Topics in ChemistryLe Chatelier's Principle: Changes in concentration and pressure in dynamic equilibrium Chemical Equilibrium: Dynamic Equilibrium in Chemistry Static and Dynamic Equilibrium explained with their Differences Chemistry Scheme of Work, SS1, First Term Chemistry Scheme of Work, SS1, Second Term Chemistry Scheme of Work, SS1, Third Term Compounds in Chemistry: Characteristics of Compounds Types of Mixture: Homogenous and Heterogeneous Mixtures Mixtures: Characteristics of Mixtures Physical Properties of Matter explained with Examples Chemical Properties of Matter explained with Examples Differences between Physical and Chemical Change Ionic Theory and Electrolysis Physical and Chemical Properties of Acids States of Matter: Characteristics of Solids Liquid State of Matter: Characteristics of Liquids Gaseous State of Matter: Characteristics of Gases Molar Mass, Worked Examples and Differences with Molecular Mass Elements: Characteristics of Elements Salts and Types of Salt in Chemistry
Academic Questions in Chemistry
Which of the following isn't an element of the periodic table.
According to the periodic table, elements in the same group have got the same number of shells.
The periodic table of elements is also called the Mendeleev's table.
The simplest formula of a compound is termed _____.
A. Emperical formula
B. Molecular formula
C. Avogadro's number
D. Mass formula
E. Molar mass formula
F. Mole ratio
A compound composed of iron (Fe) and oxygen (O) was analyzed and found to contain 69.94% iron and 30.06% oxygen. Find the empirical formula of the compound. (Molar mass of Fe=55.85, O=16)
Which of the following statement is false concerning hydrocarbons?
A. Hydrocarbons can be aromatic
B. Hydrocarbons are made up of carbon and hydrogen only
C. Alkynes are aliphatic hydrocarbons
D. Alkenes have a carbon-carbon double bond in their structure
E. Benzene ring has a carbon-carbon triple bond in its structure
F. Hydrocarbons are the main constituents of petroleum and natural gas
The ability of carbon to form long chain of itself is called _____.
A. Carbon chain reaction
E. Organic chemistry
F. Carbon moleculation
Calculate the relative molecular mass of methane. (Carbon = 12.001, H = 1.00794).
A. 13.00894 amu
B. 11.00206 amu
C. 12.00794 amu
D. 14.001 amu
E. 15.001 amu
F. 16.033 amu
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John Dalton, an English chemist is considered the Father of modern chemistry because of the understanding he brought into the composition of matter and the basis for their chemical reactions.
Recall that chemistry is the study of matter and the changes they undergo.
Some of the atomic theory which he postulated in 1808 had to be modified based on the discoveries of other scientists.
In this article, we will look into these atomic theories of Dalton and their modifications.
Based on the discovery made by Rutherford, atoms can no longer be regarded as indivisible because they can be further divided into the followings:
Protons: They are positively charged particles in the nucleus of an atom.
Neutrons: These particles have no charge (neutral) and are found in the nucleus of an atom.
Electrons: They are negatively charged particles that revolve round the shell of atoms.
Quarks: A quark is a fast moving energy and is comprised of both the protons and neutrons in the nucleus of an atom.
The discovery of isotopes has shown that not all atoms of the same elements are similar in every aspect.
Isotopy is a phenomenon whereby atoms of the same element have the same atomic number but different mass number. As a result, the same element can have a different mass and density.
Note: The difference in the mass (mass number) of isotopes is a result of the varying number of neutrons in the nucleus of their atoms.
The mass number of an atom is defined as the sum of protons and neutrons in the nucleus of the atom.
Based on the above explanations, isotopes have the same number of protons (atomic number) but different number of neutrons.
Note: The mass spectrometry experiment conducted on (isotopic) atoms had given a confirmation to the existence of isotopes.
Some elements exhibiting isotopy include:
Also, the discoveries of isobars have shown that the atoms of different elements are not completely different.
Isobar is a phenomenon whereby atoms have different atomic numbers but the same mass number. For instance:
With regards to ordinary chemical reaction, this statement remains valid.
After the discovery of radioactivity, the various radioactive elements have shown that atoms can be created (through a process called nuclear fusion) and destroyed (through a process called nuclear fission).
