Helena FaustineProperties of Chemical Bonds

Experiment 1: Electrical Conductivity

Aim: To investigate the type of chemical bonds of four unknown compounds, through its electrical conductivity (measured by the rate of charge at one point of a circuit (A))

Hypothesis: there are three types of chemical bonds: ionic, metallic and covalent. Each bond has a different set of properties based on the strength of van der Waal attraction between elements. Covalent bonds have weak intermolecular forces. Molecular substances (covalent bonds), do not conduct electricity as, there is no sufficient contact between molecules to allow electrons to move through the chosen medium (which in this case is, water). Covalent compounds do not contain electrolytes (charged particles) in them; hence they become insulators in a solution. Ionic compounds have stronger intermolecular force between its elements. Although they are insulators in solid form, ionic compounds are free to move when diluted in aqueous solutions. As a result they can carry current, or in other words are conductors as solutions. Lastly metallic bonding, described to instead have metallic positively charged particles surrounded by a sea of electrons. In this case, the valence electrons are free and mobile thus are able to carry charges. Whether it is in solid form, or when diluted in a solution, metallic bonds should be able to carry electric charges. In the case of the experiment, if the unknown compound can conduct electricity, then the compound can be declared of either ionic or metallic bonding. Whilst, if the unknown compound fail to conduct electricity, then it is a molecular substance (covalent bond). Bibliography: 1. UC Davis. Unknown year. Metallic bonding (unknown date of update). Available at: http://chemwiki.ucdavis.edu/Theoretical_Chemistry/Chemical_Bonding/General_Principles/Metallic_Bonding (16th March 2015)2. BBC. 2014. Metal Structure and Properties (unknown date of update). Available at: http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/periodic_table/metalsrev2.shtml (16th March 2015).

Variables:Independent Variable: Chemical Bonds of four different unknown compounds (Compound A, B, C, K) Dependent Variable: The electrical conductivity of the four unknown compounds (Measured by the rate of charge flow it allows (A))Control Variable: 1. Same electrode used throughout the experiment (Graphite) 2. Dimensions of electrode are kept the same throughout (Length: 5.5 cm, Radius: 0.35 cm)3. Same amount of water used (100ml) 4. Same amount of time taken before measurement (5 seconds) 5. Same power supply used throughout the experiment 6. Same input voltage induced (9 volts) 7. The same stopwatch is used throughout8. Same amount of compound used for experiment (5g)

Table 1: Apparatus and EquipmentNo.Equipment Quantity Note/Size

1.Unknown Compound 5 gramCompound A

Compound B

Compound C

Compound D

2.Water 2000ml (= 100ml x 4 variables x 5 trials)-

3.Graphite 2-

4.Digital Scale 1Measures mass in grams

5.Beaker 1150ml

6.Power Supply1Gives 9V option

7.Stopwatch 1-

8.Ampere meter 1-

9.Alligator Clip 3-

10.Stirring Rod 1-

Procedure: 1. Prepare all Apparatus 2. Assemble the circuit: 1. Plug in the power supply to the power source 2. Attach one end of both alligator clips to the two slots located in the DC section of the power supply 3. Attach the other end of one alligator clip to the graphite4. Attach the other end of the second alligator clip to the black slot of the ampere meter5. Attach an extra alligator clip to the red slot of the ampere meter and attach the other side on another graphite3. Fill the beaker in with 100ml water 4. Weigh 5 grams of compound A on the digital scale 5. Put in 5 grams of compound A into the beaker. Stir the mixture with a stirring rod until compound A is completely dissolved in water. 6. Put in both pieces of graphite into the water; note that one should not touch the other. 7. Set the power supply to 9V8. Turn on the power supply 9. As you turn on the power supply, start the stopwatch. 10. Wait for five seconds and record the number displayed on the ampere meter. 11. Turn off the power supply and throw away the used sample solution12. Repeat steps 3-11 for four more trials 13. Repeat steps 3- 12 for compounds B, C and K

Diagram of Set-up Equipment:

Table 2: Experiment Data Table Compound type Current produced (A) by solution consisting different compounds

