Chemical Compounds Chapter 4

1. Chemical CompoundsChapter 4 By Daniella Perruzza

2. What are Compounds? • Compounds are substances made of more than one kind of atom or pure element. There are two kinds of compounds, ionic compounds and molecular compounds. A molecule is composed of two or more nuclei that contain enough electrons to make it completely neutral. • If the nuclei are composed of the same element such as two elements of Carbon or two elements of Potassium it is considered a molecular element. In a molecular compound however, the nuclei are from different elements that form molecules.

3. An ionic compound is the formation of oppositely charged ions. Atoms of certain elements can transfer electrons between them when they form a compound. It usually forms between a metal and a nonmetal.

4. Table Salt • Since Na has one less electron, it has a charge of +1. The chlorine atom becomes a chloride ion and gains one electron, making it have a charge of -1. Since unlike charges tend to attract each other, the sodium and the chloride ions attract each other and form an ionic bond. In ionic bonding, electrons are transferred from one atom or to another, usually from a metal onto a non-metal. In the process of losing or gaining electrons, the reacting atoms form ions. The oppositely charged ions are attracted to each other, which form a strong ionic bond.

5. Monoatomic Ions • Another type of ion that forms is a monoatomic ion. Monatomic ions have only one atomic nucleus and are either negative or positively charged. There are two types of monoatomic ions, cations and anions. Metals form monatomic cations. Once again, cations are positively charged ions. Nickel for example forms two ions, Ni +2 and Ni +3. • There is a special process for naming these ions. Cations are named using the element name followed by a Roman numeral and the word ion. For example one could name Ni +2 and Ni +3 , nickel(II) ion and nickel(III) ion. Anions, which are monatomic ions derived from nonmetals end in the suffix –ide.

6. When there is a binary ionic compound, chemists use certain rules to organize elements and their names. The cation is always written first in the name and the anion second. For example, iron(III) iodide, Fe is a metal and is put before the element iodine which is a nonmetal. The cation is indicated using a Roman numeral immediately following the name of the cation. The anion is named by adding the suffix –ide to the element name and put after the parenthesis of the Roman numeral.

7. Chemical Formulas • When forming ionic compounds, correct formulas must reflect the electrical neutrality. Metals and nonmetals form neutral charged compounds, having canceled each other’s previous positive or negative charges. If Na +1 decides to form a compound with Sulfur –2, if would take two Na+1 ions to give enough positive charge to cancel the charge of –2 of a sulfur ion. • To show this ratio, the formula would be written as Na2S. Subscripts are used to express the smallest whole numbers in a ratio. Sulfur does not have a subscript because it is given that if there is no subscript there is only one element in the compound.

8. Orbitals Atoms or ions whose outside orbitals contain eight electrons are extremely stable then those whose outside level contain less. A total of eight electrons in the outer shell causes the element to become stable. When stating that an element is “stable”, stable simply means that change or sudden reactions would not easily affect these specific elements. This principle of filling up the energy levels to eight electrons or to the maximum capacity is called the octet rule. Metals and nonmetals strive to become stable by reacting with each other to have eight valence electrons. For example, the element Chlorine has seven valence electrons and would like to gain one more electron to have eight electrons in its outer shell.

9. The Least Reactive Element Noble gases, are the least reactive, and most stable of all the elements. The six noble gases are Helium, Neon, Argon, Krypton, Xenon, and Radon, which are in group VIII in the periodic table. All noble gases have the maximum number of electrons in their outer shell. Only Helium has two electrons in its outer shell, which is considered stable, while the rest have eight valence electrons. These noble gases form neither positive or negative ions.

10. Metals like to lose electrons while non-metals will gain them. This reaction that involves the transfer of electrons between two chemical elements is called a Redox Reaction. In a redox reaction, two elements will change the existing oxidation number. One of the elements oxidation number will become more positive or less negative. The oxidation number of the other element decrease becoming less positive or more negative.The element that loses electrons is said to be oxidized, while the element that gains the electron is said to be reduced. When there is an oxidation there must be a reduction in any reaction. The substance, which loses electrons, is oxidized and the substance, which gains electrons, is reduced. However, this can get confusing, the element that gains an electron is reduced and called the oxidizing agent, while the element that loses the electron is oxidized called the reducing agent. Redox) Cu(s) + 1/2 O2 (g) ---> CuO (s) The oxidation number of copper in the product is Cu(0), Cu(I), Cu(II) In the reaction, copper metal is reduced, oxidized, unchanged in oxidation state

11. The Forming of a Covalent Bond • A covalent bond occurs from sharing electrons between nuclei. Covalent bonds occur between two atoms in order to produce a mutual attraction in order to share electrons. The bond is formed when the electron clouds of two atoms overlap. The nuclei of both atoms feel attracted toward each other and they become bonded. In covalent bonding, the two electrons are shared and are attracted to the nucleus of both atoms. Covalent bonds usually are formed between two atoms with similar electronegativities. Neither atom loses or gains electrons as in ionic bonding.

