SYMBOLS OF ELEMENTS, VALENCY, OXIDATION NUMBER, IONS AND RADICALS

Subject : Chemistry

 

Topic :

SYMBOLS OF ELEMENTS, VALENCY, OXIDATION NUMBER, IONS AND RADICALS

Class :

SS 1

Term :

1st Term / First Term

Week :

Week 4

Instructional Materials :

• Lagos State Scheme of Work
• Textbooks On Social Studies
• Online Materials
• Picture Charts

 

 

Previous Knowledge :

The pupils have been taught

 Electronic configuration. Atomic number and mass number (nucleon number). Relative atomic mass based on C-12 isotope. Isotopy of elements

in their previous lesson

 

Behavioural Objectives :  At the end of the lesson, the pupils should be able to

• Explain symbols of elements
• Differentiate between ions and radicals.
• List four examples each of ions and radicals.

Content

Symbols of Elements 

Before we go on to discuss the symbols of elements, there are a few things you should know about them.

First of all, elements are the building blocks of matter. They are the simplest substances that cannot be broken down into anything simpler by chemical means. There are more than 100 different elements, each with its own unique properties.

Secondly, elements are represented by symbols. These symbols are usually one or two letters long, and they help us to identify the element in question.

Thirdly, the symbols of elements can tell us a lot about the element itself. For example, the symbol for iron (Fe) comes from the Latin word for iron, ferrum. This tells us that iron is a metal. Similarly, the symbol for chlorine (Cl) comes from the Greek word for green, chloros. This tells us that chlorine is a gas with a greenish color.

Now that you know a little bit about elements and their symbols, let’s take a closer look at some of the most important symbols of elements.

The first symbol on our list is H, which stands for hydrogen. Hydrogen is the lightest element on the periodic table, and it is also the most abundant element in the universe. Hydrogen’s symbol comes from the Greek word for water, hydros. This is because hydrogen was first isolated from water by the pioneering chemist Henry Cavendish.

The second symbol on our list is He, which stands for helium. Helium is the second lightest element on the periodic table, and it is also the second most abundant element in the universe. Helium’s symbol comes from the Greek word for sun, helios. This is because helium was first isolated from the sun’s atmosphere by the French astronomer Pierre Janssen.

The third symbol on our list is O, which stands for oxygen. Oxygen is the third most abundant element in the universe, and it is also the most important element for life on Earth. Oxygen’s symbol comes from the Greek word for acid, oxys. This is because oxygen was first isolated from air by the Swedish chemist Carl Wilhelm Scheele, and it was originally thought to be a component of acids.

The fourth symbol on our list is C, which stands for carbon. Carbon is the fourth most abundant element in the universe, and it is also one of the most important elements for life on Earth. Carbon’s symbol comes from the Latin word for coal, carbo. This is because carbon was first isolated from coal by the Scottish chemist James Black.

The fifth and final symbol on our list is Fe, which stands for iron. Iron is the fifth most abundant element in the universe, and it is also one of the most important elements for life on Earth. Iron’s symbol comes from the Latin word for iron, ferrum. This is because iron was first isolated from iron ore by the Swedish chemist Axel Fredrik Cronstedt.

Now that you know a little bit about the symbols of elements, try to remember as many as you can. You never know when you might need them!

 

VALENCY, OXIDATION NUMBER, IONS AND RADICALS

CONTENT

1. Valency of elements
2. Oxidation numbers of elements in compounds
3. Ions and radicals

PERIOD 1:VALENCY OF ELEMENTS

VALENCY

The valency of an element is the combining power of the element. It is defined as the number of atoms of hydrogen that will combine with or displace one atom of the element in chemical reactions. Some elements have more than one valency. For example.

 

Valency is also defined as the number of chemical bonds that an atom can form. It is determined by the number of valence electrons on the atom. The higher the valency, the more chemically reactive the element is. Valencies can be positive or negative, depending on whether the atom donates or accepts electrons in a chemical reaction. Atoms with a higher valency are more likely to donate electrons and form cations, while atoms with a lower valency are more likely to accept electrons and form anions. The valency of an element can be affected by temperature, pressure, and other factors.

Gold has a valency of 1, silver has a valency of 2, zinc has a valency of 3 and copper has a valency of 2.

First twenty elements with their valencies show this character.

Atomic Number	Element	Symbol	Valency
1	Hydrogen	H	1
2	Helium	He	Nil
3	Lithium	Li	2
4	Beryllium	Be	2
5	Boron	B	3
6	Carbon	C	2 or 4
7	Nitrogen	N	3 or 5
8	Oxygen	O	2
9	Fluorine	F	1
10	Neon	Ne	Nil
11	Sodium	Na	1
12	Magnesium	Mg	2
13	Aluminum	Al	3
14	Silicon	Si	2 or 4
15	Phosphorus	P	3 or 5
16	Sulphur	S	2, 4 or 6
17	Chlorine	Cl	1
18	Argon	Ar	Nil
19	Potassium	Ic	1
20	Calcium	Ca	2

EVALUATION:

1. What do you understand by the word chemical symbol?
2. Define valency of an element.

ASSIGNMENT:

Find out the valency of the following element.

