An element is a substance that is made from one kind of atom only. It cannot be broken down into simpler substances. An element atom

A compound is a substance that is made up of different elements chemically bonded together. It can be broken down into elements A compound made up of 3 different elements An element

Bonding Atoms  Why do atoms bond? - each atom wants a full outermost energy level - gain, lose, and share valence electrons to achieve the duet or octet rule aka: “being happy” - gives each atom an electron configuration similar to that of a noble gas ex. Group 18: He, Ne, Ar

Chemical Bonds  Chemical Bonds - attractive force that holds atoms or ions (charged atoms) together - 3 types ionic, covalent, metallic - determines the structure of compound - structure affects properties - melting/boiling pts, conductivity etc.

Chemical Structure/Models  Chemical Structure/Molecular Models - arrangement of bonded atoms or ions - bond length: the average distance between the nuclei of two bonded atoms - bond angles: the angle formed by two bonds to the same atom

Molecular Models of Compounds  Structural - chemical symbols represents atoms - lines are used to represent bonds * good for “seeing” angles

Molecular Models Cont.  Electron Dot/Lewis Structure - chemical symbol represent atom - dots represent valence electrons - 2 center dots represent a bond - no bond angles, no bond length

Ionic Bonds / Ionic Compounds  Definition - bond formed by the attraction between oppositely charged ions cation: positive: lost e-’s (Monotonic) anion: negative: gained e-’s (Monotonic) ex. Na + + Cl - = NaCl - electrons are transferred from one atom to another - negative ions attract more positive ions, and soon a network is formed

Crystalline structure The POSITIVE CATIONS stick to the NEGATIVE ANIONS, like a magnet.

Properties of Ionic Compounds  Structure affects properties - strong attractions between ions: strong bonds - high melting/boiling pt - shatter when struck (think of it as one unit) - conductivity solid: ions are so close together, fixed positions, (can’t move) NO conductivity liquid: ions are freely moving due to a broken lattice structure Good conductivity

Ionic Bonds Cont.

Covalent Bonds  Definition - chemical bond in which two atoms share a pair of valence electrons - can be a single, double, or triple bond single, 2e-’s (-); double, 4e-’s (=); triple, 6e-’s( ) - always formed between nonmetals - mostly low melting/boiling points  2 types of bonds - polar - non polar

Covalent Bond Cont.  Non Polar - bonded atoms that share e - ’s equally - same atoms bonded ex. Cl – Cl: Cl 2  Polar - bonded atoms that do not share e - ’s equally - different atoms bonded H ex. H – N – H: NH 3

Non Polar  Carbon Dioxide in non polar

- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

Covalent Bonds Cont.

Examples of common covalent bonds  Diatomic Molecules-two atoms of the same element covalently bonded together  Hydrogen  Oxygen  Nitrogen

More Examples Carbon Compounds  Methane  CH4  Ethane  C2H6

More Examples… Ammonia

Hydrogen bonding  Are the attractive force caused by hydrogen bonded to F, O, or N.  The hydrogen partially share with the lone pair in the molecule next to it.  The strongest of the intermolecular forces.

Metallic Bonds  Definition - a bond formed by the attraction between positively charged metal ion (cation) and the shared electrons that surround it (sea of electrons) ex. Cu  Properties - Conductivity: Good: electrons can move freely - Malleable: lattice structure is flexible

Sea of Electrons  Electrons are free to move through the solid.  Metals conduct electricity.

Metals are Malleable  Hammered into shape (bend).  Ductile - drawn into wires.

Malleable

Malleable  Electrons allow atoms to slide by.

Metallic Bonds Cont.

Predicting Bond Type