Importance of Science in Chemistry
The Elements in Chemistry
It was Lavoisier who produced the first fairly reliable list of elements. However, it contained substances which had not, up to that time, yielded up their true elements, such as magnesia. Only with the discovery of the electric battery by Volta did the means become available to split magnesia ( actually magnesium oxide ). The metal magnesium was obtained for the first time by Humphry Davy, using electrolysis. Davy also became famous for releasing the elements potassium, sodium, calcium, strontium and barium from their compounds, none of which had ever been seen before. All of these metals react vigorously or violently with water to produce alkaline solutions.
They are much more reactive than metals such as copper, lead, tin and iron, which humans had learnt to extract from the rocks by the process of smelting, in which the rock was heated strongly with charcoal or coke. However, the vast majority of elements are stable. Bismuth, which has the atomic number of 83, is the last element in the list with a stable nucleus. Beyond 83, all elements are unstable ( radioactive ). The atomic number of an element is the number of protons in the nucleus.
States of Matter Chemistry
Matter can exist in three states – solid, liquid or gas ( vapour ). Virtually all substances are able to exist in more than one of these three states. Water is a liquid at room temperature, for example, but can become a solid ( ice ) or vapour ( steam ), depending upon temperature and pressure.
Organic chemistry derives its name from the once-held belief that organic compounds could only be produced through living ( organic ) sources.
The element carbon readily forms covalent bonds with other elements to form compounds. In particular, carbon can bond with hydrogen, oxygen, chlorine and nitrogen. Carbon’s sheer versatility is shown not only in the different ways it can occur as an element ( such as diamond, graphite or buckminsterfullerene ), but also in the way it can create millions of different compounds. The study of such carbon compounds ( excluding carbon oxides ) is known as organic chemistry.
It used to be thought that compounds such as alcohol could only be made by living organisms – hence the name organic chemistry. However, in 1828, Friedrich Wohler made urea ( a substance found in urine ) from inorganic ( i.e. mineral ) precursors without the intervention of any living organism. It is now possible for chemists to make synthetically almost any chemical compound that nature produces.
Many useful things involve organic compounds, some made naturally, such as food and drink, cotton, wood, wool and leather. Synthetic ( man made ) organic compounds are becoming increasingly available, such as artificial fibers, plastics, explosives, dyestuffs and medicines.
Organic Compounds Definition in Chemistry
One of the main groups of hydrocarbons in petroleum is the alkanes. Alkanes have the general formula CnH2n+2. Methane, CH4, an important natural gas, is the alkane formed when n = 1. When there are four carbon atoms, the alkane is butane, C4H10, another important fuel.
Other organic compounds in everyday life include ethanol, which is the intoxicant of alcoholic drinks, and ethanoic acid, the active ingredient of vinegar.
Polymers are chemicals composed of large molecules in which a group of atoms is repeated. Nature makes many of these long – chain molecules, which structurally resemble a string of beads. The molecules that constitute the beads are called monomers, of which there can be hundreds or even millions linked together in a chain. Some polymers are naturally occurring, such as cellulose, starches, proteins, fats and DNA. There are also many artificial polymers, more commonly called plastics. Polythene ( or polythene ) is a polymer made from the monomer ethene. Other artificial polymers include polystyrene, nylon and polyvinyl chloride ( PVC ).
Modern chemistry is the study of the building blocks of matter and the fundamental units of chemistry are elements. There are about 90 naturally occurring elements. An element is one which does not contain any other simpler substance within it.
Science Chemical Reactions
Chemical reactions occur all the time – when fuels are burnt, in the industrial extraction of metals from their ores, and in many natural life processes. The study of reactions is important to chemistry, as it is the means by which substances change.
Chemical Equations in Science
Information about reactions can be recorded using balanced chemical equations. The equation will describe, in quantitative terms, how much of a product will be formed from a given mass of reactants. An example of a chemical reaction is when coal is burnt in air : C + O2 fi CO2
Here, coal ( which is a form of carbon ) reacts with oxygen molecules to give carbon dioxide ( and heat ).
Rates of Chemical Reaction
Reactions can occur at different speeds. The rate of reaction depends mostly on the reactants concerned – some naturally react faster than others. However, certain factors can help speed up reactions. These factors areincreasing the heat of the reactants, increasing the concentration of the reactants, use of a catalyst etc.
