4.1 Atomic Theory & Bonding ATOM: smallest particle of an element, has a neutral charge. PEN = proton(s) + electron(s) + neutron(s) ELEMENT: made up of 1 type of atom (eg.oxygen O) IONS: atoms with charges (eg. oxygen is O2-) MOLECULES: groups of covalently bonded atoms (eg. oxygen molecules are O2) COMPOUNDS: are made up of at least 2 atoms bonded together. Hydrogen and oxygen are atoms/elements H2O is a compound

area surrounding the nucleus Structure of an Atom: Name Symbol Charge Location Atomic Mass Proton p 1+ nucleus 1 AMU Neutron n Electron e 1– area surrounding the nucleus 1/1836 (0)

Numbers to Remember : Protons = Atomic Number Neutrons = Mass number – Atomic number (Mass # - proton #). Neutrons + Protons = Mass # Electrons in an atom = atomic number (also proton #) Electrons in an ion = atomic number – ion charge

Families of the Periodic Table: Columns of elements are called groups, or families All elements in a family have… similar properties bond with other elements in similar ways have the same number of valence electrons Family names (on the periodic table!): Group 1 = alkali metals (1+, highly reactive) Group 2 = alkaline earth metals (2+, reactive) Group 17 = the halogens (1-, very reactive) Group 18 = noble gases (0, unreactive) Periods are horizontal rows on the periodic table.

Where are the following? INCREASING REACTIVITY Where are the following? Atomic Number Period Group/Family Metals Non-metals Transition metals Metalloids Alkali metals Alkaline earth metals Halogens Noble gases

Periodic Table & Ion Formation: Ions: Atoms that gain and lose electrons to become stable (full valence shells). 1. Cations: metals that lose electrons & form positive ions (Na+) Multivalent: Some metals can have more than one charge (Fe2+ or Fe3+). 2. Anions: Non-metals gain electrons & form negative ions (O-2)

Bohr Diagrams: Bohr diagrams show how many electrons appear in each electron shell around an atom. (2, 8, 8, 18, 18) Valence electrons: electrons in the outermost shell ONLY. If the valence shell is full = stable If the valence shell is not full = reactive

Bohr Diagrams What element is this? It has 2 + 8 + 8 = 18 electrons, and therefore 18 protons It has 8 electrons in the outer (valence) shell 18 p 22 n Argon!

Electrons are transferred from the cations to the anion Ionic Bonds: Formed between Metals (cations) & non-metals (anions). Valence electrons are transferred from metal to nonmetal. Eg. Li2O Lithium Oxygen + Electrons are transferred from the cations to the anion Li+ O2- Li+ Lithium oxide, Li2O Covalent Bonds: Formed between two or more non-metals Valence electrons are shared between atoms Eg. HF Hydrogen Fluorine + Electrons are shared Hydrogen fluoride

Lewis Diagrams: Only valence electrons are shown Dots representing valence electrons are placed around the element symbols (on 4 sides, imagine a box around the symbol) Electron dots are placed singularly, then they are paired. Ex: Nitrogen atom

Lewis Diagrams for Ions: Ex. Nitrogen ion Remove or add electron dots to make full valence shells. Square brackets and the charge are placed around each ion 2+ – – • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Be Cl Cl Be Cl Cl Be Cl Since Be2+ wants to donate 2 electrons and each Cl– wants to accept only one, two Cl– ions are necessary Each beryllium has two electrons to transfer away, and each chlorine wants one more electron The ionic compound Beryllium chloride is formed

Lewis Diagrams For Covalent Bonds: valence electrons are drawn to show sharing of electrons. Remember: All atoms “like” to have a full valence shell The shared pairs (“bonding pairs”) of electrons are usually drawn as a straight line “lone pairs” are the electrons not shared