Covalent Bonding Physical Science

Covalent Bonding Covalent bonding Compounds composed only of anions (negative nonmetals) share electrons in covalent bonds. Bonding in which e- are shared. Each atom fills up its valence shell w/ shared e-. Sharing 1 pair of e- = single bond 2 pairs of e- = double bond 3 pairs of e- = triple bond

Properties of Covalent compounds ELECTRONS ARE SHARED BETWEEN NONMETALS low melting points do not break into ions / do not dissolve

Properties of Covalent compounds poor conductors of electricity liquid or gas at room temperature

Properties of Covalent compounds can be polar or nonpolar Amorphous solids – not arranged in a regular repeating pattern

Molecules Molecule Combo of atoms formed by covalent bonds. Not made of ions!

Ball-And-Stick Models Atomic Centers Shared Pairs of Electrons

MORE ABOUT COVALENT MOLECULES Monatomic Molecule– exist as single atoms (noble gases like He and Ne) Diatomic Molecule – a molecule consisting of two atoms of the same element (O2, F2) They can have double, single and triple bonds. There are only 3 molecules that form triple bonds – Carbon, Nitrogen, and Phosphorus

Diatomic Elements Diatomic elements Never exist alone as single atom. Always bonded covalently. Seven diatomic elements (know these!): Hydrogen = H2 Oxygen = O2 Chlorine = Cl2 Iodine = I2 Nitrogen = N2 Fluorine = F2 Bromine = Br2

Diatomic Elements Remember: Mr. BrINClHOF (pronounced “brinklehoff”) You will always have a molecule of each of these elements instead of a single atom.

Diatomic Elements

NOT ALL COVALENT BONDS ARE EQUAL Nonpolar Covalent Bond atoms in the bond pull equally (especially identical atoms), and share electrons equally.

NOT ALL COVALENT BONDS ARE EQUAL Polar Covalent Bond electrons are shared unequally. One atom wants the electrons really badly but isn’t strong enough to pull them away. It holds the electrons closer and is slightly negative. The other atom has a slightly positive charge.

Polar Covalent Bonding A perfect example of a polar covalent molecule is water.

Weird example time!

Little Dog and Big Dog both have strong grips and they like to share dog bones.

Little Dog and Big Dog both have strong grips and they like to share dog bones. Sharing dog bones is like a covalent bond.

When 2 Big Dogs share a bone, they share…

When 2 Big Dogs share a bone, they share equally – nonpolar covalent Because the 2 Big Dogs are the same – they represent a diatomic molecule

2 Little Dogs share a bone = DIATOMIC MOLECULE – 2 of the same elements sharing

2 Little Dogs share a bone = share equally. (nonpolar, diatomic) DIATOMIC MOLECULE – 2 of the same elements sharing

When Big Dog and Little Dog share a bone…

Big Dog has a stronger pull on the bone and the dogs share unequally – polar covalent bond

Each bone represents a PAIR of electrons.

Big Dog and Little Dog can share 1, 2, or 3 bones. SINGLE COVALENT BOND DOUBLE COVALENT BOND TRIPLE COVALENT BOND

Naming Molecules Very simple! Look at subscripts and elements in formula. 1st element: prefix (if subscript > 1) + element 2nd element: prefix + element ending in –ide. Prefixes: 1 = mono 2 = di 3 = tri 4 = tetra 5 = penta 6 = hexa 7 = hepta 8 = octa 9 = nona 10 = deca

The second element ends in –ide. Octa- 8 Hepta- 7 Hexa- 6 Penta- 5 Tetra- 4 Tri- 3 di- 2 Mono- 1 Prefix to use Number COVALENT PREFIXES If it is two negatives, the bond is covalent and you use prefixes to indicate the number of elements in the compound. The second element ends in –ide.

