Atoms – Atomic Structure Atom Movies: http://www.youtube.com/watch?v=oSCX78-8-q0 http://www.youtube.com/watch?annotation_id=anno tation_211263&feature=iv&src_vid=oSCX78-8q0&v=xA4QWwaweWA http://www.youtube.com/watch?v=FbLvy-ayi4A 3-d atomic structure Atoms, Elements, Compounds • All matter is made of tiny • • • • particles called atoms Atoms are the basic building blocks of all substances Elements are the simplest type of substance There are 109 (ish) elements Atoms of elements combine to form compounds (water…) Atoms and their parts • Atoms = the smallest part of an element that still has all the characteristics of that element • About 200 particles smaller than atoms • 3 main subatomic particles = protons, neutrons, electrons Electrons and Energy Levels • Atoms • Positively charged center (nucleus) • Protons (positive) • Neutrons (no charge) • Outside the nucleus are negative charges • Electrons Same # of electrons and protons Atomic Number Protons! • Number of protons in a nucleus = the atomic number (look at periodic table, Hydrogen’s Atomic number = 1) Atomic Mass • The atomic mass number of an atom = the number of protons plus the number of neutrons • Look on periodic table Periodic Table Songs • Elements in Order http://www.youtube.com/watch?v=zUDDiWtFtEM • Tom Lehrer version – http://www.youtube.com/watch?v=aPq3SEteEJc • First 20 Elements Rap – https://www.youtube.com/watch?v=cAnOUwPfHlk Electron Cloud • Electrons “fly” around nucleus in energy levels • Each level can only hold so many electrons • Innermost level holds 2 electrons, second holds 8(per layer), third holds 18… • Electrons in outer layer = valence electrons Quarks • Protons and neutrons are made of smaller particles called quarks Atoms and Bonding What is Chemical Bonding? • Combining of atoms to form new substances • Rules of chemical bonding are determined by the structure of atoms Attractions • Negatively charged electrons attracted to positively charged protons • This attraction is not strong enough to pull the electron into the nucleus, but it holds the atom together Stable vs. Unstable • Outermost layer is “full” (holds maximum # of electrons) or complete • Atom is stable • Will not form chemical bonds • Only “noble” gasses • Atom with outermost layer of electrons not filled will form chemical bonds Looking at the Periodic Table of Elements • Pg 166 and 167 • 18 families of elements (column) • Elements in same families have common properties (same # of valence electrons… • The number in the top corner of each elements’ box = atomic # (# of protons and electrons) • Element “families” have the same # of valence electrons! Electrons and Bonding • Atoms that do not have their outermost energy levels filled form bonds • Some, like Fluorine (F), gains electrons • Fluorine has 7 valence electrons so it will “gain 1 • Some, like Sodium (Na), lose their electrons • Sodium has 1 valence electron so it “loses” that 1 Atoms gain or lose electrons to become stable! (complete outer energy levels) Ionic Bonding • Bonding that involves the transfer of electrons • When electrons are transferred a neutral atom will become an ion • Ion = a charged atom • 1 atom gains electrons and 1 atoms loses them in an ionic bond Charges • If an atom gains an electron it becomes negatively charged • If an atoms loses an electron it becomes positively charged • Let’s draw F + Na… Energy for Ion Formation • Ionization is the process of removing electrons and forming ions • Ionization energy is the energy needed for ionization to happen • Atoms with few valence electrons have low ionization energy • The tendency of an atom to attract an electron is electron affinity Arrangement of Ions in Ionic Compounds • Ions of opposite charges strongly attract each other • Placement of ions in an ionic compound result in a regular repeating pattern called a crystal lattice structure • Gives strength • Gives shape to crystals of particular compounds (remember mineral id…) • Pg 19 Covalent Bonds • When electrons are not transferred but shared we have another form of bonding – covalent bonding • Electron sharing (co…) • By sharing electrons each atom fills up its outer energy level Nature of Covalent Bonds • The positively charged nucleus of both atoms simultaneously attract the negatively charged electrons being shared • Simplest covalent bonds is between 2 Hydrogen atoms • PG 22 Electron Dot Diagram • Chemists use these drawings to show electron sharing that happens in covalent bonds • The element symbol represents the nucleus and all the inner energy levels • The dots represent the valence electrons Let’s draw a few more Pg 22 Diatomic Elements • Covalent bonds often happened between atoms of the same elements • Hydrogen, chlorine, fluorine, bromine, iodine, nitrogen Molecule Formation • The combination of atoms from covalent bonds form molecules rather than crystal lattice structures • A molecule is the smallest particle of a covalently bonded substance • Molecules are represented by chemical formulas • HCL – 1 Hydrogen and 1 Chlorine (hydrochloric acid) Water Molecule Chemical Formula Polyatomic Ions • Covalently bonded atoms that tend to stay together and act like a single atom when they combine with other atoms • Polyatomic ions have covalent bonds, but when they bond with other atoms they usually form ionic bonds • Pg 24 • The polyatomic Ion hydrogen carbonate bonds with sodium to produce sodium hydrogen carbonate = Baking Soda! Metallic Bonds • Metals are elements that give up electrons easily (copper, silver, gold, iron, tin, zinc, nickel, chromium…) • Metallic solids = solids made entirely of 1 metallic element • Metallic bonds – outer electrons of the atoms form a common electron cloud Sea of Electrons • Electrons become the property of all the atoms bonded • The positive nuclei of the atoms are surrounded by free-moving electrons that are attracted by the nuclei Properties of metals • Malleable – hammered into thin sheets • Ductile – drawn into wire • Flexibility – metal ions can slide past each other and electrons free-flow, yet the positive and negative attractions hold the metal together • Conduct heat and electricity • High melting points Predicting Types of Bonds • Elements at the left and center of the periodic table are metals – form metallic bonds with each other • Elements at the right gain electrons easily (nonmetals) • Bonds between metals and nonmetals = ionic • Bonds between nonmetals = covalent Combining Capacity of Atoms • Oxidation Number = the # of electrons an • • • • atom gains, loses, or shares when it forms a bond Oxidation # describes combining capacity Sodium’s oxidation number = 1+ Magnesium = 2+ Chlorine = 1- Using Oxidation Numbers • We use oxidation numbers to predict how an atom will combine (or not) and to determine chemical formulas • Na 1+ plus Cl 1- = MgCl2 NaCl • Mg 2+ plus Cl 1- =