Something you learned is that 25 elements are vital for life on Earth and probably everywhere else. This is how they are shared out in the human body in percentages.

Question time

Why is the periodic table so important?

A - We can use it to predict the properties of elements we have not discovered yet.

B - It has an incredible color palette.

C - We can use it for merchandise.

Explanation - Elements are arranged by their electrons in their valence shell and some other properties which are common for the elements of a group. When Mendeleev created its table he predicted the properties of an element that was not discovered at the time - this element was Gallium.

The right answer is (A)

How many elements have we discovered to the present day?

A - 117.

B - 118.

C - 120.

D - 95.

Explanation - currently there are 118 known elements and this is why there are 118 places in the periodic table. All of the most recently discovered elements are radioactive and highly reactive and we cannot study them very precisely.

The correct answer is (B)

How many elements are essential for life?

A - 24.

B - 5.

C - 16.

D - 25.

Explanation - 25 elements are essential for the existence of life. Of course, many of them are found in trace amounts while 4 comprise 96% of the mass of everyone including you. 

The correct answer is (D)

Which is the most commonly found element in the Universe?

A - Hydrogen.

B - Oxygen.

C - Iron.

Explanation - This is hydrogen. This element has been around since the first day of the Universe as it was born first before all other elements. Hydrogen is the simplest element to exist and all others are made of it through nuclear fusion.

The correct answer is (A)

How many electrons hydrogen has?

A - 1.

B - 2.

C - 3.

D - 4.

Explanation - Hydrogen has only one electron because its atomic number in the periodic table is one. It has only one proton and therefore one electron.

The correct answer is (A).

How far away can one electron travel from the core of its atom?

A - 25km.

B - 100 miles.

C - There is no limit.

Explanation - There is no limit, however, the chance of this happening is very small as electrons tend to stay closer to the cores of their atoms.

The correct answer is (C)

Which elements make up the biggest part of the sun?

A - Hydrogen and helium.

B - Iron and helium.

C - Oxygen and helium.

Explanation - Hydrogen, and helium make up the biggest part of our sun since they are the most efficient elements for nuclear fusion and keep our star bright and shiny. 

The right answer is (A)

Which is the most important compound for life here on Earth?

A - Water H2O.

B - Carbon dioxide - CO2.

C - NaCl.

D - HCl.

Explanation - H2O or water is the most important compound for life here on Earth. Not only because we drink it but because it mixes things. When this mixing takes place some strange chemical processes happen and in some cases, their product is indeed life.

The right answer is (A)

Task 1 - Phosphorus is a chemical element with atomic number 15, atomic mass 30,9, and chemical symbol P. It is from the VA group. Determine the number of protons, electrons, and neutrons it has. Arrange its electrons in different layers using the formula 2.n.n.

Solution:

Phosphorus has an atomic number of 15 which means it has 15 protons and 15 electrons. Its atomic mass is 30,9 and by subtracting its atomic number from it we get the number of neutrons - 16. Note that phosphorus has some isotopes and the number of neutrons in them may vary.

We arrange its electrons as follows - 2 in the first layer, 8 in the second, and 5 in the final one.

Task time

Task 2 - Astatine is a chemical element with symbol At, atomic number 85, and atomic mass of 210. It is located in the group VIIA. Determine the number of protons, electrons, and neutrons and arrange the electrons in different layers.

Solution:

Astatine has an atomic number of 85 which means it will have 85 protons and electrons. We can find out how many neutrons it will have by subtracting its atomic number from its mass. 210 - 85 = 125. Note that there are many isotopes with more or fewer neutrons. 

We can arrange its electrons as follows - 2 in the first layer, 8 in the second, 18 in the third, 32 in the fourth, 18 in the fifth, and 7 in the final sixth valence shell.

NEXT

CHEMICAL BONDS.

Learn more about three chemical bonds - ionic, covalent and hydrogen. Find out how they form and why.

Practice.

In the last lesson you learned more about the four states of matter, you learned that it is made of atoms which are made out of protons, neutrons, and electrons. You already know that atoms are not happy (stable) as they are except for the 7 noble gases which have everything they need. All other elements have to play to become stable and fill their valence shell.

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Let’s put all this knowledge into practice!

We will begin with the matter. You know it has four states but it is also important to remember they are all connected. For example, if we take water (H2O) here on Earth it can be seen in three of the four states. Solid when it is frozen and turned into ice, liquid when this ice melts and if we heat it enough it becomes a gas. If we have enough energy we could possibly heat the water enough to turn it into plasma.

In solid-state molecules are connected together and cannot move a lot. If you try to change their shape they will definitely resist you. If you apply enough force the object will break or bend.

In a liquid state, molecules are not connected so tightly and have greater freedom to move. They have volume but no shape. If you pour a liquid into a glass it will take its shape. 

Gases are extremely complicated. They have neither volume nor shape. We believe they move in a straight line and one molecule is so small by itself that it probably is zero-dimensional and we do not bother to calculate its properties. Interestingly gaseous molecules do not like touching each other. But this happens and when it does energy is transmitted from the bigger to the smaller molecule. 

Plasma is an amazing state of matter. We often see it as bolts of lightning, polar lights and maybe you are reading this lesson from a plasma screen. We, people, believe one day it will provide us with clean and almost unlimited energy and will help us clear our landfills unimaginably effectively. 

This is all you need to know about the state of matter for now. Next, we will talk about atoms. 

You know that atoms are made out of protons, neutrons, and electrons. Protons have a positive charge and are located in the core of every atom. Neutrons have no charge. They can also be found in the core of every element except for a few hydrogen isotopes which have no neutrons. They play a key role in isotopes as they create the difference between one element and its isotopes.

Electrons have a negative charge and circle around the core of every atom. They play an important role in the behavior of atoms. They are distributed in layers and every layer has a certain number of electron slots. For example, the first one has two, the second has eight. 

The most important layer of all is the one farthest from the core. We call it the valence shell and every atom wants to fill it and become happy and stable. Noble gases have filled valence shells and are stable. Instead of calculating the distribution of electrons in every layer to reach the final one you can simply look at the periodic table. The number of the A group every element is located in represents the number of electrons in its valence shell. This is true only for A groups. Elements like lithium and potassium are located in the IA group and only have one electron in their valence shell. Aluminum is located in IIIA and has three electrons in its valence shell. All elements located in the same group have the same number of electrons in their final layer and behave similarly.

Let’s practice:

Sodium is a metal from the IA group. This means it has one electron in its valence shell. This is why we will draw its symbol Na and will place one dot for its one electron in the final layer. Please note that its atomic number is 11. This means it has 11 electrons but we are interested in this particular one located in the valence shell. If we are to draw all its layers we will place 2 electrons in the first one, 8 in the second, and 1 in the last.

The calculation of electrons located in every layer can be performed using the formula 2.n.n = the number of electrons in each layer. The first layer will have 2 or 2.1.1 = 2, the second one will have 8 or 2.2.2 = 8.

Boron is a chemical element located in the IIIA group. This means it has 3 electrons in its valence shell and we will draw three dots, one on every side of its symbol starting from the top and going clockwise. Boron has 5 protons and 5 electrons in total and if we need to dispense them in all its layers the first one will have 2 and the second and final one will have 3.

One final example - Arsenic is a chemical element that has 33 protons and 33 electrons which means its atomic number is 33. It is located in the VA group and has 5 electrons in its outer layer. But if we want to distribute all of them we will place 2 in the first one, 8 in the second, 18 in the third, and 5 in the final fourth.