Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chemical Symbol- One capital letter or one capital letter plus one or two small letters › Carbon: C, Argon: Ar, Oxygen: O, all on the periodic table! Atom- smallest piece of matter that has the properties of the element- represented by chemical symbol › Composed on protons, neutrons, and electrons › Protons and Neutrons exist in the center of an atom- the nucleus. › Protons are positive. › Neutrons have no charge. › Electrons are negative and surround the nucleus Even protons, and neutrons are made up of smaller particles- quarks Quarks- smallest particles- make up protons, neutrons, and electrons- 6 types › up, down, top, bottom, strange and charm To study quarks- accelerate charged particles to high speeds and cause them to collide with protons, breaking the proton http://en.wikipedia.org/wiki/Particle_accelerator A proton is made up of 2 up quarks and 1 down quark = charge of +1 a neutron contains 1 up quark and 2 down quarks, yielding a net charge of 0 All you’ve learned about atomic structure is just a model Model- help you visualize or understand something too large or small to see all at once http://www.teachersdomain.org/resources/phy03/sci/phys/matter/atoms/index.html Democritus- first to propose that atoms exist Dalton’s model- atom was a sphere Thomson’s model- plum pudding modelpositive sphere with negative charges embedded › Problems: electrons are actually around the nucleus, not inside of it Rutherford- all mass of an atom was in the center- the nucleus- discovered by gold foil experiment › Electrons surround nucleus and travel in orbits like planets around the sun › Problem: did not distinguish protons & neutrons and electrons do not actually move in the way he thought › http://www.chemsoc.org/timeline/pages/1911.html http://www.shsu.edu/%7Echm_tgc/soun ds/pushmovies/l2ruther.gif - source of animation Bohr-electrons travel in a fixed orbit around the nucleus › Problem: electrons are actually in regions or clouds around the nucleus Difference between Bohr and Rutherford: › Rutherford said electrons travel in orbits like planets- problem- electrons also emit energy and should spiral closer to the nucleus › Bohr- only certain orbits are possible – they gain and lose energy as they move from one orbital to another Distiguished between protons and neutron while Rutherford did not Electron Cloud Model- nucleus with protons and neutrons in the center › Electrons in clouds around the nucleus- very large area compared to the nucleus › Electrons move too fast to find exact location at any one time › Atoms are mostly empty space! http://www.teachersdomain.org/resource/p hy03.sci.phys.matter.atoms/ Nucleus- contains most of the mass of an atom › Protons & Neutrons contains most of an atom’s mass › Electrons- 1/2000th of the mass of a proton Grams are not used to measure mass of atoms because atoms are too small › Amu is used instead › Amu = atomic mass unit Mass of proton = mass of neutron = 1amu Amu – 1/12th the mass of a carbon-12 atom, which contains 6 protons and 6 neutrons Protons- determine the identity of an atom › Every atom has a different # of protons Atomic number- tells us the number of protons Mass number- total number of protons & neutrons # of neutrons = mass # - atomic # Electrons- determine physical and chemical properties of atoms Charges of atoms- indicates # of electrons gained or lost Cation- ion with a positive charge- lost electrons Anion- ion with a negative chargegained electrons Isotope- Atoms of the same element with different numbers of neutrons To indicate the identity of an isotope, write the element name – mass # › Carbon-12 Carbon-14 Average atomic mass- a weighted average of the masses of the isotopes of an element › Average atomic mass = (% x mass) + (% x mass) + (% x mass)…. › Reason it is an average- there are several isotopes for each element mass number 13 exact weight 12 12.0000 percent abundance 98.90 13 13.003355 1.10 To calculate the average atomic weight, each exact atomic weight is multiplied by its percent abundance (expressed as a decimal). Then, add the results together and round off to an appropriate number of significant figures. This is the solution for carbon: (12.000000) (0.9890) + (13.003355) (0.0110) = 12.011 C has an average atomic mass of 12.011 amu. This is closer to 12 than to 13, which means most isotopes must be carbon-12. This matches our known data, which say that 98.90% of carbon atoms are C-12. Periodic- Repeated in a pattern Elements are ordered by: › increasing atomic number › changes in physical & chemical properties Mendeleev- Ordered elements by atomic