0201 Atoms

The building blocks of everything

This module provides an overview of the basic building blocks of matter, and their importance.
 
Bear in mind that an understanding of every single concept in chemistry depends on an understanding of some other concepts.

We don’t learn any component in totality at first. We come to understand by learning enough about any part to function.

And so we have partial knowledge of lots of bits, growing as we need more knowledge to support other bits. We use imperfect knowledge, as needed, because all chemistry concepts are interdependent.  

So don’t expect to fully understand immediately the concepts and the ideas presented here. This module is intended as a framework (or road map) which might render further learning more meaningful

You may have realised that at about 6:41 Aussie wrongly referred to electrons in the nucleus of atoms. Prof Bob did the same!.
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​KEY IDEAS

The building blocks of everything are tiny particles called atoms – far, far smaller than we can see, even with a microscope.

For some sense of how small atoms are, by reference to the number of them in small samples of substances, see Module 0502 Avogadro constant: How many particles is that?

The composition of atoms can be summarised as follows:

• In the centre of each tiny atom is a much tinier nucleus, that consists of particular numbers of particles called protons (with positive electrostatic charge) and neutrons (with zero charge).
• ​Surrounding the nucleus are a number of electrons (equal to the number of protons in the nucleus, and with negative charge) which are best thought of as a smear or “cloud” of matter (rather than as particles).

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​Of all of the naturally occuring atoms, there are only about 90 different types: the key difference from type to type being the number of protons (from 1 to 92) in the nucleus.

All of the atoms of one type (same number of protons) are said to be atoms of a particular element. During chemical reactions, the atoms of an element always retain the fixed number of protons characteristic of that element: they cannot be destroyed nor changed into atoms of other elements.

In a circular way, we can say that an element is characterised by the type of atom (ie, by the particular number of protons in its nucleus)

The number of protons in the nuclei of all atoms of a particular element is called the atomic number (symbol Z) of that element.
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Some names of elements are, for example: 

• The element whose atoms all contain just one proton in the nucleus (Z = 1) is called hydrogen, and for this name we use the symbol H.
• The element whose atoms all contain eight protons in the nucleus (Z = 8) is called oxygen, and for this name we use the symbol O.
• The element with atoms that contain eleven protons in the nucleus (Z = 11) is called sodium, for which we use the symbol O.
• Atoms with 17 protons in the nucleus (Z = 17) are atoms of the element that we call chlorine, for which we use the symbol Cl.

And so on for all 92 naturally occurring elements. We will refer to information tables of all of the elements later – as well as to an ordered arrangement of the elements called the periodic table.
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A historical context

A reminder: The elements as substances were known, and their properties studied, long before protons were known about.

In fact after centuries of debate, it was not until the published work of John Dalton in 1808 that the scientific community accepted that matter was indeed made up of particles (called atoms)

So I am presenting here knowledge about elements and atoms from a current viewpoint.

​Names, symbols, labels: an important communication issue:

When someone (or you) uses the term “oxygen”, they may intend to refer to of several things:

• “Oxygen” is the name given to one of the elements (whose atoms all have 8 protons in the nucleus), and the symbol that we use for that name in tables and lists is O.
• “Oxygen”may be used to refer to atoms of the element oxygen, for which we may also use (in chemical equations, for example) the symbol O.
• There is a gasesous substance called oxygen, which is composed of particles (molecules) made up of two oxygen atoms joined to each other. The name “oxygen” may be used to refer to the molecules (whose composition is summarised by the symbol O2).  
• And frequently the name “oxygen” is used for the gaseous elemental substance – for which we use the symbol O2(g), where (g) indicates that it is a gaseous substance. – some stuff that has mass and that we can touch.

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How many atoms of which elements are in molecules of various substances?

Considering only examples of substances whose building blocks are atoms of elements with Z from 1 - 12 ……

Water: The number of atoms of each element in the molecules is shown here:

That is, each molecule has 2 hydrogen atoms and one oxygen atom (and no atoms of helium, lithium, beryllium, boron, carbon, nitrogen, fluorine, …. nor of any of the other elements with  Z > 12).

This combination of atoms of different elements in molecules of water is indicated in the formula: H2O  (No suffix implies “one of”)

Carbon dioxide: The number of atoms of each element in the molecules is:

The formula of carbon dioxide molecules: CO2.
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Butan-1-ol: The number of atoms of each element in the molecules:

The formula of butan-1-ol molecules: C4H10O.
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Diethyl ether: The number of atoms of each element in the molecules is:

The formula of the diethyl ether molecules: C4H10O.

Which atoms are joined to which in molecules? Structural arrangement of atoms

Molecules of both compounds butan-1-ol and diethyl ether have 4 carbon atoms, 10 hydrogen atoms and one oxygen atom. 

So they are the same? No, the atoms are joined together in different sequences: the molecules are different and the substances have entirely different behaviours (physical and chemical).
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The sequence in which the atoms are joined together in molecules of butan-1-ol (left) is different from that in molecules of diethyl ether (right). The substances are entirely different from each other.

​This is just one case of different compounds with the same elemental composition.​ Compounds such as this are called isomers.

