ELEMENTS / PERIODIC TABLE
This is a module about the chemical elements, or: the elementary substances of matter.
Of these bricks, not even hundred different ones exist.
One of the first things you should know: the symbols of these elements.
Of course, you can find them in tables, but a chemistry student cannot fail in knowing by heart a good number of the symbols.
Who, for example, does not know H2O, water, built up of the two elements: H (Hydrogen) and O(Oxygen)?
Then you must know that all these elements can be put toghether in the so called Periodic Table. Every element has its own specific position in this system.
That position depends fully of what you met in module 01: the valency electrons and the number of main orbitals per atom.
You will see dat in the periodic table, four blocks are present: s, p, d or f (see further in this module)
That the Periodic Table (PT) has a simple version; not alle elements are present.
This simple PT contains only the blocks s and p, in the so calles main groups. The position of every element in the PT can be determined with the electronic structure of the atom.
There are various films to be seen at You-tube; also look at:
all elements in position
How many different kinds of atoms kan be found in nature?
In this module 02 you will read about the history of some elements.
Consider the elements als bricks of matter, as elementary substances that have there own specific atom kind.
You must be able to determine the position of an element in the PT (the simple as well as the complete one), knowing the electronic structure of the atom.
You also will learn in this module about the concenpt 'electronegativity'. This is a very important concept to understand the properties of substances. Think in particular about the chemical bonds that such an element likes to realise (see module 03).
You will learn to read the tables and interprete graphics.
Of course we will talk about metals and non-metals. The difference between an element and a compound will be discussed later, in module 05.
Lets try to define the element:
The chemical element is a substance that we cannot - by chemical means - split into other substances.
|Every element has its own atom number and its own symbol
|Every symbol is a CAPITAL, sometimes with a small letter
The Periodic Table / groups and periods
As already said in module 01 about atoms: their most characterizing data are the number of electronic main levels and the number of electrns in the outer shell (the valency electrons).
The number of main levels can vary from 1 to 7, what coincides with the seven periods of the Periodic Table.
The number of valency electrons can vary from 1 to 8, what coincides with the number of main groups of the PT.
With these two data you can determine the position of an element in the PT.
The Periodic Table with only the main groups:
The elements of one and the same group have a same number of valency electrons.
From top to bottomthe number of main levels increases, just like the atom number.
Make a graphic:
Look at group 4 of the PT. the elements of group four are found in the x-axes.
The atom rais of the elements of group 4 are found on the y-axes. Use the data from the table, table 5
What conclusion do you draw from this graphic? Explain your asnwer.
All elements within one period have a same number of main levels. From left to right the atom number increases.
Make a graphic:
Look at period 4 of the PT. The elements of period four are fount on the x-axes.
The atom rais of the elements of period 4 are found on the y-axes. Use the data from table 5
What conclusion do you draw looking at this graphic? Explain.
Look at the Periodic Table in the tables and explain which are the similarities and differences of those two systems.
Another Periodic Table,with the opportunity to find data for every element, just by clicking website.
Think about the next problem:
The main groups do not contain all elements. In da scheme with 7 rows and 8 coloms you can place a maximum of 7 x 8 = 56 elements.
We know that there are about hundred different elements. What now?
To place the other elements, we must apply a more complete methode; for that, we need a closer look at the electronic structures.
You already knew the s- and the p-blocks, but you must know that al toghether there are s, p, d and f-blocks in the complete PT.
Please read again the story about electronic structures in module 01.
The atom of element Sodium has the following electronic structure in sublevels:
1s2, 2s2, 2p6, 3s1.
So, the outer sublevel of the Sodikum atom is of the type s and this means that the element belongs to block s,
the first block of the complete PT.
Is the statement true of false? Explain your answer.
The element X must be a metal,because the electron distribution of the element X is:
1s2, 2s2, 2p6, 3s2, 3p6, 4s2
Goto answer 02-06
Determine the position of atom number 18 in the PT, and give the electronic configuration.
idem for number 23
En element is in main group V and in the third period. What is its atom number?
Determine the position in the simple PT according to the three simple rules for electron distribution (see module 01), of the elements with the following atom numbers:
32 54 83 56 22 73 44 68 94
Make a data table for this purpose
Determine the position of the same elements again for the complete PT, according to the rules for sublevels.
Compare the two schemes and draw your conclusions.
Do you know the position of an element in the PT, than it is possible to say something usefull about the properties of this element.
1.4 The groups I, II, VII and VIII
Having only one valency electron, the atom / element belongs to group I; so also Hydrogen belongs there.
But sometimes writers have the tendency to put Hydrogen not in group I, just because of its special character.
the speciality is that the one and only electron occurs in the one and only main level of Hydrogen.
Normally, one electron in the outer shell is donated easily, but certainly not in the case of Hydrogen.
There are only two elements with only one main level, i.e. with only one sublevel 1s. They are:
Hydrogen with one electron: 1s1
Helium with two electrons: 1s2
Normally one electron in the outer shell is donated easily (and mostly we have then metals), but not in the case of Hydrogen.
Het Hydrogen atom, after losing its electron, would be 'naked'. Only a nucleus of one proton would remain.
Well, that is impossible. protons do not exist independently. That's why Hydrogen is not e metal.
All other elements in the first main group are (very reactive) metals, easily losing an electron.
Hydrogen atoms prefer to look for an electron, to gain an electron, just to have two electrons in the outer shell (what in this case is a noble gas structure). Hydrogen can do this only in cooperation with other atoms, sharing electrons with other atoms.
The result is a covalent bonding, but we will talk about that in module 03.
In very exceptional cases Hydrogen can make a negative ion, the hydride ion H-.
