Ecology and the nutrient cycle

Ecosystem

• It is a habitat which has the community of organisms living in it.
• Population is the same kind of organisms living in a particular habitat.
• Community is the different populations living in a particular habitat.

Biotic environment

• It is the interaction between organisms of either the same species or different species mainly for food and shelter.
• The interaction can be classified in terms of:
  - predator-prey: one species feeds on another species.
  - commensalism: one species gains benefits from another species without causing any harm.
  - parasitism: one species gains benefits from another species with harm
  - mutualism: two different species are benefited from each other

Abiotic environment

• The abiotic environment are light, water availability, oxygen, humidity, pH level and others.

Nitrogen cycle

• Nitrogen is removed form the air by nitrogen-fixing bacteria and lightning.
• Nitrogen is returned to the air by denitrifying bacteria.

Conservation of ecosystems

• Destructive activities such as over-hunting and deforestation disrupt the delicate balance of ecosystems.

Sex Issues

Birth Control

• Birth control is the prevention of the fusion of a sperm and an egg.
• There are temporary birth control methods and permanent birth control methods.

Temporary birth control

• Condom for male: prevents the deposit of sperms in the vagina
• Condom for female: prevents sperms from entering the vagina
• The pill: contains hormones to stop ovulation
• Cap and diaphragm: stops sperms from entering the uterus
• Spermicides: contains chemical substances that kill sperms
• Intra-uterine device (IUD): prevents implantation of embryo

Permanent birth control

• Vasectomy: The vas deferens (sperm duct) is cut and tied to prevent the transportation of sperms from the testis to the penis.
• Ligation: The fallopian tubes are but and tied to prevent the sperms from fusing with the eggs.

Sexually transmitted diseases

• It is the transmission of diseases through exchange of body fluids during sexual activity.
• The diseases are gonorrhoea, syphilis and AIDS.

Gonorrhoea

• It is caused by bacteria through unprotected sex.
• It can be treated by antibiotics at the early stages of infection.
• The symptoms include:
  - painful sensation during urination
  - infertility
  - blindness in baby

Syphilis

• It is caused by bacteria.
• The symptoms include:
  - painless sores
  - non-itchy rashes
  - insanity

AIDS

• It is caused by a virus called HIV.
• AIDS is the serious stage of HIV infections.
• The symptoms of HIV infection include:
  - loss of appetite
  - prolonged fever
  - night sweat

Prevention of sexually transmitted diseases

• The prevention include:
  - be faithful to one sex partner
  - have protected sex

Sexual reproduction in human beings

Sexual reproduction

• It is a reproduction which involves male and female sex cells.

Male reproductive system

• The male sex cells are called sperms.
• Parts: Penis - transfer sperms to the vagina
                     - allows urine to leave the body
            Testis - produces sperms and male sec hormones
            Urethra - transport sperms, semen and urine to outside of the penis
            Scrotum - holds the testis outside the body
            Vas deferens - transport sperms to the penis
            Seminal vesicles - produces fluids that mix with sperms to form semen
            Epididymis - stores sperms

Female reproductive system

• The female sex cells are called eggs (or ova).
•           Ovary - produces eggs and female sex hormones
•           Vagina - allows sperms to deposit
• Parts: Uterus - allows the implantation of embryo to occur and nourishes the growth of the foetus
            Fallopian tube - transport eggs from the ovaries to the uterus
                                   - allows fertilization to take place
            Vagina - allows sperms to deposit
            Ovary - produces eggs and female sec hormones

Fertilization

• Fertilization is the fusion of the nucleus of a sperm and the nucleus of an egg to form a fertilized egg called zygote.
• The fertilized egg contains 23 pairs of chromosomes.
• As the zygote contains both parents' chromosomes, the child will inherit certain characteristics from both parents. It is called heredity.
• The zygote develops into a ball of cells called embryo. The embryo implants into the uterus wall. The process is known as implantation.
• The function of the placenta: - provides food, oxygen and water from the mother's blood to the baby's
                                                blood
                                              - removes waster products such as carbon dioxide from the baby's
                                                 blood

Menstruation

• Ovulation and menstruation are parts of the menstrual cycle.
• A menstrual cycle has an average of 28 days.

Diffusion and Osmosis

Diffusion

• Diffusion is a process whereby a substance moves from its region of high concentration to its region of low concentration.
• The process is a passive transport which does not require energy to take place.

Diffusion in living organisms

• Organs have specialized features to increase the surface area for diffusion of materials.

