For my sample work, please refer to my Science ACE Project titled "A Case Study On Covalent Bonding", because it cannot be uploaded here. Thank you!
Friday, March 11, 2011
Science e-Portfolio Post 4
Science e-Portfolio Post 3
This is my 3rd reflection for Term 1. Please enjoy!
Independent Study
While learning this term’s topics, I have the following questions as reflected in section A, and through my self study here is my understanding.
What are the different kinds of Covalent Bond?
There are two types of covalent bonding:
- Non-polar bonding with an equal sharing of electrons between both atoms.
- Polar bonding with an unequal sharing of electrons between two different atoms. If one atom exerts a stronger pull on the electrons than the other, then we have a polar bond. Of course, there is a wide range in the degree of polarity.
What affect the kind of chemical bonding between the atoms?
Electronegtivity. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.
• No electronegativity difference between two atoms leads to a pure non-polar covalent bond.
• A small electronegativity difference leads to a polar covalent bond.
• A large electronegativity difference leads to an ionic bond.
How to compute the formal charge for polyatomic ?
Here is an abstract from http://library.thinkquest.org/C006669/data/Chem/bonding/lewis.html regarding the calculation of the formal charge.
- Divide each covalent bond down the middle, distributing one electron from the two bonding electrons in the covalent bond to each atom that formed that bond.
- Add up the electrons directly surrounding each atom after this division has been done.
- Compare the total number of electrons around each individual atom in the Lewis Structure to the number of valence electrons in each respective neutral atom.
- If the atom in the Lewis Structure has more electrons than its respective neutral element, the formal charge on that atom is negative. The number of the formal charge is equal to the difference between the electrons around the atom in the Lewis Structure and the valence electrons of the respective neutral atom.
- If the atom in the Lewis Structure has fewer electrons than its respective neutral element, the formal charge on that atom is positive. The number of the formal charge is equal to the difference between the valence electrons of the respective neutral atom and the electrons around the atom in the Lewis Structure.
- Find the net formal charge (i.e. formal charge of the overall molecule or ion) by adding up all the formal charges of each atom in the Lewis Structure. The net formal charge should be the same as the charge on the molecule or ion. Therefore, neutral molecules should have a net formal charge of 0.
Learning more about Atomic structure – Electron Orbital Configuration
Electrons Orbital Sub Shell Energy Level
| Sub-shell type | # of sub shells/ shell | Sub-shell shape | # Electrons / Full sub shell |
| S | 1 | Spherical | 2 |
| P | 3 | Dumbell | 6 (2 x 3) |
| D | 5 | X-shaped | 10 (2 x5) |
| F | 7 | Complex | 14 (2 x 7) |
Each single S orbital has two electrons in it. Each P orbital has two electrons in it and as there are three of these orbitals in a P sub-shell, the total electron number is six. D has five orbitals in its subshell, containing ten electrons (two in each orbital) when full, which form a dumbell-esque shape. F has seven orbitals each containing two electrons.
The following is the order for filling the "subshell" orbitals, which also gives the order of the "blocks" in the periodic table:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s,5f, 6d,7p
Thus the maximum number of electrons for energy level 1,2,3 and 4 are 2,8,18 and 32 respectively.
Refer to this website for the details electronic configuration of the elements http://www.ktf-split.hr/periodni/en/abc/e-config.html.
Some examples are as follows :
| Argon | Ar | 1s2 2s2 2p6 3s2 3p6. |
| scandium | Sc | [Ar] 3d1 4s2 |
| titanium | Ti | [Ar] 3d2 4s2 |
| vanadium | V | [Ar] 3d3 4s2 |
| chromium | Cr | [Ar] 3d5 4s1 |
| manganese | Mn | [Ar] 3d5 4s2 |
| iron | Fe | [Ar] 3d6 4s2 |
| cobalt | Co | [Ar] 3d7 4s2 |
| nickel | Ni | [Ar] 3d8 4s2 |
| copper | Cu | [Ar] 3d10 4s1 |
| zinc | Zn | [Ar] 3d10 4s2 |
How is the periodic table structured?
The periodic table is structured so that elements with the same type of valence electron configuration are arranged in columns.
