Topic 5: ELEMENTS, COMPOUNDS AND MIXTURES – Chemistry Form One Notes

1. ELEMENT:

Definition: Element is a pure chemical substance that cannot be split into simpler substance by chemical means.

Elements are the building blocks from which many substances (compounds) are made. There are over 118 known elements of which most of them are natural and some are man made

Examples of elements include Hydrogen, Helium, lithium, Beryllium, potassium, sulphur, calcium, Boron, Iron, Carbon, Nitrogen, Oxygen, Fluorine, Copper, Silver, Gold, Tin, Zinc, Manganese, Magnesium, Lead etc

NAMES AND CHEMICAL SYMBOLS OF ELEMENTS

CHEMICAL SYMBOLS

Defn: A chemical symbol is representation of the name of element using letters.

OR

A chemical symbol is abbreviation or short representations of an element

The chemical symbols are normally derived from one or two letters of a Latin or English name.

If an element is represented by two letters the first one should be capital letter and the second should be small letter. When an element is represented by one letter it should be in capital letter.

NB: Chemical symbols are written according to the rules of the International Union of Pure and

Applied Chemistry (IUPAC)

CRITERIA (RULES) FOR ASSIGNING CHEMICAL SYMBOLS

The following are the criteria used for assigning chemical symbols:

1. An element may be represented by a chemical symbol that is derived from the first letter of its English name.

Examples of some elements with chemical symbols derived from the first letter of its English name are shown in the table below.

NAME	SYMBOL	NAME	SYMBOL
Hydrogen	H	Phosphorus	P
Carbon	C	Iodine	I
Nitrogen	N	Fluorine	F
Oxygen	O	Vanadium	V
Sulphur	S	Yttrium	Y
Boron	B

2.If different elements have the same first letter, for example carbon (C), calcium (Ca), cobalt (Co) and copper (Cu) then only one element uses the first letter as its symbol, other elements use first letter plus another letter in the name usually the second or third.

Chemical symbols of some elements with two letters from their English names are shown in the table below

NAME	SYMBOL	NAME	SYMBOL
Calcium	Ca	Neon	Ne
Cobalt	Co	Aluminium	Al
Chlorine	Cl	Argon	Ar
Magnesium	Mg	Beryllium	Be
Manganese	Mn	Lithium	Li
Helium	He	Silicon	Si
Zinc	Zn

4. In some cases, the chemical symbols are derived from  Latin names instead of the common English names as shown in the table below

ELEMENT	LATIN NAME	SYMBOL
Sodium	Natrium	Na
Potassium	Kalium	K
Silver	Argentum	Ag
Gold	Aurum	Au
Lead	Plumbum	Pb
Copper	Cuprum	Cu
Iron	Ferrum	Fe
Mercury	Hydrargyrum	Hg
Tin	Stannum	Sn
Antimony	Stibium	Sb
Tungsten	Wolfram	W

SIGNIFICANT (IMPORTANCE) OF CHEMICAL SYMBOLS

The following are the significance of chemical symbols

(i) Enable chemists to understand elements quickly instead of memorizing full name of element

(ii) It is easy to write the chemical equation using symbol instead of writing each element in full name

(iii) Enable chemists to distinguish one element from the other

METALS AND NON- METALS

Elements are classified into Metals and Non-metals.

The systematic method to represent and organise chemical elements in a table format is called PERIODIC TABLE. See diagram below

The table above shows position of metals and non-metals in the periodic table.

METALS

Defn: A metal is an element except hydrogen that will lose electron (s) to form positive charge.

Eg Sodium, potassium, lithium, Beryllium, boron, iron, copper, silver, gold, tin, calcium, zinc

, manganese, magnesium, lead etc

Metals are mostly found at the left-hand side and at the middle of the periodic table

NON-METALS

Defn: A non-metal is an element that will gain electron (s) to form negative charge.

Eg Oxygen, sulphur, hydrogen, carbon, silicon, chlorine, fluorine, phosphorous, nitrogen etc

Most of non-metals exists in gaseous state or liquid state with exception of few such as carbon

and sulphur which exist in solid state.

NB: Although hydrogen is located at the left-hand side of the periodic table, it is a non-metal

because it possesses the characteristics of non-metal.

Metals and non-metals differ in physical and chemical properties

DIFFERENCES IN PHYSICAL PROPERTIES BETWEEN METALS AND NON-METALS

METALS	NON-METALS
1. Are good conductor of heat and electricity	Poor conductors of electricity. (they are insulators) except carbon, in the form of graphite, which conducts electricity
2. Are good conductor of heat (this is why cooking utensils are made up of metals such as aluminium and iron)	Are poor conductor of heat.
2. Have high densities	Have low densities
3. Have high melting points and boiling points	They have low melting points and boiling points
4. Are strong and tough	Are not strong and tough
5. Are ductile ie.they can be drawn into thin wires	Are not ductile. They can not be drawn into thin wires
6. Are good conductor of sound. They are Sonorous. (which means they make sounds when hit.)	Are poor conductor of sound. They are not Sonorous. (which means they do not make sounds when hit.))
7. Have high tensile strength	Have low tensile strength
8. Are malleable (i.e can be made (hammered) into thin sheets)	Are not malleable
9. Are lustrous. They produce shining surface when cut.	Are non – lustrous except a few such as diamond

NB: There are exceptions to the above properties as follow

(i) Graphite is a nonmetal (Carbon) but it is a good conduct of heat and electricity

(ii) Diamond is nonmetal (Carbon) but has high melting and boiling point.

(iii) Some metals have different characteristics from those described above, eg sodium and

Potassium. These elements have low densities

(iv) All metals are solids at room temperature but mercury is in liquid state at room temperature.

EXERCISE

1. Give three examples of metals and non- metals, and explain their uses in daily life.

2. Why are cooking pots made of metals?

3. Describe properties of metals and explain how do they make metals useful in various applications.

COMPOUNDS AND MIXTURES