Trig Lab
Step 2) Arrange the atoms and create single bonds.
The first atom listed in the molecular formula is often the central atom in the Lewis structure. (A more precise description is that the least electronegative atom is usually the central atom.) A wrong choice in the central atom will usually result in the inability to create the Lewis structure. A single bond is composed of two valence electrons and is noted as either (â— â—) or (—). In this example, 8 electrons are used to create one single bond between carbon and each of the chlorine atoms. The C atom is placed in the center and surrounded by the Cl atoms. Single lines are drawn between the atoms representing shared pairs of electrons, which may be thought of as single bonds.
Several gases are produced frequently in the laboratory and it is important to be able to identify them by their physical and chemical properties.
The gases that will be investigated in the following experiment are hydrogen (H2), oxygen (O2), and carbon dioxide (CO2). These gases will be generated using small-scale techniques through the following reactions: Hydrogen (H2):Zn(s) + 2HCl(aq) →ZnCl2(aq)+H2(g) Oxygen (O2):2H2O2(aq) MnO2−−−→2H2O(l)+O2(g) Carbon Dioxide (CO2):NaHCO3(s)+HCl(aq) → NaCl(aq)+H2O(l)+CO2(g)
If the metal has a variable charge (most metals in Groups IIIB through IIIA, and all metals in Groups IVA through VIA), then the ionic compound is named as in step 3, except
a Roman numeral is added in parentheses after the metal name to indicate the charge of the metal ion.
One way to distinguish between binary ionic compounds and binary molecular compounds is to look for
a prefix. Molecular compounds use a Greek prefix to indicate the number of each atom in the compound. Refer to Table 1.
The Lewis structure of the molecule can be drawn so that
a single dash represents the shared electrons
gas generation tube
an apparatus that contains the starting reactants involved in a chemical reaction and captures gases as they are produced. In the following experiment, a simple gas generation tube will be assembled with a test tube, a stopper having a short plastic tube through its middle, and a pipet bulb. As shown in Figure 4, the reactants are placed in the glass test tube, which is secured with the stopper. The pipet bulb is filled with water, inverted, and placed over the stopper. As the chemical reaction takes place, gas bubbles move up through the test tube and into the top of the pipet bulb. The gas slowly displaces the water in the pipet bulb; trickling down the outside of the test tube as gas takes its place in the pipet bulb. Once all of the water has been displaced, the pipet bulb may appear empty, but it is filled with the gas produced by the reaction. The isolated gas can then be subjected to further experimentation and flame tests.
The chemicals that are present before a reaction occurs are called reactants
and the chemicals produced from the reaction are called products.
Matter is defined as
any substance that has mass and volume. Matter consists of atoms which are the building blocks of molecules and compounds
tetrahedral arrangement
anytime one atom is surrounded by four other atoms (and no lone pairs), the geometry will be tetrahedral and the molecule will exist in its most stable form.
Valence electrons
are the electrons of an atom, located in the outermost shell, that are available for bonding. The number of valence electrons that an atom (element) has can be found in the periodic table. Elements in the same group (vertical column) of the periodic table contain the same number of valence electrons. See Figure 2. For example, all elements in group 7 (VIIA), including fluorine, chlorine, bromine, and iodine, have 7 valence electrons. All of the elements in group 6 (VIA), such as oxygen and sulfur, have 6 valence electrons.
EVERY time a compound contains a metal,
balance the charges of the compound when writing the formula.
octet rule
based upon the observation that atoms (other than hydrogen) are most stable when surrounded by eight valence electrons. These 8 valence electrons can either be shared (bonds) or not shared (lone pairs).
the gas sample must not be contaminated by gases that
compose the air we breathe.
the valence shell electron pair repulsion (VSEPR) model
describes the three-dimensional arrangement of the molecule. The VSEPR model arranges atoms in a manner that minimizes electron pair repulsion, maintaining the most stable form of the molecule. Consider the two-dimensional Lewis structure for methane (CH4) shown in Figure 6. The three-dimensional VSEPR model has bond angles of 109.5 degrees, placing the hydrogen atoms as far from one another as possible.
A mole (mol) is a unit of measure
describing the amount of a chemical substance that contains as many atoms, formula units, or molecules as there are in exactly 12 grams of pure Carbon (12C). One mole of a substance has 6.022 × 1023 atoms (for an element; represents Avogardro's number), molecules (for a compound), or formula units (for an ionic compound), and is equal to its molecular weight (molecular mass or formula mass). For example, the element sodium has a molecular mass of 22.99 grams, thus 1 mole of sodium is equal to 22.99 grams. Likewise, the compound H2O has a molecular mass of H + H + O (1.008 + 1.008 + 16.00), thus 1 mole of H2O is equal to 18.016 grams. The molar mass of each element is found in the periodic table. See Figure 2.
percent yield
deviation, from theoretical yield to actual yield
Stoichiometric quantities can be used to maximize the amount of product produced from the chemical reaction. For example,
f you were performing the reaction in Figure 1 and had 5.70 grams of CuSO4, you can use the balanced chemical equation and stoichiometry to determine how many grams of NaOH you would need to create the maximum amount of Cu(OH)2. More specifically, to quantitatively calculate the maximum amount of product expected through a chemical reaction, you need only a balanced chemical equation, the molar mass of each substance, and the quantity of substance available for only one of the reactants.
