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Chapter 20

Chapter 20. Chemical Bonds. Stability In Bonding. Roughly 110 elements on the periodic table can form a nearly infinite number of compounds Elements bond with each other, seeking stability Only one group of elements (Noble Gases) are stable without bonding

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Chapter 20

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  1. Chapter 20 Chemical Bonds

  2. Stability In Bonding • Roughly 110 elements on the periodic table can form a nearly infinite number of compounds • Elements bond with each other, seeking stability • Only one group of elements (Noble Gases) are stable without bonding • All others must bond with either another atom of the same element or a different element to be stable

  3. Combined Elements • Elemental copper is a shiny metal • The Statue of Liberty is copper, why is she a pale green color? • The copper that the statue is made of reacted with oxygen and sulfur to form a compound called copper sulfate, that has its own properties

  4. Combined Elements • Sodium (Na) is a soft, silvery metal that is highly reactive– it actually catches fire in the presence of oxygen • Chlorine (Cl) is a green poisonous gas. • Together, they make a compound that you can put on your food, table salt, NaCl • Table salt’s compound name is Sodium Chloride

  5. Chemical Formulas • A chemical formula tells what elements are in a compound, and in what numbers • Subscripts (a number written below) show how many atoms are in each compound. • If there is no subscript, you can assume it is 1 • Example, H2O, water, has two atoms of Hydrogen and one atom of oxygen

  6. Some Familiar Compounds

  7. Atomic Stability • An atom is considered stable if its outer shell electrons are full • This is considered an “Octet”, because 8 electrons fill the outer shell of some atoms • Outer shell electrons are called “valence” electrons and are the electrons that are involved in bonding

  8. Dot Diagrams • Uses dots around the chemical symbol to show number of valence electrons

  9. Dot Diagrams, Cont • Write the symbol of the element • Look at the periodic table and determine the number of outer shell, or valence electrons • Start on the top, put one dot on each side as you move clockwise • Exceptions: He (helium) has a full shell at two electrons, so put those dots on top • Group 1: Alkali metals (including H) put the one dot to the right

  10. Stability is Reached • Atoms form chemical bonds with each other to reach chemical stability– to fill up their outer shells • They will either give away, take, or share electrons to do this

  11. Types of Bonds • When atoms gain or lose an electron, they become an ion • A positive ion, such as Ca +2, gives away 2 electrons • A negative ion, such as Chlorine -1, gains one electron • A bond where electrons are transferred, (given or taken) is called an IONIC bond

  12. Ionic Bonds • Ionic bond is the force of attraction between opposite charges in an ionic compound • For the most part, ionic bonds are formed by elements that are far apart on the periodic table • A metal and a non-metal • Metals tend to lose electrons • Non-metals tend to gain electrons • Once ionic bonds are formed, the resulting compound has a net charge of zero

  13. Sharing Electons • Non metals, when bonding with other non metals, are unlikely to gain or lose electrons • The attraction that forms between atoms when they share electrons is called a covalent bond • A neutral particle that forms due to a covalent bond is called a molecule

  14. Types of Covalent Bonds • Single covalent bonds share one pair of electrons, example is water H2O this is called a single bond • A multiple covalent bond shares two or three pairs of electrons, called a double or a triple bond, example N2 • Covalent bonds form between non-metals • Many covalent compounds are liquids or gases at room temperature

  15. Bond Types

  16. Polar vs Non-Polar • Polar covalent compounds are molecules that have ends that have partial opposite charges • This means that the electrons are shared unevenly • One atom has a greater “pull” on the shared electrons than another • A non-polar compound mean that the electrons are shared evenly with no partial charges

  17. Polar vs. Non Polar Carbon Tetrachloride is non-polar Water is Polar

  18. Diatomic Atoms • Some atoms are so reactant that they can’t exist as only one atom • They must bond with themselves in order to reach stability • They are called “diatomic” which literally means “two atoms” • The diatomic atoms are: Nitrogen, Oxygen, Fluorine, Chlorine, Iodine, Hydrogen, Bromine • Magic 7- they make a 7 and then add hydrogen • They are all written with a subscript: Cl2

  19. Diatomic Atoms

  20. Binary Ionic Compound • A binary ionic compound is one that consists of two elements bonded together where electrons are transferred • You need to know what elements are involved and how many electrons are gained or lost • The element’s OXIDATION NUMBER tells how many electrons are transferred when ions are formed • Oxidation numbers are often referred to as “charge”

  21. Oxidation Numbers

  22. Special Ions- have more than one oxidation number

  23. Compounds are Neutral • When compounds are formed, their net charge must be zero • Therefore, when you are putting compounds together and writing their formulas, their oxidation numbers must equal zero • Sodium (Na +1) and Chlorine (Cl -1) together are NaCl • Magnesium (Mg +2) and Chlorine (Cl -1) together are MgCl2 • It takes two chlorine atoms to cancel out the +2 charge of Mg to zero • Criss-Cross method

  24. Naming Ionic Compounds • Step 1: Write the name of the positive ion • Step 2: Determine if the positive ion has a special oxidation number (refer to table 2.) If it does, you’ll have to determine its oxidation number and write roman numerals after the name • Step 3: Write the root of the negative ion (chlor-, ox-, phosph-) • Add –ide to the end of the root of the negative ion

  25. Naming Ionic Compounds • NaCl • Step one: Sodium • Step two: not needed, it only has one possible oxidation number • Step three: Sodium Chlor- • Step four: Sodium Chloride • Now, you do MgI

  26. Naming Compounds with polyatomic ions • A polyatomic ion is a special ion that is made of many atoms • Look at the chart to the right • To write the names of a special compound with polyatomic ion, you write the name of the positive ion and then the name of the polyatomic ion • Ex K2SO4 is potassium sulfate

  27. Naming Covalent Compounds • Naming covalent compounds uses prefixes that tell how many of the atoms are present in the molecule • Often the prefix for one, mono is omitted but is used for emphasis in some cases

  28. Naming Covalent Compounds • CO is Carbon Monoxide • CCl4 is Carbon Tetrachloride • H2O is Dihydrogen Monoxide Your Turn NO2 N2O5

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