Examples CS2 = carbon disulfide CO = carbon monoxide N2F4 = dinitrogen tetrafluoride P2S6 = diphosphorus hexasulfide BrF = bromine monofluoride P4O10 = tetraphosphorus decoxide

Carbon monoxide Sulfur dioxide CO SO2 Octa- 8 Hepta- 7 Hexa- 6 Penta- 5 Tetra- 4 Tri- 3 di- 2 Mono- 1 Prefix to use Number COVALENT PREFIXES CO Carbon monoxide SO2 Sulfur dioxide

Phosphorus pentaiodide Octa- 8 Hepta- 7 Hexa- 6 Penta- 5 Tetra- 4 Tri- 3 di- 2 Mono- 1 Prefix to use Number COVALENT PREFIXES N2O3 Dinitrogen trioxide PI5 Phosphorus pentaiodide

Practice CCl4 N2O carbon tetrachloride SF6 dinitrogen monoxide sulfur hexafluoride

One Final Note The final vowel in prefixes is often dropped for oxygen. Example: CO = carbon monoxide NOT: carbon monooxide Except when the prefix ends in “i” Example: SO3 = sulfur trioxide

Ionic Vs Covalent Compounds Ionic and covalent cmpds are alike b/c: Formed from 2 or more atoms bonding together. Atoms more stable w/ 8 val. e-.

Ionic Vs Covalent Compounds Ionic and covalent cmpds are diff. b/c: Ionic cmpds = metal + nonmetal Covalent cmpds = nonmetal + nonmetal Ionic cmpds  transfer of e- Covalent cmpds  sharing e- Ionic cmpds  not named using prefixes Covalent cmpds  named using prefixes

Ionic Vs Covalent Compounds Ionic and covalent cmpds are diff. b/c (cont.) Ionic cmpds do not form separate molecules. Covalent cmpds do form molecules. Ionic cmpds = high melting temps. Covalent cmpds = low melting temps. Ionic cmpds = conduct elec. current when dissolved in H2O. (electrolytes) Covalent cmpds = do not conduct elec. current when diss. in H2O (non-electrolytes)

Comparison Chart IONIC COVALENT transferred from metal to nonmetal shared between nonmetals Electrons Melting Point high low Soluble in Water yes usually not yes (solution or liquid) Conduct Electricity no crystal lattice of ions, crystalline solids molecules, odorous liquids & gases Other Properties

Metallic Bonding Metallic bonding Bond formed b/w metal atoms. “Sea of electrons” e- flow freely through metal sample. This is why metals: are good conductors have high melting points are flexible

Metallic Bonding 1. Solids (s) at room temperature ELECTRONS ARE SHARED IN A COMMON “POOL” OR “SEA” BETWEEN POSITIVE METAL NUCLEI 1. Solids (s) at room temperature 2. High melting and boiling points 3. Good conductors of heat and electricity 4. Malleable and ductile

Alloys Alloys Hom. mix. of metals. Held together by metallic bonds. Have properties of metals. Examples: Gold alloy = Au + Ag, Cu, Ni, or Zn Bronze = copper + tin Brass = copper + zinc Steel = iron + carbon Stainless steel = Fe + Cr + a little C Aluminum alloy = Al + Mg, Mn, or Cu

Types of Bonds Predicting bond type: B/w metal & nonmetal = ionic bond B/w nonmetal & nonmetal = covalent bond B/w metal & metal = metallic bond

Let’s review! Two positives (++) DO NOT BOND. Two negatives (- -) will form a covalent bond. The name is determined using prefixes.

Let’s review! A positive and a negative (+ - )make an ionic bond. Charges need to be crisscrossed to get the formula. To name it, say the cation first (with roman numerals if it is a DFP metal) and then the anion with –ide.

Let’s review! Roman numerals are ONLY for Transition metals. Prefixes are ONLY for covalent. Crisscrossing is ONLY for Ionic.

Au 2+ and AS 3- Rb 1+ and Br 1- S 2- and Se 2- P 3- and I 1- PRACTICE BONDING Au(II) and As Au 2+ and AS 3- IONIC Au3As2 S and Se S 2- and Se 2- Covalent SSe Rb and Br Rb 1+ and Br 1- IONIC RbBr P and I P 3- and I 1- Covalent PI3