H+ (the result of losing an electron) does not really exists, but very often you will find H+ in literature.
It is just easy to use H+, to pretend that is exists.
All other elements of group I, Li to Fr, easily form positive ions, and these elements are very reactive.
The use of the symbol H+ in fact is kind of illegal. Explain that.
Explain which element will be more reactive: Sodium or Potassium?
Officially Helium belongs to group II, becaus it has two valency electrons in the outmost orbital.
But, as we have seen, Helium has, just like Hydrogen, only one main orbital with these two valency electrons. The first main orbital is full! No more electrons allowed there. Helium cannot have more.
In short: Helium is perfectly content with those two electrons and will not have the least tendency to change that. He will not donate nor capture electrons.
Helium does not react at all, is a noble gas. That's why we mostly do not place Helium in the second main group of the PT, but in group VIII, toghether with the other noble gases.
The second main group contains the elements Be till Ra (2s2).
These elements want donate two electrons and are rather reactive, although less than the elements in the first main group.
Explain why the elements in the second main group are less reactive than those in the first one.
The elements of group VII are called halogenes. They have 7 valency electrons (of course in the outer shell) and they like to have one more, just to have 8 in total. With 8 electrons in the outer level, the atom (ion) becomes a lot more stable.
Below some data about group VII
Astatium (also a halogene) is radioactive
The elements of group VII can be characterised with ns2 np5, n≥2
Explain why Fluorine is the most reactive halogene.
Goto answer 02-11
It is said that the element Phosphor is extremely important for the human body.
But at the same time we know that Phosphor is very poisonous.
There we have the noble gases, including Helium.
They are 'inert'. That means that they do not like to react at all. They are inactive. Maybe they are called 'nobel' for that reason!?
They all have very stable electronic configurations and not the least tendency to react.
Is the following statement true or false?
The noble gases have a very low ionisation energy
Explain your answer.
Goto answer 02-13
Electronegativity is the tendency of a (neutral) atom to attract negative charge (electrons).
The electronegativity of the atoms depends on:
Here we must apply the Law of Coulomb. In some schools this law is not treated anymore. It used to be part of Physics in secondary education. With the Law of Coulomb you can better understand how forces between atoms and ions take place.
- The distance between the nucleus and the outer shell
- The (postive) charge of the nucleus (= number of protons)
You must just know the Law of Coulomb; no doubt.
You must imagine that two charges attract or repell each other twice as hard if a charge becomes twice as big.
But if the distance between those charges becomes twice as large, than the attraction of repelling forces become four times smaller.
F is the attraction (or repelling) force between charges.
Imagine an atom: there is a positive charge and - at some distance - negative electrons.
The nucleus attracts the negative charges (consider in particular those charges at the outer side, so at maximum distance from the nucleus).
The attraction power depends on Q1, Q2 and r (the charges and the distance)
Q symbolises the charges (of the nucleus and the electrons); the value of r in this kind of calculations is about similar withthe atom rays.
In atoms with a relative strong postive nuclear charge (G is big) and a relative small atom ray (r is small) the value of F will be big.
In the case of atoms you must indicate attraction force F with the E of electronegativity.
Analyse the above scheme and give your comment. Use tables.
- Explain why the Chlorine atom attracts electrons stronger than the Iodine atom. Use tables.
- Explain why the Chlorine atom attracts electrons stonger than the Sodium atom. Use tables.
- Control the data from the tables with electronegativity with those three elements.
- Make a graphic with the electronegativities of the elements of period 3.
- Look at the simple periodic table. Where are the elements with the bigger E-values?
Normally an atom has a preference for 8 valency electrons. Knowing that, you must show the electronic formulas of the following molecules / ions:
F2 Cl2 ICl HBr CO N2 HS- OH-
Also explain if you expect polarity in the molecule. (i.e.: one side of the molecule is a bit negative and the other side is a bit positive)
Goto answer 02-16
The molecule of dichloromethane will be polar? Explain.
Goto answer 02-17
The phylosophers of the old Greek sciences tried to understand and explain Nature. The introduces the concept "element".
Aristoteles said: there are four elements:
er zijn vier elementen: Earth, Water, Fire and Air. All substances are built up of these four.
Thus: wood must contain a lot of the element Fire, becaus, when burning, lots of Fire comes out. That makes sense, isn't it?
Later, in the Middle Ages, the alchemists continued this way of thinking and joined water and earth toghether: 'Mercure'. Air and Fire were joint to the element 'Sulphur'. They tried - in search of the right composition of these two, to make Gold.
These are phases in the development of science. Every phase contributed.
The choice to give some extra attention to these elements has to do with the fact of their abundancy; they are the most important elements in the outer earth crust of about 40 km thick. Humans have enormous profit from these elements.
About 20% of the air is Oxygen; it is number 2 after Nitrogen.
In the earth, Oxygen is the champion number one; about half of the substances in the earth is the element Oxygen, mainly in the form of oxydes.
The oxyde that occurs the most is Silicium oxyde, SiO2 (sand).
This is used, for example, in glass and in very important applications of chips in computers and many other digital apparatus.
Aluminium, like many other elements, does not occur in pure form, but only in compounds.
Earth contains a high percentage of Al in the form of Bauxite, Aluminium ore, Aluminium oxyde. You must treat that in a proces of electrolysis to get the pure Aluminium (see module 10). It is a very strong en light metal.
Iron is known for a very long time and found in iron ore (Iron oxyde of course). They obtain the pure Iron in high furnaces with help of Coal.
Calcium is found in stony places, in particular in the form of calcium carbonate.
Someone collected a sample of 2 kg of earth.
Calculate - knowing the average values - what will be the contribution of Oxygen to these two kilograms of earth.