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| hypothesized that for every chemical elements there is a corresponding species of objects called atoms; element is a substance that cannot be broken down into other substances |
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| any cluster of atoms that can be isolated |
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| "splitting by electricity" was developed in early 19th C and this allowed rapid discovery of many elements |
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| 99% made up of 6 elements: oxygen O, silicon Si, magnesium Mg, iron Fe, aluminum Al, and calcium Ca |
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| 90% made up of 6 elements, Hydrogen H, carbon C, nitrogen N, oxygen O, phosphorous P, and sulfur S |
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| identified a subatomic particle called the electron (an object of negative electrical charge that is much lighter and smaller than the smallest atom, H) |
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| the electron must have come from the atom... |
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| confirming what had long been suspected- the atom was made of smaller parts |
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| experiemented with gold radiation; scattering and reflection of radiation proved the existence of a dense center of gold atoms: the nucleus |
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Rutherford's model of the atom 1911:
A dense, postively charged nucleus surrounded |
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| by orbiting cloud of negatively charged electrons |
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| Nucleus has 2 types of particles in it- |
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| proton (positively charged particle) and a neutron (neutral particle) |
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| Electromagnetic radiation |
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| of an atom would have to come from somewhere (per 1st law of thermodynamics), so the electrons would tend to lose orbital distance over time and fall into the nucleus. They do not do this...atoms have existed for many billions of years |
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| said that electrons exist in various levels or "shells" located about the nucleus; each shell corresponds to an "energy level of the electron |
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| between energy levels when excited by outside energy |
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| all electrons in lower energy levels (shells) |
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| some or all electrons are in the highest energy levels |
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| In the Bohr model, when an electron drops to a lower energy level, it must emit some energy- |
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| this is a photon ( a packet of electromagnetic radiation...may be light or some non visible) |
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| a "packet" of energy with a paradox... it is particle like in its behavior but it it wave like in the way it moves with other photons; therefore it is must be both a particle and a wave |
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| H and He atoms in excited stages |
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| small tubes in store displays |
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| slightly orange street lights |
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| light tubes like those above |
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| different elements->different nuclei->different number of protons->different energy levels for each possible quantum leap of electrons-> |
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| there must be an "energy fingerprint" for each element (and isotope of each element) |
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| total collection of photons emitted by a given atom, therefore each has a unique spectrum |
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| astronomic study of stellar gasses & interstellar dust compositions, chemical tests on unknown substances (to determine com position), study of soil and rock and earth and other planets |
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| summary of all known chemical elements according to |
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| periodically of their chemical elements |
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| defines the sequence of elements in the table; number of protons in nucleus |
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| first column (ex: K, Na) combine 1:1 with halide elements of the 7th column, for example Cl and F, to form salts (e.g. NaCl) |
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| second column (Mg, Ca) combine 1:1 with an element the 6th column, oxygen (O), to form oxide compounds (e.g., MgO) |
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| elements of the 8th column that do not form compounds readily |
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| explained by periodic table and Bohr; when 2 atoms interact, their outermost shell electrons dictate their interactions and thus govern their bonding properties |
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| most of the table is composed of metals, an elements in which the sharing of a few electrons among all atoms results in a stable arrangement or bond |
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| structure of electron shells |
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| there are naturally occurring spaces in electron shells that can be filled by electrons, as determined by spacing and electron spin |
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1st shell
2nd shell
3rd shell
4th shell
5th shell
6th shell
7th shell |
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2 spaces
8 spaces
8 spaces
18 spaces
18 spaces
32 spaces
32 spaces |
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Rows in periodic table
1=
2=
3=
4=
5=
6=
7= |
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| electrons in outer shell: |
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| commonly involves exchange or sharing of valence electrons |
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| number of electrons in outer shell; also the combining power of atoms |
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| inert gasses (noble gasses) |
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| most stable arrangement of lowest energy because all shells are filled completely with electrons (atomic number= 2, 8, 18, or 32) |
