Chem Sa 1 8 — Introduction to Reactivity + 6 more topics

1. Electronegativity: This is an atom's ability to attract electrons in a chemical bond.
   • High electronegativity: Atoms (like fluorine, oxygen) strongly pull electrons towards themselves. They're good at gaining electrons or sharing them unequally in a bond, often forming negative ions or participating in polar covalent bonds.
   • Low electronegativity: Atoms (like francium, potassium) don't attract electrons strongly. They're good at losing electrons, often forming positive ions.
   • Trend: Electronegativity generally increases across a period (left to right) and decreases down a group (top to bottom).

The general word equation for this reaction is:
Metal + Oxygen → Metal Oxide

For example, when magnesium (Mg) reacts with oxygen (O₂), it forms magnesium oxide (MgO):
2Mg (s) + O₂ (g) → 2MgO (s)

Different metals react with oxygen at different rates and under different conditions. This difference is due to their reactivity.

Here's a simple flow of how a metal reacts with oxygen:

For example, when iron rusts:
* Anode (Oxidation): Iron metal loses electrons and turns into iron ions.
Fe(s) -> Fe2+(aq) + 2e-
* Cathode (Reduction): Oxygen gas, dissolved in water, gains these electrons to form hydroxide ions.
O2(g) + 2H2O(l) + 4e- -> 4OH-(aq)
* These iron ions and hydroxide ions then react further to form iron hydroxides, which eventually dehydrate to become hydrated iron(III) oxide – the reddish-brown substance we call rust (Fe2O3·nH2O).

Here's a common way to remember a useful chunk of the series:

Potassium
Sodium
Calcium
Magnesium
Aluminium
Zinc
Iron
Lead
Hydrogen (often included as a reference point, even though it's not a metal)
Copper
Silver
Gold

Notice hydrogen is in there. Metals above hydrogen will react with acids to produce hydrogen gas, while metals below hydrogen generally won't.

The general word equations are:
1. Reactive Metal + Cold Water → Metal Hydroxide + Hydrogen Gas
2. Less Reactive Metal + Steam → Metal Oxide + Hydrogen Gas

Let's break down the types of reactions based on metal reactivity:

Metal + Acid → Salt + Hydrogen gas

Let's break down what's happening:

Here's a common reactivity series (most reactive to least reactive):

Potassium (K) > Sodium (Na) > Calcium (Ca) > Magnesium (Mg) > Aluminum (Al) > Zinc (Zn) > Iron (Fe) > Lead (Pb) > Hydrogen (H) > Copper (Cu) > Silver (Ag) > Gold (Au) > Platinum (Pt)

(Note: Hydrogen isn't a metal, but it's included as a reference point to show which metals can displace hydrogen from acids.)