Presentation on theme: "Atom Stability * In order for atoms to be stable, they need to have their outer energy level completely filled. * In most cases, atoms need to have 8 valence."— Presentation transcript:
Atom Stability * In order for atoms to be stable, they need to have their outer energy level completely filled. * In most cases, atoms need to have 8 valence electrons in their outer energy level (8 is great ). * Atoms with 8 valence electrons are said to have octets.
The Noble Gases (group 18) naturally have octets and are said to be chemically stable. All other atoms must either lose or gain electrons to become stable. There are 2 exceptions to the octet rule: Hydrogen which will lose one electron to be stable and Helium which has a full outer shell with 2 electrons (because it only has 1 energy level)
Electron Losers & Gainers Atoms want to become stable by doing the least amount of work possible. Consider the following analogy: You are sitting at a table all by yourself . 7 of your friends are sitting at the table next to you. From a work standpoint (not popularity), will it be less work for you to join your 7 friends or all 7 of your friends to join you? Of course, from a work standpoint, it takes less work for you to join your friends.
Who gains, who loses?? Is it easier for group one atoms to lose their 1 valence electron or to gain 7more? Group 1 = Lose 1 electron Is it easier for group two atoms to lose their 2 valence electrons or to gain 6 more? Group 2 = Lose 2 electrons Is it easier for group thirteen atoms to lose their 3 electrons or to gain 5 more? Group 13 = Lose 3 electrons
Is it easier for group fourteen atoms to lose 4 valence electrons or to gain 4 more? Group 14 = Lose 4e- or Gain 4e- Is it easier for group fifteen atoms to lose 5 valence electrons or to gain 3 more? Group 15 = Gain 3 electrons Is it easier for group 16 atoms to lose 6 valence electrons or to gain 2 more? Group 16 = Gain 2 electrons
Is it easier for group seventeen atoms to lose 7 valence electrons or to gain 1 more? Group 17 = Gain 1e- In general, metals are electron losers and non-metals are electron gainers
Ions vs. Atoms After an atom has lost or gained electrons, it becomes an ion. An ion will have a positive or a negative charge. In an atom, the number of protons is equal to the number of electrons. a) The number of positive charges equals the number of negative charges. b)The overall charge of any atom is ZERO.
Example: Lithium An atom of lithium has 3 protons and 3 electrons An atom of lithium is electrically neutral because the (+) = (-), however, it is unstable + + + e e e Valence electron This energy level can hold 8 electrons, it needs 7 more to be stable
Lithium will lose its 1 valence electron to become stable. Once Lithium loses its 1 valence electron, the number of (+) = (-) Now lithium has 1 more (+) than (-). Lithium has become an ion with a charge of 1+. Written as Li 1+ + + + e e Now, Lithium has a complete outer energy level. Lithium is now stable
Example: Fluorine An atom of fluorine has 9 protons and 9 electrons. An atom of fluorine is electrically neutral; however, it is unstable + + + + + + + + + e e e e e e e This energy level can hold 8 electrons, it needs one more to become stable e e
Fluorine will gain 1 electron to become stable. Once fluorine gains an electron, the number of (+) = (-) Now, fluorine has 1 more (-) than positive. Fluorine has become an ion with a charge of 1- Written as F 1- + + + + + + + + + e e e e e e e e e e Now, fluorine has a complete outer shell.
Metals * All atoms that lose electrons and form positive ions are called cations. * All metals form cations * Metals are electron losers ++
Non - metals * All atoms that gain electrons and form negative ions are called anions. * All non-metals form anions. * Non-metals are electron gainers --
Bonding Atoms become stable by transferring or sharing electrons with other atoms. Ionic Bonds are formed between oppositely charged ions a) transfer electrons b) occur between metals and non-metals NaCl (salt) c) Conduct electricity when dissolved in water
Covalent Bonds Defined as the force of attraction between the nuclei of atoms and the electrons shared by the atoms. a) occur between non-metals b) tend to 1) have low boiling points 2) have low melting points 3) brittle in the solid state
c) Two types of covalent bonds 1) non-polar atoms share electrons equally ex:F 2 2) polar atoms do not share electrons equally ex: H 2 O Oxygen has a stronger pull for the electrons. The Oxygen end will have a slight negative charge and the Hydrogen end will have a slight positive charge. O - H +
Covalently bonded atoms are called molecules. Molecules are defined as a neutral group of atoms held together by covalent bonds Diatomic Molecules – two atoms covalently bonded together. 1) Seven elements exist as diatomic molecules naturally: Hydrogen, Oxygen, Nitrogen, Fluorine, Chlorine, Bromine, Iodine
Lewis Dots Model that only shows the valence electrons. How to draw Lewis Dots: 1) Write the symbol of the atom Mg 2) Image 4 boxes around the symbol Mg Each box can only hold two electrons. Place dots in the boxes to represent the number of valence electrons.
Draw the Lewis Dot Representations for the following: SodiumChlorine CalciumBromine OxygenBeryllium CarbonPotassium HydrogenLithium Nitrogen Aluminum Fluorine
Draw Lewis Dots showing how the following pairs will bond 1)Lithium and Bromine 2)Potassium and Sulfur 3)Calcium and Iodine 4)Magnesium and Fluorine 5)Sodium and Oxygen 6)Beryllium and Chlorine 7)Lithium and Oxygen 8)Sodium and Sulfur 9)Calcium and Oxygen 10)Magnesium and Chlorine