1.6 THE PERIODIC TABLE - STRUCTURE, TRENDS & S-BLOCK ELEMENTS (REACTIONS)

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Hi guys! I've got to be honest, I think this is the worst unit of the whole course. Not because it's boring or difficult, it is just all about remembering.

You have to remember many, many reactions, equations and observations.

I recommend visiting this topic as the last one before the exam, as there is no point to remember it all and then forget before exams come around.

First of all, we're going to focus on the periodic table and segregate it into 3 blocks.

--> You definitely know this by now: periods- going horizontal and groups- going vertical. --> Metals on the left-hand side of the periodic table, non-metals on the right-hand side of the periodic table. Between them, there are metalloids. There is a zig-zag line that shows you the border between metals and non-metals and elements such as Carbon and Silicon are metalloids (right between them). --> Elements in the periodic table are arranged in order of increasing atomic number (starting with 1 on Hydrogen). Now, let's talk about the groups in the periodic table and what happens to each group (what they 'like' to do to become 'happy'). --> Groups 1,2 and 3 - they donate their electrons to other atoms. When they give them away, they become positive and are called CATIONS. --> Groups 5,6 and 7 - they gain electrons from other atoms. When they gain these electrons, they become negative and are called ANIONS. --> Group 4 - they either gain or donate the electrons, however, this is quite hard for group 4 elements because they would either need to gain 4 electrons or lose these 4 electrons (that's a lot of electrons). Therefore, what the group 4 elements usually do is bond covalently. --> Group 8/0 - these elements are 'happy' as they are. They have 8 electrons which means they have a full shell (He has 2 electrons and it is 'happy' because in the first shell you can only have 2 electrons). We call these elements unreactive (they are not interested in doing anything because they 'feel' good as they are).

There are some trends in the periodic table. Ionisation energies follow a trend that you need to know. It is the same with electronegativity and melting points. We're going to think about what elements have the highest ionisation energy (electronegativity and meting point) and which ones have the lowest ionisation energy (electronegativity and melting point). Ionisation energy - this is the energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms.

--> Increases across the period -this is because there are more protons and the electrons are still in the same shell, so these electrons are attracted very strongly to the nucleus. --> Decrease down the group- we keep getting shells down the group and the protons don't have as much power over the electrons; the nuclear charge decreases. Electronegativity - this is the ability of an atom to attract electrons.

--> Increases across a period- there are stronger attractions as we go across the period for the exact same reason as for ionisation energy. --> Decreases down the group - the atoms become larger and the shells are further away from the nucleus therefore, protons no longer attract new electrons as much. Melting points - the melting temperature depends on the strength of the forces that hold the particles together, the atomic mass and type of solid structure. I think this is the most complicated trend to follow.

--> Increases acorss period from group 1 to 4 - this is because the number of electrons that can be donated to delocalised system increases. --> Decreases down the group 1 - there is more distance between protons in the nucleus and the electrons. This means we have a smaller overall attractions. If the attractions are smaller, it doesn't need as high temperature to be broken. -->Increases down group 7 - group 7 is different to group 1 because here the melting temperature will increase as you go down the group. The reason for this is that group 1 elements bond by interaction when they donate electron and in group 7 (halogens) there are intermolecular forces called Van der Waals. The more electrons there is, the more Van der Waals, so bigger force to overcome and the melting temperature is therefore higher. -->Decreases across period from group 5 to 8- the elements usually form diatomic molecules which are held in solid by weak forces. For example: I2 which we covered in previous post. We have weak forces, so the melting temperature is small.

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REACTIONS

You know everything there is to know (in AS-level) about periodic table. As written in the title, now it is time for reactions. This is the bit that needs a lot of remembering. In this post we are going to focus on reactions of group 1 and group 2 elements with oxygen, water, acids, hydroxides, carbonates and sulphates; and of course our flame test.

For the next several pictures you are going to see tables. They will include different elements from group 1 and 2, observations and equations. In an exam, you may be asked to write a BALANCED equation for the reactions and that's why I included them in my table. The equations for all group 1 elements will look similar (just the elements changes) and the equations for all group 2 elements will look similar (just the elements will change again). The elements that I stated are the ones you are required to know for your AS-level exam.

There is not much to explain here, because they are all observations that will not change and you just need to remember them.

Group 1 - we have lithium, sodium and potassium. They react rapidly with oxygen.

• As you can see we are starting slowly because lithium with oxygen only gives a bright light.

