Ionic and Molecular Compounds

Forming Ions

Why are noble gasses the least reactive? The last level is filled up!

Why are the alkali metals so reactive? They are close to being filled up! (only

one electron in their last shell that they can give off)

We really only need to look at the last level of electrons to see how reactive the element will be. This is called the “valence level”.

Elements become more stable when their valence level is filled up.

When elements gain or lose electrons they become charged. We call this an ion.

When an atom gains an electron, it becomes negatively charged since electrons are negative.

When an atom loses an electron, it becomes positively charged, since it is losing a negatively charged particle.

Elements can never lose or gain protons or neutrons.

For example: A sodium ion that has 11 protons and 10 electrons has what charge? +1 We represent it by Na+

A Magnesium ion has what charge? Look on periodic table… what group is

it in? Will it lose or gain electrons? Lose? It becomes positive… how many does it lose? 2 Charge? Mg 2+

You try it!

Write the ion of the following: Lithium: Potassium: Flourine: Sulfur: Chlorine: Boron: Nitrogen:

Li+

K+

Fl-

S2-

Cl-

B 3+

N 3-

Ionic Bonds

Compounds are made of more than one different element and are chemically linked together.

We call them chemical bonds One type of bond is called an ionic bond. You put one or more positive ions with

negative ion(s) in order to make it neutral. You have a metal (+) with a non-metal (-)

to form an ionic bond.

Physical Properties of Ionic Compounds Most are found in a

solid arrangement called a crystal lattice

They are also readily dissolvable in water (high solubility)

They are good conductors of electricity when dissolved in water because of the ions are free to move around.

Covalent Bonds

A molecular compound forms when atoms share a pair of electrons to form a covalent bond.

The shared electrons are attracted to the nuclei of both atoms.

Unlike ionic bonds, the electrons are not transferred, they are shared.

It is kind of like a tug of war game, both atoms want the electrons, but they have a mutual pull on them.

Forming molecular compounds is based on the same idea as ionic compounds: stability is associated with a full outer energy level.

Simple covalent compounds are made of two non-metals.

Compounds are made of 2 or more different elements. Molecules just have to be two or more elements (same element or different).

E.G. Oxygen gas is O2 and is a molecule, but not a compound!

The names of most molecular compounds tell you what element is in it, plus how many atoms of that element.

We use prefixes to tell us the # of elements:

E.G. Carbon dioxide = 1 C and 2 O’s. OR… CO2

Prefixes

mono 1 penta 5

di 2 hexa 6

tri 3 hepta 7

tetra 4 octa 8

Properties of Molecular Compounds There is a weaker attraction

between molecules than between ionic compounds.

Do not dissolve well in water Plastics are made of polymers,

which are large molecules that are very hard to break down.