CHAPTER 2.1-2.4 NOTES 2.1 atom: the smallest quantity of matter that retains the properties of matter element: substance that cannot be broken down further into simpler substances
atoms were first proposed as an idea by Democritus (philosopher) in fifth century BC * originally thought to be indivisible but can actually be further divided into subatomic particles * number of each subatomic particles as well as their arrangements and individual natures are what determine the properties of atoms and therefore the properties of the matter they form
2.2 like charges repel and opposite charges attract (Coulomb's law)
cathode ray: negatively charged plate, electrical current sent through, cathode ray goes out from the negative plate to the positive plate, then to specific points on the screen at the end of the cathode based on if there is an electrical or magnetic field around it or the two fields cancel each other out or there is no field at all. electrons discovered using this because the negatively charged plate repelled the cathode ray, indicating the presence of negatively charged particles that were repelled by the negative charge of the first plate.
Millikan used charged oil particles to determine the mass of an electron based on the amount of electric field needed to suspend a particle between two charged plates. He used the charge to mass ratio, already calculated by another scientist, and the charge of just one individual electron to determine the mass of an electron. He deduced the charge of an individual electron based off the fact that every charge he measured was a multiple of -1.6022 x 10^-19 C(coulomb), which we now know is the charge of an individual electron.
radioactivity: spontaneous emission of particles or radiation from unstable nuclei
three types of radiation: *alpha rays: made of positively charged particles (alpha particles). repelled by positively charged plate and attracted to negative. *beta rays: made of negatively charged particles (beta particles). repelled by negatively charged plate and attracted to positive. *gamma rays: no charge, higher energy, unaffected by magnetic or electrical fields.
protons(positively charged subatomic particles) are contained in the nucleus in a concentrated core. atoms are mostly empty space, so most alpha particles can pass through with out being repelled by the positively charged nucleus. however, when the alpha particles do get close to the nucleus they experience a repulsive force, making them not able to pass straight through and are thrown off course. if they travel directly at the nucleus they may be repelled so much their direction is completely reversed.
protons have same magnitude of charge as electrons, just in the opposite direction (positive not negative), and almost 2000x the mass of electrons. nucleus is very tiny but tons of mass- occupies very little volume (atom = stadium, nucleus = marble).
use picometers (1 x 10^-12 m) for most atomic dimensions
2.3 all atoms except most common form of hydrogen (has one proton no neutrons) have both protons and neutrons (nucleons).
isotope: atoms of an element that have the same atomic number (number of protons) but a different mass number (protons and neutrons). therefore isotope is determined by number of neutrons and identified by the element's mass number.
chemical properties of an element are determined mostly by number of protons and electrons, not neutrons, so what isotope an element is doesn't have very much impact on its chemical properties.
2.4
density: mass/volume (use g/cm^3 as units) volume of the nucleus can be calculated from known radius using formula for volume of a sphere(V = 4/3 π r^3). use g/cm^3 in calculations; convert other units to cm and g beforehand.
Atomic mass unit (amu) is equivalent to 1.67 x 10^-27 kg
all those protons in one tightly packed nucleus should repel each other. great force is required to maintain a stable nucleus. short-range attraction (proton-proton, neutron-neutron, proton-neutron) accomplishes this (in this case, strong nuclear force specifically). if the short-range attraction is stronger, the nucleus remains stable; if the coulombic repulsion is stronger, the nucleus deteriorates and emits particles or radiation. the electrons are kept from flying out of the orbit of the atom by their attraction to the positive protons. the electron's velocity and attraction towards the nucleus help it maintain its orbit.
nuclear stability determined by neutron to proton ratio. the higher the atomic number, the more neutrons needed to counteract the protons' repulsion.
2, 8, 20, 50, 82, and 126 neutrons or protons are most likely to be stable (contain the most stable isotopes compared to other elements). also more stable nuclei with even number of both protons and neutrons. atomic number higher than 82 are always radioactive (unstable). technetium and promethium are ALL radioactive, every isotope. ion: atom that gains or loses electrons, giving it a net charge. anion: negatively charged ion cation: positively charged ion
atomic mass isn't a whole number because it's the weighted average of the masses of each of the element's isotopes (remember each isotope has a different mass) in the percentages they were found in in the sample used (each isotope's mass is multiplied by the percentage in which it was found in the sample). ex. sample is 99% Carbon-12 and 1% Carbon-13; C-12(0.99) is added to C-13(0.01). average atomic mass which would be shown where the decimal is in the figure above = 12.01. *the isotope whose mass is closest to the average atomic mass is the most abundant. FUNDAMENTAL PARTICLES
