Chipa Maimela PHYSICAL SCIENCES GRADE 12

The formation of the dative covalent (or coordinate covalent) bond


The formation of a dative covalent bond, also known as a coordinate covalent bond, occurs when one atom donates both of its electrons to another atom to form a covalent bond. This type of bond is also known as a “dative” bond because the electrons are donated by one atom to another, rather than being shared equally.

For example, in the case of H3O+ (hydronium ion) and NH4+ (ammonium ion), the dative covalent bond forms between the oxygen atom in H3O+ and the nitrogen atom in NH4+. The electron diagram for this formation is as follows:

H3O+:

 
   O
  / \
 H   H

NH4+:

    N
   / \
  H   H
  |   |
  H   H

The oxygen atom in H3O+ has a lone pair of electrons, while the nitrogen atom in NH4+ has a partially filled outer shell. When these two atoms come into close proximity, the oxygen atom donates one of its lone pair of electrons to the nitrogen atom, forming a covalent bond. This results in the formation of H3O+ NH4+ molecule.

The electron diagram for this molecule is:

H3O+ NH4+ :

     
   O
  / \
 H   H
     |
     N
    / \
   H   H
   |   |
   H   H

In this case, the oxygen atom donates one of its electrons to the nitrogen atom, forming a dative covalent bond. As a result, the nitrogen atom now has a full outer shell of electrons, and the oxygen atom has a single lone pair of electrons.

It’s important to note that this type of bond formation can occur between other types of atoms and molecules as well, not just H3O+ and NH4+. Dative covalent bond formation can be observed in many chemical reactions and is an important concept in understanding the behavior of molecules and their interactions with other molecules.

Chipa Maimela GRADE 11 PHYSICAL SCIENCES

A chemical bond


A chemical bond is a force that holds atoms together in a molecule. It is formed by the attraction between the positively charged nuclei of atoms and the negatively charged electrons surrounding them. The strength of this attraction is determined by the distance between the atoms and the number of electrons involved in the bond.

There are several types of chemical bonds, each with its own characteristics and properties. The most common types of chemical bonds are covalent, ionic, and metallic bonds.

Covalent bond: It is formed when two atoms share electrons. The shared electrons occupy a region of space called a molecular orbital, which is located between the nuclei of the two atoms. The strength of a covalent bond is determined by the number of electrons shared and the distance between the atoms. Covalent bonds are typically found in molecules made up of non-metal elements.

Ionic bond: It is formed when one atom donates an electron to another atom. The atom that loses an electron becomes positively charged and is called a cation, while the atom that gains an electron becomes negatively charged and is called an anion. The strength of an ionic bond is determined by the attraction between the positively and negatively charged ions. Ionic bonds are typically found in compounds made up of metal and non-metal elements.

Metallic bond: It is formed by the attraction between positively charged metal ions and a sea of delocalized electrons. The strength of a metallic bond is determined by the number of delocalized electrons and the distance between the metal ions. Metallic bonds are typically found in compounds made up of metal elements.

The net electrostatic force two atoms sharing electrons exert on each other is the chemical bond that holds atoms together in a molecule. Understanding the properties of chemical bonds is essential for understanding the behavior of molecules and their interactions with other molecules.

Chipa Maimela EXPERIMENT, GRADE 10 PHYSICAL SCIENCES, PRACTICAL INVESTIGATION

Flame tests to identify some metal cations and metals.


Flame tests are a simple and effective way to identify the presence of certain metal cations in a sample. The principle behind flame tests is that when a metal cation is heated in a flame, it will emit light of a specific color that can be used to identify the metal cation.

Experimental Method:

  1. Obtain a Bunsen burner and a clean wire loop.
  2. Prepare a solution of the metal cations to be tested.
  3. Dip the wire loop into the solution and hold it in the flame.
  4. Observe the color of the flame and compare it to a known color chart or reference.
  5. Repeat the test for different metal cations to identify them.

