Chapter 6: Chemical Bonds 6.1 Ionic Bonding Chapter 6: Chemical Bonds

Stable Electron Configurations If highest energy level of an atom is filled with e-, the atom is stable and not likely to react Chemical properties of an element depend on the number of valence electrons Electron (Lewis) dot diagram = model in which each dot represents a valence electron

Stable Electron Configurations Highest energy level of a noble gas atom is completely filled Noble gases have stable electron configurations with 8 valence electrons (two electrons in helium). Elements tend to react to get electron configurations similar to noble gases

Chemical Bonding http://www.youtube.com/watch?v=_M9khs87xQ8

Chemical bonding Elements can get a stable electron configuration by transferring of electrons Ex: A chlorine atom has one electron fewer than an argon atom, adding one electron would give chlorine a stable configuration Ex: A sodium atom has one more electron than a neon atom, removing one electron would give sodium a stable configuration.

Chemical bonding When sodium reacts with chlorine, an electron is transferred from sodium atom to chlorine atom Each atom ends up with a more stable electron arrangement than it had before transfer

Chemical Bonds Electron moves from Na to CL

Formation of Ions Ionic Bonds = transfer of electrons When an atom gains or loses an electron, the number of protons does not equal number of electrons Charge on the atom is not balanced, and atom is not neutral Ion = Atom that with positive or negative charge Charge on an ion is represented by a plus or a minus sign Negative charge = anion Positive charge = cation

Ionic Bonds Ex: Ion that forms when a chlorine atom gains an electron has 17 protons and 18 electrons This ion has a charge of 1–. The symbol for the ion is written Cl1–, or Cl– for short. Anions like the Cl– ion are named by using part of the element name plus the suffix –ide. Thus, Cl– is called a chloride ion.

Ionic Bonds Sodium ion has 11 protons and 10 electrons. The sodium ion has a charge of 1+. The symbol for the ion is written Na1+, or Na+ for short. An ion with a positive charge is a cation. A cation uses the element name, as in the sodium ion.

Formation of Ionic Bonds A particle with a negative charge will attract a particle with a positive charge Chemical bond = force that holds atoms or ions together as a unit Ionic bond =force that holds cations and anions together, forms when electrons are transferred from one atom to another (metal and non-metal)

Ionization Energy Cations (+) form when electrons gain enough energy to escape from atoms Energy allows electrons to overcome the attraction of the protons in the nucleus Ionization energy = of energy used to remove an electrons The lower the ionization energy, the easier it is to remove an electron from an atom

Ionization Energy

Ionic Compounds Compounds that contain ionic bonds are ionic compounds, can be represented by chemical formulas Chemical formula = shows what elements are in a compound, and how many of each Ex: Chemical formula for sodium chloride, NaCl, indicates one sodium ion for each chloride ion in sodium chloride

Binary ionic compounds Compound made from only two elements is a binary compound The names have a predictable pattern: The name of the cation followed by the name of the anion. Examples: sodium chloride

Describing ionic compounds Formula of an ionic compound describes the ratio of the ions in the compound 2 different compounds of copper and oxygen are below Has to be at least two names to distinguish red copper oxide from black copper oxide.

Polyatomic ions Polyatomic ion = covalently bonded group of atoms that has a positive or negative charge Most simple polyatomic ions are anions

Ionic Compounds What is the chemical formula for magnesium chloride?

Ionic Compounds What is the chemical formula for magnesium chloride? MgCl2

Naming ionic compounds Write the name of the metal first and then the nonmetal. Add an -ide ending to the non-metal Use Roman Numerals to indicate charge on a transition metal Ionic compounds involving polyatomic ions follow the same basic rule: Write the name of the metal first, Then the name of the polyatomic anions

Section 6.2 Covalent Bonds Chapter 6: Bonding

Covalent Bond Sharing of valence electrons Non-metal and Non-metal Attraction between shared electrons and the protons in each nucleus hold the atoms together in a covalent bond

Covalent Bond

Covalent Bond

Sharing electrons When two atoms share one pair of electrons, the bond is called a single bond Hydrogen atom has one electron, if had two electrons, it would have the same electron configuration as a helium atom Two hydrogen atoms can achieve a stable electron configuration by sharing their electrons and forming a covalent bond

Molecules of elements Molecule = neutral group of atoms that are joined together by one or more covalent bonds Many nonmetal elements exist as diatomic molecules Diatomic means “two atoms”

Br-I-N-Cl-H-O-F Brinclhof Memory Trick: Br-I-N-Cl-H-O-F Brinclhof Sounds like a German name. There’s also: I Brought Clothes For Our New Hamster … either way…

Diatomic Molecules Bromine: Iodine: Nitrogen: Chlorine: Hydrogen: Oxygen: Fluorine:

Multiple covalent bonds 2 pairs of electrons shared = double bond 3 pairs of electrons shared = triple bond Nitrogen has five valence electrons. When the atoms in a nitrogen molecule (N2) share three pairs of electrons, each atom has eight valence electrons Each pair of shared electrons is represented by a long dash in the structural formula NN

Unequal sharing of electrons Polar covalent bond = atom with the greater attraction for electrons has a partial negative charge Other atom has a partial positive charge Happens because the e- are closer to one atom than the other (one atom attracts e- more) Type of atoms in a molecule and its shape are factors that determine whether a molecule is polar or nonpolar

Unequal sharing of electrons Except for noble gases, elements on the right of the periodic table tend to have a greater attraction for electrons than elements on the left Elements at the top of a group tend to have a greater attraction for electrons than elements at the bottom of a group have.

Polar covalent bond Covalent bonds= atoms attract electrons equally and are shared equally

Attraction between molecules Attractions between polar molecules are stronger than attractions between nonpolar molecules Bonds between polar molecule are stronger than non polar

Naming covalent bonds Prefixes tell you how many of each atom you have Prefix goes in front of the element name Mono- 1 Di -2 Tri – 3 Tetra -4 Penta – 5 Hexa – 6 Hepta – 7