Bonding Chapter 5

Bonding When atoms combine they form a chemical bond The force of attraction between two or more atoms.

Valence Electrons Are the outer most electrons of an atom. They play a huge role in how an atom bonds.

Lewis Structure Is a diagram of atoms that only shows the valance electrons Ex: Cl Na H Ar

The Octet Rule The octet rule says that atoms tend to gain, lose or share electrons so they can have eight electrons in their outer shell. They do this because they are more stable with a complete outer shell. There are some situations where it does not apply. For example, hydrogen wants to take one on to complete its outer shell with 2 electrons.

Oxidation Numbers Oxidation numbers represent the charges that an ion has when it gains or loses its valence electrons. They are listed as a + or –above each column on the periodic table.

Ion An ion is an atom which has lost or gained one or more electrons, making it positively or negatively charged. A negatively-charged ion, gains an electrons so it has more electrons then it has protons. A positively-charged ion, looses electrons so it has more protons then electrons. A polyatomic ion is an ion that is made up of more than one atom. Poly= Many Atomic= Atoms Ex: NH4+ is the chemical formula for an ammonium ion. It contains two elements nitrogen and hydrogen and has a positive charge.

Ionic Bonds Bonds that form as a result of the attraction between positive and negative ions. The atoms are attracted to each other because of their opposite charges We call the compound that results from the bond an Ionic Compound. Usually form between a metal and a nonmetal

F K In an IONIC bond, electrons are lost or gained, resulting in the formation of IONS in ionic compounds. F K

K F

K F

K F

K F

K F

K F _ + The compound potassium fluoride consists of potassium (K+) ions and fluoride (F-) ions

K F _ + The ionic bond is the attraction between the positive K+ ion and the negative F- ion

Formulas Reminder: A chemical formula is the combination of symbols that show the elements in the compound. i.e. MgCl2 If a molecule contains more than one atom of a particular element, you indicate it by using a subscript after the chemical symbol (ex: the 2 in MgCl2). It tells you the ratio of atoms in the compound (MgCl2 has a 1:2 ratio). If no subscript is written the number 1 is understood( NaCl there is a 1:1ratio). A coefficient acts as a multiplier for all of the atoms in the entire compound, it is found in front of the chemical formula Ex: the 5 in 5 MgCl2

Example MgCl2 Here we have one molecule of magnesium chloride.  The subscript 2 in the formula above only pertains to the chlorine in the compound.   The total number of atoms in the compound is 3. Now let us put a coefficient in front of the molecule and see how that changes things. 5 MgCl2 The coefficient 5 refers to the entire molecule.   It shows that there are 5 compounds of magnesium chloride. Since each molecule is made up of 3 atoms, the total number of atoms is now 15.  There are 5 magnesium atoms and 10 chlorine atoms. How many atoms are in the following bond 3Na2S Sodium(Na)____ Sulfur(S)____ Sodium Sulfide(3Na2S) ____ = total atoms 6 3 9

Naming Ionic Compounds The name of the positive ion comes first, followed by the name of the negative ion. The metal will be the positive because it gives away electrons and the nonmetal will be the negative because it gains electrons. If the negative ion is a single element the end of its name changes to –ide. Ex: NaCl- Sodium Chloride MgO- Magnesium Oxide If the negative ion is polyatomic, its name usually ends in –ate or – ite. Ex: NH4NO3- Ammonium nitrate What is the name of the ionic compound with the formula K2S? ______________ Potassium Sulfide

Properties of Ionic Compounds Hard Brittle Crystals High melting points- NaCl melts at 801˚C= 1473.8 ˚F When dissolved in water they are electrolytes. An electrolyte solution is one that can conduct electricity. Ionic bonds in solid from are poor conductors.

Covalent Bonds The chemical bond formed when two atoms share electrons. Usually form between nonmetals. We call the neutral group of atoms joined by a covalent bond a molecule.

In covalent bonding, atoms still want to follow the octet rule and have a complete valance shell

But rather than losing or gaining In covalent bonding, atoms still want to follow the octet rule and have a complete valance shell But rather than losing or gaining electrons, atoms now share an electron pair.

The shared electron pair is called a bonding pair In covalent bonding, atoms still want to follow the octet rule and have a complete valance shell But rather than losing or gaining electrons, atoms now share an electron pair. The shared electron pair is called a bonding pair

Chlorine forms a covalent bond with itself Cl2

How will two chlorine atoms react? Cl Cl

Cl Cl Each chlorine atom wants to gain one electron to achieve a full outer shell.

Cl Cl do to achieve an octet? What’s the solution – what can they Neither atom will give up an electron. What’s the solution – what can they do to achieve an octet?

Cl Cl

Cl Cl Cl Cl

Cl Cl

Cl Cl

Cl Cl complete

Cl Cl complete

Cl Cl The complete outer shell is achieved by each atom sharing the electron pair in the middle

Cl Cl The complete outer shell is achieved by each atom sharing the electron pair in the middle

Cl Cl This is the bonding pair

Cl Cl It is called a SINGLE BOND

Single bonds are abbreviated Cl Cl Single bonds are abbreviated with a dash

This is the chlorine molecule, Cl Cl This is the chlorine molecule, Cl2

O2 Oxygen is also one of the diatomic molecules

O How will two oxygen atoms bond?

O Each atom has two unpaired electrons

O Oxygen atoms want to gain two electrons.

Both electron pairs are shared.

O O 6 valence electrons plus 2 shared electrons = full valance shell

O O 6 valence electrons plus 2 shared electrons = full valance shell

O O two bonding pairs, making a double bond

O O = For convenience, the double bond can be shown as two dashes.

This is the oxygen molecule, = This is the oxygen molecule, O2

Molecular Compounds A compound that is composed of molecules. Ex: CH4- Methane H2O- Water Properties: Low melting and boiling points. Poor conductors

Polar Bonds A covalent bond in which electrons are shared unequally is called a polar bond. ex: water molecules One atom pulls more strongly on a shared electron causing a slight charge. Polar molecules tend to pull close together because the negative end of each molecule is attracted to the positive end of other molecules.

Nonpolar Bonds If the electrons are shared equally it is called a nonpolar bond. A molecule may contain a polar bond and still be nonpolar overall. In order for this to happen the molecule must bond in a straight line with opposite pulling. Ex: carbon dioxide There is little attraction between non polar molecules

Why Doesn’t Oil & Water Mix? The molecule in vegetable oil are nonpolar and have little attraction to other molecule. Water molecules are polar and are strongly attracted to one another. SO, the water stays with the water which leave the oil by itself. Adding soap allows them to mix easily because the soap molecule contains one end that is an ionic bond and the other end is a nonpolar covalent bond. The nonpolar end mixes with the oil and the charge on the ionic end attracts the water

Metallic Bonds An attraction between a positive metal ion and the electrons surrounding it. In other words: Many electrons are shared by many atoms. A metal consists of positively charged metal ions embedded in a “sea” of valence electrons.

Metallic Properties The “sea of electrons” model of solid metals explains their properties: Heat/electrical conductivity The free moving valance electrons make it easier for the particles to move faster. Changes in shape Ductile Malleable This happens because the ions in the metal are not attracted to each other, instead they are attracted to the loose electrons all around them. Luster A metals luster is due to its valance electrons. They absorb and then reflect the light which we see has shiny.