Trial 1Trial 2Trial 3Trial 4Trial 5

A0.480.470.460.450.46

B0.020.020.030.030.03

C2.112.092.122.112.10

K0.000.000.000.000.00

Table 3: Average data Type of compoundAverage current produced (A)

A0.464

B0.026

C2.106

K0.000

Calculation: Unit: A: Average (result)s: total value of individual values that are being averaged n: number of terms

Formula used: A =

Example calculation (Average current calculation for compound A): A= A= A= 0.464

Thus, the average current produced when the solution consists of compound A is 0.464 Ampere

Discussion:It can be seen from the graph that the strongest current that is allowed to flow is 2.106 Amperes. This strength of current is the rate of charge when graphite pieces are submerged in compound C solution. The smallest current exerted is 0.000 Amperes. No current flows when graphite pieces are submerged in compound K, in other words compound K is not an electrical conductor, whereas compound A, B and C are conducts electricity when they are diluted in aqueous solutions. Compound A showed a moderate amount of electrical conductivity, letting flow a current of 0.464 Amperes. Compound B allows very little electrical current to flow thus it is not a good electrical conductor. Compound K proves to be a good conductor for electricity. The experiment data is accurate and reliable. The experiment is conducted five times for each variable using separate samples to ensure that the collected data has no errors. The highest percentage of error is shown in compound B where the percentage is 21.066%. Even then, there is only 0.01-Ampere difference between the trials, proving that trials were handled with great degree of accuracy. Despite the fact that, collected data are closely spaced, the percentage is still quite high thus proving that there were some humane weaknesses made in this experiment. Although the time taken before measurement has been decided before hand, there is always a possibility of slipping up a few microseconds later or earlier before stopping the stopwatch, or when starting the stopwatch. This has to do with the human reaction time, and thus cannot be avoided. The amount of time before measurement plays an important part in the current exerted in the circuit, thus why it is kept constant (As shown by the formula charge = current x time, time and current are inversely proportional. Thus current decreases as time goes. This shows how time and current influences one another thus influencing the data collected.). This human mistake may be fatal for the collected data as some trial results may be the result of additional microseconds to the designated measurement time. To overcome this problem, it is required that the experiment be conducted with the help of technological aids. In this case, video cameras. Video cameras displays both time and visuals of what is happening in the present. Instead of recording based on the human reaction time, a video camera can be used as a more reliable source of time. Video cameras can be fast forwarded to adjust to the measurement time, thus giving out more accurate data.

Experiment 2: Melting Point

Aim: To investigate type of chemical bonds of four different unknown compounds through its melting point (how long it takes to melt the compound)

Hypothesis: There are three types of chemical bonds; ionic, metallic and covalent bonds. The melting or boiling point of these three bonds depends on the strength of intermolecular forces (or forces of attraction between elements). Ionic compounds have higher melting points because they have strong van der waal attraction and thus requires strong forces (heat) before elements are freed from the lattice. On the other hand, molecular substances (covalent compounds) have relatively weak force of attraction. Thus the bonds do not have to be broken in order to melt. Metallic bonds have bonds even stronger than that of ionic bonds, and thus a lot of energy is needed to break through those bonds. In relation to the experiment, the unknown compounds have to be of either one of these three chemical bonds. If the compound is shown to have higher melting points (takes more time to melt completely) then it is of ionic or metallic bonding. On the other hand, if the unknown compound have low melting points then it is a compound with covalent bonds. Bibliography: BBC, 2014. Metal structure and Properties (unknown date of update) Available at: http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/periodic_table/metalsrev1.shtml (16th March 2015)

Variables:Independent variables: Chemical bonds of four different unknown compounds (Compound A, B, C, K)Dependent variables: The melting point of these unknown compounds (measured by time taken to melt them (seconds)) Control Variables: 1. Same amount of compound used throughout the experiment (5 gr)2. The same stopwatch is used throughout 3. The same size of aluminum foil used for each trial (12x12 cm) 4. Same tripod used throughout the experiment (12 cm in diameter)5. Same Bunsen burner used throughout the experiment 6. Same distance between one compound to the other during an experiment trial (4 cm) 7. Same vertical distance between Bunsen burner and aluminum foil (1 inch) 8. Same room temperature of 28 o C9. Same digital scale used throughout experiment

