Chemical Bonds

Chemical Bonds Vocabulary Chemical bonds are the forces that hold atoms together to form compounds. Valence electrons: The ‘s’ and ‘p’ electrons in the highest occupied energy level. They are transferred or shared to make chemical bonds.

Vocabulary (Cont.) There are 4 main types of bonds: Ionic, Covalent, Metallic, Hydrogen. Noble gases have 8 electrons in their valance shells which is why they will not form bonds under normal circumstances.

Ionic Bonds The bond formed when one or more electrons are transferred from the valence shell of one atom to the valence shell of another atom. Oppositely charged ions attract. Metal + Nonmetal = Ionic A positive ion is called a cation and a negative ion an anion.

Ionic Rule of Thumb: Metals lose electrons to become cations. Non-metals gain electrons to become anions. Metalloids may gain or lose electrons.

Ionic Bonds (Cont.) Ex: NaCl Na – 1s 2 2s 2 2p 6 3s 1 Cl -- 1s 2 2s 2 2p 6 3s 2 3p 5 } Before } After The 3s 1 electron from Na goes to Cl and becomes a 3p 6 electron. Na – 1s 2 2s 2 2p 6 +1 Cl -- 1s 2 2s 2 2p 6 3s 2 3p 6 - 1

Properties of Ionic Compounds Hard High melting points Good insulators Electrolytes: conduct electricity when dissolved in water (don’t conduct as solids)

Covalent Bonds Covalent bonds are attractive forces that are produced by the sharing of electrons between two atoms. Elements combined by covalent bonds form molecules. Nonmetal + Nonmetal = Covalent

Covalent Bonds The valence orbitals overlap in covalent bonds, allowing the atoms to share electrons and achieve full valence shells.

Multiple Bonds A Single covalent bond has one shared pair of electrons. Covalent bonds can form with 2 or 3 pairs of electrons giving Double & Triple Covalent bonds. O ═ C ═ ON ≡ N H H C H H

Properties of Covalent Molecules Low melting and boiling points Generally gases or liquids at room temperature Poor conductors Non-electrolytes in solution – don’t conduct electricity

Non-Polar Covalent Bonds Non-Polar Covalent Bonds In a non polar covalent bond there is equal attraction for the shared electrons This results in an equal distribution of charge throughout the molecule Ex. H—H

Polar Covalent Bond In a polar covalent bond there is an unequal attraction for the shared electrons This results in an unequal distribution of charge in the molecule The molecule has a portion that is slightly positive and an area that is slightly negative.

Polar Covalent Bond Higher electronegative element is partially negative and the lower electronegative element is partially positive. This creates a dipole. (A molecule in which the centers of positive and negative charges do not coincide.) One end of a dipole is slightly positive and one end is slightly negative (like a tiny magnet).

Polar vs. Non-Polar Electronegativity greater than 1.7 = ionic. Less than 1.7 = covalent. Polar Covalent = 0.4 – 1.7; Non-Polar Covalent = 0.0 – 0.4. Important: With polar and non-polar compounds – Like dissolves Like! Polar things dissolve polar things and visa versa. Note ionic compounds dissolve in polar substances. Water is polar and oil is non-polar. That is why they don’t mix.

Polar vs. Non-Polar: Shape Matters!! Water is a Polar molecule with a slightly positive and negative side. Symmetrical CCl 4 is non-polar, even though the bonds are polar.

Ionic vs. Covalent Bonds IonicCovalent Made of:Ions (Metal + Non-Metal) 2 or more atoms (all non-metals) Electrons are:TransferredShared They formIonic Compounds Molecules

Ionic vs. Covalent Bonds IonicCovalent Melting/Boiling Points: Very HighLow to Medium ConductivityOnly in molten form or when in solution Not conductive AppearanceCrystalline solidsSolid, liquid or gas

Polar vs. Non-Polar Formula Electronega- tivity diff. Type of Bond Atom w/greater electron share NO MgO Br 2.5 Polaroxygen 2.3Ionic -- 0 Non-polar --

Metallic Bonds Metallic Bonds are described as metal ions “floating in a sea of electrons”. The electrons are attracted to many metal ions at the same time. They are loosely held and can move around quite freely.

Metallic Bonds

Metallic Bonds (Cont.) Because of this, metals will conduct electricity as a solid or when molten; and are malleable and ductile. Metallic bonds form between metals only (when one metal atom is bonded to another metal atom). Ex. Copper wire or Iron nail

IonicCovalentMetallic Metal + NonmetalNonmetal + Nonmetal Metal + Metal Types of Atom Combinations and The Resulting Bond

Practice WS #3 Chemical Bond Overview WS #4 Chemical Bonds

Hydrogen Bonds Intermolecular – occurs between molecules not within a molecule (that would be intramolecular) Occur between positive hydrogen atoms and slightly negative atoms in other molecules Explains (for water): –Why ice floats –Why water has a high boiling point –The Surface tension of water

Fats & Bonding In saturated fats all of the carbon atoms have single bonds. When hydrogen atoms are removed, double bonds are formed creating monounsaturated or poly-unsaturated fats which are healthier but have a shorter shelf- life. At room temperature, saturated fats are solids while unsaturated fats are liquids.

All single bonds mean a saturated fat. One double bond means a mono-unsaturated fat. Multiple double bonds mean a polyunsaturated fat.

Partially Hydrogenated Oil

Trans Fats