Example of radioactive elements are Thorium-232 and Uranium-238
This statement is true for simple inorganic chemical reaction. With regards to complex organic compounds or molecules, the statement becomes false because they don’t combine in simple whole numbers; rather, they do so in complex numbers. For instance, glucose molecule has a chemical formula of C12H22O11.
Starch is another organic compound that contains many repeating units of simple sugars and with a chemical formula of (C6H10O5)n, where "n" is a large whole number.
This theory cannot explain allotropy.
Allotropy is phenomenon whereby atoms of the same element exist in different forms but in the same physical state.
For instance; carbon in its solid state can exist in four different forms. These are:
Note: The above forms of carbon have got different physical properties or characteristics. For instance, graphite is soft while diamond is very tough (hard).
1. His theory gave a clearer explanation to the laws of chemical combination which includes:
2. Dalton created the distinctions between atoms, molecules and compounds.
You can read on Physical and Chemical Changes here
3. His work paved way for the discovery of atomic bomb.
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Amazing facts in Chemistry
The only letters that failed to appear on the periodic table are letters:
Gold and copper are the only two non-silvery colored metals.
Copper is the only metal that is naturally antibacterial. For this reason, some children utilize 'copper water bottles' in schools
Water freezes faster when it’s warm than when it’s cold
Most element in their pure state exists physically in different forms. For instance, pure carbon can exist as both diamond and graphite. This phenomenon is called allotropy
If you pour a handful of salt into a full glass of water, the water level will go down rather than overflowing the glass.
Similarly, if you mix half liter of water and half litre of alcohol, the total volume of the liquid will be les than one litre
NOTABLE POINTS IN Chemistry
In chemistry, hydrocarbons can be classified as either aliphatic or aromatic. Recently, both classifications of hydrocarbon were based on their structure rather than their origin.
Aliphatic hydrocarbons are put into three main groups according to the types of bonds they possess. These are:
They are shown in the image below:
It's important to note the followings:
Alkanes have single bonds (only) in their structures.
Alkenes always have a carbon-carbon double bond present in their structure.
Alkynes always have a carbon-carbon triple bond present in their structure.
Aromatic hydrocarbons are classified into:
Organic chemistry is the study of carbon and it's compounds.
Carbon is the focus of organic chemistry because it has a wide chemical diversity in the sense that it can combine with other carbon atoms to form a long chain of carbon molecule. This ability and process whereby carbon can form a long chain of itself is called catenation.
A major challenge encountered when calculating molecular mass is that it becomes difficult or impossible to calculate especially when the relative molecular mass of large molecules, polymers and macromolecules are involved.
Examples of large molecules (with indefinite molecular masses) include carbohydrates, cellulose and complex sugars.
The large molecules (above) have no specific chemical formula throughout their volume.
Understand that Relative Molecular Mass prove to be useful only when we calculate substances with small and definite molecular sizes. This was proven through the modifications of Dalton's atomic theory.
Calculate the Relative Molecular Mass of methane (CH4). (Carbon=12.001 and H=1.00794)
Molecular Mass = Atomic mass of carbon + Atomic mass of Hydrogen
Methane is composed of one atom of Carbon and 4 atoms of Hydrogen.
12.001 + (1.00794 x 4)
Molecular Mass of Methane = 16.033 amu
Calculate the Relative Molecular Mass of water (H2O). (Oxygen=15.9994 and Hydrogen=1.00794)
Molecular Mass = Atomic mass of Hydrogen + Atomic mass of Oxygen
Water contains 2 atoms of Hydrogen and 1 atom of oxygen.
(1.00794 x 2) + 15.9994
Molecular Mass of Water = 18.015 Da
Below are some facts about gold:
It is the only metal that has a gold (golden) color
Gold is present inside the earth crust in all the seven continents
Pure gold is soft and very stretchable (It can even be stretched into threads)
The Latin name of Gold is aurum which means 'shining dawn'. For this reason, its chemical symbol is 'Au'
Gold is a very good conductor of electricity. This is why it’s sometimes used in making USB and audio cables
Gold is non toxic and can be eaten with food. It is sometimes added to desserts in some expensive restaurants
The term Gold originated from an ancient English word 'geolu' which means yellow
24karat gold is the purest gold element