Science Chemistry Modules 4,5,6

Chemistry 4: Chemical PatterensThe Periodic TableAn element is made of only one kind of atom. All the atoms of an element have the same number of protons.different elements have different proton numbers and they're arranged in order of increasing proton number in the modern periodic table. This gives repeating patterns in the properties of elements.you can use the periodic table as a reference table to obtain the following information about the elements: Relative atomic mass - the total number of protons and neutrons in an atom. Symbol Name Atomic (proton) number - the number of protons (and electrons) in an atom. you can also tell if the elements are metals or non-metals by looking at their position in the table.Groupsa vertical column of elements is called a group. Elements that are in the same group have similar properties.Group 1 elements include: Lithium (Li) Sodium (Na) Potassium (K) PeriodsA horizontal row of elements is called a period. Examples of elements in the same period are lithium (Li), carbon (C) and neon (Ne).

The group number corresponds to the number of electrons in the outer shell of an atom. For example: Group 1 elements have one electron in their outer shell. Group 7 elements have seven electrons in their outer shell.

The period number corresponds to how many shells there are in an atom of a particular element. For example, elements with three shells are found in the third period.

The Development of the Periodic TableMany years ago, scientists identified elements as chemicals that couldn't be broken down. Some tried to find patterns in these but others thought this wouldn't be possible.In 1817, Döbereiner realised that some elements with similar properties formed groups of three - he called these triads. One example is lithium, sodium and potassium.In 1865, Newlands suggested that when the elements were arranged in order of increasing atomic weight, some repeating patterns in properties could be seen. He called this the law of octaves, after the musical scale. Other scientist thought this was ridiculous. In 1869, Mendeleev presented his periodic table - it looked much like the one we use today. His table allowed similar elements to be grouped together and also showed the repeating patterns that other chemists had noticed.Mendeleev deliberately left some gaps in his periodic table, which were for elements that he suggested hadn't been discovered yet. He even correctly predicted the properties of these elements.New technologies have been very important in discovering new elements. For example, spectroscopy helped to discover the noble gases, which Mendeleev didn't include in his periodic table because they were yet to be found.

AtomsAn atom has a small, central nucleus, made up of protons and neutrons. The nucleus is surrounded by electrons, which are arranged in shells (energy levels).An atom has the same number of protons as electrons, so the atom as a whole is neutral (i.e. no electrical charge.A proton has the same mass as a neutron. The  mass of an electron is negligible (nearly zero).Atomic Particle     Relative Mass      Relative ChargeProton                           1                             +1Neutron                         1                               0Electron                  Nearly zero                    -1You can use information from the periodic table to work out the number of protons, electrons and neutrons in any atom.

Science C4