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UNIT 2: CHEMISTRY

8) Naming Ionic Compounds:

Rules for naming ionic compounds:

• Names of cations (metals) should come before names of anions

  e.g. sodium chloride

• Names of cations remain constant

  e.g. sodium

• Names of anions have -ide at the end

  e.g. chloride

Chemical formulas for simple ionic compounds:

Rules for writing chemical formulas:

• Write the symbol of the positively charged ion first

• Use subscripts to indicate the number of each ion, writing them after the ion they match to.

• If there is only one ion of an element, don’t put subscript 1.

• Don’t include the charges of ions in the balanced formula.

Example:

In this example, the Lithium symbol is first, since it is positively charged. The Oxygen ion is negatively charged, so it is second. The number of the negative charge of the Oxygen ion goes as a subscript next to the Lithium ion, and vice versa.

More examples:

K₂O = K¹⁺O^2- Potassium Oxide

NaOH = Na¹⁺OH^1- = Sodium Hydroxide

CaBr₂ = Ca²⁺Br^1- Calcium Bromide

Al₂S₃ = Al³⁺S^2- = Aluminium Sulfide

Li₃N = Li¹⁺N^3- = Lithium Nitride

Be(NO₃) = Be²⁺NO₃- = Beryllium Nitrate

10) Metallic Bonds:

Ionic bonds:

• Valence electrons from the cation go to the anion

• The cation (transition metal)‘donates’ its valence electrons to the anion (nonmetal).

• Solid crystals with repeating patterns of cations and anions.

Covalent bonds:

• They share valence electrons

• Usually liquid or solid

Metallic bonds:

• Metallic bonds are surrounded by electron clouds (delocalised sea of electrons)

• Valence electrons move freely around the metal ions.

• There is only one type of metal cation

• They are uniformly structured

• Occurs in pure metals

• Occur as ‘crystal lattice”.

A crystal lattice of a metallic bond. The red circles are cations, while the blue circles are the delocalised sea of electrons.

This type of non-directional bond is called metallic bonding.

Metal atoms are hard to separate, but relatively easy to move (malleable).

Alloys: A mixture of two or more elements, where one element is a metal combined via metallic bonding.

Alloys are generally harder than the pure elements, due to the cations having different sizes and radii.

Examples of alloys:

Steel: combination of iron (metal) and carbon (nonmetal)

Bronze: Combination of copper (metal) and tin (metal)

Brass: Mixture of copper (metal) and zinc (metal)