--Chemical stability is the ability to resist chemical change.
--The noble gases are chemically inert or unreactive, they are stable.
--When an atom has 8 valence e-, a stable octet, that atom is chemically stable.
Except for Helium, all noble gases have 8 valence e-.
--The most likely interactions between elements are those which tend to produce a stable octet and interactions are less likely once a stable octet has been achieved.
--The predictability of this behavior in the alkali metals, alkaline earth metals and main block elements (IIIA - VIIIA) is known as the Octet Rule.
--The alkali metals have 1 valence e-, in order to achieve a stable octet they simply lose
1 e-. The resulting stable particle has had a change in the number of electrons, thus giving the atom an electrical charge. It is now called an ion. Example: K loses 1 e- and has a stable octet much like argon.
--Lose e-+ ion
Gain e-- ion
--Any change that tends toward a greater stability will be favored
Thought: Will water run uphill or downhill?
--Most atoms will tend to form bonds in order to achieve more stability.
--When atoms combine in a chemical reaction, energy is often released, and a bond is formed. This exothermic energy can be measured.
--The more energy that is released in forming a bond, the more energy is required to break the bond. Ex. If 500 kJ is required to form a bond 500 kJ will be needed to break it.
--A bond which was formed with a large release of energy will be stronger than a bond which released a small amount of energy. The stronger the bond the more stable the product.
--Sodium is another example of an atom that may lose an e- in order to become stable.This results in a positively charged ion, or Cation --- Na+
--Chlorine is an example of an atom that may gain an e-in order to become stable. This results in a negatively charged ion, or Anion --- Cl-
--The attraction between a cation and an anion creates an ionic bond.
--A neutrally charged ionic compound is the result.Na++C1-=NaCl
--Salts are good examples of ionic compounds. These form when an ionic bond forms between a metal and a halogen.
--Ions and compounds are named systematically and consistently. This is known as a nomenclature.
--Monatomic ions are those formed when one atom loses or gains electrons.
The symbol of the ion must include its charge----Na+, O2-, Mg2+
--Names of monatomic ions
Sodium ion, magnesium ion
--Anions---Replace the end of the element’s name with -ide+‘ion’
ion, oxide ion
--Transition metals---Name of most transition metals will include the charge
written in roman numerals.
Iron (Fe)Fe 2+ --------Iron (II) ion
Fe3+ --------Iron (III) ion
--You must memorize the following transition metals since they do not form
--Metals usually form cations, while nonmetals usually form anions.
--Polyatomic ions are ions composed of multiple atoms. These have specific names, you should be familiar enough with these to use them properly.
--Naming ionic compounds is as simple as writing a compound word:
(1) name of the cation+(2) name of the anion=name of the ionic compound
WARNING: Do NOT use the word ‘ion’ in the compound's name!
--The other type of bonding involves the sharing of electrons as opposed to the gain/loss of them. A bond resulting in the sharing of electrons is called a covalent bond and most often forms between two nonmetals.
--There are two main types of covalent bonds - (1) polar and (2) nonpolar.
--In a polar molecule the electrons are shared unevenly toward one side of the molecule, water for example. This results in a molecule with a positive and a negative end, "poles".
--In a nonpolar molecule the electrons are shared nearly evenly, methane for example.
-- Due to the large number of compounds formed by covalent bonding, covalent bonding is studied more in depth as organic chemistry
Now we know what basic ionic compound formulas look like: cation/anion and the amount of each ion. The next step is to explore the actual reaction that takes place during the formation of the ionic compound. For example:
The two ions are known as the reactants of a chemical reaction, while the resulting compound is the product. We can write this combination in words:
Magnesium reacts with sulfur to produce magnesium sulfide
In order to properly represent the chemical reaction scientists use chemical equations that are a symbolic form of the word version above:
Once you have the basic equation you must make sure the law of conservation of matter/mass is not violated. You can do this by counting all the atoms of each element present on each side of the equationàà
There is one atom of each element on each side of the equation so it is properly representing what is taking place during the reaction.
Hydrogen gas combusts with oxygen gas to produce water:
In this case the equation violates the law of conservation of matter since one oxygen atom is lost in the reaction. This problem must be corrected by balancing the equation. This process is similar to forming ionic compounds because you can only balance by multiplying the number of each reactant or product without changing the actual chemical makeup of any of them. Instead of using subscripts as in a chemical formula we use coefficients placed before each substance as necessary. The coefficient multiplies all atoms located within the substance it proceeds. You cannot simply change H2O to H2O2 since this changes the substance itself.
The coefficients can be worded into the reaction:
2 molecules of hydrogen gas combust with 1 molecule of oxygen gas to produce 2 molecules of water.
The coefficients can also be used to indicate a large number of particles called a mole:
2 moles of hydrogen gas combust with 1 mole of oxygen gas to produce 2 moles of water.
A mole is simply a unit representing 6.02 x 1023 of anything. (e.g. a pair of shoes, a dozen donuts) One mole of water has a mass of about 18 g and a volume of 18 mL. This unit is equal to Avagadro’s number and is very useful in “human scale” chemistry. Let’s face it, we do not work with individual atoms but rather large collections of them.
There are four main types of chemical reactions which you should be able to identify (notice the balance of each equation):
1.Synthesis – multiple reactants producing one product.
2.Decomposition – one reactant producing multiple products.
3.Single displacement – one element replaces another in a compound to produce an element and a compound.
4.Double displacement – two reacting compounds where one element from one compound will replace another element in the other compound.