Classification and Elements, Compounds and Mixtures

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Classification  The periodic table is a way of classifying elements.  Elements are arranged in order of increasing proton number  There are 7 rows of elements called periods. There are 8 columns of elements called groups. The elements in the same group have the similar chemical properties. Question(s):   Why is classification important in Chemistry? Elements, Compounds and Mixtures (Read up chapter before class as homework) Element - Pure substance that cannot be split up into 2 or more simpler substances by chemical means or by electricity. Chemical symbols are used to represent elements. For example, Sodium is         represented by the symbol Na and Magnesium is represented by the symbol Mg.   Elements are split (or classified) into 2 main groups - metals and non-metals. Physical properties of metals: 1) Shiny appearance (lustrous); 2) Solid at room temperature and pressure; 3) Sonorous (makes a ringing sound when struck; 4) Malleable (can be hammered into different shapes without breaking); 5) Ductile (can be drawn into wire); 6) High melting point and boiling point (except for mercury, sodium and potassium); 7) Good conductors of heat and electricity.   Physical properties of non-metals: 1) Dull appearance (non-lustrous); 2) Either gas, volatile liquids or solid with low melting points at room temperature and pressure (except for carbon); 3) Brittle if solid (easily broken when hammered); 4) Low melting point and boiling point (except for carbon and silicon); 5) Poor conductors of heat (except for carbon in the form of diamond and graphite); 6) Poor conductor of electricity (except for carbon in the form of graphite)  Atoms - smallest particles of an element that have the same chemical properties of that element.  Atoms can still be split but the particles obtained no longer have the properties of the element.  Not all elements exist as atoms. Only, helium, argon, neon, krypton, xenon and radon exist as atoms. They are called monatomic atoms.  Molecules - A group of 2 or more atoms that are chemically combined.  Molecules formed by the combination of 2 atoms are called diatomic molecules (eg. Oxygen)  Molecules formed by the combination of 3 atoms are called triatomic molecules.  Molecules formed by the combination of 4 or more atoms are called polyatomic molecules.(eg. Sulphur) Compound - Pure substance that contains 2 or more elements chemically combined. (Eg. Common salt made of chlorine and sodium) Rules for naming compounds: 1) Compounds that are made of 2 elements have a name that ends with an -ide; 2) Compounds that contain hydroxide ions is named a hydroxide; 3) Compound that contains a negatively charged polyatomic ion containing oxygen usually ends with an -ate. A compound is made of different elements chemically combined in a fixed ratio. The smallest particle of a compound that can exist independently is a molecule.  Chemical formula states: 1) The type of atoms present in the compound; 2) The ratio of the different atoms present in the compound. Rules for writing chemical formulas: 1) Compounds that have both metallic and non-metallic elements, the symbol of the metallic element is written first; 2) The number of atoms is written as a subscript, to the right of the atom's symbol; 3) It is not necessary to write the subscript '1'; 4)The oxygen atom is usually written the last.  Heat can be used to form compounds and break down compounds (thermal decomposition) Mixtures - formed when 2 substances are added together without chemical bonds being formed.  Differences between mixtures and compounds: 1) Separation: Mixture - can be separated by physical methods, Compounds - can only be separated by chemical means or by electricity; 2) Properties: Mixture - Chemical properties of the mixture is the same to that of its components, Compounds - Physical and chemical properties of a compound are different from its elements; 3) Energy change: Mixtures - no chemical reactions take place, Compounds - Chemical reactions take place, causing energy change; 4) Composition: Mixtures - The component of a mixture can be mixed in any proportion, Compounds - Elements in a compound are always combined in a fixed proportion. Alloy is an example of a mixture. It is a mixture of elements. Hence, alloys have similar chemical properties to those of the elements they contain but have different physical properties.

[Classification activities]  Activity one (in groups of 3, classify these soft toys: Teddy bear  Dog  Rabbit  Giraffe Duck Sheep Monkey  Snake Elephant  Lion Hyena  Turtle Panda Hamster Polar bear Ponyo Totoro Carebears Shrek  Bear Koala Angry Birds Mickey Mouse Doll Kangaroo Dolphin Pooh Eeyore Wombat Puppy Stitch  Penguin Piglet St. Bernard Ninja My group's classification: Activity 2 (Classification of elements, compounds and mixtures) Classification of Matter Matter can be classified into 3 groups, elements, compounds and mixtures.   Elements - Substance that is made up of only one type of atom and cannot be broken down into simpler substances by chemical reactions or by electricity. Chemical reactions (eg. over heating sugar made of hydrogen, carbon and oxygen -> carbon + water) Chemical reactions are not easily reversed. Rusting (iron + oxygen -> oxide of iron) is also a chemical reaction Water (l) -> water (g) is NOT a chemical reaction. Dry ice - Carbon dioxide (s) -> Carbon dioxide (g) is also not a chemical change. Ice melting is also not a chemical reaction. These are physical changes. Distinguishing chemical reaction and physical changes: Check if new substance is formed, if the process can be easily reversed, if heat or light is involved. 116 identified elements (some man-made and some natural) Stable elements (group 0, noble gases) are usually radioactive (harmful)   Our body is made up of 26 important elements such as oxygen, hydrogen, carbon, nitrogen, calcium, phosphorus and other elements.  Chemical symbol - first letter is always capitalised.  Name and chemical symbols are standardised internationally by IUPAC.  Elements can be further classified into 2 main groups, metals and non metals.  Elements can also be classified and arranged according to their chemical properties into groups.  Horizontal row of elements are called periods.  Vertical row of elements are called groups. Elements in the same group show similar chemical properties. Listen to element song. A compound is a substance which consists of 2 or more elements chemically combined together. It is made up of 2 or more types of atoms chemically combined. Examples of compounds - water (hydrogen and oxygen), sodium chloride (sodium and chlorine), sugar (carbon, hydrogen and oxygen)  Compounds are formed by chemical reactions. Many elements combine directly to form compounds. Example: Burning of magnesium in oxygen to form magnesium oxide. Properties of compounds are different from the properties of its constituent elements.  Compounds have fixed compositions (eg. water always contains 11% hydrogen and 89% oxygen by mass) A compound may be broken down into simpler substances by chemical reactions (decomposition). Decomposition is usually carried out using heat (thermal decomposition), electricity (electrolysis) or even bacteria. [Activity compare and contrast compound and elements] A mixture consists of two or more substances which are not joined together chemically.  Similarities of mixture and compounds: both contain 2 or more substances. [Refer to textbook page 68 for the differences between mixtures and compounds]  Alloys are mixtures.