Osmosis

• Osmosis is a process whereby water molecules move from the region of high water concentration (high water potential) to the region of low water concentration (low water potential) through a partially (or semi- or selectively) permeable membrane.
• Partially permeable membrane is a membrane that only allows certain substances to pass through.
• All cell membranes of living organisms are partially permeable membranes.

Active transport

• Active transport is a process whereby substances move from their region of low concentration to their region of high concentration.
• Energy is needed for this process to occur. 

Cells

Cells

• Cells are the building blocks of all living things.
• Living things can be classified into unicellular organisms (one cell only) or multicellular organisms (many cells).

Animals cells

• Animals cells have no cell walls.
• The structure and its function of a cell:
  -Cell membrane: control the movement of substances in and out of a cell
  -Nucleus: controls the activities of a cell and stores hereditary materials called chromosomes
  -Vacuole: stores food and nutrients
  -Cytoplasm: allows chemical reactions to take place

Plant cells

• Plant cells have cell walls.
• The structure and its function of a cell:
  -Cell membrane: control the movement of substances in and out of a cell
  -Nucleus: controls the activities of a cell and stores hereditary materials called chromosomes
  -Vacuole: stores food and nutrients
  -Cytoplasm: allows chemical reactions to take place
  -Chloroplast: contains chlorophyll to absorb sunlight for photosynthesis
  -Cell Wall: supports and maintains the shape of the cell

Division of Labour

• Division of labour in living organisms allows more efficient and smooth functioning in the multicellular organisms.
• When a group of cell perform the similar function, they are known as tissue.
• When a group of tissues perform the similar function, they are known as organ.
• When a group of organs perform the similar function, they are known as organ system.
• Various organ systems make up an organism.

Acids and Alkalis

• The characteristics of an acid:
  - Sour taste
  - Able to conduct electricity
  - Turns blue litmus paper red
  - Reacts with metals, carbonate or alkalis
• The common acids used in the school laboratory are sulfuric acid (H2SO4), nitric acid (HNO3) and hydrochloric acid (HCl).

• The characteristics of an alkali:
  - Bitter taste
  - Soapy feeling
  - Turns red litmus paper blue
  - Corrosive

• Universal indicator is used to test the acidity or alkalinity of a solution by showing different colour corresponding to different pH values.
• It is red in strong acids, pale green in neutral and blue or violet in strong alkalis.

Materials

1. The process of grouping and sorting out is called classification.
2. Grouping of object in a proper way always help us to do our work efficiently.
3. Classification can be based on similarities and differences.
4. Materials which are non-living things are mainly two types.
   - Naturally occurring.        - Man-made
5. Materials can be classified as metals, glass, ceramics, plastics and fiber.
   Metals: An element which is shiny, a good conductor of heat and electricity, ductile, malleable, has a high melting point (eg. silver, gold)
   Glass: Sand (silica), soda (sodium carbonate) and lime (calcium carbonate) are mixed and melted. Glass is fragile and transparent.
   Ceramics: Greek word, 'Keramos' - which means potter's clay - All ceramics are made from various clay. Ceramics are compounds of silicon, carbon, oxygen and nitrogen combined with other elements like sodium, potassium, calcium and boron.
   Plastics: Plastics do not occur naturally but are man-made. 'Plastikos' - a greek word meaning 'to mould'. Common types of plastics are polythene, polystyrene, PVC and nylon. Plastics have many uses.
   Fiber: Fibers can be both man made like polyester, nylon or natural like cotton or wool.

Classification of materials

1. Matter is anything which occupies space and has mass.
2. Matter includes both living and non-living things.
3. It is with our five senses that we recognise matter and most of its properties. Colour, size, shape are some of the common physical properties where our sense of sight is used.
4. Materials have both similarities and differences amongst them. Choice of a material for various purposes depends on the properties of the material.

Reflections on Term 3 Science

My science results for term 3 was 80/100 and I personally felt that this could be improved for my end-of-year despite a massive improvement of 20 marks as compared to term 3. I studied hard for science and hoped to be able to achieve better for my end-of-year

Hydroponics farm visit

On 26th May 2011, the Science Department organised a learning journey for the secondary 2 I-Spark students.About 20 students went to Oh Chin Huat Hydroponics Farm located at Yishun.

We were assigned to a guide who explained very clearly the various stages of growing crops using the hydroponic method. While explaining, the guide also showed us how crops such as onions, butterhead lettuce and other crops are grown in the greenhouse.