There are many ways by which the arrangement of atoms in molecules with the same composition can differ: such as (i) What is joined to what? (ii) How are they arranged spatially? [More later]
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Neutrons and electrons, too
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All of the above focusses on the number of protons in the nuclei of atoms of each element. By way of overview, let’s remind ourselve of two other components of atoms:

• Neutrons in the nucleus. These have negligible effect on the chemical behaviour of elements. They mainly affect the mass of atoms of an element, and give rise to isotopes of the element.
• Electrons surrounding the nucleus, equal in number to the protons in the nucleus. The chemical behaviour of the elements depends almost entirely on the energies of the electrons – particularly those with most energy, generally further from the nucleus.

 

Atoms as building blocks

It is astonishing that every single substance is composed of some combination of only 90 different sorts of atoms - whether it be a substance with simple molecules, like water, or large biological molecules, or biological polymers like DNA strands, or new materials, or new medicinal reagents for cancer, or whatever …





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SELF CHECK
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Put the numbers, symbols and terms in the following list into the appropriate place in the text with gaps.
Warning: There is one "wild card" in the list.

1; 2; 8; 11; 17; 93; C3H8O; Cl2(g); Z; atomic number; chlorine; cloud; electrons; element; gaseous; indestructible; nucleus; number; protons; protons; substance; the same; zero.
 

Atoms are particles that consist of a ……………….. surrounded by an electron “………………..”. The nucleus is composed of two types of particles called ……………….. and neutrons. Protons have an electrostatic charge of +1, while neutrons have ……………….. charge.

Atoms can differ in the ……………….. of protons in the nuclei. The number of protons in atoms of naturally occurring substances can be from ……………….. to 92. All atoms with the ……………….. number of protons in their nuclei are said to be atoms of a particular ……………….. .

For example, atoms of the element oxygen have ……………….. protons in their nucleus, and all atoms of ……………….. have 17 protons.

The number of protons in the nucleus of the atoms is called the ……………….. of the element, for which we use the symbol ……………….. . Different elements have atomic numbers from 1 to 92. The atomic number of sodium is 11.

Except in nuclear reactions, atoms are ……………….. , and they cannot change the number of ……………….. in their nucleus: that is, atoms of one element cannot be changed into atoms of another element. Elements with atomic number ………………..  or above have been created in laboratory conditions.

Chlorine is the name of the element with atomic number ……………….. . We also say that atoms with 17 protons in each atom are chlorine atoms. The molecules of chlorine gas are composed of ……………….. chlorine atoms (with formula Cl2), and are referred to as chlorine molecules. The ……………….. substance composed of chlorine molecules is also called chlorine, and its formula is written ……………….. .

Every ……………….. is comprised of different combinations of atoms of the various elements. For example, every molecule of propan-2-ol has 3 carbon atoms, 8 hydrogen atoms, and one oxygen atom (and no atoms of any other elements), and the formula of the molecules is ……………….. . Molecules of sucrose (table sugar) are composed of 12 carbon atoms, 22 hydrogen atoms, and ……………….. oxygen atoms, and the formula of the molecules is C12H22O11.
 

Before you go to the answer, you should be aware that university tests have shown that if you tackle the task completely before looking at the answer, consolidation of learning is on average 7.236 times that if you "peek" before doing the task, and 5.55 times that if you "peek" while you are doing the task.




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Answer

Atoms are particles that consist of a nucleus surrounded by an electron “cloud”. The nucleus is composed of two types of particles called protons and neutrons. Protons have an electrostatic charge of +1, while neutrons have zero charge.

Atoms can differ in the number of protons in the nuclei. The number of protons in atoms of naturally occurring substances can be from 1 to 92. All atoms with the same number of protons in their nuclei are said to be atoms of a particular element.

For example, all atoms of the element oxygen have 8 protons in their nucleus, and all atoms of chlorine have 17 protons.
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The number of protons in the nucleus of the atoms is called the atomic number of the element, for which we use the symbol Z. Different elements have atomic numbers from 1 to 92. The atomic number of sodium is 11.

Except in nuclear reactions, atoms are indestructible, and they cannot change the number of protons in their nucleus: that is, atoms of one element cannot be changed into atoms of another element. Elements with atomic number 93 or above have been created in laboratory conditions.

Chlorine is the name of the element with atomic number 17. We also say that atoms with 17 protons in each atom are chlorine atoms. The molecules of chlorine gas are composed of 2 chlorine atoms (with formula Cl2), and are referred to as chlorine molecules. The gaseous substance composed of chlorine molecules is also called chlorine, and its formula is written Cl2(g).

Every substance is comprised of different combinations of atoms of the various elements. For example, every molecule of propan-2-ol has 3 carbon atoms, 8 hydrogen atoms, and one oxygen atom (and no atoms of any other elements), and the formula of the molecules is C3H8O. Molecules of sucrose (table sugar) are composed of 12 carbon atoms, 22 hydrogen atoms, and 11 oxygen atoms, and the formula of the molecules is C12H22O11.
 

The "wild card" in the list is the word electrons (which was not needed for the task). The word protons was listed twice because it was needed twice for the task.