Atoms - The Smallest Particles PDF

Atoms – the smallest particles  Everything is made up of billions of extremely small atoms.  The smallest atom is hydrogen, represented as a sphere having a diameter of 0.000 000 07 mm (or 7×10−8 mm)  Atoms of different elements have different diameters as well as different masses. Cont. ...

Atoms – the smallest particles  Everything is made up of billions of extremely small atoms.  The smallest atom is hydrogen, represented as a sphere having a diameter of 0.000 000 07 mm (or 7×10−8 mm)  Atoms of different elements have different diameters as well as different masses. Cont.  Chemists use symbols to label the elements and their atoms.  The symbol consists of one, two or three letters, the first of which is always a capital.  The initial letter of the element’s name is often used and, where several elements have the same initial letter, another letter from the name is added. For example, C is used for carbon, Ca for calcium and Cl for chlorine.  Some symbols seem to have no relationship to the name of the element, for example, Na for sodium and Pb for lead. These symbols come from their Latin names: natrium for sodium and plumbum for lead. Cont.  Some common elements and their symbols. The Latin names of some of the elements are given in brackets. Molecules  Atoms of some elements are joined together in small groups called molecules.  The atoms of some elements join in pairs, for example, hydrogen, oxygen, nitrogen, fluorine, chlorine, bromine and Iodine and are known as diatomic molecules e.g. Chlorine (Cl2).  The atoms of some other elements, such as phosphorus and sulfur, join in larger numbers, four and eight respectively, which we write as P4 and S8. Cont.  The gaseous elements helium, neon, argon, krypton, xenon and radon (which are all gases at 0°C at sea level and atmospheric pressure) are composed of separate, individual atoms and their molecules are said to be monatomic.  In chemical shorthand these monatomic molecules are written as He, Ne, Ar, Kr, Xe and Rn respectively. Cont.  Chlorine molecule (Cl2). Cont.  Molecules are not always formed by atoms of the same type joining together as elemental molecules.  Most molecules consist of atoms of different elements, for example, water exists as molecules containing oxygen and hydrogen atoms. Practice Questions 1) How many atoms of hydrogen would have to be placed side by side along the edge of your ruler to fill just one of the 1 mm divisions? 2) How would you use chemical shorthand to write a representation of the molecules of iodine and fluorine? 3) Using the Periodic, write down the symbols for each of these elements and give their physical state at room temperature. a) chromium b) krypton c) osmium Cont. Periodic table.