ES 106 2006 April 7 Matter and atoms I Matter is composed of atoms smallest particle that retains properties A Atoms 1 composed of subatomic particles three fundamental ones a protons 1 have mass 1 atomic mass unit 2 have positive electrical charge b neutrons 1 have mass 1 atomic mass unit 2 have no electrical charge c electrons 1 have mass of 1 2000 atomic mass unit 2 have negative electrical charge 2 structure of atom a nucleus contains protons and neutrons subequal numbers 1 number of protons determines the element 2 number of neutrons may be different in different atoms of the same element leading to different isotopes a most isotopes are stable b unstable isotopes are radioactive and disintegrate over time i in a certain length of time one half of the atoms of an unstable isotope will decay into another substance ii this length of time is the half life of the isotope a half life is constant for an isotope b can be used to determine age of material by measuring how much of the daughter and parent b electrons surrounding in cloud 1 occur on average in more likely positions 2 called shells which have energy levels 3 outermost shell are valence electrons a responsible for reactions with other atoms b full shells are not reactive i first shell can contain 2 electrons ii successive outer shells can contain 8 electrons c atom is electrically neutral when it has the same number of electrons and protons II Periodic table of elements A Each atom is represented by a letter symbol 1 one or two letters a capitalize the first letter b do NOT capitalize a second letter if present 2 letters often initials in a foreign or even obsolete language for the element or a major substance that contains the element B Arranged in rows or periods according to atomic number increasing mass in each succeeding row C Columns are called groups 1 determined by number of valence electrons a same number of valence electrons results in similar properties b full shells of electrons are not reactive with other elements c most atoms lose gain or share electrons with other atoms in order to attain a full shell electron configuration 1 elements gaining or losing electrons become ions a gaining electrons results in overall negative charge anion b losing electrons results in overall positive charge cation 2 groups a far right Noble Gases have full electron shells b next to far right Halogens missing one electron of a full shell c far left Alkali Metals single electron in outer shell d next to far left Alkaline Earth Metals two electrons in outer shell D Elemental structure can be shown with diagrams of electron shells 1 Bohr diagrams named after Niels Bohr who discovered numerous elements a few hundred years ago and presented the hypothesis of electrons filling shells 2 Show element with its symbol and arcs indicating the electron shells a First shell filled with two electrons e2b Successive shells filled with eight electrons c Number of arcs corresponds to the row number of element in the periodic table E Electron dot diagrams are useful for predicting bonding of elements dots surrounding the element represent its valence electrons 1 Show how elements bond by filling or emptying dot shell 2 become ions with dots charges and electrons a Ca Ca2 2eb Br e Brc Show ionic bonding reactions by transfer of electrons only 3 Covalent bonds share electrons a Show unfilled shells on left b Show sharing of electrons on right c Cl Cl Cl2 d Electrons shared equally by same type of atom nonpolar e Different types of atoms bonded covalently have one element hog the electrons resulting in a molecule that has polarity or is polar like a magnet has poles III Elements in Earth s crust A Most common eight 1 Oxygen a 47 by weight b 63 by number of atoms c 94 by volume 2 Silicon a 28 by weight b 21 by number of atoms c 1 by volume 3 Aluminum a 8 by weight b 6 by number of atoms c by volume 4 Iron 5 wt 2 by volume 5 Calcium 4 wt 2 1 by volume 6 Sodium 3 wt 3 1 by volume 7 Potassium 3 wt 1 2 by volume 8 Magnesium 2 wt 2 by volume B Minerals are composed of bonded elements 1 naturally occurring inorganic solid with an orderly internal arrangement of atoms crystalline structure and a definite chemical composition that can vary within limits 2 most minerals in Earth s crust are silicates a compounds containing oxygen and silicon b building block is the silica tetrahedron one oxygen four silicon
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