Resonance structures must have same connectivity.

Slides:

Advertisements

Similar presentations

The term valence refers to the outermost shell.

Advertisements

QUESTION: A 25.0 gram sample of a compound is found to be 24% chlorine by mass. What is the percentage of chlorine in a 50.0 g sample of the compound?

Bohr assumed electrons move around the nucleus in circular orbits.

Step 1. Count number of valence electrons

Na: 11 electrons, Na+: 10 electrons

A mole of atoms contains exactly 6.02x1023 atoms.

Mass of proton : x kg, or u QUESTION: Which of the following has the largest total mass? A. 2 protons + 4 electrons B. 2 neutrons.

QUESTION: Which of the following elements is a transition metal? A. silicon, B. lead, C. sodium, D. chromium SCRIPT: Which of the following elements.

A dot represents a valence electron.

Which is the correct Lewis structure of nitrite ion, NO2-?

SO3: one Sulfur atom: 16 protons

Uncertainty of g: tenths place

Choice B: Br2(l)  Br2(g)  2 Br(g)  2 Br+(g) + 2e-

Which of these is the formula of a reactant in this reaction?

Which of the following has the largest size? A. K, B. K+, C. Se, D. Li

Ions are formed by loss or gain of electrons.

If w=1, then which of these is true? A. y=2, B. z=3, C. x=6

QUESTION: Consider the following partially-drawn structure of 2-butene (C4H8) where only the C atoms are shown: C-C=C-C When this structure is completed.

QUESTION: Which of the following describes an anion? A. a sodium ion (Na+), B. a calcium ion that has lost 2 electrons C. an ion with 8 protons and 10.

QUESTION: Which of the following is a metalloid? A. Potassium, B. Silicon, C. Iron, D. Helium SCRIPT: Which of the following is a metalloid? A.

Steric number of C in the structure is 3  sp2 hybrid

Mass of proton or neutron: 1.0 u Mass of electron: u

Trends in atomic size: opposite of trend in ionization energy

QUESTION: Which of the following elements is the best electrical conductor? A. carbon, B. germanium, C. manganese, D. iodine SCRIPT: A. carbon,

Ions are formed by loss or gain of electrons.

Ammonium sulfide is an ionic compound. Cation is ammonium ion. NH4+

A. 0.8 g/mL, B g/mL, C g/mL, D. 1.3 g/mL

To construct the ground state electron configuration,

There are 3 orbitals in a p subshell (ml = -1, 0, or +1).

Ions are formed by loss or gain of electrons.

Bond angles depends on steric number of the atom at the vertex.

QUESTION: How many atoms in the acetic acid molecule (CH3COOH) are capable of hydrogen bonding interaction with water molecules? A. 1, B. 2, C. 3, D.

Isolated O atom: 6 valence electrons

The molecule shown in the figure has two blue spheres.

QUESTION: Which of the following is not a valid name for an atomic orbital? A. 1s, B. 2s, C. 2d, D. 3p Principal quantum number (n) is the number.

QUESTION: Which type of element has the lowest electronegativity? A. a metal, B. a nonmetal, C. a metalloid Electronegativity is a measure of the.

Mathematically, this implies that the ratio of the amount of element

QUESTION: What is the electron configuration of Fe3+? A. [Ar] 4s2 3d6 B. [Ar] 4s2 3d3 C. [Ar] 4s1 3d4 D. [Ar] 3d5 SCRIPT: What is the electron configuration.

How many neutrons does an O-18 atom have? A. 8, B. 10, C. 16, D. 18

QUESTION: How should the result of the following calculation be reported, assuming that 1.8 and 32 are exact numbers? 32 + (1.8)(2.37) A. 36,

Steric number of C in the structure is 3.

What is the Kelvin temperature equivalent to 50.00oF?

HIGHLIGHT carbon in legend

The oxygen-to-carbon ratio in that sample is x over 36.0 HIGHLIGHT

Uncertainty is at least +1/10 of smallest interval.

