Topic: Covalent Bonds and Properties 1.Why do atoms form bonds? 2. How do atoms form bonds? To attain a noble gas configuration By gaining, losing, or sharing electrons Gain or loss of electrons  ionic bonding Sharing of electrons  covalent bonding Sharing of electrons  covalent bonding

REVIEW… Forming a bond = more stable = releases energy –A + B  AB + energy Breaking a bond = elements by themselves are less stable = requires energy –CD + energy  C + D

- Review: Ionic Compounds – made of ions Form crystal lattice All are solid at room temp Ion is surrounded by 6 opposing ions…So, strong electrostatic attraction Thus, high MP/BP, low VP

Covalent Bonding Results from Nonmetals ONLY There is an electrostatic attraction between nucleus (protons) one atom & electrons of neighbor’s atom Electrons are shared

Compounds with covalent bonds are molecular!  covalent compounds are often called molecules

Structure of Covalent Compounds NOT necessarily empirical - a lot are molecular….we can keep adding atoms! glucose lipids C 6 H 12 O 6 (fats) empirical molecular

Covalent Molecules are held together by IMF IMF holds molecules together IMF can be dispersion (nonpolar) Dipole-dipole (polar) H-bond (polar) Remember IMF determines phase

weakest IMF = dispersion forces - occur between nonpolar molecules - occur between nonpolar molecules ● Monatomic molecules: He, Ne, Ar, Kr, etc. ● Diatomics of same element: O 2, H 2, N 2, etc ● Pure Hydrocarbons: C x H y ● Small Symmetric molecules: CO 2, CCl 4 Dispersion forces ↑ as size molecule ↑

Properties of Covalent Molecules Depend on strength of IMF between “particles” or separate units (molecules)

Properties of Covalent (Molecular) Substances are determined by IMF between the molecules Poor conductors of heat & electricity (no charged particles!) Low mp & low bp easy to pull molecules apart from each other Majority of solids are soft Low H f and H v compared to ionic & metallic substances High VP compared to ionic & metallic substances

mp, bp, H f and H v and vapor pressure depend on how hard it is to pull particles apart Weak IMF – easy to pull particles apart Strong IMF – more difficult to pull apart

Which substance has the strongest intermolecular forces? The weakest? Water Ether

bond formed when: – 2 atoms share pair electrons but both electrons donated by same atom many polyatomics have coordinate covalent bonds must be able to recognize them Another Type of Covalent Bonding: Coordinate Covalent Bonding = Polyatomic Ions from Table E

Ammonium, NH 4 +1 H : N : H H H +1 2 electrons just hanging around no electrons at all!

Ammonium, NH 4 +1 H : N : H H.. H.. +1 Both electrons in this bond were donated by the N atom

Hydronium, H 3 O +1 H : O : H H +1 2 pairs of nonbonding electrons zero electrons

Hydronium, H 3 O +1 H : O : H H Both electrons are provided by the oxygen atom

Another Type of Covalent Bonding: Network Covalent Bonding Atoms (often Si or C) covalently bonded to one another – THEY MAKE A LATTICE Example: SiO 2 (sand), Diamonds (C), Graphite (C) They are very hard, Low Vp, High MP Not soluble in water It networks – that’s where it gets it’s strength (so diff. properties)

Carbon = forms networks, like above and in organic chemistry it can also form long chains and rings