Atomic Structure: Ions

All atoms are neutral, but when they have a higher or lower number of electrons compared to protons, they become CHARGED IONS. These are divided into two groups:

Cations — Positively charged ions
Anions — Negatively charged ions

How to remember which is which? Just remember that ANIONS are A-Negative-ION. Wallah, so genius, I know.

TRENDS...

• Elements in group 1 to 4, all their atoms tend to lose an electron to complete their shells. Meanwhile, Elements in group 5 to 7, all their atoms tend to gain an electron.
• All metals are cations. All non-metals are Anions.

To help remember their charge, we can always go back to that beautiful valency table we had in the last post!

Atomic Structure: Valency

So remember in the last post when we talked about ELECTRON SHELLS? Remember that they could have many many many shells, and yet a maximum number of electrons in each shell? If you don't it's okay, we'll recap.

So basically, the way electrons are arranged in an atom is also called electronic configuration. If you want to represent it visually, it'd look like this:

If you want it in orbital notation it'd look like this:

I would continue with spdf and all but that's for another day. ANYWAYS...

The circles you see with the x's on them? That's called a shell. And those x's are electrons. So the first shell can hold up to 2 electrons and the second and subsequent ones can hold up to 8 electrons. Now, now, here's the complicated part.

A VALENCE ELECTRON is an electron that lies on the outermost shell of an atom. The outermost shell is also called the "valence shell". So what is this complicated "valency"?

Valency --> No. of electrons needed to be gained or lost to complete the shell

"Complete the shell?" Simi lanjiao. 

"Completing the shell" means making the shell is full. So for example, iodine, has seven valence electrons yes? To complete the shell, you need to gain another electron, to ensure you have the maximum number of electrons in the shell (8).

Here's the complicated part. Sometimes an ion will also lose electrons to complete the shell. In the case of lithium for example, a lithium ion has only one valence electron. So what does it do to complete the shell? It loses that electron. 

Why does it do that? Because losing one electron is easier than gaining seven more. (informal answers you must not use in exam) BUT YES, VALENCY IS COMPLICATED. So here's a little valency table for you:

Things to note:

Down the group, elements all have the same number of valence electrons. 

However, number of valence shells increase down the group.

Across the period, number of valence electrons increase

Why does all this happen? Moving on to electron affinity...

Atomic Structure: Parts of an Atom

So before we delve into the deep and confusing processes, we need to know the parts of an atom, also known as SUB-ATOMIC PARTICLES.

Okay so parts of the atom...

THE NUCLEUS
This is made up of protons and neutrons.

THE ELECTRON SHELL
The electron is just a rough gauge for where the electrons move. The inner most shell can carry up to 2 electrons, while the ones further away can carry up to 8 electrons. And you can have many many many electron shells, but we'll get to that later.

ALL THE LITTLE 'ON'S
Protons — Determine the identity of the atom (like on the periodic table)
Electrons — Determine the charge of the atom (the less you have, the more positive the charge. Vice versa)
Neutrons — Determine the mass of the atom

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Okay, so maybe I'm not very good at describing and you might still be wondering:

So let's put a little link to the periodic table. So on the periodic table they usually give you a little bit of information on each element. For example, carbon here, on this lovely image I found on Google.

So like the diagram says, the number above the letter, that is the atomic number, AKA proton number. This is, as you might've guessed, the number of protons in that atom. And if you haven't noticed, this is how elements in the periodic table are arranged: By proton number.

The number below that is the nucleon number or atomic mass. You might wonder, why is this the mass?? Remember that ATOMS ARE ELECTRICALLY NEUTRAL. Sooooo... in every atom, there will be an equal number of protons and electrons, cancelling each other out. So what's the only thing that actually has mass? That's right, your good old buddy neutrons.

If an atom does not have an equal amount of protons and electrons, it will be an ion, which we'll be covering in the next post!

Acids and Bases: Concentration

What is concentration?

Concentration is the amount of substance dissolved in a fixed volume of solution. In other words it's: 

Amount of substance / Volume of solution

Main Points:

• The strength of the acid is relative to the % dissociated

That's why even if the acid has higher strength, if the concentration is higher, it can have a lower pH. This is the formula for pH by the way:

Anything with square brackets mean it's "concentration of" apparently.

• The concentration of H+ ions determines the pH

There are always H+ ions and OH- ions in every acid. The weaker the acid, the higher the amount of OH- ions and the lower the amount of H+ ions. Therefore, your H+ ions are relative to your acidity and the OH- ions to your basicity. 

If you still don't get it it's fine. Just remember that the higher the concentration of H+ ions, the lower the pH. 

Other points:

• pH is only dependant on the concentration of H+ ions.
• pH is non-linear

Acids and Bases: Dissociation

What's that?

Dissociation is really just "to take apart what was associated". In chemistry terms, it is 

Splitting a soluble substance in water into ions. 

The simplest formula would be:

AB --> A + B

Here are some other facts:

• During dissociation, the ionic bonds are broken, but the covalent ones are not.
• Dissociation is actually a reversible process due to equilibrium, but the amount it so small it's really almost negligible.
• Dissolving is a dissociation process.

Acids and Bases: Bases

What are Bases?

Bases, according to this genius guy named Arrhenius (yes, they rhyme), is a substance that releases hydroxide (OH⁻) ions. These substances react to acids to give salt and water only. All metal oxides and hydroxides can act as bases. Here are some examples of bases:

Here are the properties pertaining to ALL bases:

1. They turn red litmus paper blue; and on blue litmus paper the paper remains blue

2. They have a bitter taste and soapy feel

3. They react with acids to form salt and water only

4. When heated up with an ammonium salt, ammonia gas is produced

5. Strong bases can dissolve in water to form solutions that can conduct electricity 

Soluble bases, which are also strong bases, are called alkalis. 

Extra bits: Not all metal oxides and hydroxides are alkalis. This is because not all of them are soluble, a property of alkalis.

Acids and Bases: Acids

What are Acids?

Acids are substances that release hydrogen ions when dissolved in water. They can be classified as weak or strong as seen in this table:

And their properties are as the following:

1. Acids have a sour taste (Not that you should ever taste them)

2. Acids turn blue litmus paper red

3. Acids react with reactive metals to form hydrogen and salt

4. Acids react with metal oxides and hydroxides to form salt and water only.

5. Strong acids dissolve in water to form solutions that can conduct electricity


Extra bits:
The reason why strong acids are stronger electrolytes is because they form ionic compounds. When an ionic compound has charged particles, it can conduct electricity.