Elements and compounds

 

Matter,

1.       Pure substance

*  Elements

 * Compounds

 

2.       Mixtures

  *Homogenous

  *Heterogenous

 

Pure substance;

·         It is a distinct type of matter that has the same properties throughout the sample

 

Elements;

• ·          It is the simplest substance that cannot be broken down chemically.
• ·         The term “Element” was first used by “Robert Boyle” in 1661.
• ·         The element was experimentally proved first by Lavoisier.

·         Example: Cu, O, Fe, H, Hg, etc….,

·         Total no. of element is >100

·         92 are naturally occurred element.

 

Points to remember;

·         No. of elements >100

·         92 are naturally occurred element

·         11 elements à gaseous state

·         At room temp,2 element à liquid (Mercury, Bromine)

1.       Mercury – Metal and Liquid

2.       Bromine – Non- metal and liquid

·         At 303k, 2 elements à Liquid (Gallium, Caesium)

 

·         About 99% of the mass of human body is made up of six elements (oxygen, carbon, hydrogen, nitrogen, calcium and phosphorus) and the rest 1% by other elements.

 

·         All the living things, both plants and animals, are made from a few elements only. They are, Oxygen (65%), Carbon (18%), Hydrogen (10%), Nitrogen (3%), Calcium (2%) along with some other elements.

 

·         Hydrogen and helium are the main elements in the universe and stars.

Compounds;

·         A compound is a pure substance composed of two or more elements combined together chemically in a fixed ration by mass.

                                                    Element + Element  à Compound

                                                                          N₂+3H₂ à 2NH₃

 

Characteristics of a compound;

·         A chemical compound is formed by the chemical reaction between two or more elements in a fixed proportion by mass.

·         The components of the compound cannot be separated by simple physical methods

·         Formation of a compounds is associated with evolution or absorption of heat.

·         A compound has a fixed melting and boiling point.

·         Compound is homogenous.

 

 Uses of a compound;

·         Water             – hydrogen oxide (H₂O)                 -- Hydrogen and oxygen

·         Table salt       – sodium chloride (NaCl)               – sodium and chlorine

·         Sugar              – Sucrose (C₁₂H₂₂O₁₁)                      – carbon, hydrogen and oxygen

·         Baking soda   – sodium bicarbonate (NaHCo₃)   – sodium, hydrogen, carbon and oxygen

·         Washing soda            – Sodium Carbonate (Na₂CO₃)       – Sodium, carbon and oxygen

·         Bleaching powder    – Calcium Oxy chloride (CaOCl₂)    – Calcium, oxygen and chlorine

·         Quick lime                 – Calcium Oxide (CaO)                     – Calcium and oxygen

·         Slaked lime               – Calcium Hydroxide (Ca(OH)₂)      – Calcium, oxygen and hydrogen

·         Lime stone                – Calcium Carbonate (CaCo₃)          – Calcium, carbon and oxygen

 

 

Acids;

• ·         A liquid substance that can dissolve metal and may burn your skin or clothes.
• ·         Acids have a pH value of less than 7.
• ·         A certain type of chemical compounds present in them gives sour taste.
• ·         The word ‘acid’ is derived from the Latin name “Acidus” which means sour taste.
• ·         They contain one or more replaceable hydrogen atoms.
• ·         Hydrogen irons cannot exist alone, but they exist in combined state with water molecules.
•  

Source	Acids Present
Apple	Malic acid
Lemon	Citric acid
Grape	Tartaric acid
Tomato	Oxalic acid
Vinegar	Acetic acid
Curd	Lactic acid
Orange	Ascorbic acid
Tea	Tannic acid
Stomach juice	Hydrochloric acid
Ant, Bee	Formic acid

 

 

  

 

 

 

 

 

 

·         All acids essentially contain one or more hydrogens.

·         But all the hydrogen containing substances are not acids.

·         For example;

Ø  Methane (CH4) and ammonia (NH30) also contain hydrogen.

Ø  But they do not produce H+ irons in aqueous solution.

Classification of acids;

·         Based on their sources:

Ø  Organic acids:

                                         Acids present in plants and animals (living things) are organic acids.

                Example: HCOOH (formic acid), CH₃COOH (acetic acid)

Ø  Inorganic acids:

                 Acids prepared from rocks and minerals are inorganic acids or mineral acids.

                  Example: HC1, HNO₃, H₂SO₄

·         Based on their basicity;

Ø  Monobasic acid:

       Acid that contain only one replacement hydrogen atom per molecule is called monobasic acid.

         Example; HC1, HNO₃

Ø  Dibasic acid:

         An acid which gives two hydrogen iron per molecule of the acid in solution.

          Example: H₂SO₄, H₂CO₃

Ø  Tribasic acid:

           An acid which gives three hydrogen irons per molecule of the acid in solution.

             Example: H₃PO₄

 

·         Based on Ionisation;

                  Ionisation is the condition of being dissociated into ions by heat or radiation or chemical reactions or electrical discharge.

Ø  Strong acids:

             These are acids that ionise completely in water.

             Example: HC1

Ø  Weak acids:

              These are acids that ionise partially in water.

               Example: CH₃COOH.

 

·         Based on concentration;

Ø  Concentrated acid:

                It has relatively large amount of acid dissolved in a solvent.

Ø  Dilute acid;

                It has relatively smaller amount of acid dissolved in solvent

 

·         Properties of acids;

Ø  They have sour taste.

Ø  Their aqueous solution conduct electricity since they contain ions

Ø  Acids turns blue litmus red

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