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52 Cards in this Set
- Front
- Back
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Which sequence of Group 18 elements demonstrates a gradual decrease in the strength of the Van der Waals forces? All the choices are elements in the liquid state.
1. Ar, Kr, Ne, Xe 2. Kr, Xe, Ar, Ne 3. Ne, Ar, Kr, Xe 4. Xe, Kr, Ar, Ne |
4. Xe, Kr, Ar, Ne
Van der Waals forces are weak forces of attraction between molecules. These forces decrease as the molecule gets smaller and increase as the molecule increases. Look at the periodic table and notice how in answer 4, the elements are getting smaller. Therefore the Van der Waals forces would also be decreasing. |
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This question may require the use of the Chemistry Reference Tables or the Periodic Table of Elements.
Which formula represents a molecular substance? 1. CaO 2. CO 3. Li2O 4. Al2O3 |
2. CO
Use Ref. Table S to determine the electronegativity difference of each of the choices. The difference between C (2.6) and O (3.4) is 0.9 or in the range of covalent bonding (covalent bonds have electronegativity differences of less than 1.7). The other three compounds have differences in the ionic bond range or over 1.7. |
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Which substance is an example of a network solid?
1. nitrogen dioxide 2. sulfur dioxide 3. carbon dioxide 4. silicon dioxide |
4. silicon dioxide
Only silicon dioxide forms a network solid, a network of covalent bonds extending throughout the crystal without forming a molecule. |
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This question may require the use of the Chemistry Reference Tables or the Periodic Table of Elements.
Which combination of atoms can form a polar covalent bond? 1. H and H 2. H and Br 3. N and N 4. Na and Br |
2. H and Br
See Reference Table S. The electronegativity difference between H (2.1) and Br (3.0) is 0.9. If the difference is less than 1.7 (but not zero, usually more than 0.4), a polar covalent bond is formed. A nonpolar covalent bond is formed when the difference is close to zero (usually up to 0.4). If the difference is more than 1.7, an ionic bond is formed. |
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This question may require the use of the Chemistry Reference Tables or the Periodic Table of Elements.
A strontium atom differs from a strontium ion in that the atom has a greater 1. number of electrons 2. number of protons 3. atomic number 4. mass number |
1. number of electrons
Strontium has 2 valence electrons in its outer shell. It is easier to lose these 2 electrons than it is to gain 6 more electrons. Losing 2 electrons will give the strontium ion a charge of +2. Ions are charged atoms. An neutral atom has no charge because it has the same number of protons and electrons. An ion can have more or less electrons than an atom of the same element does. A strontium atom would have 2 more electrons than a strontium ion. |
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This question may require the use of the Chemistry Reference Tables or the Periodic Table of Elements.
Which bond has the greatest ionic character? 1. H---CL 2. H---F 3. H---O 4. H---N |
2. H---F
See Ref. Table S. H has an electronegativity of 2.1 and F has an electronegativity of 4.0. Subtract the two values and the difference is 1.9. Ionic bonds have differences of 1.7 or greater. Find the electronegativity differences for the other choices. H--F has the greatest difference and is the most ionic of the choices. |
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organic chemistry
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study of the compounds of carbon; how C, H, O , N combine by sharing e- pairs to form bonds and ultimately molecules.
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diameter of nucleus of atom
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10^-14 to 10^-15 meters
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extra-nuclear space where e-'s are found has a much larger volume with a diameter of ?
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10^-10 meters
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shell
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region of space around a nucleus that can be occupied by e-'s, corresponding to a principle quantum number.
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Quantum mechanics
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The branch of science that studies the interaction of matter and radiation.
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Quantized
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Having specific values for energy and momentum.
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Delocalization
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the spreading of electron density over a large volume of space.
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The 1 shell contains how many electrons
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2
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The 2 shell contains how many electrons
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8
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the 3 shell contains how many electrons
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18
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the 4 shell contains how many electrons?
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32
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from lowest to highest relative energies of electrons
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lower --> 1-2-3-4-->higher
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shells are divided into subshells s,p,d,f.... and within these subshells electrons are grouped into orbitals. What is an orbital?
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region of space that can hold 2 electrons.
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1st shell contains what?
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a single orbital called a 1s orbital holding two electrons.
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the 2nd shell contains what?
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one s orbital and 3 p orbitals . each orbital holds two electrons. the three 2p orbitals reflect orthogonal angular momentum states in 3-D space.
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Orthogonal
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in all cases, means having no net overlap. Results in 90 degree angles b/t the orbitals. Directed along the x,y, and z axes with designations 2Px, 2Py, and 2Pz.
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The 3rd shell contains what?
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one 3s orbital, three 3p orbitals and five 3d orbitals.
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ground state electron configuration
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every atom has an infinite number of possible electron configurations. the lowest energy electron configuration for an atom or molecule.
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The Aufbau (:Build-Up") Principle
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The Aufbau principle (from the German Aufbau meaning "building up, construction": also Aufbau rule or building-up principle) is used to determine the electron configuration of an atom, molecule or ion. The principle postulates a hypothetical process in which an atom is "built up" by progressively adding electrons. As they are added, they assume their most stable conditions (electron orbitals) with respect to the nucleus and those electrons already there.
