Chemical Bonds. A chemical bond is the force of attraction holding atoms together due to the transfer or sharing of valence electrons between them.

Transcription

1 Chemical Bonds A chemical bond is the force of attraction holding atoms together due to the transfer or sharing of valence electrons between them. Atoms will either gain, lose or share electrons in order to chemically combine with other atoms and fill their valence shells. (either 2 or 8 electrons) Atoms react in a way that will make them more stable. May 22 12:03 PM IONS When atoms gain or lose electrons, they become ions with an electrical charge. Anions have a negative charge due to the gain of Cations have a positive charge due to the loss of Ionic Bonds May 22 12:05 PM 1

2 May 22 2:25 PM Ionic Bonds Ionic bonds form from attractions between cations and anions when electrons are transferred from a metal to a non metal atom. *Exception Metal atoms form (+) ions when they lose all of their valence Non metal atoms form ( ) ions when they gain enough electrons to get an octet*. image found at nacl.gif Mar 19 7:45 AM 2

3 Characteristics of Ionic Bonds pull out the main characteristic of ionic compounds and write them on the notepad Ionic compounds tend to be solid at room temperature. When dissolved in water, they conduct electricity. Ionic compounds are made from a metal and nonmetal and have large differences in electronegativity. They also have higher melting points and boiling points than the molecules formed from covalent bonds. Na Cl Mar 19 7:45 AM Chemical Formulas Compounds are represented by chemical formulas that show the ratio of the elements that compose them. The subscript is the number of atoms of each element in the compound. Number 1 is understood if no number is shown. May 22 12:07 PM 3

4 Covalent Bonds A covalent bond is the chemical bond formed between two typically non metal atoms when they share When the atoms come near each other, the electrons of one atom are attracted towards the protons of the other atom. If the outside shell is not filled, this attraction becomes stronger. The electrons are now being shared by both atoms, and they both have a full outer shell. Nov 28 8:21 AM Characteristics of Covalent Bonds pull out the main characteristic of ionic compounds and write them on the on the notepad Covalent compounds tend to be gases at room temperature. They are not conductive. Covalent compounds are also known as molecules and are made from two or more nonmetals. They have small differences in electronegativity. Molecules also have lower melting points and boiling points than ionic compounds. O C O Mar 19 7:45 AM 4

5 Multiple Bonds A double bond occurs when 2 atoms share 2 pairs of A triple bond forms when 2 atoms share 3 pairs of May 22 12:07 PM Polar Bonds A polar bond is a covalent bond where electrons are shared unequally. It is formed because atoms of some elements pull more strongly than others on shared Polar molecules like water are attracted to each other, as nonpolar molecules are attracted to nonpolar molecules. May 22 12:10 PM 5

6 How many Valence Electrons are in each group? Click on group # to see the answers, remember that He is different and has Valence Electrons Remember atoms with 1,2 or 3 valence electrons will give away their valence electrons to look like a noble gas in the period above. Pos ionic table 6

7 Atoms with 5,6 or 7 valence electrons will steal valence electrons to look like a noble gas in their period. neg periodic table Steps for determining ionic and covalent bonds Figure out valence electrons Will the atom steal or give? 1, 2 or 3 will give and 5, 6, or 7 will steal If it gives it will become a positive ion. It will be positive the number it needs to get rid of. If it steals it will become a negative ion. It will be negative the number it needs to steal to get 8. Negative & negative will be covalent, negative & positive will be ionic. Steps ionic/covalent 7