Unit 4 Bonding Notes

 All chemical compounds are held together by bonds  We will be learning about 3 types of bonds  Ionic, Covalent, and Metallic.

Chemical Bonding  Combining atoms of elements to form new substances  The types of chemical bonds are determined by the structure of the atom  The type of bond determines the physical properties of the substance

Chemical Bonding  Electrons within an atom are arranged in energy levels  Electrons in the outermost energy level are called valence electrons  Atoms that have a complete (filled) outermost energy level are very stable (& unlikely to bond) Example??

Ionic Bonding  Ionic Bonding – bonding that involves a transfer of electrons between atoms  One atom gains electrons (nonmetal) and the other atom loses electrons (metal)  When an atom gains or loses electrons it is no longer neutral and becomes an ion  Ions – charged particles  Atom that gains electrons has a negative charge  Atom that loses electrons has a positive charge

Ionic Bonding  Formed between cations and anions  Cation=positive ion  Anion=negative ion  The attraction between the positive and negative charges holds the ions together  Have no net charge due to balancing of the charges Salt (NaCl)-it’s ionic!

Ionic Bonding

 Ions in an ionic compound form a regular, repeating arrangement or crystal lattice  Combine in a fixed ratio.  Chemical formula (NaCl) shows the ratio of ions present in the crystal lattice

Crystal Lattice

Properties of Ionic compounds  Common physical properties of ionic compounds include:  High melting point  Brittleness  Soluble in water  Conduct electricity when dissolved  Do not conduct when in solid form

COVALENT BONDING  Covalent bonds form between two non-metals (usually)  As always, the guiding principle is the octet rule…atoms try to form an electron configuration like their nearest noble gas neighbor  Both atoms share electrons to meet the octet rule (instead of transferring like ionic)  Called molecules

Polar Covalent Bonding  Atoms share the electron, but the sharing is unequal.  Why is the sharing unequal?  One of the atoms has a higher electronegativity  It pulls harder on the electron(s) than the other atom  Now the electron is closer to one atom than the other

POLAR COVALENT  This results in a polar molecule-  Has ends that are differently charged (+ and -)  Overall has a neutral charge

METALLIC BONDING  Metallic bonds are made of metals (no duh!)  In this type of bonding, electrons can freely move amongst metal atoms…sometimes metal bonding is called a “sea of electrons”  No electron really belongs to any one atom but rather to any atom around

Metallic Bonds

 This sharing of electrons between all the metal atoms results in the characteristic properties of metals  Malleable-you can bend and shape it and it won’t break  Good conductors of electricity  High melting point

Element Composition (usually) Metals! M Non-metals with non- metals N-N Metals (M) combined with non- metals (N) (M+)(N-) MetallicCovalentIonic

Covalent (Polar & Non Polar) Metallic Crystals Hard, Brittle High melting pt Very Soluble in Water High Electrical Conductivity in solution Solids, liquids, gases. Soft solids but many liquids and gas Low melting point Some dissolve, some don’t Low to No Conductivity in solution Shiny Malleable High Electrical Conductivity High melting point

Atoms share electrons communally! Atoms share electrons to complete stable valence shells. Oppositely charged ions attract! (How do ions form?) MetallicCovalentIonic M+ O N-M+ How they Bond H H