Use the note cards that will be created in Exercise 1
for every compound in Exercise 2.
An aqueous physical state distinguishes binary acids
from simple molecular compounds.
Lewis structure
hows how valence electrons are arranged among atoms in a molecule. In arranging valence electrons, the duet and octet rules are very important. The duet rule applies to molecules containing hydrogen, as hydrogen is most stable when sharing two valence electrons.
Unlike solids and liquids, gases have great mobility, and gas molecules are
in a constant state of random motion. Properties of gases are dependent upon the pressure, temperature, and volume of the container they are in, as well as the number of gas particles present. Gas laws are equations that can be used to find unknown values of pressure, temperature, volume, and the number of gas particles (moles).
chemical equation
is a written representation of the process occurring in a chemical reaction. Chemical equations use letters and numbers to represent the chemical elements and the amounts or ratios of those elements present that are either participating in the reaction or a product of the reaction. For example, one methane molecule contains one carbon atom and four hydrogen atoms and is denoted as CH4.
states of matter
solid, liquid, or gas. The states of matter are distinguishable by having either a fixed or fluid structure or volume
Inert gases
such as nitrogen gas and noble gases, are not flammable.
If there is no metal present in the compound
the compound is likely a molecular compound.
Molecules are surrounded by an electron cloud
the electrons belong to the entire molecule, rather than the individual atoms. It is useful, however, to model atoms and electrons in an organized manner to better understand the structure of a molecule.
According to the Law of Conservation of Mass
the mass of the products in a chemical reaction must equal the mass of the reactants.
Gases are composed of one or more elements. They are often difficult to detect because many are colorless and odorless. The human senses are unable to detect
the nitrogen, oxygen, and argon gases that are the primary components of the air we breathe. One way of detecting a gas is to observe its behavior in a chemical reaction. Gases that are produced by a chemical reaction are commonly observed as bubbles. For example, when a metal is placed in an acidic solution, bubbles may form indicating that a gas has been produced.
Oxygen fluorine, nitrogen, and carbon atoms always obey
the octet rule.
When naming ionic compounds (a metal and a nonmetal or polyatomic ion), if the metal ion has a fixed charge (all metals in Groups IA and IIA, and some metals in Groups IIIB through IIIA), then
then the cation is named first. The anion is named second: monatomic ions have the suffix "-ide," and polyatomic ions have no suffix.
Molecular modeling kits are used to visualize the
three-dimensional structure of a molecule. Lewis structures are two-dimensional.
A hydrate is a solid compound that contains
water molecules
precipitation reaction
where two solutions are mixed and an insoluble substance (precipitate) forms, which is then able to be separated or removed from the solution. The (s) after Cu(OH)2(s), denotes that a solid was formed as a product from the two aqueous (aq) reactants. The stoichiometry of a balanced chemical equation can be used to calculate the mass and number of moles of each reactant and each product in a chemical reaction.
Bonding of hydrogen fluoride (HF).
Hydrogen has two valence electrons and obeys the duet rule; fluorine has eight valence electrons and obeys the octet rule.
The goal of the VSEPR model is to
arrange the position of the atoms and lone pairs surrounding the central atom in a manner that minimizes repulsion.
allotropes
Different structural modifications of an element are referred to as
Print or write down the steps on naming ionic and molecular compounds in the background
, and use them for every example.
Double check your work. After you have written the name of a chemical compound
, cover the name and try to write the corresponding formula, and vice versa.
When writing the formula for ionic compounds
, write the symbol for the cation first, followed by the anion.
Did you know?
Chemists can have a sense of humor at times when naming molecules. Some of the more classroom "appropriate" include, Draculin which is a large glycoprotein found in vampire bat saliva. Penguinone, name from its similarity in 2D structure to a penguin. The keto acid of moralic acid, isolated from the mora tree, is named moronic acid with derivatives called moronates, as in "which moron-ate all of the pie?" Traumatic acid is a plant hormone that causes injured cells to divide and help repair trauma to the plant. Uranium has resulted in the creation of numerous silly names such as the uranium oxide anions known as urinates, uranium nitrate which is also known as uranyl nitrate, and U4+ known as the uranous ion.
Did you know?
Flammable gases are used by a variety of everyday technologies. Gas grills are fueled by propane gas (C3H8), many homes are heated by natural gas (a mixture of gases), and lighters contain "lighter fluid," which is pressurized butane gas (C4H10).