12. There are two types of covalent bonding, non-polar bonding and polar bonding. Non-polar bonding involves the equal sharing of electrons between identical non-metal atoms. Polar bonding is the unequal sharing of electrons between two different non-metals.

13. The Lewis Structures • The Lewis structures and Lewis octet rule was named after Gilbert Newton Lewis who proposed that chemical bonds be formed between atoms because electrons from the atoms interact with each other. He suggested that atoms with less than eight valence electrons bond together to share electrons and become stable with eight electrons in their valence shell. • The electron-dot symbols for atoms show the symbol for the element and the number of electrons. The number of electrons is represented as dots around the symbol for the element. The number of valence electrons is the number of s and p electrons in the outermost shell. The number of valence electrons can also be determined by counting across the period, until the element is found.

14. The Formation of an Ion The formation of ions can be shown by electron- dot symbols. If Potassium decides to react with Chlorine, Potassium loses its electron and no dot remains. The valence shell of Chlorine accepts this electron and now has eight valence electrons and obtains a negative charge. Brackets are added around the symbol of the ion Chlorine to show that has no more room for electrons. Atoms that form covalent bonds have the intention of forming noble gas configurations by gaining as many electrons as they need to fill their outermost shell. Covalent bonding occurs between atoms with similar electronegativities; where there is insufficient energy to completely remove an electron from another atom.

15. Building Block to Compounds • Polyatomic ions are the basic building blocks of many ionic compounds and theses atoms that form bonds have a net electrical charge. • Polyatomic cations are usually ammonium, hydronium and mercury. Polyatomic anions occur in “families.” The electron dot structure of ammonia, NH3 has one unshared pair of electrons left. • Another hydrogen ion H+, after losing its 1s electron, comes along and decides to bond to NH3, making it an ammonium ion NH+4. The cluster of atoms that shared electrons is an example of a polyatomic ion.

16. The Acid-Base Relationship • Acids tend to react with most metals, such as Sodium. In an operational sense, an acid is a substance that increases the concentration of the H+ ion when it dissolves in water. Bases are compounds that increase the concentration of the OH- ion, after dissolved in water. • Bases can be defined as a proton acceptor. Bases combine with hydrogen ions, unlike acids. To distinguish whether a compound is an acid or base, one can dissolve it in water and test the solution for an increase in H+ or OH- concentration. An acid- base reaction can be called a proton transfer.

17. Creating a Lewis Structure • The less electronegative element will usually be the central atom, the atom which the others are grouped. Normally the first atom of the formula will be the central atom. • The only exception to this rule if the element Hydrogen. Hydrogen can never be a central atom because it can only bond once and accommodate two electrons. Hydrogen houses only two electrons in its first shell. In H20, Oxygen must be the central atom, H O H. • In CO2, the Lewis structure would be written O C O. Oxygen is usually not the central atom, but because it was bonded with hydrogen.

18. VSEPR Theory • The Valence Shell Electron Pair Repulsion Theory or also known as the VSEPR theory can predict the three-dimensional shape of the molecules based on their Lewis Dot structure. After a covalent bond has been made, electron clouds of one pair repel an electron cloud of another, which forms a certain shape. • The shape is determined by each of these electron clouds to stay out of each other’s way. The repulsion are smallest when the electron pairs or groups of electron pairs are as far apart as possible.

19. The H20 Model • Polar molecules are the arrangement of the atoms where in some molecules one end of that molecule has a positive charge and the other side has a negative charge. A positive and a negative electrical charge simply mean that the molecule has electrical poles. • Normally, an atom has an even distribution of electrons, but if the electron end up one side more than the other, a resulting electrical field may occur. Water Molecule

20. Last But Not Least A solution is a homogenous mixture of two or more substances. Usually the solution, is a liquid. A mixture has a solvent and a solute. The solvent has a greater number of moles, while the solute has less. The most common solvents if water, and a solution may be described as aqueous. Water and oil, which is a non-polar molecule, form a solution.