Atoms contain even smaller units calles SUBATOMIC PARTICLES. Scientists have found more than 200 of these. Some exist for only a tiny fraction of a second. Others are stable and do not break down easily. Protons, neutrons and electrons are stable particles.
ABAll plants and animals need nitrogen, presented in proteins and nucleid acids. Most living things, however, cannot use nitrogen directly from the atmosphere.
(1) Nitrogen in the air.
(2) Nitrogen in atmosphere is trapped by some plant roots.
(3) Plants use nitrogen for making proteins.
(4) Animals eat plant proteins.
(5) The proteins in dead organisms and in body wastes are converted to ammonia by bacteria and fungi.
(7) Artificial nitrates added to soil as fertilizers. When too much is added, water supplies become polluted with nitrates.
(8) Plants absorb the nitrates.
e stable particles.
%CCarbon compounds make up the living tissues of all plants and animals. The carbon cycle is the circulation of carbon between living organisms and their surroundings. It describes the processes which increase and decrease the amount of carbon dioxide in the environment.
(1) Carbon dioxide is in the air.
(2) It is breathed in, or absorbed by plants.
(3) Animals eat the plants.
(4) Carbon dioxide is breathed out as waste by plants and animals.
(5) Dead plants and animals are broken down by bacteria.
(6) Bacteria convert the carbon compounds to carbon dioxide and the cycle starts again.
(7) The remains of living organisms which have been dead a long time and microscopic organisms form fossil fuels. When burnt, carbon dioxide enters the atmosphere.
(8) Volcanoes release carbon dioxide into the air.
OAis a vital part of life on Earth. All living things need oxygen to live and breathe.
(1) Oxygene is in the air.
(2) The oxygen is breathed in by animals.
(3) It is breathed out as carbon dioxide.
(4) The carbon dioxide is absorbed by plants which combine it with water to make food.
(5) Plants release the surplus oxygen into the air.
ASulphur is an important part of every almost protein.
(1) Sulphates, or sulphur-oxygen compounds, are absorbed by plant roots.
(2) The oxygen in the sulphates is replaced by hydrogen in a plant process making amino acids.
(3) Animals eat the plants.
(4) In dead animals and plants the amino acids which contain sulphur are broken down by decomposer micro-organisms to obtain hydrogen sulphide.
(5) Bacteria extracts sulphur from sulphides.
(6) Other bacteria combine sulphur with oxygen to produce sulphates.
Ais made of two or more elements chemically joined to form a new substance which has different qualities from the element which produced it. Water is a compound. It is liquid made from two elements, HYDROGEN and OXYGEN. In a compound the proportions of the elements are always the same.
SOLUTION: of two or more substances which cannot be separated by using mechanical methods such as filtering. It can be solid, liquid or a gas.
SUSPENSION: mixture where one substance spreads evenly through another without dissolving. It includes solids in liquids or gases, gases in liquids and liquids in gases.
EMULSION: liquid which is evenly spread through another liquid. Droplets of one liquid are evenly spread in the but in time the two separate.
ATwo or more atoms joined together form a molecule. The atoms may come from the same element or from different elements. Molecules that contain atoms from two or more elements make a compound. When a molecule is broken down it splits into the atoms of the elements from which it was made. Molecules can be made of two atoms or thousands of atoms, i.e. an oxygen molecule has two atoms but a rubber molecule has between 13000 and 65000 atoms.
AThe number of neutrons in an atom can vary without the element changing identity. Forms of an element with different numbers of neutrons in the nucleus are called an element's isotopes. A neutron is electrically neutral as it carries no charge. It has a mass of 1.6748x10-27 kg.
APERIODS
Each element is shown by its symbol in the table. The elements are arranged in seven rows called PERIODS. They are read from left to right and show a progression from metals to non-metals. HYDROGEN does not belong to any of these classes.
Elements are arranged in the periods according to their atomic number, from 1 to 103. This appears in the top left corner of the box. The number states how many protons are in the element's nucleus.
_AEach column in the table is a group, read vertically. It contains elements with similar properties. There are eight major groups of elements, arranged according to how many electrons, negatively charged particles, are in the outer shell of the atom. Elements have between 1 and 8 electrons in the outer shell. Elements in each group behave similarly.
AAlkali metals:
Lithium, sodium, pottassum, rubidium, caesium and francium are the elements in Group 1 of the Periodic Table. Alkali metals are so reactive that they are stored in oil to protect them from oxygen and water vapour in the air. Their melting and boiling point are low for metals, they float in water and they can be cut with a knife. They react with water to form alkaline solutions.
dAAlkaline-earth metals
The elements in group 2 are beryllium, magnesium, calcium strontium, barium and radium. These elements are greyish-white in colour. They are malleable although varying in hardness. The alkaline-earth metals have a pair of electrons on the outermost shell which can be removed from their atoms relatively easily to form positive ions.