We can look up isotopic abundance for Mg and find:

B. Mg + O2  MgO + O C. Mg2 + O2  2 MgO D. 2 Mg + O2  2 MgO

Choice A is obviously a correct formula --- it has four hydrogen atoms

Allowed values of principal quantum number (n): positive integers

Which figure below best represents an aqueous solution of CaCl2?

Valence electrons: Cl – 7, O – 6, C – 4, N – 5

Oxoanions have names ending in “ate” or “ite”

Therefore, the correct answer is A.

Ions are formed by loss or gain of electrons.

For which pair of molecules does dipole-dipole interaction occur?

CLICK PAUSE END RECORDING

QUESTION: What is the maximum number of of electrons that can be assigned to a 2p orbital of an atom? A. 2, B. 3, C. 6, D. 10 Pauli’s Exclusion.

A. an element and two compounds, B. two elements and a compound,

QUESTION: Assume that circles and squares in the figure below represent atoms. According to Dalton’s theory, which of the changes indicated is possible?

X-78: mass=78.0 u, abundance = 30.0%

For n=1, 2(1)2 = 2. Ex. H cannot exceed a duet.

QUESTION: Which of the structures below is valid for the HOCl molecule? A. 1, B. 2, C. 3, D v.e. 12 v.e. 10 v.e. SCRIPT: Which of the structures.

0.800 m has three significant digits

What do molecules and polyatomic ions have in common?

We now have a mixture of 3 substances --- the original compound

QUESTION: Which of the Lewis structures shown below for azide ion (N3-) has a nitrogen atom with a formal charge of +2? A. Structure I only, B. Structure.

80.00 g has four significant digits

represented by a pair of filled circles,

Mole is a group count (just like dozen).

Which of the following is not a balanced chemical equation?

Presentation transcript:

Resonance structures must have same connectivity. QUESTION: Which of the structures shown below are resonance structures? A. Structures I and II, B. Structure II and IV, C. Structures I and III, D. Structure II and III SCRIPT: 3-7-1 Which of the structures shown below are resonance structures? A. Structures I and II, B. Structure II and IV, C. Structures I and III, D. Structure I and IV CLICK Resonance structures refer to different ways of distributing electrons, for atoms that are connected the same way. So, the first thing we look for is a pair of structures where the atoms are connected the same way. For a triatomic molecule, it’s fairly simple. Note that in structures one and three, Sulfur is between Carbon and Oxygen HIGHLIGHT S in both structures We say that the connectivity of the atoms is the same So, structures one and three COULD be resonance structures. …. So, choice C is a possible answer at this point. CALLOUT Put “?” next to choice C. In structures two and four, Carbon is between oxygen and sulfur. Choice B is also a possible answer at this point… CALLOUT Put “?” next to choice We can rule out choice A. Structures one and two cannot be resonance structures --- the atoms are connected differently. CROSS OUT choice A We can also rule out choice D. Structures two and three have different connectivities. CROSS OUT choice D. How do we decide between B and C? For two structures to be considered resonance structures, they must have the same total number of valence electrons. Resonance structures differ only in the way the electrons are distributed. Let’s examine structures one and three… Structure one has sixteen valence electrons… Eight Plus eight CLICK equals 16. Structure three, on the other hand, has only twelve valence electrons…. Six Plus six Equals twelve. Therefore, structures 1 and 3 are not resonance structures. In fact, structure three is not even a valid Lewis structure. The sulfur and oxygen do not folow the octet rule. Obviously structures 2 and 4 are resonance structures. Structure two has 8 CLICK plus 8 CLICK or a total of 16 valence electrons And structgure 4 has CLICK or a total of 16 valence electrons as well. The correct answer is B. PAUSE END RECORDING Resonance structures must have same connectivity. Resonance structures are just different ways of distributing valence electrons –-- must have same total number of valence electrons.

Video ID: 3-6-1 © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08