Describe the difference between a mixture and a compound
The matter is classified as an element, mixture, or compound, which varies due to composition and separation. A compound is described as a substance, where atoms of various elements are chemically bonded by either ionic or covalent bonds to give a substance that has physical as well as chemical properties that vary from the constituent elements. It is a pure substance that cannot be easily separated through physical means but only by chemical reactions.
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Besides, individual elements abandon their properties while they form a compound. A compound has a fixed composition having constant ratios of elements as well as a fixed boiling and melting points (Ramsden, 2001).
A mixture on the other hand is a substance that results from a combination of more than two dissimilar materials in a manner that they are not chemically bonded together. A mixture is an impure substance that comprises numerous elements or even compounds that can be separated easily through physical processes based on solubility, size, and density. Mixtures can be formed by mechanical means and do not subsist in definite proportions. The results to colloids, alloys, suspensions as well as solutions that can be separated by evaporation, crystallization, distillation, sifting, decanting, visual sorting, magnetism, or filtering.
No energy is absorbed or released as mixtures form or separate. The constituent elements in a mixture retain their individual properties. A mixture has neither a fixed boiling point nor a sharp melting point. To illustrate, sodium (Na) and chlorine (Cl) are distinct elements that undergo a chemical reaction to give a compound referred to as sodium chloride (NaCl). Dissolving sodium chloride in water results in a mixture (brine) that can be separated through crystallization to come up with salt or through distillation to give out water (Ramsden, 2001).
Suppose that you have a pure substance. How can you tell whether it is a compound or an element?
A pure substance comprises one element or a compound. An element is a pure substance that cannot be chemically broken down into simpler components through procedures such as heating, cooling, electrolysis, or other chemical reactions, unlike compounds. Elements comprise the basic form of matter and are the building blocks of compounds. Elements can be distinguished from compounds by their chemical and physical properties as either metals, nonmetals, and metalloids. Just a single kind of atom is present in an element and cannot be disintegrated into simpler substances (Tillery et al., 2008).
Identifying the pure substances that are regarded as elements can be attained by the use of a Periodic Table where they are grouped about their chemical properties. Here elements are listed by symbols and have an atomic number. This is the number of protons that consisted of the nucleus of an atom.
Elements add up to a hundred and eighteen where some like oxygen are natural while others are artificial since they are radioactive and unstable. An element can exist in atomic or molecular form (Ramsden, 2001). Conversely, compounds consisting of more than two elements as a chemical structure which varies from constituent elements. Compounds are stable due to chemical bonding, which lacks in elemental molecules.
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However, to differentiate an element from a compound can be done by disintegrating the sample. A compound can be broken down to give out elements through chemical reactions. Besides, a compound consists of different properties other than those of the constituent elements. It consists of a definite ratio of component atoms. For instance, two elements iron (Fe), which is yellow, and Sulphur (S), which is grey can combine. The two could be heated up to form a compound iron sulfide that is black (Ramsden, 2001).
What is the difference between an ionic and a covalent bond?
Molecules and compounds are linked together by chemical bonds, which are either ionic or covalent and vary by properties and structures. Ionic or electronegative bonds consist of atoms that are joined together electrostatically through attractive forces of ions with opposite charges to form a strong bond with an indefinite shape. Besides, it has a high boiling point, high polarity, and a high melting point and exists as solids at room temperature.
For instance, Na+ + Cl– = NaCl (Ionic Bond). Ionic bonds result from a combination of two opposite atoms i.e. positive and negative charged atoms from metallic and non-metallic atoms respectively. Metallic atom donates valence electrons 1, 2 & 3 (to become a positive ion or cation) to the nonmetallic one with valence electron of 5, 6 &7 (to become a negative ion or anion) in pursuit of stability (8 electrons) (Aldridge et al., 2009).
Covalent bonds are comprised of atoms that are held together through shared electrons in a fixed orientation depending on their electronegativities (Aldridge et al., 2009). Nonmetals with the same electronegativities combine and can result from similar atoms (Hydrogen/nonmetallic) or different atoms (nonmetallic). Atoms sharing an electron equally form nonpolar covalent bonds but if it’s more attracted to a single atom, polar covalent bonds are formed.
Two nonmetallic atoms with a valency of 5, 6, or 7 join by electron sharing to become stable while hydrogen joins by sharing its lone electron to achieve stability as a duplet. Covalent bonds have definite shapes, low boiling points, low polarity, and low melting point and exist as liquids or gases at room temperature. For instance, a water molecule (H2O) is bound by polar covalent bonds (Aldridge et al., 2009).
Explain why ionic compounds are formed when metal from the left side of the periodic table reacts with a nonmetal from the right side. Give two examples of such compounds
Ionic bonds result from the bonding of metals and nonmetals. Electronegativity exceeding 1.7 forms ionic bonds where atoms with higher electronegativity can attract electrons from atoms with fewer electro-negativity to form ionic bonds. Nonmetal ions possess a negative charge and gain electrons while metals with a valency of 1, 2, and 3 possess a positive charge by donating an electron. In NaCl, each atom, Na, and Cl form ionic bonds.
Cl has 7 valence electrons on the outer orbit and to attain stability, it has to get one more electron to become an octet (Aldridge et al., 2009). Na contains 1 valence electron and requires 7 more to attain stability. Cl contains greater electronegativity of 3.16 while Na has 0.9 and their electronegativity difference is greater than 1.7. Hence, Cl has an easier attraction to Na’s single valence electron to result in an ionic bond while both elements attain stability as crystalline atoms.
This has the potential to conduct electricity when melted or dissolved Ionic bonds results from the complete transfer of electrons. Sodium becomes reduced in size as it donates its valence electron and CL enlarges due to gaining. Sodium Cyanide (NaCN) forms ionic bonds from cation as Na+ and anion as CN– (Aldridge et al., 2009).
Explain why covalent bonds are formed when nonmetals from the right side of the periodic table bond with each other. Give two examples of such compounds
Covalent bonds result from sharing electrons between two or more atoms, which are nonmetallic and have large electronegativities e.g. fluorine and oxygen, and other elements from the right side of the periodic table. Electronegativity becomes greater from left to right and becomes less down the columns. The electronegativities of the atoms should be equal or have a small difference (up to 1.7) to form covalent bonds. Methane (CH4) for instance, forms covalent bonds.
Carbon contains 6 electrons with 4 in its outer orbit (Aldridge et al., 2009). Octane rule dictates that atoms must gain, lose, or share electrons to gains stability of 8 electrons. Therefore, carbon requires 4 more electrons to attain stability, and to do this it could share electrons with four hydrogen atoms to form methane through a covalent bond. Multiple bonding is also possible with nonmetallic atoms. Hydrogen gas (H2) is formed when two hydrogen atoms combine.
H contains 1 valence electron in the outer orbit and to attain stability as a duet, it has to gain another electron by sharing with another hydrogen atom to form a covalent bond. This form of bonding dictates that molecules retain their true form and therefore, they are gases and liquids at room temperature (Aldridge et al., 2009).
Aldridge, C., Kaplan. & Lee, K. (2009). Kaplan SAT Subject Test: Chemistry 2009-2010 Edition. New York: Kaplan Publishing.
Ramsden, E. (2001). Key Science Chemistry. 3rd Ed. Cheltenham: Nelson Thornes Ltd.
Tillery, B. W., Enger, E. E., & Ross, F. C. (2008). SCI110: Integrated science: 2009 custom edition. 4th Ed. New York: McGraw-Hill.