We also had an exciting and interesting quiz session towards the end of the tour. Those who got right answers to the questions brought home a small potted plant each. Before we boarded the bus back to school, all teachers and students were each given a packet of butterhead lettuce.

Nutrient cycles in the ecosystem

1. The cycles in nature maintain a balance in the ecosystem, which ensure that all living things are able to live and grow.
2. Recycling is important because natural resources are limited.
3. Organisms that feed on dead plants and animals are called decomposers. Decomposers play a major role in recycling.
4. Circulation of carbon through and ecosystem is called the carbon cycle.
5. The only process, which removes carbon from the atmosphere, is photosynthesis. Carbon is added to the atmosphere during respiration by living things and due to decomposition of dead and decayed matter.
6. The continuous cycle through which nitrogen in the form of nitrogenous compounds is removed from the soil and returned to it is called the nitrogen cycle.
7. Nitrogen is removed from the soil due to absorption of nitrogenous compounds by the roots of the plants and by the action of denitrifying bacteria.
8. Nitrogen is returned to the soil by the process of nitrogen fixation by root nodules of leguminous plants, by the action of certain free living bacteria and by the decomposition of plant./animal wastes by certain bacteria.
9. Addition of fertilizers increase the nitrogen content of the soil.
10. Carbon and nitrogen cycles are important because, carbon forms a part of carbohydrates, proteins and fats; while nitrogen forms a part of proteins, which are used to build tissues in living things.

Energy transfer in ecosystem

1. The prime source of energy in living things is the sun. Energy from the sun enters the ecosystem through the plants (photosynthesis) and the flow of energy within an ecosystem can be shown by food chains and food webs.
2. The food chain shows the feeding relationship between living things. Each organism in the food chain is called a link.
3. A food chain starts with green plants which are the producers. Animals that eat only plants are the primary consumers and animals that eat other animals are called the secondary consumers.
4. Interconnected food chains constitute a food web.
5. As energy passes along a food chain, the amount of energy transferred gradually decreases due to energy lost to the environment at each link. Only about 10% of the energy available at one link in a food chain is passed on to the next link.
6. The number of organisms decrease from one link to another along the food chain. This gives a pyramid of numbers for living things.
7. The balance between the number of plants and animals in and ecosystem is called the balance of nature.

Ecology: Living things in and ecosystem

1. A place where plants and animals live is called habitat (eg) ponds, rocks, trees etc.
2. The environment of an organism is affected by physical factors such as sunlight, temperature, wind, pH and biotic factors such as all the living things.
3. Plants and animals have special body features or ways of behaving which help them to survive. There are called adaptions.
4. Owls are adapted to see in the night, polar bears are adapted to hibernate in the winter and so on.
5. Cactus plant is adapted to grow in deserts. They have thick and juicy stems to store water and their leaves are modified into spines.
6. Aquatic animals are adapted to live in water with less oxygen. They come to the surface to take in air.
7. pH value of water and soil also affect the organisms living in a habitat.
8. In any habitat there is usually more than one kind of organism, which depend on each other for food, shelter and protection and constitute to biotic factor.
9. Different plant and animal population living together in a habitat constitute a community. The habitat, together with the community of organisms living in it, forms an ecosystem.
10. Various physical factors and biotic factors affect life in and ecosystem. Organisms interact with each other in an environment and are adapted to live in an environment.
11. Human activities such as deforestation and over hunting damage our ecosystem. It is important to conserve the world's ecosystem and to use them wisely. 

Transmission of heat energy

1. Heat or thermal energy is one of the vital energy source on earth. This heat energy needs to be transferable if life processes on earth are to continue. Heat is a form of energy that flows from a region of   higher temperature to another of lower temperature.
2. The three main types of heat transfers are
   (i) conduction,     (ii) convection and    (iii) radiation
   
