Unit 2 Study Topics

What is an orbital? An orbital is just the area with the highest probability of finding an electron. We don’t know how an electron is moving There is a fundamental limitation to just how precisely we can know both the position and momentum of a particle at a given time. So, we use orbitals to show the most likely locations of an electron

#2 Where are the different subatomic particles found? Which vary in number for a given element, what are atoms called when these numbers change? What particle # never changes for an element? Which particle is easy to remove from an atom? e- in an orbital surrounding the nucleus p+ in the nucleus no in the nucleus e- can vary, called an ion n0 can vary, called an isotope P+ never change for an element e- are the easiest particle to remove from an atom

#3 Valence e- is an electron in an atoms outmost electron shell Everything in group 1 has 1 valence electron (H, Li, Na, K, Rb, Cs, Fr) Everything in group 2 has 2 valence electrons Ignore the middle part for now (transition metals and rare earth elements). Everything in group 13 has 3 valence electrons. Groups 14-18 have 4-8 valence electrons respectively Therefore, group # on the PT helps to identify the # of valnce e-’s

#4 Atomic number- number of protons Atomic mass- average mass of all isotopes for a given element Group number- vertical columns, families of elements with similar properties like reactivity and # of valence electrons Period number- horizontal rows, represents 3 of energy levels for elements in that row

#5 A mole is unit of measurement that represents an amount of something. 1 mole = 6.022 x 1023 particles Particles can be anything( atoms, molecules, ions, pencils, blades of grass, etc.) Similar to how a pair of anything is always 2 of that something

#6 The main significance of Heisenbergs work is: The more accurately we know the particle’s position, the less accurately we can know it momentum and vice versa. We can’t know the exact motion of the electron around the nucleus. The area that an electron orbits is called an “electron cloud”

#7 The mass of a p+ is 1amu The mass of a no is 1 amu The mass of an e- is 0.0006amu Protons and neutrons have equal masses, and the electron is essentially massless

#8 Democritus- first theorized atoms. Thought matter could not be divided infinitely. At some point one would have to reach a smallest possible piece. Labeled it the atom. He had no evidence to support the idea. John Dalton- experimented with gases and found they acted as if made of tiny microscopic solid particles. He predicted the formation of multiple compounds between two elements. He also offered an explanation of known observations from the time that become known as Daltons Atomic Theory. Daltons atomic theory Elements are made of tiny particles called atoms All atoms of a given element are identical The atoms of a given element are different from those of any other element Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same numbers and types of atoms Atoms are indivisible in chemical processes. Meaning atoms are not created or destroyed in chemical reactions, just rearranged

#8 con’t JJ Thomson- preformed the cathode ray experiment. Showing that negative particles could come form neutral elements. This showed the atom was divisible into smaller things. He successfully identified a negative particle, the electron. As a result he produced the ‘Plum Pudding Model’ of the atom Ernest Rutherford- Gold foil experiment. fired protons at a sheet of gold foil most went through unaffected, some bounced away. there is a small dense area of positive particles at the center of the atom- the nucleus electrons are scattered near the outside of the atom with mostly empty space between the nucleus and the electrons. Added a nucleus with electrons surrounding it to our atomic model Niels Bohr- electrons move in definite orbits around the nucleus. These orbits or energy levels are located at certain distances from the nucleus. Identified discrete amounts of energy being absorbed or emitted which was different for different elements. Added energy levels to our model of the atom

#8 Con’t de Broglie- stated that electrons (particles) have wave properties, and he viewed these as standing waves, like those produce when a guitar string is plucked (classical physics.) Schrodinger- assumed that the electron in Hydrogen behaves as a standing wave. When Schrodinger’s equation is analyzed, many solutions are found. Each solution represents an atomic orbital. An atomic orbital is the most probable location for finding an electron. Heisenberg- uncertainty principal- The more accurately we know the particle’s position, the less accurately we can know it momentum and vice versa. We can’t know the exact motion of the electron around the nucleus. The area that an electron orbits is called an “electron cloud”

#9 Atomic mass is the average mass of all the isotopes for a given element. multiply mass of an isotope by # of atoms or abundance. Do this for all isotopes Add these totals together for total mass of the atoms Divide this answer by the total number of atoms or by the sum of the abundances This is your average atomic mass

#10 Four main forces of nature are gravity, electromagnetism, strong nuclear force, and weak nuclear force Forces holding an atom together(electromagnetic, gravity, strong nuclear force) Gravity- attraction between masses. Holding subatomic particles together Electromagnetism- attraction between opposite charges. Holds protons and electrons together. Strong nuclear force- works over extremely short distances, balances the repulsion of like charged protons, keeping them in the nucleus rather than them being forced apart by repulsion

#11 Niels Bohr and his research over light emitted by different elements Discrete means specific amounts These specific amounts of energy released by elements corresponds to their electrons locations or energy levels Niels Bohr- electrons move in definite orbits around the nucleus. These orbits or energy levels are located at certain distances from the nucleus. Identified discrete amounts of energy being absorbed or emitted which was different for different elements. Added energy levels to our model of the atom

#13 Protons = atomic number Neutrons = mass number – atomic number Electrons = protons In Ions, charge shows the change in electrons. Positive charge = loss of electrons. Negative charge = gain of electrons

#14 Niels Bohr- electrons move in definite orbits around the nucleus. These orbits or energy levels are located at certain distances from the nucleus. Identified discrete amounts of energy being absorbed or emitted which was different for different elements. Added energy levels to our model of the atom Discrete means specific amounts of energy. As electrons move from excited back to the ground state they release a certain amount of energy that corresponds to their orbital and energy level

#16 Masses are decimals on the PT because they are averages of all isotopes for that element. They are not specific to an individual atom but rather a representation of all forms of that element