- The left-most columns include the alkali metals and the alkaline earth metals. In these elements the valence S orbitals are being filled
- On the right hand side, the right-most block of six elements are those in which the valence P orbitals are being filled
- In the middle is a block of ten columns that contain transition metals. These are elements in which D orbitals are being filled
- Below this group are two rows with 14 columns. These are commonly referred to the F-block metals. In these columns the F orbitals are being filled
Important facts to remember:
- 2, 6, 10 and 14 are the number of electrons that can fill the S, P, D and F sub-shells (the l=0,1,2,3 azimuthal quantum number)
What is a transition metal ?
A transition metal is one which forms one or more stable ions which have incompletely filled d orbitals. Transition metals are elements with valence electrons in two shells instead of only one. This structure gives them their outstanding ability to form ions containing more than one atom (complex ions, or coordination compounds), with a central atom or ion (often of a transition metal) surrounded by ligands in a regular arrangement. When D-block elements form ions, the 4s electrons are lost first.
For example, Zinc has the electronic structure [Ar] 3d104s2. When it forms ions, it always loses the two 4s electrons to give a 2+ ion with the electronic structure [Ar] 3d10. The zinc ion has full D levels and doesn't meet the definition of transition metals.
However on the other hand, copper, [Ar] 3d104s1, forms two ions. In the Cu+ ion the electronic structure is [Ar] 3d10. Where as, the more common Cu2+ ion has the structure [Ar] 3d9.
Why do Transition metals have more than one stable ions?
The interesting thing about transition metals is that their valence electrons, or the electrons they use to combine with other elements, are present in more than one shell. This is the reason why they often exhibit several common oxidation states.
Oxidation state shows the total number of electrons which have been removed from an element (a positive oxidation state) or added to an element (a negative oxidation state) to get to its present state.
For example, copper, [Ar] 3d104s1, forms two ions. In the Cu+ ion the electronic structure is [Ar] 3d10. However, the more common Cu2+ ion has the structure [Ar] 3d9.
What is the simple definition of acids and bases ?
§ Acid - a substance that produces protons, H+
§ Base - a substance that produces hydroxide ions, OH-
Science e-Portfolio Post 2
Hi everyone, this is my 2nd e-Portfolio post. Please enjoy!
Reflection on science experiences, laboratory sessions
| Topics | Reflection |
| 2P01- Properties of Acids and Bases | This was our 1st science lab lesson. I learnt about alkaline and acids. I got to taste acid and feel alkali for the 1st time in my life. I learnt that acid’s taste is sour while alkali feels soapy. I also learnt that different reagents have different effects on different pH indicators. In addition, I learnt that an acid can neutralize an alkali and vice versa.
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| 2P02 -Strength of Acids and Alkalis | In this laboratory session, I learnt that acids and alkalis are conductors of electricity, unlike water, which is a non-conductor of electricity. The stronger the acids and alkalis, the better they conduct electricity. Strong acids are substances that ionise completely in water to produce hydrogen ions (H+), while strong alkalis are substances that ionise completely in water to produce hydroxide ions (OH-). However, weak acids and alkalis can only conduct electricity to a certain extent.
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| 2P03 | For this lab session, I learnt that the higher the volume of dilute sodium hydroxide, the higher the pH level. I also learnt that when alkali is added to acid, pH increases whereas when acid is added to alkali, pH decreases. |
| 2P04 - When Dilute Acid Meets Metals | Today, I learnt that dilute acids react with reactive metals to produce hydrogen gas. To test for hydrogen, we can use a lighted splint into a test tube containing the gas. If the gas is hydrogen, the lighted splint will be extinguished and a ‘pop’ sound will be heard.
I have also learnt that copper is a noble metal, therefore it is not affected by non-oxidizing acids. Copper's oxidation potential is lower than that of hydrogen, so it cannot displace hydrogen from hydrochloric acid. The measure of a material to oxidize or lose electrons is known as its 'oxidation potential.'
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| 2P05 - When Dilute Acid Meets Carbonates
| This experiment concludes that Dilute acid reacts with a carbonate to produce carbon dioxide gas.
However the exception is when calcium carbonate reacts with sulphuric acid. This is because the reaction between calcium carbonate and sulfuric acid is incomplete. The product, calcium sulfate, is insoluble in water. It will form a coating around the insoluble calcium carbonate, hence preventing further reaction from taking place. Generally, all sulphates are soluble EXCEPT those of silver, lead, mercury(I), barium, strontium and calcium.
