METALS AND NON-METALS

foreign [Music] in our physical world there are metals such as those in Steel and non-metals such as sulfur sulfur carbon oxygen silicon phosphorus and iodine are among the 22 elements usually classed as non-metals other elements including sodium silver magnesium aluminum tin and copper are among those that make up the remainder of the elements 81 in number that are usually classed as metals to see how metals are different from non-metals let's first compare the atomic structure of two metals sodium and magnesium in the outer shell of a sodium atom there is one electron this electron like the others in the inner shells is held in the atom by the positive charge of the protons in the nucleus in a magnesium atom there is one more electron in the outer shell and a greater positive charge in the nucleus this holds the electrons closer than in a sodium atom making the Magnesium atom the smaller of the two and making the force that holds its outer electrons greater than the force in a sodium atom we think of this force in terms of the energy required to overcome it in order to pull a single electron from an atom this energy is called the ionization energy or potential the ionization energy determines the tendency of an atom to lose electrons in the periodic table elements are arranged generally according to the number of outer electrons in their atoms each vertical column is called a group each horizontal row a period as we move to the right along the periods of the table ionization energy tends to increase in helium and the other rare gases ionization energy is at a maximum for each of the periods a kind of division among each of the periods of the table occurs along this line here ionization energy has become high enough that atoms no longer tend to lose electrons instead they tend to gain electrons this is the key difference between metals and non-metals metals tend to lose electrons whereas non-metals tend to gain or share electrons the elements lying along the line of separation between the mems called the metalloids under different circumstances they may either gain or lose electrons remember that this grouping based on ionization energy depends on the number of electrons in an atom's outer shell ionization energy is also affected by the number of energy levels occupied by electrons in an atom each energy level or shell screens out some of the attractive force between the nucleus and the outer electrons the more shells an atom has the weaker is the force that binds the outer electrons as we move down the periodic table each period of elements has one more shell than the previous one elements to the lower left have the most shells and least number of outer electrons so they are the most metallic those in the upper right have the least number of shells and greatest number of outer electrons so they are the most non-metallic now remembering that metals tend to lose electrons and non-metals tend to gain or share them we can go on to explain the physical and chemical differences between metals and non-metals one physical property we can notice in the aluminum panels on this building is that they have a luster or shine to them metallic luster is a physical property of All Metals non-metals like sulfur do not have a metallic luster metals usually have high melting points aluminum for example melts at about 660 degrees Centigrade whereas sulfur melts at approximately 120 degrees Centigrade because metals like aluminum are malleable they can be rolled out into flat sheets or paper-thin foils like steel metals can be hammered into different shapes without breaking sulfur like other non-metals will break or crumble when it is pressed or hammered non-metals are generally not malleable metals are ductal they can be drawn into wires of varying diameter without breaking in wires we often put to use another physical property of metals High conductivity metals are good conductors of both electricity and Heat although this aluminum frying pan is hot the non-metallic plastic handle is quite cool non-metals are poor conductors of both heat and electricity metals like the metal that makes up this steel cable generally resist forces that tend to pull them apart metals have high tensile strength another physical property of metals is high density this steel beam is quite heavy as compared with this wooden board of about the same size differences in density and other physical differences between non-metals and metals can be explained in terms of bonding whether atoms tend to lose gain or share electrons atoms of non-metals like sulfur cannot lose electrons to each other but they do form molecules with covalent bonds eight sulfur atoms make up the sulfur molecule in which outer electrons are shared between adjacent atoms giving each one an outer shell of eight electrons because the bonds extend in fixed directions only there is a good deal of empty space between the molecules in a non-metal just as there is between boards that have been joined in an open pattern but there is little space between the boards when they are stacked this is essentially what happens in the case of metals take aluminum for example because metals tend to give up electrons their atoms do not bond together to form molecules instead the metallic bond occurs in most metals in this metallic bond atoms are packed tightly together each one adjacent to the maximum number of neighboring atoms a single atom can have three atoms beneath it six on the same level and three above it this illustrates one type of closest packing and causes the high density of metals as well as other physical properties because metals tend to lose electrons the outer electrons move freely among the atoms causing each of the atoms to become positively charged ions attraction between the positive ions and what is sometimes called the Sea of electrons accounts for the high tensile strength of most metals this sea of electrons is responsible for the high heat and electrical conductivity of metals closest packing also explains the high ductility and malleability of metals which can be demonstrated with close packed aluminum discs because all the ions are held together by the Sea of electrons Under Pressure they can be made to slip past each other rather easily and the metal will still hold together as long as the distance between ions is not increased too much here is a photograph of the arrangement of atoms in Platinum magnified more than a million and a half times in which a close packing Arrangement is suggested this close packing results from the tendency of metals to lose electrons whether the atoms of an element tend to lose or gain electrons affects not only its physical properties but also its chemical properties for example the metal sodium will combine violently with chlorine a non-metal in the reaction sodium chloride is formed in general metals react readily with non-metals because metals tend to lose electrons and non-metals tend to gain or share them usually forming ionic bonds electrons are usually not transferred in reactions between non-metals such as sulfur and oxygen in the burning of sulfur sulfur dioxide a covalent compound is formed non-metals tend to form covalent bonds and the sulfur dioxide results from a sharing of electrons although non-metals frequently react with each other metal seldom react with each other liquefied lead and Tin for example can be mixed and no chemical reaction will take place let's allow this mixture of metals to cool this cooled material is the familiar solder not a compound but an alloy a solid solution of one metal in one or more other metals Alloys form because the closely packed ions of a metal have Mobility when the metal is liquefied allowing ions of other liquefied metals to mix freely with them this forms a solution of ions held together in a metallic bond by a sea of electrons when the solution hardens an alloy is formed a result of one of the properties of metals that make them different from non-metals metals and non-metals differ in that metals tend to lose electrons whereas non-metals tend to gain or share electrons this one difference helps to explain the physical and chemical properties of nearly all metals and non-metals the elements that make up all the materials of our physical world [Music]