For Science I: CLASSIFICATION OF MATTER: ELEMENTS and COMPOUNDS

- There are 92 elements found to occur naturally around us. However, new elements have been produced artificially in laboratories. Elements have names but they can also be written in symbols to facilitate writing. The names and symbols are organized in a table called the PERIODIC TABLE OF ELEMENTS.

- The chemical symbols of elements are usually written with one or two letters while recently discovered elements are given three-letter symbols.

- Elements can be classified  by their properties:
a. Metals - are shiny and can conduct electricity.
b. Nonmettals - have dull color and do not conduct electricity.
c. Metalloids (semimetal group) - have properties of both metals and nonmetals. Examples are silicon and boron. They can conduct electricity at room temperature but when heated and are slightly impure, they become conductors like metals.
d. Noble Gases - do not easily participate in a chemical change. These are: helium, neon, argon, krypton, xenon, and radon.

Some Elements and Their Uses

Element	Principal Use(s)
Gold	In jewelry making
Helium	- in inflating materials lighter than air craft - in low-temperature work
Hydrogen	- in production of ammonia and hydrogen chloride - in synthesis of methyl alcohol - in hydrogenation of edible oils
Nitrogen	In fertilizer production
Neon	In producing lights for advertizing signboards
Sodium	As fillers of street bulb and lamps
Uranium	As fuel in nuclear plants

PERIOD TABLE OF ELEMENTS
- The periodic table we have today is essentially the same as the one developed by Russian chemist Dmitri Mendeleev more than a century ago. He arranged the elements in a horizontal row in the order of increasing atomic mass.

- Atomic Mass refers to the sum of the protons and the neutrons of the atom. If an element has properties similar to those of a previous element, it is place3d in a vertical row. In modern periodic table, elements are arranged in increasing atomic number or the number of protons in the nucleus.

- The periodic table of elements indicates the properties of elements. The periodic table is arranged in 18 groups and 7 periods. Example the noble gases are in Group 18. They are generally described as inert or inactive gases except for krypton and xenon.

COMPOUNDS
- is another kind of substance. It consists or more than one kind of atom. This means that a compound is  made up of two or more kinds of elements combined chemically. This makes the elements in a compound difficult to separate  by ordinary means.

- Components of a compound are always present in constant proportions. For example, pure water always 11.9 % hydrogen and 88.1 % oxygen anywhere in the world. This is called the law of definite proportions or the law of constant composition which states that when two or more elements combine to form a given compound, they always do so in a fixed proportions.

- Compounds are products of chemical reactions. They may be solids, liquids, and gases. They may also be compounds containing carbon ( organic ) or compounds containing no carbon ( inorganic ).

- Chemical formula tells which atoms and how many of them combine to form the compound. Example,

H₂O is the chemical formula of water. This tells that the water is made up of 2 atoms of hydrogen combined chemically with 1 atom of oxygen.

- Compounds may be classified into:

a. Acids - taste sour and are found in many of the products you take like acetic acid in vinegar, citric acid in oranges and lemons, carbonic acid and phosphoric acid in softdrinks, and hydrochloric acid produced int he stomach that helps in the digestion of proteins. They are also used in industries and laboratories like:

1. Hydrochloric acid (HCl) more commonly known in its less concentrated form muriatic acid, is used in an industrial process called pickling or a process in which an acid or chemical solution is used to remove oxides and scales from the surface of metals before plating or finishing.

2. Sulfuric acid (H₂SO₃) is commonly used in automobile batteries so it is also known a battery acid. 

3. Nitric acid (HNO₃) is important in agriculture and in the production of explosives.

- Acids readily reacts with metals. They are differ in strength. Weak acids are found in fruits and strong acids in car batteries. Concentrated forms of hydrochloric acid, sulfuric acids, and other strong acids can burn the skin.

b.Bases - are compounds that usually taste bitter and feel slippery to touch. Strong bases are caustic or corrosive. Examples are:

1. Sodium hydroxide (NaOH) is lye used as the main ingredient in drain cleaners and soap production.

2. Ammonia (NH₃) is a base found in cleaning products such as cleansers and glass cleaners. It is also used in the preparation of fertilizer.

-There are chemical indicators used to test whether a substance is an acid or a base. These3 indicators include bromothymol blue and phenolphthalein.

- The strength of compounds , whether it is an acid or a base can  be compared using pH scale - a sclae which expresses the concentration of hydrogen ions. The scale ranges from 0 to 14.

c. Salt - is the 3rd group of compounds. It is formed when acids and bases of equal strengths  combine chemically. Table salt is a common salt that u use every day. It is composed of 2 elements - sodium and chlorine. Chalk or calcium carbonate is also a salt. Sodium sulfate is another salt and is formed when sulfuric acid reacts with sodium hydroxide. It is used in detergent and paper production. Potassium permanganate is a salt to purify water from wells and in tanning leather.

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