Data Analysis:

The color of the flame can be used to identify the metal cation present in the sample. Different metal cations will emit different colored flames. For example, sodium ions produce a yellow flame, copper ions produce a blue-green flame, and lithium ions produce a red flame.

Conclusion:

Flame tests are a simple and effective way to identify the presence of certain metal cations in a sample. By observing the color of the flame, it is possible to identify the metal cation present in the sample. It’s important to note that flame tests can give false positives, so chemical tests like spectroscopy should be used to confirm the results.

Chipa Maimela GRADE 12 PHYSICAL SCIENCES, PHYSICAL SCIENCES GRADE 12

Alkanes and alkenes react differently with bromine and potassium permanganate.


Reaction of Alkanes with Bromine:

Alkanes typically do not react with bromine in the absence of light or heat. However, when exposed to light or heat, alkanes can undergo a free radical substitution reaction with bromine, which results in the formation of a bromoalkane. The equation for this reaction is:

CnH2n+2 + Br2 → CnH2n+2Br

Reaction of Alkenes with Bromine:

Alkenes can react with bromine in the absence of light or heat. This reaction is called an electrophilic addition reaction, and it results in the formation of a dibromoalkane. The equation for this reaction is:

CnH2n + Br2 → CnH2nBr2

Reaction of Alkanes with Potassium Permanganate:

Alkanes do not react with potassium permanganate in the absence of heat or an acid catalyst. However, when heated with an acid catalyst, alkanes can undergo an oxidation reaction that results in the formation of carboxylic acids or alcohols. The equation for this reaction is:

CnH2n+2 + KMnO4 + H+ → CnH2n+1COOH or CnH2n+1OH

Reaction of Alkenes with Potassium Permanganate:

Alkenes do not react with potassium permanganate in the absence of heat or an acid catalyst. However, when heated with an acid catalyst, alkenes can undergo an oxidation reaction that results in the formation of carboxylic acids or alcohols. The equation for this reaction is:

CnH2n + KMnO4 + H+ → CnH2n-1COOH or CnH2n-1OH

It’s important to note that the reagents used and the conditions for the reaction can affect the products formed in these reactions.

Chipa Maimela EXPERIMENT, GRADE 12 PHYSICAL SCIENCES, PHYSICAL SCIENCES GRADE 12, PRACTICAL INVESTIGATION

Position vs. Time and velocity vs. time for a free-falling object:


The position of a free-falling object is measured downward from a certain starting point.

The position of the object increases with time as it falls.

The graph would be a straight line with a negative slope, starting at the initial position and ending at the final position.

Velocity vs. Time graph for a free-falling object:

The velocity of a free-falling object increases with time as it falls.

The graph would be a straight line with a positive slope, starting at zero and ending at the final velocity.

To determine the acceleration due to gravity, we can use the equation:

a = v^2/s or a = 2s/t^2

Where a is the acceleration, v is the final velocity, s is the final position, and t is the time of fall.

Since the acceleration due to gravity is constant, the slope of the velocity vs time graph is the acceleration.

Position vs. Time:

The graph for position vs. time for a free-falling object would be a straight line that starts at a non-zero position (the initial height of the object) and decreases as time goes on. The slope of this line would represent the velocity of the object. The equation for this line would be:

y = -g*t + h

where g is the acceleration due to gravity, t is the time, and h is the initial height of the object.

Velocity vs. Time:

The graph for velocity vs. time for a free-falling object would be a straight line that starts at a non-zero velocity (the initial velocity of the object) and decreases as time goes on. The slope of this line would represent the acceleration of the object. The equation for this line would be:

y = -g*t + v

where g is the acceleration due to gravity, t is the time, and v is the initial velocity of the object.

Determining the Acceleration due to Gravity:

To determine the acceleration due to gravity, we can use the slope of either the position vs. time or velocity vs. time graph. For the position vs. time graph, the slope is -g, and for the velocity vs. time graph, the slope is -g. Therefore, we can conclude that the acceleration due to gravity is -g.