(i)Gold (ii) Silver (iii) Zinc and copper

 

There are many symbols for elements that chemists use. Some of the more common symbols are shown in the table below.

The valency of an element is the number of atoms of that element that it takes to form a molecule of the compound. The oxidation number of an element is a measure of how much it has been oxidized. The ionic charge of an atom is the number of protons it has. The radical of an atom is the atom with the unpaired electron.

ELEMENT SYMBOL VALENCY OXIDATION NUMBER IONS RADICALS

carbon C 4 0 +4
hydrogen H 1 0 +1
oxygen O 2 2 -2
chlorine Cl 1 0 +1
iodine I 1 0 +1

 

One important use of symbols is to represent elements in equations. In general, an element is represented by its symbol enclosed within square brackets. For example, the symbol for oxygen is [O]. The valency of an element is the number of atoms of that element that are combined with one atom of another element to form a molecule. The oxidation number of an element is the number of electrons that the atom would lose if it completely reacted with another atom. Ions are atoms or molecules that have lost or gained electrons and radicals are molecules that have at least one unpaired electron.

PERIOD 2:

OXIDATION NUMBER OF ELEMENTS

To be able to write correctly chemical formulae for compounds, a system of small whole numbers, related to the combining ratio of element has been developed on the basis of arbitrary rules. Such numbers are called oxidation numbers or oxidation states.

Rules for assigning oxidation number

1. The    ON    of    an    uncombined    free    element,    whether    monoatomic    or polyatomic is zero; e.g. Noble gases (He, Ne, etc), metals (Na, Zn, etc),solid non-metals (O3, N2, F2,etc)
2. The oxidation number of a monoatomic ion is equal in magnitude and sign to its ionic charge; e.g., the ON of bromide ion, Br-1, is -1; that of F+3, is +3.
3. The ON of hydrogen atom is +1 in its compounds, except in hydrides of metals (e.g. NaH), where it is -1
4. For any neutral compound the sum of the ONs of all the atoms adds to zero.
5. The ON of oxygen in a compound is always -2 except in peroxides, H2O2, Na2O2, where it is -1
6. In any radical, the sum of the ON of all the atoms is equal to the charge on its ion.

Worked examples on oxidation numbers

1. Calculate the ON of copper in Cu2O Solution

Let y represents the ON of each copper atom.

ON of one hydrogen atom, O is -2.

In a neutral compound, sum of all ON is zero. Therefore, in Cu2O:    Cu2O

2y + (-2) = 0 2y = +2 y = +2/2 = +1 Thus, ON of a copper atom in Cu2O = +1

1. Determine the ON of X in X2O72-

Solution

ON of each O atom = -2

The net charge on the ion = -2

Therefore, in X2O72-

2X + 7(-2) = -2

2X – 14 = -2

2X = -2 + 14 = + 12

X = + 12/2 = +6 Therefore, ON of each X in X2O72- is +6

EVALUATION:

1. What do you understand by the term “oxidation number”.
2. States four rules guiding the derivation of oxidation number of elements.
3. Determine the oxidation number of the boldened atoms in the following:(a) H2SO4 (b)Cr2O7(c)Fe2O3 (d) MnO4–

PERIOD 3:

IONS AND RADICALS

DEFINITION:

An ion is any atom or group of atoms which possess an electric charge. Some substances are not built of atoms or molecules but are made up of charged particles called ions. Ions are formed when an atom losses or gains electron.

There are two types of ions. The positively charged ions or cations e.g. K+, Ca2+, Zn2+, Al3+ etc. they are formed when atoms loss electrons and negatively charged ions or anions which are formed when atom gain electrons e.g. Cl–, N3-, O2-, S2- etc.

RADICALS: These are groups of atoms of different elements that come together and react as a unit. These radicals are charged, that is, they either carry a positive or a negative charge. An acid radical is thus a small group or cluster of atoms carrying a negative charge that keeps its identity. These groups of atoms originate from the acids which have formed the salts. For examples

Radical	Symbol	Valency	Oxidation No
Ammonium ion	NH4+	1	+1
Hydroxyl ion	OH–	1	-1
Trioxocarbonate (iv)	CO32-	2	-2
Tetraoxosulphate(vi )	SO42-	2	-2
Trioxonitrate(v)	NO3-	1	-1

EVALUATION:

1. Differentiate between ions and radicals.
2. List four examples each of ions and radicals.

State the valencies of the following radiclas: (a) PO43-(b) MnO4–(c) C2O42