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Chemical Bonds.  Roughly 110 elements on the periodic table can form a nearly infinite number of compounds  Elements bond with each other, seeking stability.

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Presentation on theme: "Chemical Bonds.  Roughly 110 elements on the periodic table can form a nearly infinite number of compounds  Elements bond with each other, seeking stability."— Presentation transcript:

1 Chemical Bonds

2  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  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  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  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, H 2 O, water, has two atoms of Hydrogen and one atom of oxygen

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7  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

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9  Uses dots around the chemical symbol to show number of valence electrons

10  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

11  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

12  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

13  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

14  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

15  Single covalent bonds share one pair of electrons, example is water H 2 O 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 N 2  Covalent bonds form between non-metals  Many covalent compounds are liquids or gases at room temperature

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17  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

18 Water is Polar Carbon Tetrachloride is non-polar

19  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: Cl 2

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21  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”

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24  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 MgCl 2  It takes two chlorine atoms to cancel out the +2 charge of Mg to zero  Criss-Cross method

25  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

26  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

27  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 K 2 SO 4 is potassium sulfate

28  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

29  CO is Carbon Monoxide  CCl 4 is Carbon Tetrachloride  H 2 O is Dihydrogen Monoxide Your Turn NO 2 N 2 O 5


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