   (i) Conduction:
        - The process of heat transfer, where there is no physical visibility of matter moving from their
          position, but pass heat in the form of kinetic energy is called as conduction.
        - Those substances which are capable of conducting heat are called as conductors and those
          substances through which heat cannot pass through are called as insulators.
        - Usually metals are good conductors of heat, while wood, thermacoal, plastics, ceramic are
          examples of insulators. Vacumm is considered to be the best insulator.
   (ii) Convection:     - Fluids, (liquids and gases) are usually bad conductors of heat. In fluids heat travels by the
          process called convection. Here the molecules themselves move, carrying the heat energy with
          them in the form of kinetic energy.
        - The upward movement of the hot fluid and the downward movement of the cold fluid causes the
          movement in the fluid called the convection current.
        - Land and sea breeze are caused by convection current.
   (iii) Radiation:     - The transfer of heat energy from the sun through vacuum in the form of electromagnetic waves
           is called radiation.
        - The sun gives off heat energy in the form of rays or radiant energy. When these rays fall on an
           object, they are absorbed and the object gets heated up.
        - All hot bodies give off radiant heat even if they are not glowing. White, silvery or highly polished
           surfaces are good reflectors of radiant heat. Black or dark bodies are good absorbers of heat.
           Good absorbers of heat are also good radiators.
3. Heat absorbed or given out due to radiant energy depends on
   (i) Colour of the object     (ii) Texture of the object     (iii) Surface area     (iv) Temperature
   Black and rough surfaces absorb and radiate more heat energy than light and smooth surfaces. Objects with more surface area and at high temperature absorb and radiate more heat energy than the objects with low temperature and less surface area.
4. Applications of conduction, convection and radiation
   Conduction: Pans used for cooking are made of metals, while the handles are made of insulators.
   Convection: Boiling of water in an electric kettle, land and sea breeze.
   Radiation: Black umbrellas, rough black surfaces behind refrigerators.
5. Thermos flaskVacuum flasks also called commonly as Thermos flask maintains the hot or cold temperature of the contents inside. It reduces the heat transfer from inside which could occur by the three modes viz conduction, convection and radiation. The flask is made in such a way that heat is not lost or gained by conduction, convection and radiation. Thus, the temperature inside a thermos flask is maintained.
   
   

Heat and its effect

1. Heat is a form of energy that a substance possesses due to the movement or vibration of its atoms, molecules or ions.
   Solids, liquids and gases generally expand on heating causing increase in volume. On cooling, they contract and the volume decreases.
2. Thermal expansion of solids, liquids and gases.
   Solids - Solids expand the least compared to liquid and gases for the same rise in temperature. The most commonly used experiment to demonstrate the thermal expansion of solids is the ball and ring experiment. When hot, the metal ball expands and does not pass through the metal ring.
   Liquids - Liquids expand to temperature and mostly it is demonstrated using water. Various liquids expand to various levels for the same rise in temperature.
   Gases - Gases contain independent particles-in-random motion. They expend the most with temperature and the particles move faster and faster as the temperature increases. The bombardment of the gas particles against the sides of the container creates pressure. Thermal expansion of gas can be explained using the hot air balloon experiment. Warmth on the flask causes expansion of air inside resulting in production of bubbles.
3. Effects on thermal expansion and contraction
   Changes in temperature brings about expansion or contraction in railway tracks, concrete blocks, bridges, overhead cables, telephone lines, pipes etc. Allowance given in for the expansion helps to overcome the adverse effects of thermal expansion and contractions.
4. Usefulness of thermal expansion and contraction
     - Riveting --> Rivet is the nail shaped metal which helps to hold two metal plates together. Red hot rivets are put through the holes in two metal plates and the rivet is hammered flat. As the rivet cools it contracts and pulls the two metal plates together and firmly holds them together.
     - Bimetallic strip --> As the name denotes the strip is made of two metal strips having different metal expansion. When heat is applied to a bimetallic strip, made of brass and steel, brass expands more than steel and the strip bends with the brass on the outside of the curve. Till a certain temperature the bending does not take place and the contract is maintained. Once the heat increases and the strip bends due to uneven expansion of the two metals and the electrical contact is broken.
5. Thermometers
   Thermometers are instruments which are used to measure temperatures. Any physical property of a material which changes steadily with temperature can be used to measure temperature. Thermometer uses the principle of thermal expansion of liquids. The most commonly used liquid in a thermometer is mercury.
   
   Clinical thermometers are both graduated in Fahrenheit and in Celsius. In the Celsius scale the ice point is 0 degree Celsius. It is the temperature at which ice melts. The steam point is the temperature at which pure water boils. There two reference points are equally divided into 100 divisions, each of which is 1 degree Celsius.
6. The other thermometers are the constant volume thermometer, liquid crystal thermometer, the bimetallic thermometer, and the  resistance thermometer.