Diatomic elements do not have full valence electron shells and cannot exist as a single atom.
For example, the reactivity of hydrogen causes lone atoms to combine into diatomic (two atom) molecules forming hydrogen gas (H2(g)) or liquid hydrogen (H2(l)). Element names ending in "-gen" or "-ine" are diatomic. The names and formulas for the seven diatomic elements can be found in Table 4.
Step 4) Check your work: ensure the duet and octet rules are satisfied and count the total number of valence electrons.
Review the molecule to ensure that all atoms are surrounded by 8 valence electrons, satisfying the octet rule. Ensure that hydrogen atoms (when present) satisfy the duet rule. Count the number of electrons represented in your diagram. Ensure that the number of electrons you count matches the number calculated in step 1.
Step 3) Calculate the number of remaining valence electrons; then distribute the electrons with the goal of satisfying the duet rule or octet rule.
Since each single bond (represented by a line) contains 2 shared electrons, 8 electrons have already been added to the Lewis structure. As determined in step 1, the molecule contains 32 valence electrons total. Thus, there are 24 more electrons (32-8=24) to add to the Lewis structure. C already satisfies the octet rule. Placing the remaining 24 valence electrons around the chlorine atoms satisfies the octet rule for each Cl. The lone pairs are represented by pairs of dots.
Example 2: Oxygen gas (O2)
Step 1) Calculate the total number of valence electrons in the molecule. (2)6=12 electrons(2)6=12 electrons Oxygen atoms have 6 valence electrons, and there are a total of 2 atoms. There are 12 valence electrons total.
Example 1: Carbon tetrachloride (CCl4)
Step 1) Calculate the total number of valence electrons in the molecule. 4 + (4)7=32 electrons↑ ↑C Cl4 + (4)7=32 electrons↑ ↑C Cl Carbon is located in group 14 of the periodic table; thus, carbon has 4 valence electrons. Chlorine, located in group 17, has 7 valence electrons and there are 4 chlorine atoms total. The total number of valence electrons in the molecule is 32.
Oxidizers
Such as chlorine and oxygen gas, facilitate combustion of other materials. For example, fanning oxygen over a wood fire causes flames to surge and the carbon compounds (or carbon-containing substances) that compose the wood burn more quickly.
Flammable gases
Such as hydrogen, butane, and methane gas, burn in the presence of flame, and can be explosive in the correct proportions
stoichiometric quantities
The quantities of reactants that are needed to fully react with one another at the same time. stoichiometry can be used to determine how much of each reactant is required for all reactants to be used up at the same time.
Step 2) Arrange the atoms and create single bonds.
The two oxygen atoms should be placed in a line and linked with a single bond that represents shared electrons.
localized electron model
This model assumes that a molecule is bonded through the sharing of valence electron pairs. The localized electron model also highlights valence electron arrangement, Lewis structures, and molecular shape.
stoichiometry
This quantitative proportion which can be used to determine how much of each reactant is needed to produce a specific amount of each product.
Step 3) Calculate the number of remaining valence electrons; then distribute the electrons with the goal of satisfying the duet rule or octet rule.
Two electrons (held in 1 single bond) have already been added to the Lewis structure. This molecule has 12 valence electrons total, as determined in step 1. Ten more electrons must be added, and this can be accomplished through a trial-and-error process. Creating a double bond between the atoms and then adding lone pairs satisfies the octet rule for all atoms and also generates the correct number of valence electrons. (Double bonds represent 4 shared electrons.) Consider the outcome if the Lewis structure was drawn with a single bond, and the octet rule was fulfilled. The total number of electrons would be 14. In step 1, we determined that the molecule has 12 valence electrons, so we know that the Lewis structure below is incorrect, even though the octet rule is fulfilled. Consider the outcome if the Lewis structure was drawn with the correct number of total valence electrons and a single bond. The Lewis structure below is incorrect because, although 12 electrons are present, the octet rule is not fulfilled. Remember this tip: Multiple bonds are used ONLY when there are not enough lone pairs present for each atom to fulfill the octet rule. In the incorrect Lewis structure above, we know a multiple bond is needed because the correct total valence electrons are present but the octet rule is not fulfilled.
When a molecule has more than one interior atom
more than one geometry may be used to describe the molecule
To test the gas or gases produced during a chemical reaction, the gas
must first be captured.
Resonance
occurs when there is more than one option for the Lewis structure model.
solid
phase of matter consists of particles that are closely packed into a fixed volume and shape.
liquid
phase of matter has a fixed volume but a fluid shape, giving it the ability to conform to the shape of its container.
gas
phase of matter has no fixed volume or shape, conforming to both the shape and the volume of its container
a chemical equation will also quantitatively identify the
proportion of reactants to products