Table 1: Apparatus and Equipment No.Equipment Quantity Note/Size

1.Unknown Compound 5 gramCompound A

Compound B

Compound C

Compound D

2.Tripod 1Diameter: 12 cm

3.Bunsen burner 1-

4.Lighter 1-

5.Aluminum foil 10 pieces 12x12 cm

6.Digital scale1Measures mass in grams

7.Ruler130cm

8.Stopwatch 1-

9.Scissor 1-

Procedure: 1. Prepare the apparatus 2. Place the Bunsen burner below the tripod 3. Use ruler to measure the vertical distance between the Bunsen burner and the tripod. Adjust the tripod to make sure the vertical distance is 1-inch4. Measure 5 grams of compound A and B separately on the digital scale 5. Take a piece of 12x12cm sized aluminum foil and fold it to form four equal parts. This will allow you to find its center. 6. Place compound A, 2cm from the center. 7. Place compound B, 2cm from the center in the direction opposite compound A8. Place the aluminum foil on the tripod 9. Light the Bunsen burner using a lighter 10. As the Bunsen burner is ignited, start the stopwatch 11. Stop the stopwatch when the compound is completely melted 12. Record the time displayed on the stopwatch 13. Enclose the wick (of Bunsen burner) to kill the flame 14. Repeat steps 4-13 for four more trials 15. Repeat steps 4-14 for compound C and K

Diagram of Set-Up Equipment:

Table 2. Experiment Data Table Compound type Average time taken for different compounds to melt (seconds)

Trial 1Trial 2Trial 3Trial 4Trial 5

A0.00.00.00.00.0

B10.09.38.89.19.5

C5.74.85.25.15.5

K8.09.58.27.89.0

Table 3: Average data Type of compoundAverage time taken for compounds to melt (seconds)

A0.00

B9.34

C5.26

K8.50

Calculation: Unit: A: Average (result)s: total value of individual values that are being averaged n: number of terms

Formula used: A =

Example calculation (Average current calculation for compound B): A= A= A= 9.34Thus the average time taken for compound B to melt is 9.34 seconds

Discussion: It can be seen from the graph that it takes the longest to melt compound B, in other words compound B has the highest melting point. It took 9.34 seconds for compound B to be fully melted on the aluminum foil. Compound C took the shortest time to melt, taking only 5.26 seconds in average before melting completely. Compound K proved to have a melting point somewhere in between that of compounds B and C, whilst compound A did not melt. This suggests that compound A has an extremely high melting point as it takes very long amounts of time to melt compound A completely. The data taken is extremely accurate. Again, 5 trials are done to ensure that the results are of close intervals. For this experiment, the highest percentage of error 8.47% for compounds K. this percentage is relatively low thus proving that this experiment is accurate. However, this experiment is not with no mistakes. There was an error in the experiment condition, while doing the experiment; the air conditioner was on thus affecting the direction of the Bunsen burners flame. Thus the heat produced by the Bunsen burner is not always equally spread on the aluminum causing one substance to perhaps melt faster or slower than it should. This is the reason why the intervals of data between trials were unequally spaced. If I were to do this experiment again next time, the experiment room condition should be more isolated. The room should not experience change in air humidity, temperature or artificial winds. Thus the heat would be spread more equally on the aluminum foil. To do this, air conditioning should be turned off so that the air around stays constant as is.

