Chemical Formulas and Bonding Chapter 7

Ionic Bonding In an ionic bond, a positively charged ion is attracted to a negatively charged ion. –Ionic compounds are composed entirely of ions. Cations are positively charged ions Anions are negatively charged ions

Ionic compounds are electrically neutral, so the electrical charges of the cations and anions must balance. –Example: NaCl

The Octet Rule – atoms tend to gain, lose, or share electrons in order to acquire a full set of valence electrons (8 in the s and p orbital, except hydrogen and helium) Electron moves here!

Lewis Dot Diagrams or Electron Dot Diagrams – Valence electrons are represented as dots placed around the element symbol. Small x’s or o’s can also be used instead of dots. Sodium

Types of Ions –Monatomic Ions – made up of one atom –Cations are named according to the element name –Anions are named according to the element name, but add “ide” to the end Monatomic cations and anions examples:

–Polyatomic ions – made from more than one atom Polyatomic cations and anions examples:

–Binary Ionic Compounds – compound which contains only two elements Empirical formula – ratio of ions in a compound Examples: Na +1 Cl -1  Na 1 + Cl 1 -  NaCl Ca +2 F –1  Ca +2 F –1  Ca 1 F 2  CaF 2

Covalent Bonding Formed by a shared pair of electrons between two non-metal atoms –Molecule – a group of atoms that are united by covalent bonds Molecular substance – a substance that is made of molecules Molecular formula – tells how many atoms are in a single molecule of the compound. Structural Formula – specifies which atoms are bonded to each other in a molecule Lewis structures – based on the Lewis dot diagrams for atoms

Lewis structures can be drawn using either dots or dashes. –Each dot represents an electron –Dashes represent a pair of electrons –Lone pairs are electrons that are not used in covalent bonding. –Bonding pairs are the shared electrons between atoms.

Ammonia NH 3 made up of a covalent bond between nitrogen and hydrogen Each atom in the bond has a stable electron configuration ~ hydrogen only needs 2 electrons, but nitrogen needs 8.

Carbon tetrachloride CCl 4 –Carbon and chlorine both have a stable octet of electrons surrounding them.

Multiple Bonds – bonds between atoms where more than two electrons are shared –Single covalent bond – one pair of electrons are shared –Double covalent bond – two pair of electrons are shared –Triple covalent bond – three pair of electrons are shared

Methane – single covalent bonds between hydrogen and carbon Ethyl Alcohol, Ethanol C 2 H 5 OH– single covalent bonds between hydrogen, carbon and oxygen

Carbon dioxide – double covalent bond between carbon and oxygen, giving each element an octet Oxygen gas – double covalent bond between oxygen atoms, giving each an octet..

Cyanic acid – triple covalent bond between carbon and nitrogen, giving each an octet. Hydrogen only needs two to be stable! Nitrogen gas – triple covalent bond between nitrogen atoms, giving each an octet...

Nonpolar covalent bonds occur when atoms exert an approximately equal pull on the electrons in the bond.

Exceptions to the octet rule cause bonding that is unusual. B F F F

Naming Chemical Compounds Compounds are named according to the atoms and bonds that compose it Ionic compounds are named based on the ions that are involved –Cations are named according to their element name –Anions are named according to their element, but the ending is changed to “ide” or polyatomic ion name Example: KI is called potassium iodide, not potassium iodine –Cu(NO 3 ) 2 is called copper II nitrate

Molecular Compounds are named similar to ionic compounds, except for the anion. –First element is named according to the element name. If it has more than one of that element, then you must use a prefix –Second element is named according to the element name, plus the “ide” ending, but depending on the number of atoms of that element, a prefix must be used Example: CO 2 is called carbon dioxide, because of the 2 oxygen atoms

Naming acids depends on the ions that make up the acid –Diatomic compounds, such as HF, are named first by hydro for the hydrogen, then fluoride for the fluorine –However, fluoride is changed to fluoric, giving the name hydrofluoric acid –Acids containing polyatomic ions do not have hydro as a prefix, but are named according to the polyatomic ion The ending for the ion depends on the number of oxygen atoms or the name of the polyatomic ion

Example: HNO 3 is called nitric acid, but HNO 2 is called nitrous acid ate = ic ite = ous At the right are common acids and their anions Sulfate = sulfuric Phosphate = phosphoric