mass › Left blank places in his table to line up elements according to their properties › Elements were later discovered and fit into the places he left blank Moseley- organized elements by atomic number rather than atomic mass › Same arrangement as today Groups/Families- vertical columns of the periodic table Rows of Periodic Table- periods Electrons › › › › Around the nucleus in an electron cloud Energy levels dictate location of electrons Closer to nucleus = less energy Fill energy levels from inner to outer levels Electrons in outer shell – determine chemical properties of elements Complete outer shell- needs 8 electrons to be stable Energy levels and # of electrons in each: › › › › Level 1 Level 2 Level 3 Level 4 Holds 2 Holds 8 Holds 18 Holds 32 Sublevel s p d f # e in sublevel Shape 2 sphere 6 dumbbell 10 double dumbbell 14 complex http://library.thinkquest.org/3659/structur es/shapes.html Level 1 Level 2 Level 3 Level 4 s s&p s, p, d s,p,d,f Valence 2 electrons 2 + 6 = 8 electrons 2 + 6 + 10 = 18 e2 + 6 + 10 + 14 = 32 e- Electrons Group 1A – 8A have 1-8 valence electrons Electron dot diagram (or Lewis dot diagram) - A symbol of an element surrounded by dots to represent electrons in the outer energy level › First 2 electrons go together › Next electrons go one on each side, then start to double up http://www.ausetute.com.au/lewisstr.h tml Properties of elements in the same group- similar due to same # of valence electrons Alkali metals- group 1A- very reactive metals Alkaline metals- group 2 A- less reactive than alkali Halogens- group 7A › Likely to react with Alkali metals- group 1A Noble Gases- group 8A- not reactivedon’t form compounds Hydrogen and Helium › Combine to form elements with larger atomic numbers – can only occur through nuclear reactions › http://www.teachersdomain.org/resources/ phy03/sci/phys/matter/origin/index.html › http://www.teachersdomain.org/resources/l sps07/sci/phys/matter/stability/index.html › http://www.teachersdomain.org/resources/ ess05/sci/ess/eiu/fusion/index.html Metals- good conductors of heat & electricity. › All but one (Hg) are solid at room temperature. › Lustrous- reflect light › Malleable- can be hammered or rolled into sheets, › Ductile- can be drawn into wires Metals- have 1-3 valence electrons, so they lose electrons to become stable- they become cations Metallic bonding- positively charged metallic ions are surrounded by a cloud of electrons. › Outer electrons are not held tightly and can move among the ions- allows conduction of electricity http://www.eng.auburn.edu/~w fgale/intro_metals/section1.ht m Alkali- Group 1 A very reactive because they have 1 valence electron Alkaline earth- Group 2A- fairly reactive- have 2 valence electrons Transition elements- Groups 3-12 or 1B-8B, metals, often form colored compounds Lanthanides are elements after lanthanum and many are used to produce colors on our TV screens Actinides- follow actinium. All are radioactive and unstable, so they are difficult to research Elements beyond Uranium are radioactive› As # of protons increases, the repulsive force within the nucleus also increases- forces the atom to break apart. › (Radioactive substances are substances in which the nucleus breaks down and gives off particles and energy ) Nonmetals- gases or brittle solids at room temperature. › not malleable or ductile. › do not conduct heat or electricity well › not shiny Nonmetals don’t conduct electricity because- electrons are strongly attracted to the nucleus Gain electrons to form anions Can form either covalent or ionic bonds › Covalent- shared electrons › Ionic- gain and loss of electrons Diatomic- molecule that consists of two atoms of the same element covalently bonded › Includes (memorize these!!) H2 Cl2 F2 N2 O2 Br2 I2 Hydrogen is diatomic because it is very reactive. › Bonding makes it more stable Halogens- nonmetals from group 7A or 17. › very reactive. 7 valence electrons › form reactive diatomic molecules with distinctive colors › Noble gases- stable due to full outer energy levels. › don’t make compounds naturally Metalloid- can form ionic or covalent bonds. › properties of both metals and nonmetals Semiconductor- element that conducts electric current under certain conditionslike Silicon (Si is a metalloid) Allotrope- same element with different forms and different properties › Example: Diamond and graphite Both are made of carbon. Diamond- clear, hard › each C atom bonded to four other C atoms forming a giant crystal. Graphite- black powder with hexagonal layers of C atoms. › Each C is bonded to 3 other C. › Layers can slide past each other, so graphite is a good lubricant.