Evaluation and Discussion:From this experiment, the unknown compounds are divided into two categories, those who can conduct electricity when dissolved in water, and those that cannot conduct electricity. From the melting point experiment we discover two categories as well, those that have low melting points or in other words take less time to melt, and those with high melting points. Chemical bonds that can conduct electricity have either metallic bonds or ionic bonds. Metallic bonds are bonds between two or more metallic elements. Such substances would have closely packed atoms. With metallic bonds, electrons in the valence shell overlap with those of neighboring atoms thus moves from one atom to another perpetually. In other words, valence electrons are not associated with any particular atom, thus resulting on delocalized electrons meaning that, electrons move freely throughout the crystal (also known as the solid structure). This is known as non-directional bonding. The system of sea of electron or delocalized and mobile electrons creates strong bonds between metal ions within the lattice. Properties of metal owe its properties to van der Waal attraction of the substance, for instance: its electrical conductivity. The valence electrons are still relatively free when electrical fields are applied, when potential difference is applied, electrons would move to the opposing direction conducting electrical current to the other side. Corresponding to strong van der Waal attraction between ion particles of metal, it automatically takes more energy to break through bonds than other chemical bond types. This causes metal to have higher melting points, as it needs higher temperature (more heat) to break its bonds and melt. When it comes to electrical conductivity, the more electrons in its valence shell, the better it conducts electricity. This is because more electrons allow electrical current to flow from one point to another point of the lattice. Whilst when it comes to melting points, metallic bonds and its electron sea, attracts more cations (positively charged ions) thus creating a stronger structure. In cases where metals have high amount of protons in its nucleus, it would attract more delocalized electrons thus strengthening its interaction, in which case bond would also be stronger and the metal would have higher melting points. Similarly, ionic compounds can conduct electricity in aqueous solutions and has a relatively high melting point, although ionic compounds do not take electrical conductivity and melting points to an extreme level. Ionic compounds are what is known as non-directional, in other words they pack according to their relative sizes. Ionic substances are also always have local charge neutrality (positive and negative ions producing neutral states, like the structure of NaCl). In ionic bonds there are always electrostatic attractions from ions of opposing charges, thus why it has a relatively strong bond. Bonds in ionic compounds are formed when electrons from an atoms valence shell is transferred to another atom (balancing atoms). What happens then is the atom that gains becomes negatively charged, whilst the atom that lost becomes positively charged (cation). Afterwards, these two atoms become attracted to one another as they are of opposing charges. Ionic bonds are formed between non-metals and alkali earth metals. Repulsion and attraction of ionic bonds causes ionic substances to be arranged in such way so that positive and negative charges balance one another to produce neutrally charged substances. Ionic compounds do not have mobile electrons and thus cannot conduct electricity in its solid form. However, when diluted in aqueous solutions, ionic compounds can conduct electricity well. This is because; aqueous solutions disassociate ions and thus will carry charge through the solution. In ionic compound, the intermolecular attraction is relatively strong, thus there is still a need for large amounts of energy to overcome the bonds, as a result, ionic compounds have high melting points. Distinctly different from properties of the other two chemical bonds are covalent substances also known as, molecular substances. Molecular substances have low melting points and are unable to conduct electricity in solid form or when diluted in aqueous solutions. In molecular substances, it is its interatomic linkage that bonds to atoms together. In covalent bonds the binding of atoms are formed due to electrostatic forces between an electron and their two (or more) nuclei. Covalent substances are mostly insoluble. However there are rare cases in which they do, however do not form solutions as a chemical reaction takes place instead. This makes the solution consist of materials that differ from the original solute. Unlike ionic compounds, covalent compounds do not dissociate when dissolved in water, thus they do not conduct electricity. There is also insufficient amount of contact between ions of covalent compounds, and thus does not conduct the flow of electricity in solid or liquid form. Covalent molecules have relatively weak bonds, and thus requires small amount of energy to overcome its bonds and melt it. Thus why covalent molecules are usually in liquid or gas form. Out of three chemical bonds, covalent molecules are the easiest to melt. Besides its electrical conductivity, solubility can help determine which types of chemical bonds are present in a compound. Ionic compounds are the only soluble one in this case. Metallic compounds do not dissolve when mixed with water. Whilst molecular substances do not as well, however when it comes to covalent bonds there are special cases in which they do. In these special cases, the substances do not form solutions with the solvent, instead a chemical reaction takes place with hydrogen and thus produces a substance that is not the same to the original solute.

Metallic compounds Ionic compounds Molecular substances

Electrical conductivity

Melting point HighHighLow

Solubility Molecular substances are soluble however do not form a solution.