Comparing with 2P04, hydrogen is a neutral gas, however carbon dioxide is acidic.
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| 2P06 - When Acid Meets Alkali
| This experiment demonstrates that an acid reacts with an alkali to produce a salt. Salt is neutral pH.
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| 2P07 - When Alkali Meets Ammonium Salts
| Alkali reacts with ammonium salt to produce ammonia gas. The ammonia gas is alkaline in nature. An alkali only shows its alkaline properties in the presence of water, thus dry red litmus paper does not change color when it reacts with ammonia gas.
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Thank you!
Science e-Portfolio Post 1
This is my 1st reflection of my Science e-Portfolio. Please enjoy!
Reflection of learning in Science and personal growth
This term for Science, we covered the following Chemistry Topics:
- Periodic Table
- Atomic Structure
- Chemical Bonding
- Equation Writing
- Isotopes
- Acids, bases and salts
I am glad that at the end of Term1, I have learnt the followings:
- Interpret the Periodic Table and predict the elements properties based on their position in the periodic table
- Represent the atomic structure and bonding via the dot and cross diagram
- Balancing of the chemical equation
- Understand the properties of Acids and Bases and how metals react with them
| Topics | Issues in Learning Sciences & Reflection of Growth |
| Periodic Table | Elements are arranged in periodic table in order of their proton number.
In each group, the number of outer shell electrons is the same for every element in that group and is equal to the group number. These electrons in the outer shell are used to form bonds between atoms. These electrons are called valence electrons. Thus, elements in the same group form the same type and number of bonds as they have the same number of valence electrons.
Groups 1, 2 and 3 forms positive ions with 1+, 2+ and 3+ respectively, where as Group 5,6,7 forms negative ions with 1-,2- and 3- respectively. However I do not understand why transition metal has more than one type of ions, such as Fe(II) and Fe(III).
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| Atomic Structure | It is interesting to learn that from the 21st element onwards, they have different electronic configuration compared to the first 20 elements in the Periodic Table. For the first 20 elements, the first, second and third shell can hold maximum 2,8,8 electrons respectively. However for elements after the Calcium, the third shell can hold up to 18 electrons. I would like to understand why there is this difference.
Initially, I was having difficulty understanding the charge of polyatomic ions such as OH, NO3 and SO4. However, this website http://library.thinkquest.org/C006669/data/Chem/bonding/lewis.html , has though me how to derive the charge.
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| Chemical Bonding | The two extreme chemical bondings are Ionic Bonding and Non-Polar covalent Bond. Ionic Bonding is resulted when electrons are transferred from an atom to another atom, forming negative ions (anions) and positive ions (cations), whereas Covalent bonding are results of atoms which are joined together by sharing of electrons to form molecules.
Typically, Ionic bond exists between metal & non-metal atoms and Covalent bond exists between non-metals. However, Aluminum chloride and Beryllium chloride are polar covalent bond due to the small electronegativity differences which is not great enough to create an ionic bond.
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| Writing Equation | To balance the equation is actually not difficult; we just need to observe the principle that the number of atoms of reactants must be equal to the number of atoms of products.
Balancing chemical equations literally means counting the number of times the atom symbols appear in the reactants and products to make sure the counts are the same on both sides. Conservation of mass is linked to "conservation" of element symbols.
What I find more challenging is to derive the products of the reactants. For example, how one would know that when methane (CH4) reacts with Oxygen(O2) the products are Carbon Dioxide (CO2) and Water (H2O) and not Carbon, Oxygen and Hydrogen separately.
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| Isotopes | Isotopes are atoms of the same element with different numbers of neutrons. As they have the same number of protons and electrons, they will have the same chemical properties. However they do have some small differences in their physical properties, because of the difference in the number of neutrons the particular isotope has.
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| Acids, Bases (Alkali) and Salts | Is interesting to note that acids only behave as acids when they are dissolved in water. The properties of acid are due to presence of hydrogen ions H+ (aq). Similarly the properties of bases are due to presence of hydroxide ions.
In order to write correct equation, one must remember the reaction of metals with acid vs. bases.
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Thank you!
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