Covalent Bonds Bonding of nonmetal to nonmetal. All elements want to gain electrons, so they must SHARE valence electrons. Study your ion chart everyday!! Quiz this Friday!

A.6 Chemical Bonding It’s a lot like dogs…

ATOMIC STRUCTURE HELIUM ATOM NEON ATOM Label the protons, neutrons, and electrons in their correct locations on the diagrams below. This first shell surrounding the nucleus can hold ________ electrons and the second shell can hold ________ electrons. Where are the valence electrons??

ELECTRON-DOT DIAGRAMS The valence electrons of an atom can be written in the following way, where the electrons are represented by dots around the chemical symbol of the element. Imagine that you are writing the dots on a square around the chemical symbol.

Atomic Structure NAMESYMBOLATOMIC NUMBERNUMBER OF ELECTRONS IN OUTERMOST ENERGY LEVEL ELECTRON DOT FORMULA HYDROGE N H11 H LITHIUM BORON NEON FLUORINE

Why do atoms bond together? Atoms bond together to become more like Noble Gases in electron arrangement. Bonding produces new substances. Involves only the 'outer shell' or 'valence' electrons stable

Atoms can bond in several ways … COVALENT BONDING – sharing electrons to form molecules with covalent bonds –formed between two nonmetals in a molecule. IONIC BONDING - By one atom transferring electrons to another atom.

Covalent and Ionic Bonding

Covalent Bonding Example 1: 2 hydrogen atoms (1) form the molecule of the element hydrogen H2 Two hydrogen atoms with their valence electrons. How many electrons would make these atoms stable? Both atoms need one electron to fill their outer valence level, so they SHARE an electron. Now they both have 2 electrons in the outer energy level.

Covalent Bonding Example: 2 atoms of hydrogen (1) combine with 1 atom of oxygen to form water H 2 O H2OH2OH2OH2O

Molecular shapes determine the chemical and physical properties like boiling point and viscosity VSEPR Model –V alence S hell E lectron P air R epulsion specific bond angles are formed between terminal and central atoms. Lone pairs of electrons occupy a slightly larger orbital and “push” shared electron bonding orbitals together.

Molecular Shapes e-pairsNotationName of VSEPR shape Examples 2AX 2 LinearHgCl 2, ZnI 2, CS 2, CO 2 3AX 3 Trigonal planar BF 3, GaI 3 AX 2 ENon- linear (Bent) SO 2, SnCl 2 4AX 4 Tetrahed ral CCl 4, CH 4, BF 4 - AX 3 E(Trigonal ) Pyramida l NH 3, OH 3 - AX 2 E 2 Non- Linear (Bent) H 2 O, SeCl 2 5AX 5 Trigonal bipyrami dal PCl 5, PF 5 AX 4 EDistorted tetrahedr al (see- sawed) TeCl 4, SF 4 AX 3 E 2 T-ShapedClF 3, BrF 3 AX 2 E 3 LinearI 3 -, ICl 2 - 6AX 6 Octahedr al SF 6, PF 6 - AX 5 ESquare Pyramida l IF 5, BrF 5 AX 4 E 2 Square Planar ICl 4 -, BrF 4 -

Bond Polarity and Electronegativity Electronegativity and Bond Polarity There is no sharp distinction between bonding types. The positive end (or pole) in a polar bond is represented  + and the negative pole  -.

Electronegativity: measure of the tendency for an atom to attract bonding electrons Trends: increases left to right within period and from bottom to top within group.

covalent bonds revisited in a covalent bond between atoms with same electronegativity, there is “equal” probability of finding electrons around either bonded nucleus. in a polar covalent bond the more electronegative atom gains partial (-) charge, and the less electronegative atom gains partial (+) charge. This partial charge separation gives rise to “dipoles”.

“polar” vs. “non-polar” molecules A molecule is considered “polar” if it has a net “dipole moment”. A molecule is “non-polar” if it has no net dipole moment (or if the dipole moment is negligibly small) Characteristics of a polar molecule: –Polar covalent bond(s) –Molecular geometry that gives rise to a net dipole moment

Intermolecular forces Van der Waals Forces

Intramolecular vs. Intermolecular Forces

Intramolecular Forces Intermolecular Forces Intramolecular vs. Intermolecular Forces (IMFs) STRONGER WEAKER

Dispersion force Weakest Intermolecular Force (IMFs) Present in all atoms and molecules. The random movement of electrons will sometimes result in their unequal distribution. –One area of the atom then becomes more negatively charged and one more positively charged.

Element with more electrons have stronger dispersion forces since they have more charge. –Halogen family: explains why F & Cl are gases. Br is liquid. I & At are solid. Dispersion forces increase as atom size increases. Dispersion force Weakest Intermolecular Force

Dipole-Dipole Forces (IMFs) Attractions between oppositely charged regions of polar molecules

Intermolecular Forces (IMFs) Hydrogen Bonding Special Type of dipole-dipole attraction between molecules containing: a hydrogen atom (H) a small, highly electronegative atom (N,O,F) at least one lone pair Of electrons

Complete the Chart: Intermolecular Forces (IMFs) Dispersion Dipole-dipole Hydrogen Relative Strength How it’s Formed Molecular Examples

Identifying Intermolecular Forces What type of intermolecular forces must be overcome to: a.Melt ice? b.Boil water? c.Melt NaCl? d.Sublime I 2

Intermolecular Forces Which of the following compounds can form dipole-dipole forces? Cl 2 CO NO CH 4

States of Matter & Intermolecular Forces Focus on the following criteria: How the Strengths of forces between molecules Affect the properties of gases, liquids and solids (like viscosity, melting point, and boiling point) **Emphasize dispersion, dipole- dipole, & hydrogen IMFs

Hydrocarbons: Petroleum Phase Changes, IMFs, & Naming Chapter

Provides ½ of US energy needs for transportation, heat, & electricity Provides raw materials for manufactured productsmanufactured products What is Petroleum used for?

Crude oil is a mixture of hydrocarbons What is in petroleum?

Who has the oil? Who uses it? Where is it found?

How is crude oil separated? Fractional Distillation Fractional Distillation separates distinct mixtures from crude oil. Fractions Lowest bp = WEAK intermolec ular forces highest bp = STRONG intermolecul ar forces

Separation by Distillation

Liquid mixtures can be separated by their boiling points (bp). Every substance has it own specific bp. When a substance is undergoing a phase change, its temperature stays the same. 2-propanol H2OH2O

Boiling Point/ Condensation Point Freezing point/ Melting point Phase Change Graph Time The horizontal parts of the graph represent the temperatures at which a phase change will occur. All substances have their own specific melting and boiling points.

Examining Petroleum’s Molecules Intermolecular Forces are BETWEEN molecules Lowest bp = weak intermolecular forces = small hydrocarbons Highest bp = strong intermolecular forces = large hydrocarbons

Examples: Butane Nonene decyne 2-methylbutane