• Once we go down the group, the observations are more vigorous, with sodium we have bright light but much stronger because it breaks the glass.

• Lastly, potassium is even more violent.

On the right of the table, there are equations. They have the same numbers in front of the elements (they're all from the same group). If you can't remember the numbers in front, write the elements first and then balance it yourself.

Group 2 - we have magnesium and calcium. The reactions are not as rapid and violent as with group 1 elements.

• The observation is the same as with group 1 elements, we have bright light for magnesium.

• Again, the observations are more violent as you go down the group 2. Calcium gives a very bright light.

We also have the equations and as you can see there is a different mole ratio (the numbers in front of the elements). This is due to the different number of valence electrons compared to group 1.

Now, we have the same table but we added some more group 1 elements and changed group 2 elements.

Group 1- lithium, sodium, potassium, rubidium and caesium are the ones we will observe reacting with water.

• If you put lithium in the water, it is floating and it releases hydrogen gas. When you place a lighted splint in this hydrogen gas, you will hear a squeaky pop (that's a way of checking if you have hydrogen gas present).

• Now, we put sodium in water. Again, it floats on water and releases hydrogen gas. The heat produced melts the sodium piece and forms it into a ball.

• Potassium is even more vigorous, we have everything above but the heat is so strong, it produces a lilac flame and sparks.

• Rubidium and Caesium react similarly, they are very violent. They both burn and spark but Caesium breaks the glass (container in which the reaction takes place).

Group 2 - calcium and barium reacting with water also produce hydrogen gas.

• Calcium bubbles vigorously when added to cold water.

• Barium also gives bubbles and reacts more violently than calcium.

The equations for group 1 and group 2 reactions are shown on the right again. This time we put water in the place of oxygen.

As a conclusion, we can see that the reactivity increases down the group 1 and 2 when reacting with oxygen or water.

All s-block metals react vigorously with acids.

--> Group 1 - both group 1 and 2 react with acids, however, group 1 metals are more reactive than group 2. This is because there is only one electron that needs to be removed.

--> Group 2 - reacts readily and by the equation:

METAL + ACID --> SALT + HYDROGEN

I also prepared a worked example for you using this equation and a group 2 metal, Magnesium.

In the example below, we have a magnesium metal reacting with hydrochloric acid. This forms a magnesium chloride salt and hydrogen.

Sometimes, in the exam, you might be asked to write an ionic equation for this reaction, therefore, I wrote a one like this for you too. We have practised this type of equations in my previous posts in Unit 1, so go there and check it out first if you're not sure about it.

Reactants:

• Magnesium is solid, so it doesn't go into ions;

• Hydrochloric acid dissociates into ions because it is in an aqueous state;

Products:

• Magnesium chloride is in an aqueous state, so dissociates into ions;

• Then you have hydrogen gas which is not dissociated;

You can cancel out chlorines and you are left with an ionic equation.

In this equation, magnesium metal is a REDUCING AGENT, therefore it is itself OXIDISED (OIL- lost electrons).

We have three more reactions of group 2 metals:

1.Group 2 with hydroxides: First of all, all group 1 salts (metal with hydroxide) are soluble in water. On the picture above, I included an equation for the reaction of group 2 metal with a hydroxide. As you can see in the table (above in the picture), the solubility of group two hydroxides starts with magnesium hydroxide which is insoluble in water and the solubility increases down the group. Furthermore, the thermal stability increases down the group. Thermal stability - how much heat it needs to decompose. 2.Group 2 with sulphates: When you react a group 2 metal with a hydroxide, a white precipitate forms. Again, you have an equation. This time barium sulphate is insoluble in water and the solubility increases up the group. 3.Group 2 with carbonates: Now, we have a metal reacting with carbonate and a white percipitate is produced. I also prepared an example equation for you. Every time I give you an example equation, it works exactly the same for any other group 2 metal. All carbonates are insoluble in water.

The thermal stability increases down the group.

Here is the flame test. There is not much that I can explain about it. The colour appears when you burn a metal. The colours for different group 1 and 2 metals are in the table above.

Both Calcium and Magnesium have a use in the human body and nature. Let's start with: --> Calcium: - strengthens and supports bones and teeth; - it is found in plant leaves as a phosphate; --> Magnesium: - acts as a co-factor in many enzyme systems; - it is essential in order to convert carbon dioxide from the atmosphere into carbohydrates.

PS. Please remember, I am only a student, and as anyone, I can make mistakes. If you think you can see one, don't hesitate and comment (either here on on my youtube channel) Thank you!