4.1 Atomic Theory & Bonding What is an Atom?  smallest particle of an element that still has the properties of that element  An atom = proton(s) + electron(s) + neutron(s) (PEN)  Fun Fact: 50 million atoms, lined up end-to-end = 1 cm

An ELEMENT is made up of one type of atom  The element, oxygen, is O  IONS are atoms with a charge.  The ion of oxygen is O 2-  Atoms can join together to form MOLECULES.  The oxygen molecules are O 2  COMPOUNDS are made up of several (2+)atoms  Hydrogen and oxygen are atoms/elements  H 2 O is a compound

Structure of an Atom: The nucleus is at the centre of an atom The nucleus is at the centre of an atom  composed of protons (positive charge) and neutrons (neutral charge) Electrons (negative charge) exist in the space surrounding the nucleus

Subatomic Particles:  Atoms are made up of smaller particles known as sub-atomic particles. NameSymbolChargeLocation Atomic Mass Protonp1+nucleus 1 AMU Neutronn0nucleus Electrone1– area surrounding the nucleus 1/1836 (0)

Numbers to Remember :  # of protons = # of electrons in every atom AND ONLY IN ATOMS!!! (not ions)  Nuclear charge = charge on the nucleus = # of protons  Atomic number = # of protons = # of electrons in atoms = # of electrons in atoms

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  Group 2 = alkaline earth metals  Group 17 = the halogens  Group 18 = noble gases  Periods are horizontal rows on the periodic table

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:  Atoms gain and lose electrons to form ions  Metals lose electrons & become positive ions (cations)  Some metals can have more than one charge (multivalent)  ie. Iron, Fe, loses either 2 (Fe 2+ ) or 3 (Fe 3+ ) electrons  Non-metals gain electrons & become negative ions (anions)  Atoms do this in an attempt to have the same number of valence electrons as the nearest noble gas – to become stable

Bohr Diagrams:  Bohr diagrams show how many electrons appear in each electron shell around an atom.  Each shell holds a maximum number of electrons (2, 8, 8, 18, 18)  Electrons in the outermost shell are called valence electrons  Except for the transition elements, the last digit of the group # = # of valence electrons Note: Think of the shells as being 3D like spheres, not 2D like circles!

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

 Note: The noble gas elements have full electron shells, and are very stable. Bohr Diagrams for the first 20 elements

Covalent Bonds:  Formed between two or more non-metals  Electrons are shared between atoms Hydrogen Fluorine + Electrons are shared Hydrogen fluoride  When two atoms get close together, their valence electrons interact. Bonding Types:

Ionic Bonds:  Metals give electrons to non-metals (transfer of electrons)  cations (+ ions) and anions (- ions) form  For example, lithium and oxygen form an ionic bond in the compound Li 2 O Lithium Oxygen + Electrons are transferred from the cations to the anion Li + O 2- Li + Lithium oxide, Li 2 O

Lewis Diagrams:  Like simplified Bohr diagrams  Only valence electrons are shown  Dots representing electrons are placed around the element symbols (on 4 sides, imagine a box around the symbol)  Electron dots are placed singularly, until the fifth electron is reached, then they are paired. Example: Nitrogen atom

Lewis Diagrams:  Note: the Lewis diagrams are the same (except for the symbols) for elements in the same family because they have the same number of valence electrons

Lewis Diagrams for Ions:  For positive ions: one electron dot is removed from the valence shell for each positive charge of the ion.  For negative ions: one electron dot is added to each valence shell for each negative charge of the ion.  Square brackets and the charge are placed around each ion Example: Nitrogen ion

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

BeCl Each beryllium has two electrons to transfer away, and each chlorine wants one more electron BeCl BeCl Since Be 2+ wants to donate 2 electrons and each Cl – wants to accept only one, two Cl – ions are necessary The ionic compound Beryllium chloride is formed 2+ – – Lewis Diagrams For Ionic Bonds: