Lewis Structures - Winston-Salem/Forsyth County Schools
Lewis Dot Diagrams and Ions Valence Electrons The valence electrons are the electrons in the outermost shell of the atom Consider sodium: How many protons? How many neutrons? How many electrons?
Draw a Bohr model for sodium Valence Electrons Bohr The model for sodium: electron(s) in the highest shell are valence electrons
Lewis Dot Diagram To draw a Lewis Dot Diagram: Write the element symbol Figure out how many valence electrons the atom has Use dots to represent the valence electrons Put
them in pairs around the 4 sides of the element symbol For example try sodium Lewis Structure Practice Draw a Lewis Structure for:
Calcium Neon Silicon Ions Ions are atoms that have the same number of protons, but different numbers of electrons An ion forms when an atom gains or loses electrons to become more stable
Which group is the most stable? How many valence electrons does that group have? Ions When nonmetals form ions, they tend to gain electrons to fill their valence shell with 8 electrons When metals form ions, they tend to lose all of their valence electrons
Positive Ion Formation Atoms in Group 1 lose 1 electron to form ions with a +1 charge Atoms in Group 2 lose 2 electrons to form ions with a +2 charge Atoms in Group 13 lose 3 electrons to form ions with a +3 charge Positive ions are called cations
Negative Ion Formation Atoms in Group 17 gain 1 electron to form ions with a -1 charge Atoms in Group 16 gain 2 electrons to form ions with a -2 charge Atoms in Group 15 gain 3 electrons to form ions with a -3 charge Negative ions are called anions Ionic Compounds
When atoms form ionic compounds, an atom transfers one or more of its valence electrons to another atom. Consider NaCl Na loses 1 electron to become Na+1 Cl gains 1 electron to become Cl-1 The transfer of electrons from one atom to the other causes a more stable arrangement of electrons.
Ionic Compounds May be made from a metal and a nonmetal - KI May be made from a metal and a polyatomic ion (Look at your reference table) LiOH May be made from two polyatomic ions - NH4C2H3O2 Naming Ionic Compounds
The name of the positive ion stays the same The end of the element name of the negative ion is changed to an ide suffix Chlorine to chloride Sulfur to sulfide Phosphorus to phosphide Polyatomic ions stay as they are written Ionic Formulas
What ion does sodium form? Na+1 What ion does chlorine form? Cl-1
What do we change the name of the negative ion to? Chloride What is the name of the compound? Ionic Formulas What
is the formula for the compound made from sodium and chloride ions? What is the compound made from potassium and iodide ions? Ionic Formulas Activity Work in pairs to complete the activity. Please put all of the shapes back in the bags when you are finished.
Rules for Naming Ionic Compounds The first element keeps its name. For monatomic ions, the second element gets the ide suffix (ending). Polyatomic ions always keep their names whether they are first or second. Practice
Name the following ionic compounds: KF MgBr2 Li2S Ca3N2 NaNO3 Mg(OH)2 Exit Ticket
Draw a Lewis Structure for magnesium Give the charge on a magnesium ion Give the formula for a compound made from magnesium and bromine Give the name for CaCl2
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