Conclusion: Now is the time to draw conclusions on whether or not these unknown compounds are of, metallic, ionic or covalent bonds. However, as it has been revealed that non of these are of metallic bonding, it leaves two possible choices choices for the unknown compounds chemical bond type: ionic and covalent. Compound A: compound A allowed electrical current of 0.464 Amperes to flow through when it is diluted in aqueous solutions. Although the current exerted is relatively weak, compound A is still a conductor. Correspondingly, compound A prove to be very difficult to melt, in fact, during this experiment we failed to melt compound A. owing to the fact that it has an extremely high melting point, and it conducts electricity, compound A has ionic bonds. Compound B: compound B allowed electrical current of 0.026 Amperes, which is very low for a current. This showcases how compound B is a very bad conductor if not an insulator; moreover it took compound B an average of 9.34 seconds to begin to melt. This is a relatively short time. Thus proving that compound B has covalent bonds. Compound C: Compound C allowed an electrical current of 2.106 Amperes, which is very high compared to the electrical current exerted when the electrical circuit goes through solutions consisting of other unknown compounds. However, compound C prove to have the lowest melting point, which in this case is 5.26 seconds. However since, it shows a relatively high electrical current, it is safe to assume that compound C has ionic bonds. Compound K: Compound K proves to not be a conductor, conducting 0 current for all trials. It also has a low melting point of 8.5 seconds. Thus shows how compound K has covalent bonds. This experiment proved my hypothesis true, I found out that metallic compounds have the strongest bonds and thus conducts electricity in solid form as well as liquid form. Ionic compounds have a relatively strong bond, and thus they also have high melting points however does not exceed that of metallic compounds. Lastly, covalent compounds have the weakest bonds and thus have lower melting points and cannot conduct electricity due to insufficient amount of contact between particles. My data corresponds to my hypothesis as well, in which compounds with ionic bonds like C and A can conduct electricity and have higher melting points. On the other hand, compounds with covalent bonds like B and K have lower melting points and cannot conduct electricity (or are bad conductors of electricity). The fact that the hypothesis corresponds with the research done also proves that it is true. In conclusion, each chemical bond has its own specific set of properties that corresponds with its structure. Metallic bonds have an electron sea and thus there are many mobile electrons that help it conduct electricity. Metallic bonds also have very strong bonds that are harder to break and thus has high melting points. Ionic compounds whose bonds depend on electrostatic forces between atoms, and thus its bonds are relatively strong. This makes ionic compounds electrical conductors (only when dissolved in water) as it does not have enough free electrons in solid form. Its relatively strong bonds also make it have high melting points. Lastly, covalent bonds whose structure depends on a shared electron between two atom nuclei. They have relatively weak bonds due to that, and thus, covalent bonds cannot conduct electricity and have lower melting points. In this experiment there were no compounds with chemical bonds. Compound A and C showed to have ionic bonds whilst compound B and K have covalent bonds.

Bibliography: 1. UC Davis. Unknown year. Metallic bonding (unknown date of update). Available at: http://chemwiki.ucdavis.edu/Theoretical_Chemistry/Chemical_Bonding/General_Principles/Metallic_Bonding (16th March 2015) 2. UC Davis. Unknown year. Covalent Bonds vs Ionic Bonds (unknown date of update). Available at: http://chemwiki.ucdavis.edu/Theoretical_Chemistry/Chemical_Bonding/Covalent_Bonds_vs_Ionic_Bonds (16th March 2015) 3. BBC. 2014. Metal Structure and Properties (unknown date of update). Available at: http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/periodic_table/metalsrev2.shtml (16th March 2015). 4. Senese. Fred, 2010. What Properties distinguish Ionic compounds from Covalent compounds? (15th February 2010). Available at: http://antoine.frostburg.edu/chem/senese/101/compounds/faq/properties-ionic-vs-covalent.shtml (16th March 2015) 5. IB Chemistry. 2011. Bonding (SL) (unknown date of update). Available at: http://ibchem.com/IB/ibnotes/bon-sl.htm (17th March 2015)