Ionic Bonds: Understanding The Relationship Of Atoms

An ionic bond is a type of bonding involving the transfer of electrons between atoms to form oppositely charged ions, which are held by strong electrostatic attraction. This type of bonding typically occurs between metals and nonmetals, forming a neutral ionic compound such as table salt. The transfer of electrons allows both atoms to achieve a stable noble gas electron configuration.

1. IONIC BOND LESSON 1:

2. THE OCTET RULE Everyone is seeking for stability. STABILITY refers to the strength to stand or a resistance to chemical change or physical disintegration. If humans seek stability, so are the atoms. Stability in atoms involves the possession of eight (8) electrons in its outermost energy level or valence electrons. Atoms of all elements, therefore, to become stable, need to have 8 valence electrons. We call this the OCTET RULE which was proposed by Gilbert Newton Lewis, an American chemist. Lewis spent one year in the Philippines as the superintendent of the Bureau of Weights and Measures. The Octet rule-states that bonds are formed due to valence electrons. It is also known as the electronic theory of chemical bonding. All atoms desire to become octet. Gilbert N. Lewis

3. GILBERT NEWTON LEWIS (1875-1946) Gilbert N. Lewis was an American physical chemist and a dean of the college of chemistry at the University of California, Berkeley. He was born on October 25, 1875 and died on March 23, 1946. Lewis was best known for his discovery of the covalent bond and his concept of electron pairs; his Lewis dot structures and other contributions to valence bond theory have shaped modern theories of chemical bonding.

4. As explained by the Octet rule previously, the configuration of electrons and valence electrons are highly important in the study of bonding. As previously defined, electron configuration refers to the distribution of electrons at different positions in an atom. It becomes more complex as you move along the periodic table due to an increase of atomic number and, therefore, an increase of energy level of atoms. On the other hand, valence electrons are the electrons occupying the highest energy level in an atom. Sometimes called the outermost electrons, the valence electrons are the ones actually involved in chemical bonding and not the electrons closest to the nucleus. However, there are atoms that do not comply with the Octet rule. Others have lesser valence electrons than 8. These atoms are the ones located in the ones located in the Group/Column 1 to 17 of the periodic table, including the transition elements. Group 1 has 1 valence electron; Group 2 has 2 valence electrons; while Group 15 and 17 have 5 and 7 valence electrons, respectively. These elements have valence electrons that are less than 8. This means that they are not stable. Therefore, they need to react with other atoms to attain 8 valence electrons, just like that of noble gases by way of a chemical reaction producing a new substance. This is in fact the most important principle of chemical bonding. Atoms bond in such a way that they achieve the electron configuration of a noble gas. In doing so, atoms either gain, lose, or share their electrons.

5. LEWIS ELECTRON DOT STRUCTURE (LEDS) A system known as LEDS, proposed by Gilbert N. Lewis, is used to emphasize the atom’s valence electrons. It is a shorthand method which consists of a symbol of the element surrounded by dots. The symbol represents the nucleus of the atom, while the dots represent the valence electrons of the atom. You might be asking “How did they identify the valence electrons of these elements using the dot structure of Lewis or the LEDS?” Well, in the next page, you will be guided on how to draw the LEDS, and its accurate measurements of valence electrons.

6. HOW DO YOU DRAW THE LEDS? STEP 1: Write the chemical symbol of the atom. Carbon’s chemical symbol is “C”. STEP 2: Determine the column or group where an atom belongs in the periodic table or write down its electron configuration to find out the atom’s number of valence electrons. For representative elements, the number of valence electron is the same as the atom’s group number or column. Carbon, a representative element, belongs to Group 4A, therefore, its number of valence electron is 4, Carbon with 6 electrons has configuration of 1sˆ2 2sˆ2 2pˆ2. This reveals that carbon has 4 valence electrons. STEP 3: Draw the dots that will correspond to the number of the atom’s valence electrons. Distribute the dots evenly, where it may be above or below and/or either side of the chemical symbol.

7. IONIC CHARGES To date, there are 118 known elements presented in the periodic table of elements. However, talking about the substances existing here on Earth, there are even more than that number because elements react with one another forming new substances called COMPOUNDS. A compound is different both in its physical and chemical aspects from the original atom or element to which it came from. The compounds are bound together by a strong attractive force called CHEMICAL BOND . A type of chemical bond formed when there is transfer of electrons from one atom to another is called an IONIC BOND. The compound formed is an IONIC COMPOUND. This type of bond involves the gaining and losing of electrons. In doing so, the atom becomes a charged particle and will now be called an ION. An atom that loses an electron becomes positively charged, hence called CATION , and the one that gains electrons becomes negatively charged, and is called an ANION.

8. CONSIDER THIS! The element SODIUM (Na) is a silver-colored metal. It is highly reactive in water. Sodium atom belongs to Group 1A, and therefore, has a valence electron of 1. This time, let us see what charge will a chlorine atom have. CHLORINE (Cl) is a yellow-green gas at room temperature and is poisonous. It belongs to Group 7A in the periodic table which would mean that chlorine has a valence electron of 7.

