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.

1. 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.
2. Add up the electrons directly surrounding each atom after this division has been done.
3. 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.
4. 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:

1. 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^-