Inorganic Chemistry/Introduction to Elements

Introduction to Elements
An Element is one of a limited class of substances composed entirely of atoms that have an invariant nuclear charge and which cannot be further divided by ordinary chemical methods. Atoms having the same nuclear charge have the same number of protons in the nucleus. This number is called atomic number, denoted as Z, derived from the first letter of name of the greatest Ancient Greek god Zeus. As of May 2011, 118 elements have been found.

An Isotope is a set of atoms that have the same number of protons and neutrons in the nucleus. For example, Element Hydrogen (denoted as H) is a set of atoms that have one proton in their nuclei. This set has 3 subsets (Isotopes): Protium or Hydrogen-1 (the first name is rarely used), Deuterium and Tritium. A protium is an atom that has one proton in its nucleus and no neutrons, while a deuterium not only has one proton but also 1 neutrons. In case of tritium, the number of neutrons is double: 2 neutrons in the nucleus.

In the context of this book, I use lower case for the reference to an object of a set, and use upper case for that set. For example, I use 'Deuterium' when I want to refer to a set of atoms that have one proton and one neutron in the nucleus, and use 'deuterium' when I want to refer to a single atom of the set. I use 'Isotope' for the reference to an Isotope, and 'isotope' to refer to an atom of that Isotope. The same thing for 'Element' and 'element'. Although the name of an element is considered as uncountable, in the scope of this book I use that name as a short-handed version for 'an atom of an Element'. For example 'an atom of Hydrogen' can be written as 'a hydrogen' in this book.

Another note is: every time you want to refer to element and you don't care about the different in the number of neutrons they have, use the Element's name in lower case. If you want to refer to an atom of a specific set of an element, use the Isotope's name in lower case. For example:

1) Water consists of hydrogen and oxygen (I don't care about the isotopes of Hydrogen and Oxygen)

2) A tritium has 1 proton and 2 neutrons in its nucleus (now I care!)

Rule: upper case for set, lower case for object

Element Denotation
The following assumes you have already known the mass and charge of a proton, neutron and electron. If you don't know or you have forgotten, review lesson 1, First Glance At Subatomic Particles

Every Element has a symbol, usually the first letter of its name in English, but sometimes derived from the element's name in Latin or some other language. Hydrogen is H, Oxygen is O, Nitrogen is N etc. This symbol also represents an element (an atom of an Element). A atom of Hydrogen is H, of Oxygen is O and of Nitrogen is N etc. This convention (using the same letter for an Element and an element) is particularly popular in chemical equations. As many other convention in science is not always convenient with all people, this one is not convenient with me since it violates my rule. Nevertheless, you can use any symbols you like as long as you understand the concept. Remember you are learning how the nature works, not how the scientists denote things :)

I use lower case all together when writing chemical equations to avoid confusion. But when I publish it, I use LibreOffice to switch them back to upper case :)

Okay, let's go back to our study. Instead of writing 'Protium', 'Deuterium' or 'Tritium', you can write 1H, 2H and 3H respectively. The '1', '2', '3' above the H to the left is the mass number, denoted as A, which is the total number of protons and neutrons in the nucleus. Sometimes it can be called more appropriately as nucleon number. I prefer the second name, so I will use it throughout this book. This denotation is particularly useful to refer to an Isotope of an Element

Sometimes you can see the atomic number (the number of protons in the nucleus) written below the nucleon number, as in $$_1^{1}\text{H}$$, $$_1^{2}\text{H}$$, $$_1^{3}\text{H}$$. However, it is not necessary, because the 'H' has already told us that this is a set of atoms having one proton in the nucleus.

Again, the note comes in. When you see 1H elsewhere apart from this book, it can mean a set of atoms or an atom.

List of Elements
If we define atomic number as the number of protons an atom has in its nucleus, then atomic number should be applied to a specific atom, not a set of atoms. Therefore, the first column is named 'Atomic number of element'.

Exercises
The following exercises help you utilize the concepts you have learned. Work through them yourself, try to think a way to tackle the problem.


 * 1) How many protons are there in the following atoms: h, fe, cu, al, n, o, c.
 * 2) How many neutrons are there in the following atoms: $$^{4}\text{he}$$, $$^{31}\text{p}$$, $$^{130}\text{ba}$$, $$^{23}\text{na}$$, $$^{39}\text{k}$$, $$^{19}\text{f}$$, $$^{22}\text{ne}$$.
 * 3) Draw an illustration for each of the following atoms: $$^{9}\text{be}$$, $$^{24}\text{mg}$$, $$^{25}\text{mg}$$, $$^{26}\text{mg}$$, $$^{32}\text{s}$$, $$^{33}\text{s}$$, $$^{35}\text{cl}$$, $$^{37}\text{cl}$$. Assume electrons are on a same circle. Draw each proton, neutron and electron as a ball.
 * 4) Specify the name of each of the following atoms. Because of the large atomic number. I draw all protons (and neutrons) as a big ball.

Hints

 * 1) Look up the List of Elements to find the atomic number, which is the number of protons an element has.
 * 2) You see the nucleon number as a left superscript. Look up the List of Elements to find the atomic number. Since the nucleon number is the sum of particles in the nucleus, when you subtract it by the atomic number, you get the number of neutrons the atom has.
 * 3) First you need to look up the atomic number of an element. It is the number of protons the atom has. Subtract it from the nucleon number then you have the number of neutrons. Neutrons and protons make the nucleus of the atom. In normal stage, the number of protons equals the number of electrons in an atom. Draw electrons moving around the nucleus.

Thinking
This session helps you build your critical thinking. Try to answer yourself, write it down a paper. The answers provided here are only a reference, there may be other answers as well. If you have another answer, feel free to add :)


 * 1) You know the atomic number is denoted as a Z. You also know why scientists choose that letter. But why is the nucleon number denoted as an A?
 * 2) Why are protons, neutrons denoted as p and n respectively?
 * 3) Why are electrons denoted as e-?
 * 4) Can protons and neutrons be denoted as p+ and n+ respectively?
 * 5) In the scope of this book, what does an element and an isotope mean? What details are they different from?

Answers to Thinking

 * 1) In convention, the atomic number is written as a subscript to the left of the Element's name, such as in $$_1\text{H}$$. The nucleon number is written above it, such as in $$_1^{1}\text{H}$$. Nucleon number is the above, atomic number is the below, just the same as 'A' is the first letter, 'Z' is the last.
 * 2) They are denoted after their first letter.
 * 3) Electrons can be denoted as the letter e, just the same as the case of protons and neutrons. But latter the scientists found their anti-particles, called positrons. Positrons have almost the same characteristics as electrons, except for the charge. The charge of a positron over the elementary charge is +1, while in case of an electron, -1. Positrons were latter named e+, electrons e-
 * 4) Yes, I think protons can be denoted as p+ while their anti-particles, p-. But the neutrons would not. They have no charge, so '+' or '-' doesn't have any meaning. If they were ever denoted like that, there would be other reasons.
 * 5) An element is an atom of an Element. An isotope is an atom of an Isotope. When we say a hydrogen, we refer to an atom that may be a protium, deuterium or tritium. When we say a tritium, we only refer to an atom of Tritium.