact effectively with polar water molecules. 

lone pairs

is where paired electrons that arent shared

multiple covalent bonds

exist when 2 atoms share more than one pair of electron

dative covalent/coordinate bond

is a covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only

average bond enthalpy

serves a measurement of covalent bond strengths. the larger the value of the average bond enthalpy, the stronger the covalent bond

metallic bonding

is a special type of bonding for metals

delocalised electrons

that they arent confined to a single atom and is free throughout the whole structure

giant metallic lattice

billions of metal atoms are held together by metallic bonding

giant covalent structure and its properties

many billions of atoms are held together by a nerwork of strong covalent bonds to form a GCL

eg diamond (carbon)

• strong covalent bonds between atoms

• very high M/B point (strong C.B)

• mostly non-conductors (except graphite)

• Insoluble

• very hard (dia) or slippery (graphene)

properties of metals

• malleable

• high m/b points due to strong metallic bonds

• great conductors of heat and electricity due to delocalised electrons

• most metals are solid at room temps

allotrope and examples

different structural form of the same chemical element in the same physical state - carbon; diamond, graphite, graphene

Why do melting points increase from Na → Mg → Al in Period 3?

Metallic bonding gets stronger: ion charge increases (+1 → +2 → +3), more delocalised electrons, stronger attraction between ions and electrons.

Why does Si have the highest melting point in Period 3?

It has a giant covalent structure with strong covalent bonds throughout, which need lots of energy to break

Which order do P₄, S₈ and Cl₂ melt?

S₈ > P₄ > Cl₂ (because S₈ is the biggest molecule, Cl₂ the smallest).

Why does Argon have the lowest melting point in Period 3?

Ar exists as single atoms, so only very weak forces between atoms