According to the principle, electrons fill orbitals starting at the lowest available (possible) energy states before filling higher states (e.g. 1s before 2s). The number of electrons that can occupy each orbital is limited by the Pauli exclusion principle. If multiple orbitals of the same energy are available, Hund's rule states that unoccupied orbitals will be filled before occupied orbitals are reused (by electrons having different spins). |
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What three rules must you follow in placing electrons in orbitals?
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The physical and chemical properties of elements is determined by the atomic structure. The atomic structure is, in turn, determined by the electrons and which shells, subshells and orbitals they reside in. The rules af placing electrons within shells is known as the Aufbau principle. These rules are:
1. Electrons are placed in the lowest energetically available subshell. 2. An orbital can hold at most 2 electrons. 3. If two or more energetically equivalent orbitals are available (e.g., p, d etc.) then electrons should be spread out before they are paired up (Hund's rule). |
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The Aufbau (:Build-Up") Principle
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orbitals fill in order of increasing energy, from lowest to highest. Orbitals fill in the order 1s,2s,2p,3s,3p.....
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Pauli Exclusion Principle
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No more than two electrons may be present in an orbital. If two electrons are present, their spins must be paired.
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two electrons with opposite spins are said to have
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paired spins. Just as the earth has N and S poles, so do electrons. called spin states. The quantum mechanical property of spinn gives an electron a tiny magnetic field and when their tiny magnetic fields are aligned N-S, the electron spins are paired
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Hund's Rule
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When orbitals of equal energy are available but there are not enough electrons to fill all of them completely, one electron is put in each before a second electron is added to any.
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energy-level diagrams
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chemist use these to pictorially designate where electrons are placed in an electron configuration.
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Write and compare the ground state electron configurations for each pair of elements.
C and Si O and S N and P |
C (6e-) 1s^2, 2s^2, 2p^2
Si (14e-) 1s^2, 2s^2, 2p^6, 3s^2, 3p^2 O (8e-) 1s^2, 2s^2, 2p^4 S (16e-) 1s^2, 2s^2, 2p^6, 3s^2, 3p^4 N (7e-) 1s^2, 2s^2, 2p^3 P (15e-) 1s^2, 2s^2, 2p^6, 3s^2, 3p^3 |
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Show how each chemical change leads to a stable octet:
S forms S^-2 and Mg forms Mg^2+ |
S (16e-) 1s^2, 2s^2, 2p^6, 3s^2, 3p^4
forms S^-2 (18e-) 1s^2, 2s^2, 2p^6, 3s^2, 3p^6 Mg (12e-) 1s^2, 2s^2, 2p^6, 3s^2 forms Mg^2+ ( 10 e-) 1s^2, 2s^2, 2p^6 |
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Summary of Hund's rule
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1. each orbital fills with one electron before the next is filled with a single electron
2. Electrons "spread out"into different orbitals before pairing up into individual orbitals. 3. Electrons fill orbitals with the same spin before "spin pairing" |
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a pair of electrons that are associated with a single nucleus
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nucleus means proton
_ :C:::N: ^ The neg sign indicates an extra proton that is attached to this pair of electrons. the 6 dots in the center indicate a triple bond. |
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2 pairs of valence electrons shared b/t 2 atoms
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O : : C : : O . . ^ . . the double bond b/t the O and C |
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an atom that shares 3 pairs of electrons with other atoms and is associated with one lone pair
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:C:::N: ^ |
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Sulfur
SF4 |
Sulfur has 4 bonds (that adds up to eight electrons) and has one lone pair (with two electrons.
This is an exception to the OCTET RULE |
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Term : Aufbau principle
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Definition : The principle that atomic orbitals are filled one at a time, starting with the orbital that has the lowest energy.
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VSEPR is based on twin concepts
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Atoms are surrounded by regions of electron density.
Regions of electron density repel each other. |
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To determine if a molecule is polar, we need to determine
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if the molecule has polar bonds and
the arrangement of these bonds in space. |
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each wave function is called
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an orbital
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wave fxn or wave/particle duality determined by who?
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Louis deBroglie
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energy is quantized E=hv light has particle properties
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Albert Einstein
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Erwin Schrödinger:
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wave equation
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wave function,
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: A solution to a set of equations that depicts the energy of an electron in an atom.
each wave function is associated with a unique set of quantum numbers. |
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orbital.
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each wave function represents a region of three-dimensional space and is called an
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2
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is the probability of finding an electron at a given point in space.
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Antibonding MO
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...
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Bonding Molecular orbital
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A MO in which electrons have a lower energy than they would have in isolated atomic orbitals.
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Sigma () bonding molecular orbital:
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A MO in which electron density is concentrated between two nuclei along the axis joining them and is cylindrically symmetrical
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A principle of valence bond (VB) theory
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is that bonds are created by the overlap of atomic orbitals.
Therefore in VB theory, bonds are localized between adjacent atoms rather than delocalized over several atoms as in MO theory. The VB model correlates with Lewis pictures where two electrons are visualized between atoms as a bond. However, localization of bonds between atoms presents the following problem. In forming covalent bonds, atoms of C, N, and O use 2s and 2p atomic orbitals. If these atoms used these orbitals to form bonds, we would expect bond angles of approximately 90°. However, we rarely observe these bond angles. |