9. Meanwhile, chlorine accepts the 1 electron of sodium to also achieve the stable configuration of 8. In this manner, both atoms become stable. Electrons are being transferred. The transfer is made possible as the electron affinity is met. ELECTRON AFFINITY is a measure of how much energy is released when an electron is gained by a certain atom. Its trend generally increases across period and decreases as you go down the group. As sodium losses an electron and chlorine gains this electron, both atoms now become stable resulting in a positively charged Na ion and a negatively charged Cl ion. Since these two are oppositely charged, they attract each other forming a chemical bond known as IONIC BOND. This type of bond is normally formed by the attraction of a metal to a nonmetal. It is a bond common to representative elements or those in Groups 1A, 2A, and 3A, and the elements in Groups 6A and 7A. The compound formed by this bonding is known as IONIC COMPOUND.

10. Chemical formulas and name of ionic compounds Ionic compounds are compounds composed of ions or charged particles. They are generally solid at room temperature and have high boiling and melting points. Ionic compounds are poor conductors of electricity, but when dissolved in water, these compounds conduct electricity and ions are free to move and carry the charge.

11. WRITING CHEMICAL FORMULA Compounds can be represented through a chemical formula. A chemical formula is a shorthand method in writing the name of the compound. It shows symbols to represent the elements and a subscript to represent the exact number of atoms used. To write the chemical formula of compounds… Write the symbol of the cation first followed by the anion. Write down the ions’ respective charges. Put them together using the CRISSCROSS METHOD. The CRISSCROSS METHOD is done by writing the charge value of the first anion as subscript of the second anion and vice versa. Drop the positive and negative signs. Lastly, reduce the subscripts when possible to the greatest common factor. An understood value of 1 is given if no number accompanies the charge symbol and this should not be written anymore as subscript during the crisscross. In here, you need to take note that the total positive charge must be equal to the total amount of negative charge. TAKE A LOOK AT THESE EXAMPLES: Lithium reacts with oxygen to form lithium oxide. Same is done with the following compounds When magnesium is chemically bonded with bromine to form magnesium bromide. When calcium is chemically bonded with fluorine to form calcium FLUORIDE.

12. BINARY AND TERNARY COMPOUNDS The previously mentioned compounds (magnesium bromide and calcium fluoride) are called BINARY COMPOUNDS since they involve only 2 elements. The anion used involves only 1 atom or a MONOATOMIC ANION. There are also compounds that contain 3 different elements. These compounds are called TERNARY COMPOUNDS. Most of these compounds consist of metallic cation and a polyatomic anion. To write the formula for ternary compounds, the crisscross method used in binary compounds can also be used. On the next slide shows a chart containing the list of common polyatomic ions.

13. TABLE 1.0: LIST OF COMMON POLYATOMIC IONS

14. If there is more than one polyatomic ion in the formula, put the ion in parenthesis and put the subscript after the parenthesis. Such that the reaction of aluminum (AL3+) to sulfate (so4^2) would produce a compound with a chemical formula al2(so4) and the reaction of barium (Ba^2+) to phosphate (Po4^3) would produce Ba3(Po4)2.

15. NAMING BINARY AND TERNARY COMPOUNdS Naming binary and ternary compounds is so simple. For binary compounds, you should name the cation first (specify the charge if many). Then name the anion changing its suffix to –ide. Thus, NaCl is named as sodium chloride, and MgBr is named as magnesium chloride, while CuBr is named as copper (ii) bromide, and SnCl2 is named as tin (ii) chloride. The last two examples were named using the STOCK SYSTEM. The system uses the Roman numeral to describe an ion’s charge. It is enclosed in a parenthesis and placed immediately after the metal name. Such elements are said to have more than one ion or with variable oxidation number and the list of those elements is found on the next slide. Meanwhile, to name ternary compounds, you just need to name the cation first, followed by the name of the polyatomic ion. Thus, NaOH is named as sodium hydroxide; CaCO is named as calcium carbonate; Fe2(SO4) is named as iron (iii) sulfate; and Pb (NO3) is named as lead (iv) nitrate.

16. IMPORTANT IONS AND IONIC COMPOUNDS Ions are necessary to plants and animals for them to perform important cellular activities of the body. The body ions, known as ELECTROLYTES, are needed for the activation of the nervous system. The next table shows some of the most important ions in our body and their functions. Table 1.2, on the other hand, shows some important ionic compounds with their uses

17. TABLE 1.1: IMPORTANT IONS IN THE BODY ION FUNCTION Na+ (sodium) Controls and regulates bodily fluids K+ (potassium) Controls and regulates bodily fluids particularly the osmotic balance in the kidneys Ca2+ (calcium) Component of bones and teeth; essential for muscle contraction Mg2+ (magnesium) Component of chlorophyll; plays assisting role in metabolic functions Cl- (chlorine) Most abundant anion; necessary in gastric juice TABLE 1.2: IONIC COMPOUNDS AND THEIR USES COMPOUND USE/S NaNO3 (sodium nitrate) Used as meat preservative CaF2 (calcium fluoride) Component of toothpaste; helps prevent tooth decay AgBr and AgCl (silver halides) Used in the photographic industry to make films for capturing images; light sensitive ingredient used in photographic film NaOH (sodium hydroxide) Used in the manufacture of soaps Al2O3 (aluminum oxide) One of the most used compounds in engineering processes like in the making of airplanes due to the compound being lightweight

18. CONCEPT MICRO The octet rule states that atoms must attain 8 electrons in its outermost energy level just like the noble gases to become stable. To attain this, atoms enter chemical bonding; and in the bonding process, atoms either gain, lose, or share electrons. Ionic bond involves the transfer of electrons from one atom to another. Atoms either gain or lose electrons in the bonding. Ionic bond exists in substances composed of a metal and a nonmetal. To name ionic compounds, name the cation and then name the anion changing the suffix with –ide.