Solutions and Suspensions : Acids and Alkalis

1. Solution is a homogeneous mixture of two or more substances.
2. Solute is the substance that dissolves in a solvent to form a solution.
3. Solvent is the substance in which the solute dissolves to form a solution.
4. We come across many type of solutions in our daily life. Generally the term solution is understood with relation to liquids. But, the solvent can be a solid, liquid or gas which can dissolve one or more substances (solutes) to form a solution. The combination is of various types like solid-solid, solid-liquid, solid-gas, liquid-liquid, liquid-gas and gas-gas etc. are examples of solute-solvent combination to form a solution.
5. Example of solid-solid are alloys like brass (solute zinc in copper)
   Example of solid-liquid is sugar in water (solute sugar in water)
   Example of gas-liquid are carbonated drinks (solute carbon dioxide in water)
6. Water is called the universal solvent. We cannot imagine a life on earth without water. The main reasons for considering water as an universal solvent is,
        (i) Due to its polar nature it dissolves many ionic compounds.
        (ii) The hydrogen atoms of water form loose hydrogen bonds which help in dissolving many covalent
             compounds.
        (iii) Water undergoes chemical combination with many compounds resulting in their dissolution.
7. Suspension is a mixture in which small solid orwhich  liquid particles are suspended in a liquid or gas.
8. Solubility: The maximum amount of solute which can dissolve in 100g of the solvent is known as the solubility of that solute in that solvent at that given temperature. Solubility is influenced by (i) the nature of the solute, (ii) the nature of the solvent and (iii) the temperature of the solution.
   
   The solubility of solids in liquids usually increases with increasing temperature.
   The solubility of gases in liquids usually decreases with increasing temperature.
9. Strength of solutions:
   Dilute or weak solutions: When the concentration of the solute is less compared to the amount of solvent.
   Concentrated or strong solutions: When a large amount of solute is dissolved in a small amount of solvent.
   Saturated solutions: A solution in which no more solute can be dissolved at the given temperature.
   Unsaturated solution: A solution in which more solute can be dissolved at the given temperature.
10. Some of the uses of solutions and solvents.
    At home
      - Water is the most important solvent used in cooking, cleaning, washing etc. Other solvents like
        turpentine, petrol are used to remove grease. Acetone is used in removing the nail polish applied to
        nails.
    In industries
      - Apart from water, which is used in food, beverage, detergent, dye and other industries, most
        solvents used in industries are organic in nature, Ethanol is used in perfume industry, Acetone,
        benzene, ether are other solvents used industrially.
    In agriculture
      - Water is the important solvent in agriculture. Minerals, fertilizers and other nutrients reach the plant
        only due to the solubility of these in water. Organic solvents are used in pesticides and insecticides.
    In medicine
      - All the syrups and decoctions used in medicines are solutions. Water again serves an an important
        solvent for many of the herbal medicines. Some vitamins are water soluble, which others are fat
        soluble.
11. Colloidal solutions: A solution is which the size of the solute particles are between that of the solution and suspension. eg. milk, blood
      - The size of a colloidal particle is between 10 to the power of -7 and 10 to the power of -5.
      - The particles of a colloid can pass through filter paper.
      - The solution here is translucent.
      - It scatters light which makes its path visible.
12. Acids
    Acids are those compounds that contain hydrogen and can donate the H+ ions.The basic properties of acids are:
      - they have a sour taste.
      - they turn blue litmus red.
      - they are corrosive in nature.
      - they react with alkalis to give salt and water.
      - they react with carbonates to give CO2.
      - they react with active metals to produce H2 gas.
13. The some of the common acids and their uses.
    Hydrochloric acid:  - found in the stomach and helps in digestion of food.
                                  - used in cleaning.
    Nitric acid:  - used in the preparation of fertilizers like ammonia.
                       - used in the preparation of explosives.
    Sulfuric acid:  - used in car batteries.
                         - used in the preparation of fibers and plastics.
    Carbonic acid:  - used in making carbonated drinks.
                            - helps in the pH balance of the biological systems.
    Ethanoic acid:  - used in the preservation of food stuffs.
14. AlkalisAlkalis are bases when dissolved in water yields hydroxide ions (OH- ions). The basic properties of alkalis are:
      - they are bitter to taste and have a soapy feel.
      - they turn red litmus blue.
      - generally corrosive in nature in concentrated form.
      - they are good conductors of electricity.
      - they react with acids to form salt and water.
      - the react with ammonium salts to produce ammonia gas.
15. Some of the common alkalis and their uses 
    Potassium hydroxide:  - used in dyeing.
                                      - used to remove paint and varnish.
    Sodium hydroxide:  - used in the preparation of soaps.
    Ammonia solution:  - used to make fertilizers.
                                  - used in the preparation of cleaning liquids.
    Calcium hydroxide:  - used to adjust the pH of acidic soil.