Chemical Groups in Science
The broad classifications of the elements is metals and non – metals. Each of these groups can then be further divided and categorized.
Metals : Metals form the majority of the elements and their chemical reactivity ranges from gold, which is found ‘native’ ( uncombined ),
to metals such as potassium and sodium. Metal oxides are basic. A basic oxide is able to react with an acid to produce a salt and water only, for example : MgO + H2SO4 fi MgSO4 + H2O magnesium sulphuric magnesium water oxide acid sulphate.
The alkali metals are the most reactive metals in the Periodic Table. These elements – lithium, sodium, potassium, rubidium, caesium and francium – ( located in group 1 of the Periodic Table ) are soft metals. Their softness and low melting point are the result of the weakness of their metallic bonding. The alkaline earth metals are the elements of group 2 – beryllium, magnesium,
calcium, strontium, barium and radium. Of these elements, calcium and magnesium are the most common. The alkaline earth metals are not as reactive as the alkali metals.
Non – Metals : Non – metals atoms generally have four, five, six or seven electrons in their outermost shells. By sharing electrons with other non-metal atoms, so as to create ‘bonding-pairs’ of electrons, non-metal atoms can manage to resemble their aristocratic cousins, the noble gases. Nonmetal oxides are either acidic or neutral.
Noble gases : The noble gases, a family of elements found on the far right of the Periodic Table, are extremely unreactive. This seems to be associated with the fact that they have an especially stable arrangement of electrons in their outermost shells.
Halogens : Halogens, consistingof fluorine, chlorine, bromine and iodine ( plus astatine ), are reactive non-metals. Halogen atoms have one electron less in their outer shells than noble gases, and must gain an electron to gain a stable structure, making them reactive. Halogens react vigorously with metals and hydrogen to form halides ( organic compounds with halogen atoms in their molecules ).
Science Chemical Bonds
Although there are only 112 known elements, there are millions of chemical substances found in nature or made artificially. These substances are not simply mixtures of two or more elements, but chemical compounds, formed by combining two or more elements together in a chemical reaction. The chemical ‘glue’ that holds compounds together is called chemical bonding. Chemical bonding also holds together atoms in the molecules of an element. There are two main types of chemical bond : covalent and ionic. Both work by bringing two atoms together in such a way as to make them appear stable. This is achieved by interaction in the atoms’ outermost shell of electrons ( valence shell ). By either sharing or donating electrons, both atoms can fill up their valence shell with electrons and achieve a stability similar to the noble gases.
Covalent bonding occurs when two atoms share electrons in their outer shell. Fluorine atoms, for example, each have seven outer electrons, but to gain a stability they need eight outer electrons. Thus two fluorine atoms can share an electron each, forming a covalent bond.
Ionic bonding ( or electrovalent bonding ) occurs when one atom ‘donates’ an electron to another atom. For example, sodium ( Na ) has one electron in its outer shell, whilst fluorine has seven. If the sodium atom transfers an electron to fluorine, both atoms attain a stability in their outer shell. When this transfer happens, both atoms become ions.
Atomic Theory in Chemistry
Atoms are the smallest particle of an element that can exist, and can be regarded as the building blocks of everything. Atoms can combine to form molecules. Molecules are the smallest particle of either an element or a compound that can exist independently.
Subatomic Particles in Chemistry
The atom is made up of sub-atomic particles: the proton, the neutron and the electron. The protons and neutrons are concentrated together in a tiny, enormously dense structure in the centre of the atom, called the nucleus. The electrons orbit this nucleus at a very high speed. The various elements differ from each other in the number of protons and electrons they have. For example, gold has 79 protons in its nucleus, whilst carbon has 6. The subatomic particles carry an electrical charge: the proton is positively charged, the electron is negatively charged, whilst the neutron is neutral. Atoms are electrically neutral because they contain equal numbers of protons and electrons.
The chemical properties of elements depend on the structure of their atoms. It is the arrangements of the electrons around the nucleus that give elements their particular chemical properties. Electrons are arranged in ‘shells’, and it is the state of the outermost shell which is crucial. A stable atom has a complete outer shell – only the elements known as the noble gases (such as helium) have this structure, and so they are stable as single atoms. Other elements have incomplete outer shells, so they bond with other atoms to form stable molecules.
Isotopes of Chemistry
Isotopes are atoms of an element with the same number of protons and electrons but with a different number of neutrons and therefore differing atomic masses. Isotopes are either stable or radioactive.
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