What You Should Know So Far.

Since September we’ve practiced chemistry.  Below is a somewhat comprehensive list of all the things you should know how to do, and a bunch of words you should understand enough to use in a sentence, and define.  Review it and see if there is anything here that you might need to ask about.

Matter, homogeneous, heterogeneous, mixture, atom, molecule, HONClBrIF twins, metal, nonmetal, Periodic Table, counting protons, neutrons and electrons in any atom.

Converting back and forth from:

grams to milligrams or kilograms; meters to centimeters and kilometers and inches, feet, yards, or miles.  Going from seconds to years, or mlliliters to gallons or liters, centigrade to Kelvin.

Being able to compute density from mass and volume, or volume when given mass (density is on table S), or figuring the mass when given volume (density is still on table S).

Significant Figures:  the math rule is that your answer in any math problem is limited to the LEAST amount of sig figs in the math.  Any time you use an equality, or known value (from table S) those numbers have unlimited SF.  They will never limit your answers.  You must pay attention to the numbers you use, say it out loud in your head how many SF they have as you write them, then round only once at the end to the proper number of SF.

There are several zero rules, that cover every situation.  Look again at the Significance of Significant figures handout.  And again.  And again.

Particle diagrams are cartoons to help you think and grasp vocabulary words like the ones in the first line of this note. Also to help you imagine solids, liquids and gases.  Each symbol means an atom.  If two are touching they are bonded.  Two or more different ones touching means a compound.  Two of the same symbols touching means HONClBrIF twins.  etc.

Noble Gases are in group 18.  Metals are all on the left side of the “staircase” on the table.  Nonmetals are all on the right side of the stairs.  Hydrogen is weird, it’s a nonmetal but it’s “sorta-like” in group 1 too.  It is a nonmetal.  Groups go up and down on the table, there are 18 groups in total.  Periods go left to right, there are 7 periods on the table.  Atoms in the same group are similar.  Atoms in the same period have the SAME number of electron orbitals, but are not alike.  Atoms in period 2 have 2 orbitals.  Atoms in period 5 have five orbitals.

Protons and neutrons live in the nucleus of the atom.  Each has mass of 1 atomic mass unit (1 amu) in high school, although in real science they are both slightly more than 1.00000 and not quite exactly equal.  Electrons fly around the nucleus, and in high school they have no mass, which is untrue, but the mass is so small that in our level of chemistry it doesn’t matter.

Protons have charge of +1, which is equal and opposite to the charge of electrons at -1.  Neutrons have no charge.  One proton and one electron sum to no charge.  Atoms have equal numbers of protons and electrons which makes all atoms electrically neutral.  The mass of an atom on the periodic table has decimals, and you don’t know why yet, you will soon.  Those decimals are not the mass of the electrons.  We will round the atomic masses to the nearest whole number.

The mass of an atom equals the total number of protons plus neutrons in the nucleus.  As an example, aluminum has mass of 27 amu.  That means there are 27 total protons plus neutrons.  We know that the atomic number for aluminum is 13 (most unfortunate!) which means of the 27 nuclear particles, 13 of the are protons.  27 – 13 = 14 left over.  The 14 are the neutrons.  Since aluminum has 13 positive protons, it must have 13 negative electrons.  It does.  Those electrons live in particular orbitals:  2 in the first orbital, 8 in the second orbital, and the last 3 live in the third orbital.  The electron configuration for aluminum is 2-8-3, and if you add 2 + 8 + 3 = 13 total.

This 2-8-3 electon configuration is called the ground state, which is the lowest energy state for this atom.  It turns out if you heat up, or run electricity through, or zap with radiation, atoms can get “excited”, which is the technical term.  Atoms change the electron configuration from ground state to excited state.  If aluminum is 2-8-3 in the ground state, an excited state could be 2-7-4.  Still thirteen electrons, but no longer in the lowest possible state.  This is a temporary shift, and unstable, so the atoms will revert back to the ground state, but must emit that exact amount of energy they gained, as visible light.

Since each atom (and each compound) has a unique number of protons, pulling on unique numbers of electrons, it takes unique amounts of energy to excite any atom or compound.  That amount of energy is called a quanta of energy.  Once sufficient energy is absorbed, an electron (or more than one) has enough energy to “jump” to a higher orbital temporarily.  This electron soon “decides” to go back to the ground state, but to do that has to emit that exact amount of energy it gained to jump up in the first place.  The energy released is visible light, and is called spectra.  Every atom and every compound has unique spectra, like it’s fingerprint.

The modern model of the atom has evolved over a long period of time due to the work of many scientists.  We learned of Democritus, Dalton, Thomson, Rutherford, Bohr, and then the modern atom.

Democritus “thought” of the ultimate particle which he called ATOMOS or atoms in English.

Dalton came up with Atomic Theory, and the billiard ball model.

Thomson discovered the electron with a cathode ray tube, and made up the plum pudding model.

Rutherford did the gold foil experiment and said atoms had positive nuclei, with electrons flying around the outside (somehow).

Bohr was really a physicist who did math to prove Rutherford’s model worked for little hydrogen atoms, but no one could do the math for the larger atoms.  He also showed us atoms had electrons living in “orbits” like planets.  Each orbit was an energy level, and electrons could “jump up” if they gained a uniquely required quanta of energy.  They returned to the ground state configuration when releasing this energy as visible light.  He showed us that we could measure that visible light called spectra, like an atom fingerprint, or even a compound fingerprint.

The modern model of the atom is more complex.  Electrons live not in orbits, but in orbitals or zones of where they are most likely to be found.  The model is statistically based, not really on the exact locations of electrons.  Orbitals are still energy levels.

Electron orbitals are sized, the first orbital is smallest and can fit up to 2 electrons.  The second orbital fits up up 8 electrons.  The third, and subsequent orbitals all can fill, or stretch bigger and feel full with more electrons living in them.  The third orbital can “fill up” with 8 electrons, or be super stretched by sub-orbitals to hold up to 18 electrons.    If you can’t remember how many electrons fit into any orbital, look at the electron configurations of group 18 noble gases.  They all have ONLY full orbitals.

Their full electron orbitals are as follows.

Helium 2………………………….. only 2 electrons fit in the first full orbital
Neon 2-8…………………………..2 electrons in first orbital, 8 fit into second,both full
Argon 2-8-8……………………….three full orbitals in a row
Krypton 2-8-18-8………………..four full orbitals, but here the 3rd orbital “stretched out” to hold 18!
Xenon 2-8-18-18-8……………..five full orbitals
Radon 2-8-18-32-18-8…………six full orbitals, but the fourth stretched to hold 32!