Separation of mixture

1. The physical methods by which mixtures can be separated are

• Filtration
• Evaporation
• Crystallization
• Distillation
• Chromatography    

1. To separate mixture into its components from which it is made, we have to understand the differences in properties of its constituents.
2. Filtration: Insoluble solids in a solution can be separated by this method. The solids which are separated forms the residue  and the liquid is called the filtrate.
3. Evaporation: Soluble solids (dissolved solids) in a solution are separated by this method.
4. Crystallization: Soluble solids in the solution, which will decompose on heating are separated by this method.
5. Distillation: separates a solvent from a solution. The liquid which is condensed is called a distillate.
6. If more than one liquid component in a mixture of liquid needs to be separated, fractional distillation is used.
7. Chromatography is used to separate and identify the different components of dyes and inks. In paper chromatography the fact that some components of a liquid mixture ravel faster on the whatmann filter paper than other components is used.
8. Sieving is a method used to separate mixtures, when the particles in the mixture are of different sizes.
9. Winnowing is a method used to separate light and heavy solids.
10. Particulate matter in matter can be separated by a method named loading. A piece of alum is added to water. As the alum dissolves, it sticks to the fine particles, makes them heavier and settles down easily.
11. Decantation is a process where solid particles in a liquid are separated by allowing the liquid to stand undisturbed for sometime. After a while, the solid particles will settle down while the liquid on top can be poured off. 

Compounds and Mixtures

1. A compound is a substance made up of two or more elements chemically combined together. A compound may be formed in any of the following ways.
   (i) (element) + (element) --> compound
       (eg) Sodium + Chlorine --> sodium chloride
   
   (ii) (element) + (compound) --> compound
        (eg) oxygen + carbon monoxide --> carbon dioxide
   
   (iii) compound + compound --> compound
        (eg) carbon dioxide + water --> carbonic acid
   
2. Properties(i) The properties of the compound are different from the properties of its constituent    elements. (Eg) Water (compound) is made of hydrogen and oxygen. When hydrogen catches fire easily, oxygen helps in burning, the compound water made of the two is used to put out fire.
   
   (ii) Compounds can be broken down into simpler substances only by chemical methods.   Water is a compound and it can be spilt into H2 and O2 through chemical process called electrolysis.
   
   (iii) The proportion of the elements in a compound are fixed.
         In NaCl, Na and Cl are in the ratio 23 : 35.5 by mass.
   
3. MixturesA mixture consists of two or more substances not chemically combined. Constituents of a mixture may be all elements, all compounds or combination of elements and compounds. These substances could be in the solid, liquid or gaseous states.
   
4. Properties of a mixture(i) No chemical change occurs when a mixture is formed.     When we mix salt and water, we get saltwater a mixture. No heat or light is given off in this
        process.
   
   (ii) The properties of a mixture are the properties of the substances with which it is made.
         The saltwater can also be used to put out fire like water.
   
   (iii) A mixture can be separated easily by physical methods.      The salt and water can be separated easily from saltwater by evaporation.
   
   (iv) The proportion of the constituents in a mixture are not fixed.       There is no fixed ratio in which they should be mixed. The proportion may change. We can add
          1tsp of salt to 200ml water or 2tsp of salt to 100ml water, the result is saltwater.
    

Elements

1. Elements form the simplest basic unit of matter.
2. An element is a substance that contains atoms of only one type. An element cannot be broken into two or more simpler substances by any chemical method.
3. Air and water, the most common substances are not elements as they are made of more than one type of element.
4. There are around 106 elements and these are grouped and classified systematically according to their properties. This results in The Periodic Table.
5. Periodic Table is a ready reckon-er chart where elements are arranged according to their atomic number (ie) number of protons in the nuclei.
6. Each element is given a symbol, with its atomic number written near it.
   (eg) Nitrogen is represented by the symbol N, in the periodic table.
7. The vertical column (top to bottom) in the periodic table is the group. Elements in a group share similar chemical properties.(eg) Helium, Neon, Argon, Krypton, Xenon and Radon
8. Each horizontal row in the table is called a period. Properties of elements in a period change gradually from metallic to non-metallic, as we move from left to right.
9. The elements on the left side of the periodic table are mainly metals, while those on the right are non-metals. For example in period ll, elements Boron, Carbon, Nitrogen are non-metals.
10. The zig-zag line separates the metals from non-metals.