AHalogens
elements in Group 7. They are fluorine, chlorine, bromine, iodine and astatine. They are so reactive they never occur free in nature. Instead, they are found combined with metals in salts such as sodium chloride. This has led to them being called halogene or salt-formers. They occur in compounds with negative ions. Astatine is the other element in the group that does not occur in nature.
BCarbon
Carbon is an important element. It is a nonmetallic element and forms only 0.2 per cent of the earth's crust. Carbon is found naturally both in pure form and in combination with other elements. It occurs in three forms: diamond, graphite, charcoal. In diamond the carbon atoms are arranged regulary in a framework. Each atom is surrounded by four others producing a strong crystal structure and making diamond the hardest substance known. In graphite each atom is surrounded by three others. This produces a layer pattern, and makes graphit soft. Charcoal has a non-regular structure.
Carbon is the basis of organic chemistry and all living systems.
PALanthanide and actinide series
The two bottom rows of the table (57-71, 89-103) are lanthanides and actinides. They are shown separately because their properties are so similar that they only cover two elements on the main table. Lanthanides are rare metallic elements. Actinides are chemically similar to them. Uranium is an actinide.
9AA proton is part of the nucleus ( the central core) of an atom. An electron is identified by the number of protons in the atom = atomic number. If an atom gains or loses a proton, it becomes an atom of a different element. A proton has a positive electrical charge of one unit. It has a mass of 1.6726x 10-27 kg.
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Mixture
is made from two or more substances which have not been chemically joined. Each element can be separated without a chemical change. A mixture can have ingrediants in any portion.
Molecules
Neutron
Periodic Table
General
It was devised in 1869 by the Russian chemist Dmitri Mendeleyev. The table groups elements into seven lines or periods. As we read from left to right the elements become less metallic. The elements in each vertical group have similar chemical properties.
Periodic Table
Grouping the Elements
Periodic Table
Groups (1)
Periodic Table
Groups (2)
Periodic Table
Groups (3)
Periodic Table
Groups (4)
Periodic Table
Groups (5)
Noble gases
Group 8 contains very unreactive elements. This group includes helium, neon, argon, krypton, xenon and radon. They are all colourless gases at room temperature, with low melting and boiling points. They all exist as separate single atoms.
Periodic Table
Groups (6)
Periodic Table
Groups (7)
Transition elements
atom nos. 21-30, 40-48, 72-80. Each element differs from its neighbor in another numbered period by the number of electrons in its next to outer electron shell.
Periodic Table
Groups (8)
Protons
Solids
A solid takes up a specific amount of space. Its molecules cannot move around freely, although they are not completely still. A solid will not alter its shape unless it is forced to do so.
?AElectrons move around the nucleus of an atom at high speed. The arrangement of electrons in an atom determines the element}s chemical behaviour. An electron has a negative charge of 1 unit. Atoms are electrically neutral as they have the same number of electrons and protons. An electron has a mass of 9.1096x10-31 kg.
BCombustion
rapid burning that occurs when oxygen combines quickly with another substance
Corrosion
happens on metal surfaces which react to air, chemicals or moisture.
Destructive distillation
decomposing substances in a closed container
Digestion
In animals this involves the breakdown of food by protein catalysts calles enzymes.
Dissociation
the braek-up of a compound's molecules into simpler ingrediants which may be recombined.
Electrolysis
occurs when an electric current passed through a liquid breaks up its parts.
Fermentation
a change to organic substances caused by enzymes.
Oxidation
occurs when a substance loses electrons. These are gained by another substance, which undergoes reduction. The two reactions occur together (redox reaction)
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Literature used
The text and expressions of the following data are taken with many thanks from
COLLINS GEM ENCYCLOPEDIA
HarperCollins Publishers, Glasgow, 1993, ISBN 0 00 470371 5.
Brought by Eberhard Rompf to the Series 5 data file format for ChemTools users.
Atomic Structure
Atoms
is a minute unit of matter. Everything around us is made od atoms. They are the smallest units that can take part in a chemical reaction to produce a chemical change. They do not vary much in size but they do vary in weight.
Biochemical Cycles
General
The Earth's resources are constantly being used and reused. Biochemical changes recycle some of the elements required by living things.
Biochemical Cycles
The carbon cycle
Biochemical Cycles
The nitrogen cycle
Biochemical Cycles
The oxygen cycle
Biochemical Cycles
The sulphur cycle
Chemical reactions
Common reactions
Compound
Electron
Element
a single substance which cannot be broken down chemically into simpler substances. There are 90 elements which occur naturally, another 20 have been produced artificially but not all of these have been recognized.
Examples of mixtures
A gas does not have a specific shape or size. Its molecules can move around completely freely so a gas will spread out to fill a container.
LiquidsaA liquid occupies a specific amount of space but, unlike a solid, it can alter its shape easily.
MATTERGMatter on Earth is made up of atoms forming solids, liquids and gases.
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