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| to achieve the lowest energy state it can; so when atoms come near each other they may exchange or share electrons to achieve this state (total shared electrons = 2, 10, 18 or 36) |
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| Chemical bonds) strategies of the atoms: usually one of three modes... |
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| 1, give up electron(s); 2, accept electron(s); or 3, share electron(s) |
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| Chemical Bonds) result of bonding: |
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1 spontaneous- a release of energy
2 due to outside energy - may release or absorb energy |
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| Ionic bonds) atoms with one less or one more... |
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| than the "noble gas" number of atoms (2, 10, 18, and 36) are particularly unstable and tend to react very readily to gain or lose one electron in their outer shells |
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| examples of atoms with one-less-than-noble: number of electrons: |
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| H(1), F(9), Cl(17) and Br(35) |
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| examples of atoms with one-more-than-noble: number of electrons: |
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| Li(3), Na(11), K(19), & Rb(37) |
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| chemical bond in which the elctrical force between two oppositely charged ions holds the atoms together; commonly one atom gives up an electron and the other bonded atom recieves the electron |
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| electrons are continually redistributed so |
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| that they are shared by many atoms at one time |
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| Atoms "float" in a sea of electrons. Most elements are metals. Examples: Na(11e); Al(13e); Fe(26e); Cu(29e) |
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| Na readily releases its one lone electron in its outer shell to achieve a stable 10 electron configuration |
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| many gasses that are very highly compressed can act as metals |
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| 2 or more metallic elements combined in a metallic bond |
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| molecules (strongly bonded clusters of 2-millions of atoms) that share electrons (in a way, similar to metallic bonds) |
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| examples of covalent bonds: |
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| diatomic gasses H2, N2, O2 |
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| one electron from each atom is shared; example: H+H->H2 |
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| The "carbon-carbon system", complex bonding among C atoms |
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| lower energy results from sharing of outer electrons with up to 4 other C atoms |
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| study of C bonding and related bonding |
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| Long chains of C and other atoms: |
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| cholesterols, proteins, DNA, fats, etc |
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| Polarization (effect of polar molecules): electrons of neighbor atoms or molecules tend to be pushed away from positive "side" of water; |
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| polarization makes substances like water act as solvents (materials are more easily dissolved in them as a result of polarization) |
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| all charged parts of an atom (+ or -) exert electrical forces on all other neighbor atoms, so even if all atoms in a substance are electrically neutral and/or non-polar, the sum of the electrical charges within all atoms may still add up to an overall attraction |
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| minerals with layered structures (sheet like cleavage) |
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| atomic/molecular movement in a gas: |
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| random bouncing off one another; vigor of bouncing depends upon temperature and pressure of gas |
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| can be confined by a magnetic field; conducts electricity; can grade into a gaseous state (plasma-gas mixes occus in nature) |
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| most common liquid on earth, but rare on other planets as far as we know; along with biological fluids, the only fluid that is common on earth |
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| groups of atoms that occur in a regularly repeating sequences forming a structure in which atoms or molecules occur in a regular and predictable way |
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| composed on interlocking crystals |
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| groups of atoms that are may be regular on a local scale, but are not regularly distributed throughtout the solide. ex: natural volcanic glass (obsidian), made made window glass |
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| made of silcon and oxygen in a 1:4 ratio |
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| long and large molecules that are formed from numerous smaller molecules; regular pattern of atoms in one direction (polymer chain) |
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| hair, plant, cellulose, cotton, spider webs, plastics, nylon |
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| changes between liquid and solid |
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| changes between liquid and gas |
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| driving force: temperature, |
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| which included these transitions as a result of vibration energy of atoms and molecule in the substance |
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| reactions that give off energy while it occurs; when atoms or molecules combine, the total energy is less, so excess is given off (usually as heat or light) |
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| reactions that take in energy while it occurs; when atoms or molecules combine, the total energy is more, so energy must be absorbed (usually heat is applied to drive reactions) |
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